Latest Articles Include:
- Molecular golems
- Nat Nanotechnol 7(1):1-2 (2012)
Nature Nanotechnology | Thesis Molecular golems * Chris Toumey1Journal name:Nature NanotechnologyVolume: 7,Pages:1–2Year published:(2012)DOI:doi:10.1038/nnano.2011.239Published online 28 December 2011 Corrected online19 January 2012 The golem stories of Jewish history can provide a framework for thinking about some of the ethical questions involved in nanotechnology and nanomedicine, as explains. Subject terms: * Ethical, legal and other societal issues Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg © EUREKA ENTERTAINMENT LTD/ROWMAN & LITTLEFIELD PUBLISHING GROUP One of the contributions of Jewish thought to Western ethics has been a series of golem stories. In these tales, which began to appear in the third century AD, a golem was a humanoid creature made of earth or clay. It was assembled and brought to life by a holy man using divine knowledge, used for a virtuous purpose, and then returned to its lifeless earthen origin. A later variation depicts the golem-maker as using secular knowledge, or having a non-virtuous reason for assembling a golem, or being irresponsible and failing to control the creature. Mary Shelley's Frankenstein is the best-known example of the latter1. "Golem stories raise issues about the reasons why one makes artificial life." Golem stories raise issues about the reasons why one makes artificial life, about the status of the golem, and about the ethical obligations of the golem-maker. Under what circumstances is it legitimate for someone to create humanoid life outside of natural processes of reproduction? What are the rights of the golem? What are the responsibilities of the golem-maker? As there were multiple versions of the golem story, there are many different ways to express and explore these ethical questions2. Many of these questions are relevant to visions of the future that involve advanced robots, cognitive-enhancing drugs (that is, drugs that are not needed for therapeutic purposes, such as the use of Ritalin by students to help them do better in exams), and the possibility that nanotechnology will enable the human brain to be interfaced with information technology so that people can permanently store their personal thoughts and emotional experiences3. The essence of who you are as an individual could endure eternally so long as the hardware available preserved the record of your spiritual self and made that data available to others4. I prefer to think of nanomedicine in terms of modest and realistic near-future developments, such as targeted drug delivery and lab-on-a-chip-based diagnostic tools, but I understand that others expect that nanomedicine will deliver more dramatic changes, which is why these sorts of ethical issues deserve attention. Golem stories might help us th! ink about these possibilities. Beginning in 1966, a small number of Jewish writers began to use the ethical issues in golem stories as a template for thinking about issues in information technology and biotechnology. If a certain technology had a quality similar to a human quality — intelligence, reasoning ability or the power to direct human reproduction, for example — then golem stories might help researchers think about the ethical implications of the technology. "Scholem suggested that a new computer at the Weizmann Institute should be named Golem Aleph (Golem One)." In 1966, in an article5 that is considered the original text for the golem-technology analogy, Gershom Scholem suggested that a new computer at the Weizmann Institute in Israel should be named Golem Aleph (Golem One). Scholem's reasoning took the form of a series of similarities between legendary golems and the computer, especially the idea that both represent man's creative powers and each was "a technical servant of man's needs". Scholem adopted a friendly tone in his article, asking the reader not to fear the power of the computer, and concluding with the following message for golems and computers: "Develop peacefully and don't destroy the world". An article on the same topic by Azriel Rosenfeld later the same year was more alarmist6. Rosenfeld warned that the development of intelligent robots would raise a number of troubling questions: * What is a man? "How much of a person's body can be replaced by artificial limbs and organs before he is no longer a 'man'?" * If biologists synthesize sperm and ova to make human bodies without parents, is the creature a human or an android? * If the intelligence of dolphins and other higher animals approaches human intelligence, do these animals deserve a human-like status? Then golems entered his discussion. There were solid reasons why a golem was not considered "legally human", wrote Rosenfeld, and why it was more like "an animal in human form". But if an intelligent golem expressed itself by speaking, should it not be considered human? Decades later, Byron Sherwin developed the golem-technology analogy more fully. In a book2, Golems Among Us, and a subsequent paper7, he created a framework for thinking about how, in Jewish tradition, technology was permitted to affect nature. This had two themes. First, God's creation of the natural world is incomplete, which gives humans an invitation, even a responsibility, to improve the creation through technology, provided that this is "tempered by moral wisdom". Secondly, Talmudic tradition and other Jewish sources say that it is permissible within certain limits to create artificial life. Sherwin indicated that, according to these two principles, genetically modified food and cloning were acceptable2. Sherwin also included an atom manipulated by nanotechnology in his list of modern-day golems2, but based on the principle that a golem is not permitted to procreate, self-replicating nanobots were excluded from the list. However, with the power to create artificial! life must come wisdom and responsibility. One of the lessons from the golem stories is that the golem-maker has a responsibility to control the creature he or she makes. This is the difference between Rabbi Loew of Prague, the most famous of all golem-makers, and Victor Frankenstein. Loew controlled his golem; Frankenstein did not. This framework of ethical insights provided by golem stories could help to guide our thinking about the tools and procedures of nanomedicine and the people who make them. But there is a caveat. The idea of golems in nanomedicine constitutes a thought experiment by Sherwin and his predecessors. It is a provocative idea that is worth exploring, but the applications of nanomedicine will not always fit neatly into the moral lessons that we find in golem stories. Some Christian thinkers have had similar ideas. Irving Hexham has written that robots in science fiction offer us "a debate on the meaning and purpose of existence"8. What is a person? What is a soul? How should a technology be controlled? For Hexham, robot stories were a way to ask these questions: indeed, he wrote that Christian theology was inferior to science fiction in pursuing these questions. Nanomedicine and other forms of nanotechnology confront us with questions about how we might change human life and human nature. Some might say that this is so novel that there are no precedents for the moral issues that accompany these possibilities. That is wrong. In these issues there are more difficult questions than there are easy answers, but the golems of the past 1,800 years can visit us again to remind us that there are precedents for thinking about how technology makes human nature interesting. Change history * Change history * References * Author informationCorrected online 19 January 2012In the Thesis article 'Molecular golems' (Nature Nanotech.7, 1–2; 2012), the surname of the author of ref. 5 was spelled incorrectly in the main text; it should have read Scholem. This has now been corrected in the HTML and PDF versions. References * Change history * References * Author information * Toumey, C.Sci. Technol. Hum. Val.17, 411–437 (1992). * Article * Sherwin, B.Golems Among Us (Ivan R. Dee, 2004). * Bainbridge, W.The Futurist25–29 (March–April 2006). * Walker, R.NY Times Magazine30–37, 44, 46 (8 January 2011). * Scholem, G.Commentary41, 62–65 (January 1966). * Rosenfeld, A.Tradition8, 15–23 (Fall 1966). * Sherwin, B.Zygon42, 133–143 (2007). * Article * Hexham, I.The Christian Century97, 574–578 (21 May 1980). Download references Author information * Change history * References * Author information Affiliations * Chris Toumey is at the University of South Carolina NanoCenter Corresponding author Correspondence to: * Chris Toumey Author Details * Chris Toumey Contact Chris Toumey Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Our choice from the recent literature
- Nat Nanotechnol 7(1):3 (2012)
Nature Nanotechnology | Research Highlights Our choice from the recent literature Journal name:Nature NanotechnologyVolume: 7,Page:3Year published:(2012)DOI:doi:10.1038/nnano.2011.244Published online 28 December 2011 Electron beams: An atom-sized vortex * Electron beams: An atom-sized vortex * Magnetic nanoparticles: At the crime scene * Nanoelectromechanical systems: Keeping the noise down * Electron microscopy: Mapping ensembles Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Appl. Phys. Lett. 99, 203109 (2011) © 2011 AIP Electron beams are typically plane waves. This means that the beam phase is identical for all points in a plane perpendicular to the beam direction. The phase of an electron vortex beam, on the other hand, describes a spiral. As a result, vortex beams carry orbital angular moment and magnetic moment, which leads to unique interactions with matter. Jo Verbeeck of the University of Antwerp and colleagues from Austria, the Netherlands and Canada have now demonstrated an electron vortex beam with a diameter of less than 1.2 Å. Electron vortex beams were first created by passing a plane wave beam through a graphite film that spontaneously formed a spiral structure, and acted as a phase plate. This was difficult to reproduce and gave limited control over the resulting beam. Verbeeck and co-workers had improved on this approach by creating a vortex beam with a holographic mask inside a transmission electron microscope. However, the effective beam diameter was several micrometres. Verbeek and colleagues have now reduced this beam diameter to atomic dimensions by placing a holographic mask in the condenser plane of a state-of-the-art microscope with double aberration correction. At 1.2 Å, the beam size is comparable to the size of the 2p orbital in a nitrogen atom (see image; left and right panels show the beam and the 2p orbital respectively, drawn approximately to scale). The tiny vortex beam may allow atomic-resolution mapping of magnetic states. MS Magnetic nanoparticles: At the crime scene * Electron beams: An atom-sized vortex * Magnetic nanoparticles: At the crime scene * Nanoelectromechanical systems: Keeping the noise down * Electron microscopy: Mapping ensembles Analysthttp://dx.doi.org/10.1039/c1an15200a (2011) DNA profiling is widely used by forensic investigators to identify an offender from just a single cell. However, equally valuable is the ability to detect and identify traces of body fluids such as saliva, semen and blood on various objects at the crime scene. At present, methods and tests used to analyse body fluids are destructive and have a low specificity. Now, Nunzianda Frascione and colleagues at King's College London have shown that magnetic nanoparticles conjugated with specific antibodies can detect and identify blood and saliva in situ on different types of substrates. The researchers functionalized magnetic nanoparticles with fluorescently labelled antibodies that recognize specific components of red blood cells, white blood cells or saliva. They applied the nanoparticles to human blood or saliva that had been smeared onto a glass slide. After 30 mins the unbound nanoparticles were removed by a magnet and the bound conjugates were visualized under a fluorescent microscope. The antibodies showed good specificity and had little cross reactivity with other body fluids. Furthermore, blood stains that were treated with the nanoparticles could still be used for DNA profiling, suggesting that this method could potentially save money as DNA profiling would only be carried out on identified sections of the samples. The method also worked on samples on substrates such as ceramic, paper and dark fabrics, thereby increasing the likelihood of uncovering important evidence at the crime scene. ALC Nanoelectromechanical systems: Keeping the noise down * Electron beams: An atom-sized vortex * Magnetic nanoparticles: At the crime scene * Nanoelectromechanical systems: Keeping the noise down * Electron microscopy: Mapping ensembles Nature480, 351–354 (2011) Any device that amplifies a signal inevitably adds noise, and quantum mechanics prevents this added noise being reduced below a certain value. It is possible to approach this quantum limit by using superconducting devices to amplify electrical signals, but these devices are complex. Now Francesco Massel and co-workers at Aalto University and the VTT Technical Research Centre of Finland have shown that nanomechanical resonators can amplify microwave signals, and that it may be possible to reach the quantum limit with this approach. The Finnish team start by using lithography and focused ion-beam etching to define a mechanical resonator and a microwave cavity in a 150-nm-thick layer of aluminium on a silica surface. When a pump signal is fed into this system, energy is transferred from the cavity to the resonator if the pump frequency is higher than the resonance frequency of the cavity, and vice versa. And if a weak probe signal is sent into the system when energy is being transferred to the resonator, this probe can also be amplified. Massel and co-workers show that approximately 20 noise quanta are added to the signal, and predict that it should be possible to reach the quantum limit of adding just half a quantum of noise. PR Electron microscopy: Mapping ensembles * Electron beams: An atom-sized vortex * Magnetic nanoparticles: At the crime scene * Nanoelectromechanical systems: Keeping the noise down * Electron microscopy: Mapping ensembles Nano Lett.http://dx.doi.org/10.1021/nl203975u (2011) Electron microscopy is routinely used to characterize the structure of metal nanoparticles, and with the help of electron energy-loss spectroscopy, chemical maps with atomic resolution can also be obtained. A chemical map of a single particle can, however, take hours to record. Therefore, acquiring a statistically significant sample of a system that contains nanoparticles with a variety of different compositions, such as a heterogeneous catalyst, is impractical. David Muller, Zhongyi Liu and colleagues at Cornell University, General Motors and Florida International University have now shown that the improved electron optics of an aberration-corrected electron microscope can allow hundreds of platinum–cobalt nanoparticles to be chemically mapped. The US team used a scanning transmission electron microscope that can correct up to the fifth-order of aberrations and allows data to be collected around a thousand times faster than on a conventional microscope. With the instrument, the platinum–cobalt nanoparticles — which are promising as a fuel-cell catalyst but are known to degrade over time — were mapped at various stages of ageing in a proton-exchange-membrane fuel cell. By mapping ensembles of nanoparticles, the precise structure and composition of the catalyst could be linked to its bulk electrochemical performance with statistical confidence. OV Written by Ai Lin Chun, Peter Rodgers, Michael Segal and Owain Vaughan. Author information * Electron beams: An atom-sized vortex * Magnetic nanoparticles: At the crime scene * Nanoelectromechanical systems: Keeping the noise down * Electron microscopy: Mapping ensembles Additional data - Molecular electronics: Flipping a single proton switch
- Nat Nanotechnol 7(1):5-6 (2012)
Nature Nanotechnology | News and Views Molecular electronics: Flipping a single proton switch * Peter Liljeroth1Journal name:Nature NanotechnologyVolume: 7,Pages:5–6Year published:(2012)DOI:doi:10.1038/nnano.2011.242Published online 28 December 2011 A four-level conductance switch can be created by using a scanning tunnelling microscope to remove a hydrogen atom from the central cavity of a porphyrin molecule. Subject terms: * Molecular machines and motors * Surface patterning and imaging Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The basic idea of molecular electronics — using molecules as components in electrical circuitry — has been verified experimentally by using molecules as diodes, switches and transistors1, 2, 3. The use of molecules in electronics is conceptually appealing because the required function can be encoded into the molecule through chemical synthesis, making molecules an ideal tunable nanoscale building block. However, the molecular components have to be interfaced with the macroscopic world and this places a number of constraints on their design. In molecular switches, for example, the switching action should not change the overall size of the molecule because this will disturb the external contacts to the switch. Ideally, small changes of the atomic structure of the molecule should lead to changes in the electronic properties of the whole molecule that are large enough to allow the different states to be distinguished from each other by measuring the electric current through the molecule. The switching unit should also be protected in some way so that the switch is not affected by changes in its immediate environment. In addition to these strict requirements, it might also be beneficial to have access to more than two levels (states) in a switch. Furthermore, if the switching unit is part of a molecule that already has a well-developed chemistry, this could help broaden the range of different molecular architectures that the switch can be incorporated into. Writing in Nature Nanotechnology, Willi Auwärter and colle! agues at the Technical University, Munich, now report using a porphyrin molecule to create a four-level molecular switch that fulfils all of the above criteria4. Porphyrins are flat organic molecules composed of four modified pyrrole (C4H4NH) subunits connected by CH bridges. The molecules have a central cavity that can incorporate a metal ion or two hydrogen atoms. When the porphyrin has two central hydrogen atoms — a free-base porphyrin — the two protons can transfer between the two pairs of opposing nitrogens in the cavity of the molecule, a reaction know as tautomerization. It has also been shown previously that a related molecule (a phthalocyanine) can function as a tautomerization-based two-level molecular switch5. To upgrade such two-state systems, Auwärter and colleagues used voltage pulses from the tip of a low-temperature scanning tunnelling microscope (STM) to controllably remove one of the hydrogens from the cavity of a porphyrin molecule that was deposited on a silver surface (Fig. 1a). This allowed the remaining central hydrogen to then hop between the four pyrrole rings giving rise to a four-level molecular switch! based on the transfer of a single proton. Figure 1: Atomic control of molecular switches based on porphyrin molecules. , An STM is used to selectively remove one of the two hydrogen atoms (shown in green) from the central cavity of a free-base porphyrin molecule. The position of the remaining hydrogen atom can be switched between the four different positions that give rise to four distinct electric current levels through the molecule. , Porphyrins that can be linked together to from long chain-like molecules with multiple cavities, such as butadiyne-linked oligo-porphyrins6 () and meso-meso-linked oligo-porphyrins7 (), could also prove useful in molecular electronics. * Full size image (203 KB) The above process is initiated by electrons from the STM tip that have sufficient energy to excite certain molecular vibrations and drive the molecule over the reaction's activation-energy barrier. The switching reaction only occurs with high STM bias voltages and STM imaging at low bias voltages can therefore be used to accurately record the position of the hydrogen atom. Furthermore, the position of the hydrogen atom affects the symmetry of the molecular orbitals and determines the current measured through the STM tip positioned anywhere over the molecule. That is, the switching action is confined to the central cavity of the molecule, but it is reflected in electronic changes over the entire molecule, which would lead to different current levels if the switch was coupled to external leads. The switch is also robust and can function directly on a metal surface. Despite the progress that has been made in developing new molecular switches and the increased atomic control of the switching process itself, it is unlikely that devices based on single molecular switches will form the basis of a viable post-CMOS (complementary metal-oxide-semiconductor) technology. This is due in particular to the formidable problems that exist in reliably wiring single molecules with mesoscopic leads. However, if several active molecular components can be coupled in a controlled manner, more complex molecular devices could be constructed from modular building blocks. In the end, only the complete device would then have to be wired up to the external world. For example, a molecule-based logic gate could be built from suitably coupled molecular switches that control the charge transport through the system. This would allow basic logic operations (AND, OR and so on) to be carried out on a molecular circuit. The controlled coupling of active molecular-scale building blocks is naturally demanding, and sufficient levels of control perhaps requires the use of covalent bonds defined through chemical synthesis. In this regard, porphyrins have a particular strength because their chemistry is well developed. For example, there are strategies for synthesizing covalently linked oligo-porphyrins based on butadiyne-6 or meso-meso-linked7 porphyrins (Fig. 1b,c). These molecules have been synthesized in the past because of their useful properties in organic optoelectronics, for example as near-infrared dyes and organic conductors. Their conductivity stems from the conjugated structure, which also suggests that they could act as molecular wires. Such species could be used to form well defined, covalently connected one- and two-dimensional arrays of molecular switches. By making this chemical treasure trove available for molecular electronics, the work of Auwärter and co-workers could lead to! the construction of novel computing units at the molecular scale. References * References * Author information * Chen, F., Hihath, J., Huang, Z., Li, X. & Tao, N. J.Annu. Rev. Phys. Chem.58, 535–565 (2007). * ChemPort * ISI * PubMed * Article * Van der Molen, S. J. & Liljeroth P.J. Phys. Condens. Matter22, 133001 (2010). * ChemPort * PubMed * Article * Song, H., Reed, M. A. & Lee, T.Adv. Mater.23, 1583–1608 (2011). * ChemPort * ISI * PubMed * Article * Auwärter, W.et al. Nature Nanotech.7, 41–46 (2012). * Article * Liljeroth, P., Repp, J. & Meyer, G.Science317, 1203–1206 (2007). * ChemPort * ISI * PubMed * Article * Sedghi G.et al. Nature Nanotech.6, 517–523 (2011). * ChemPort * Article * Tsuda, A. & Osuka, A.Science293, 79–82 (2001). * ChemPort * ISI * PubMed * Article Download references Author information * References * Author information Affiliations * Peter Liljeroth is at the Department of Applied Physics, Aalto University School of Science, PO Box 15100, 00076 Aalto, Finland Corresponding author Correspondence to: * Peter Liljeroth Author Details * Peter Liljeroth Contact Peter Liljeroth Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Nanofluidics: Neither shaken nor stirred
- Nat Nanotechnol 7(1):6-7 (2012)
Nature Nanotechnology | News and Views Nanofluidics: Neither shaken nor stirred * Aldo Jesorka1 * Owe Orwar1, 2 * Affiliations * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:6–7Year published:(2012)DOI:doi:10.1038/nnano.2011.236Published online 28 December 2011 Bioinspired nanoreactor arrays can be used to controllably mix subattolitre volumes of liquids. Subject terms: * Nanofluidics * Nanomaterials Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The controlled mixing of reactants and catalysts is an important first step in carrying out chemical and biochemical reactions, but is a significant practical challenge when using ultrasmall volumes of material. Reducing the scale on which a reaction takes place decreases the consumption of reagents and allows the products of the reaction to be screened with high throughput. Working at the nanoscale also allows researchers to perform single-molecule studies that can yield insights that are difficult to obtain when using larger volumes. Therefore, considerable effort has been devoted to developing reactors with ultrasmall volumes1, 2. Biologically inspired nanoreactors are of particular interest because they could be used to control volumes much smaller than 10−12 l, which is the typical limit of microfabricated fluidic devices. Writing in Nature Nanotechnology, Dimitrios Stamou and colleagues at the University of Copenhagen now report an artificial bioreactor system compos! ed of unilamellar vesicles that can mix aqueous volumes as small as 10−19 l in a reproducible and parallelized fashion3. Microfluidics and microelectrofluidics that use channel- or droplet-based4, 5 protocols are well-established. However, the engineering of chemical reactor systems with nanoscale dimensions is still at an early stage of developement6, 7, 8. There are several elegant examples of solid-state reactor systems that operate at this scale9, 10, but such structures often use top-down fabrication techniques that require traditional clean-room processes and can therefore be difficult to implement. Thus, creating nanoreactors using dynamic self-assembly or self-organizing materials would be significantly simpler. The self-assembly of such structures is not exactly new. The biological cell is capable of precisely mixing, processing and separating catalysts, reactants and products, and achieves this using nanoscale vesicular and tubular lipid-membrane containers. Artificial nanoreactors have yet to reach such levels of structural complexity and diversity, but by borrowing operating principles from nature a number of notable technological advances have been achieved11, 12. Stamou and colleagues have developed a platform that uses phospholipid vesicles to mix subattolitre (1 attolitre = 10−18 litre) volumes of liquids (Fig. 1). Repeated reactions are achieved by placing one set of reactants in target vesicles that are immobilized on a surface, and placing a complementary set of reactants in mobile cargo vesicles. The target vesicles are immobilized by patterning a glass surface with the protein streptavidin, which binds instantly and tightly to biotin, a small organic molecule attached to the surface of the target vesicles. The fusion of the vesicles and the formation of the products are monitored using fluorescence microscopy. Figure 1: Simplified schematic illustrating sequential enzymatic reactions initiated by the fusion of nanoscale phospholipid vesicles. , The target vesicles (blue spheres with orange outer layer) have diameters of ~400 nm, are immobilized on a surface, contain a hydrolase enzyme (the catalyst; dark-blue shapes), and have a positively charged membrane. The cargo vesicles (yellow) are mobile, contain an enzyme substrate (the reactant; white circles), and have a negatively charged membrane. The membranes of the target and cargo vesicles are also fitted with the acceptor and donor moieties of a FRET dye. When a suspension containing the cargo vesicles is deposited on the surface, the target and cargo vesicles fuse, and fluorescent emission from the FRET dye is observed. The enzyme substrate then enters the target vesicle and reacts with the catalyst to produce fluorescein (green circles), which can be detected through its fluorescent emission. ,, By depositing a second suspension containing different cargo vesicles on the same target vesicles, a second set of reactions can be initiated. Stamou and colleagues3 r! eported up to four consecutive reactions. , After all the reactions are complete the target vesicles are now mostly neutral and highly fluorescent. * Full size image (134 KB) Previously, there were no reliable means to initiate chemical reactions in containers of such a small size. For larger, micrometre-sized vesicles, which typically encapsulate picolitre volumes, this has been achieved by direct injection, electrofission, electroporation or nanotube-mediated merging13. Stamou and colleagues were able to carry out the controlled fusion of their nanocontainers by functionalizing the target and cargo vesicles with lipids of opposite charge to create an attractive interaction between them. The target vesicles are loaded with alkaline phosphatase — a hydrolase enzyme capable of catalysing the removal of phosphate groups from organic molecules — and their membranes are fitted with the acceptor moiety of a fluorescence resonance energy transfer (FRET) dye. The cargo vesicles contain the enzyme substrate — a fluorescein derivative in which the emission of light is blocked by phosphate groups — and their membranes are fitted with the donor moiety of the FRET dye. When the cargo and target vesicles fuse, it is possible to excite the FRET donor and simultaneously detect emission from the acceptor (when the acceptor and donor moieties come into close proximity and energy is transferred between them). It also becomes possible to detect product emission (at a different wavelength) once the hydrolase enzyme has catalysed the removal of the phosphate groups from the fluorescein. Approximately 88% of the surface-immobilized containers generated product. Furthermore! , up to four consecutive fusion-reaction events could be performed by tuning the size ratio and charge balance between the target and cargo containers. The Copenhagen team also illustrates the versatility of the approach by carrying out two further catalytic reactions; one involving a membrane-activated lipase from a thermophile source and the other using a horseradish peroxidase. Efficient, precise and reproducible solution processing is a requirement of all modern bioanalytical applications, and the work of Stamou and colleagues could be useful in a number of these applications. Assays used in medical diagnostics, and the rapid screening of large chemical libraries to discover novel biologically relevant chemical entities, would, in particular, benefit from an ultrasmall volume fluidic platform technology. However, a number of challenges must be overcome for such developments to become possible. These include improving control over the reactor geometry and increasing the percentage of active reactors, as well as developing simpler surface immobilization schemes and improving the shelf-life of the devices. Methods to transfer or harvest products from such vesicle reactors in a similarly controlled way would be highly desirable. References * References * Author information * Renggli, K.et al. Adv. Funct. Mater.21, 1241–1259 (2011). * ChemPort * ISI * Article * Van Oijen, A. M.Curr. Opin. Biotechnol.22, 75–80 (2011). * ChemPort * ISI * PubMed * Article * Christensen, S. M., Bolinger, P-Y., Hatzakis, N. S., Mortensen, M. W. & Stamou, D.Nature Nanotech.7, 51–55 (2012). * Article * Whitesides, G. M.Nature442, 368–373 (2006). * ChemPort * ISI * PubMed * Article * Wheeler, A. R.Science322, 539–540 (2008). * ChemPort * ISI * PubMed * Article * Monteiro, M. J.Macromolecules43, 1159–1168 (2010). * ChemPort * ISI * Article * Tanner, P.et al. FEBS Lett.585, 1699–1706 (2011). * ChemPort * ISI * PubMed * Article * Bolinger, P. Y., Stamou, D. & Vogel, H.J. Am. Chem. Soc.126, 8594–8595 (2004). * ChemPort * ISI * PubMed * Article * Levene, M. J.et al. Science299, 682–686 (2003). * ChemPort * ISI * PubMed * Article * Bruckbauer, A., Zhou, D., Ying, L., Abell, C. & Klenerman, D.Nano Lett.4, 1859–1862 (2004). * ChemPort * ISI * Article * Collier, C. P. & Simpson, M. L.Curr. Opin. Biotechnol.22, 516–526 (2011). * ChemPort * ISI * PubMed * Article * Comellas-Aragones, M.et al. Nature Nanotech.2, 635–639 (2007). * ChemPort * Article * Jesorka, A.et al. Nature Protoc.6, 791–805 (2011). * ChemPort * ISI * Article Download references Author information * References * Author information Affiliations * Department of Chemical and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden * Aldo Jesorka & * Owe Orwar * Sanofi-Aventis R&D, 91385 Chilly-Mazarin Cedex, France * Owe Orwar Corresponding author Correspondence to: * Owe Orwar Author Details * Aldo Jesorka Search for this author in: * NPG journals * PubMed * Google Scholar * Owe Orwar Contact Owe Orwar Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Nanoimaging: Image contrast using time
- Nat Nanotechnol 7(1):8-9 (2012)
Nature Nanotechnology | News and Views Nanoimaging: Image contrast using time * Kevin Tvrdy1 * Michael S. Strano1 * Affiliations * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:8–9Year published:(2012)DOI:doi:10.1038/nnano.2011.241Published online 28 December 2011 Laser-based imaging can distinguish between semiconducting and metallic nanotubes in vitro and in vivo, offering a way to study the interactions of carbon nanostructures in biological systems without the use of labels. Subject terms: * Carbon nanotubes and fullerenes * Surface patterning and imaging Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg "Astronomy is not like a physics lab," said Brian Schmidt shortly after it had been announced that he had shared the 2011 Nobel Prize in Physics1. "You can't design an experiment. You need to look up into the heavens, and sort of figure out what the cosmos has given you." What Schmidt and his fellow laureates, Saul Perlmutter and Adam Reiss, did in their prize-winning work was something that astronomers have been doing for decades — they looked back in time. But what they discovered shocked the world of physics and astronomy — the expansion of the universe was accelerating. Traditionally, biologists have designed microscopy experiments around two- or three-dimensional spatial imaging. Now, writing in Nature Nanotechnology, Ji-Xin Cheng and co-workers2 at Purdue University — much like this years' winners of the Nobel Prize in Physics — show that using the fourth dimension of time can lead to a new form of image contrast in biological samples. They used a method called pump–probe spectroscopy3 to distinguish between metallic and semiconducting single-walled carbon nanotubes in vitro (in cells) and in vivo (in mice), offering a technique to better understand the interactions of carbon nanostructures with biological systems. Pump–probe spectroscopy is a dynamic technique that involves using a laser pulse (the pump) to perturb the sample, and a second pulse (the probe) to measure the sample after it has been perturbed. To use time as a dimension, Cheng and colleagues spatially overlapped the pump beam (which is modulated at a controlled frequency) with the probe beam, which is monitored at the same frequency (Fig. 1). A lock-in amplifier was used to measure the phase shift (the time delay) between the pump and probe pulse trains. This phase shift, which is insensitive to the broad range of bandgaps in a sample of unsorted nanotubes, was used to identify whether the nanotubes were metallic or semiconducting. Figure 1: Schematic showing the experimental set-up used to image carbon nanotubes in the time domain. The intensity of the pump beam (blue) is modulated by a Pockels cell at a controlled frequency of 1.13 MHz. The pump beam perturbs the electronic states of the carbon nanotubes and the enhanced (shown) or reduced absorption of the probe beam (red) is indicative of the semiconducting or metallic nature of the nanotubes. When the overlapping pump and probe beams emerge from the sample (blue rectangle), the phase shift between the two beams, which depends on the nature of the material in the sample, is measured by the lock-in amplifier. The nanotubes can be distinguished because semiconducting nanotubes produce a positive signal, whereas metallic nanotubes produce a negative signal. Because both signals are independent of the thermal lens signals from red blood cells, the technique can be used for in vivo imaging with submicrometre resolution. * Full size image (260 KB) Cheng and colleagues first tested the spatial resolution of the method by obtaining a phase-shift map of aligned nanotubes grown on a quartz substrate. A line-scan across two nanotubes, one of which was metallic and the other semiconducting, revealed a lateral resolution of less than 400 nm for both tubes. At this spatial resolution, they studied how a sample of DNA-wrapped carbon nanotubes4 with different metallicity behaved inside an intact mammalian cell. It turns out that incubating the nanotube sample with cells for more than eight hours caused the metallic nanotubes to aggregate in the cell culture medium and on the cell surface, whereas no such aggregation of the semiconducting nanotubes was observed. Although the aggregation behaviours were different, both the semiconducting and metallic nanotubes showed similar trafficking mechanisms inside the cell. For example, both were actively transported into the cells by fusion with the cell membrane and were eventually retur! ned to the cell surface for expulsion from the cells. Because this imaging technique relies on relatively low laser power, the intracellular trafficking of the nanotubes could be monitored without the risk of photobleaching or photodamage5. Furthermore, the method could be used to image and track nanotubes in vivo. In biological samples, the signal of interest has to be detected against a high level of background noise produced by various biological components, particularly the red blood cells. Cheng and co-workers injected nanotubes into mice and monitored the nanotubes in a blood vessel in the mouse ear-lobe. Because the method can monitor the signals from the nanotubes and those from the red blood cells in separate lock-in detector channels, both signals could be observed at the same time without the need for signal deconvolution. The technique demonstrated by Cheng and co-workers is similar in some ways to transient absorption microscopy6, but the reported signal is unique, due to a lack of direct comparison between transmission of the probe pulse when there is a pump pulse with the transmission when there is no pump pulse. However, the origins of the phase differences measured by the Purdue team are still not completely understood2, 3. To fully utilize this technique, further investigations on the origin of the signal, its presence in other nanomaterials, and the type of quantitative data that can be drawn from it would be required. Being able to visualize and differentiate metallic and semiconducting nanotubes with submicrometre resolution and without any tissue damage will clearly have a big impact in various fields of nanotechnology and in cell biology. And as scientists, it is useful to remember that whether gazing into the heavens or squinting at the darkest corners of a living cell, doing so within the time domain offers an entirely new, and sometimes unforeseen, dimension of insight. References * References * Author information * http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/schmidt-telephone.html * Tong, L.et al. Nature Nanotech.7, 56–61 (2012). * Article * Jung, Y.et al. Phys. Rev. Lett.105, 217401 (2010). * ChemPort * PubMed * Article * Zheng, M.et al. Nature Mater.2, 338–342 (2003). * ChemPort * ISI * Article * Lin, Y.et al. J. Mater. Chem.14, 527–541 (2004). * ChemPort * Article * Berera, R., van Grondelle, R. & Kennis, J. T. M.Photosynth. Res.101, 105–118 (2009). * ChemPort * PubMed * Article Download references Author information * References * Author information Affiliations * Kevin Tvrdy and Michael S. Strano are in the Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA Corresponding author Correspondence to: * Michael S. Strano Author Details * Kevin Tvrdy Search for this author in: * NPG journals * PubMed * Google Scholar * Michael S. Strano Contact Michael S. Strano Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Bionanoscience: Nanoparticles in the life of a cell
- Nat Nanotechnol 7(1):9-10 (2012)
Nature Nanotechnology | News and Views Bionanoscience: Nanoparticles in the life of a cell * Huw Summers1Journal name:Nature NanotechnologyVolume: 7,Pages:9–10Year published:(2012)DOI:doi:10.1038/nnano.2011.207Published online 06 November 2011 The cycle of cell birth, growth and division can affect the uptake and dilution of nanoparticles in cells, suggesting that the evolution of nanoparticle dose within a cell population is linked to the life cycle of cells. Subject terms: * Nanomedicine * Nanoparticles * Environmental, health and safety issues Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Nanomedicine promises to use nanotechnology to treat diseases at the cellular level using drug therapies that are targeted to malignant tissues. Over the past decade, new nanoparticles have been developed for drug delivery, imaging, the detection of biomarkers, and other diagnostic and therapeutic applications1. It has been shown that nanomaterial properties such as size and surface charge can affect the dose of nanoparticles that is delivered into a biological system2. However, more recently it has been realized that cells are active components in this delivery and uptake process, and that the biology of mammalian cells is therefore extremely important in determining the pharmacology of nanodrugs. Now, writing in Nature Nanotechnology, Kenneth Dawson and colleagues at University College Dublin report that the cycle of cell birth, growth and proliferation has an important role in determining nanoparticle dose3, with cells early in the cell growth cycle accumulating more nanoparticles than those later in the cycle. The cell growth cycle, which leads to cell division and replication, consists of four phases: G0/G1, S, G2 and M. In most studies on nanoparticle uptake, cells are exposed to fluorescently labelled nanoparticles and the fluorescence of the nanoparticles inside the cells (as a result of uptake) is measured by flow cytometry. However, this measurement gives the mean fluorescence averaged over all the cells, each in different phases of their life cycle. Because various cellular processes (such as expression of membrane proteins) vary in each phase of the cell cycle, it is important to understand how the different phases may affect nanoparticle uptake. To directly correlate the dose of fluorescent polystyrene nanoparticles with the phase of the cell cycle on a cell-by-cell basis, Dawson and co-workers exposed cells to different concentrations of nanoparticles for different periods of time, and resolved the population of treated cells into different phases of the cell cycle by monitoring DNA synthesis. The cell nucleus is stained with a fluorescent dye that binds to DNA to give a measure of the total nuclear content of the cell. As cells pass from initial growth (G0/G1 phase) to synthesis of DNA (S phase), the fluorescence intensity of the cell nucleus doubles and then subsequently halves as the cells divide into daughter cells during the G2 and M phases. This generates a distribution of cell fluorescence that resolves the total nuclear fluorescent signal from flow cytometry measurements into different phases of the cell cycle for the population of nanoparticle-treated cells examined4. Thus, the nanoparticle fluorescence in! individual cells can be directly related to their nuclear fluorescence to obtain measures of particle dose and cell cycle position. Although the dilution of nanoparticle dose through cell division has been studied previously5, these are the first detailed measurements of the kinetics of how accumulation of nanoparticle dose competes with its dilution when the cell divides. Dawson and co-workers find that the rate of uptake of nanoparticles is constant across the cell cycle, and so the total accumulated dose increases linearly with time until a cell divides, at which point the dose is shared between the two daughter cells. Under these conditions, the maximum nanoparticle dose delivered to a given cell is dependent on its age at the start of nanoparticle exposure; new-born cells will accumulate nanoparticles across the whole of their life cycle (approximately 22 hours for the cancer cells used in the study), whereas older cells will have a limited accumulation period before the dose is reduced by division (Fig. 1). Figure 1: The cell cycle is a series of events that lead to cell division and replication. As the cycle progresses from left to right, cells prepare for cell division. , When cells (green ovals) in the early phase of the cycle are exposed to nanoparticles (red dots), there is plenty of time for the nanoparticle dose to increase before they are ready to divide. , Cells in the late phase of the cycle have less time to accumulate nanoparticles before cell division occurs, and the division process further reduces the nanoparticle dose. * Full size image (161 KB) By specifically labelling S-phase cells and tracking their progression through the cell cycle, they show that the nanoparticle dose is constant until the point of cell division. This confirms that dose dilution is due to cell proliferation rather than particle expulsion from the cells. Further evidence for the linear dose accumulation hypothesis is provided by experiments in which the whole cell population is forced into the early phase of the cell cycle by depriving them of serum. In this case, the maximum nanoparticle dose showed an increase because all cells accumulated particles for their entire life cycle. Mathematical modelling of the dose kinetics corroborates the experimental data. The evolution of the nanoparticle dose within a cell population is intrinsically linked to the point in the life cycle of the cells at which the nanoparticles are introduced. These findings are particularly important for the development of nanotherapeutics that deliver nanoparticles to tumour cells, either as direct anticancer agents or as delivery vectors for other drugs6. As cancer cells have a higher rate of proliferation, nanoparticles may be diluted more rapidly and this can affect the dose. Knowing the phase in which the majority of the cells are in may in effect help us deliver an optimum dose of drugs. In future work, we will need to unravel how the complex behaviour of an active biological system interacts with the molecular dynamics of nanoparticles, and taking into account the life cycle of cells is the first step. Recent work on the variability of viral infection across a colony of cells7 highlights the need to start considering cell–nanoparticle interactions by viewing cells within the context of a community. The cell's position within the web of interactions found in a cohesive colony, such as a tumour, may affect individual cell behaviour through the spatial, temporal and lineage relationships that link populations of cells. It is only with this community perspective that full knowledge of the impact of nanoparticles on the life of cells will be gained. References * References * Author information * Murthy, S. K.Int. J. Nanomed.2, 129–141 (2007). * ChemPort * ISI * Hardman, R.Environ. Health Persp.114, 165–172 (2006). * ISI * Article * Kim, J. A., Åberg, C., Salvati, A. & Dawson, K. A.Nature Nanotech.http://dx.doi.org/10.1038/nnano.2011.191 (2011). * Krishnan, A.J. Cell Biol.66, 188–193 (1975). * ChemPort * ISI * PubMed * Article * Summers, H. D.et al. Nature Nanotech.6, 170–174 (2011). * ChemPort * Article * Ferrari, M.Nature Rev. Cancer5, 161–171 (2005). * Article * Snijder, B.Nature461, 520–523 (2009). * ChemPort * ISI * PubMed * Article Download references Author information * References * Author information Affiliations * Huw Summers is in the Centre for Nanohealth, College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP, UK Corresponding author Correspondence to: * Huw Summers Author Details * Huw Summers Contact Huw Summers Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - The properties and applications of nanodiamonds
- Nat Nanotechnol 7(1):11-23 (2012)
Nature Nanotechnology | Review The properties and applications of nanodiamonds * Vadym N. Mochalin1 * Olga Shenderova2 * Dean Ho3, 4 * Yury Gogotsi1 * Affiliations * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:11–23Year published:(2012)DOI:doi:10.1038/nnano.2011.209Published online 18 December 2011 Abstract * Abstract * Author information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Nanodiamonds have excellent mechanical and optical properties, high surface areas and tunable surface structures. They are also non-toxic, which makes them well suited to biomedical applications. Here we review the synthesis, structure, properties, surface chemistry and phase transformations of individual nanodiamonds and clusters of nanodiamonds. In particular we discuss the rational control of the mechanical, chemical, electronic and optical properties of nanodiamonds through surface doping, interior doping and the introduction of functional groups. These little gems have a wide range of potential applications in tribology, drug delivery, bioimaging and tissue engineering, and also as protein mimics and a filler material for nanocomposites. View full text Subject terms: * Nanomaterials * Nanomedicine * Synthesis and processing Figures at a glance * Figure 1: Detonation synthesis of nanodiamonds. , To synthesize nanodiamonds, explosives with a negative oxygen balance (for example a mix of 60 wt% TNT (C6H2(NO2)3CH3) and 40 wt% hexogen (C3H6N6O6)) are detonated in a closed metallic chamber in an atmosphere of N2, CO2 and liquid or solid H2O. After detonation, diamond-containing soot is collected from the bottom and the walls of the chamber. , Phase diagram showing that the most stable phase of carbon is graphite at low pressures, and diamond at high pressures, with both phases melting when at temperatures above 4,500 K (with the precise melting temperature for each phase depending on the pressure). The phase diagrams for nanoscale carbon are similar, but the liquid phase is found at lower temperatures38, 39. During detonation, the pressure and temperature rise instantaneously, reaching the Jouguet point (point A), which falls within the region of liquid carbon clusters of 1–2 nm in size for many explosives. As the temperature and pressure decrease along the isentrope! (red line), carbon atoms condense into nanoclusters, which further coalesce into larger liquid droplets and crystallize39. When the pressure drops below the diamond–graphite equilibrium line, the growth of diamond is replaced by the formation of graphite. , Schematic of the detonation wave propagation showing (I) the front of the shock wave caused by the explosion; (II) the zone of chemical reaction in which the explosive molecules decompose; (III) the Chapman–Jouguet plane (where P and T correspond to point A in Fig. 1b, indicating the conditions when reaction and energy release are essentially complete); (IV) the expanding detonation products; (V) the formation of carbon nanoclusters; (VI) the coagulation into liquid nanodroplets; and (VII) the crystallization, growth and agglomeration of nanodiamonds39. * Figure 2: Structure of a single nanodiamond particle. , Schematic model illustrating the structure of a single ~5-nm nanodiamond after oxidative purification. The diamond core is covered by a layer of surface functional groups, which stabilize the particle by terminating the dangling bonds. The surface can also be stabilized by the conversion of sp3 carbon to sp2 carbon. A section of the particle has been cut along the amber dashed lines and removed to illustrate the inner diamond structure of the particle. , Close-up views of two regions of the nanodiamond shown in . The sp2 carbon (shown in black) forms chains and graphitic patches (). The majority of surface atoms are terminated with oxygen-containing groups (; oxygen atoms are shown in red, nitrogen in blue). Some hydrocarbon chains (green, lower left of ) and hydrogen terminations (hydrogen atoms are shown in white) are also seen. , Each nanodiamond is made up of a highly ordered diamond core. Some nanodiamonds are faceted, such as the one shown in this transmission electr! on micrograph, whereas most have a rounded shape, as shown in . The inset is a fast Fourier transform of the micrograph, which confirms that this nanodiamond has a highly ordered diamond core. Panel , reproduced with permission from ref. 19, © 2011 ACS. * Figure 3: Raman spectroscopy and structure of nanodiamond. Electron micrographs showing detonation soot (bottom), purified nanodiamond (middle) and oxidized nanodiamond (top). The diamond cores in detonation soot seem to be completely covered by graphitic shells, and this is confirmed by the Raman spectrum (black line), which is dominated by the G-band of graphitic carbon at 1,590 cm−1 and has no diamond peak. Purified nanodiamonds are partially covered by a thin layer of graphite, so a diamond peak can be seen at 1,328 cm−1 in the Raman spectrum (blue line). This thin layer of graphite is completely removed by oxidation in air, so the Raman spectrum of oxidized nanodiamonds has an even stronger diamond peak (red line). The diamond peak in the Raman spectrum of purified and air oxidized nanodiamond (inset ) is a combination of peaks originating from larger (I) and smaller (II) coherence scattering domains. The phonon confinement model84 gives a good fit (blue line) to experimental data (open circles). The broad feature at 1,500�! ��1,800 cm−1 in the spectrum of air oxidized nanodiamond (inset ) originates from surface functional groups and adsorbed molecules, with some contribution from sp2 carbon atoms. The Raman spectra were recorded following excitation by an ultraviolet laser (325 nm). * Figure 4: Optical properties of nanodiamonds. , De-aggregation by salt-assisted dry milling reduces the size of diamond particles from ~1 μm to less than 10 nm (), and makes suspensions of the particles both darker and more transparent (). The changes in colour are not related to the presence of graphitic carbon56. , Photonic structures formed by centrifugation of suspensions of nanodiamonds in deionized water. , Covalently attaching ODA to nanodiamonds changes their optical properties. ND–ODA absorbs and re-emits light over a wide range of wavelengths, as can be seen in these excitation (purple) and emission (blue) spectra (). Moreover, and in contrast to non-functionalized nanodiamond, ND–ODA is strongly blue fluorescent when illuminated with ultraviolet light (). , ND–ODA can be used for bio-imaging, as illustrated by this confocal micrograph of the fluorescent scaffold made of ND–ODA–PLLA with 7F2 osteoblasts grown on it (see main text for details). Panel , reproduced with permission from ref. 62, © 2008! IOP. * Figure 5: Surface modification. Precise control over surface chemistry requires a sample of purified nanodiamond with only one kind of functional group attached to its surface. Nanodiamond terminated with carboxylic groups (ND–COOH; green region) is a common starting material (and is made by air oxidation or ozone treatment of nanodiamond, followed by treatment in aqueous HCl to hydrolyse anhydrides and remove metal impurities). The surface of ND–COOH can be modified by high-temperature gas treatments (red) or ambient-temperature wet chemistry techniques (blue). Heating in NH3, for example, can result in the formation of a variety of different surface groups including NH2, C–O–H, C≡N and groups containing C=N (refs 9, 48). Heating in Cl2 produces acylchlorides, and F2 treatment forms C–F groups (not shown)67, 137, 138. Treatment in H2 completely reduces C=O to C–O–H and forms additional C–H groups. Hydroxyl (OH) groups may be removed at higher temperatures or with longer hydrogenation tim! es, or by treatment in hydrogen plasma66. Annealing in N2, Ar or vacuum completely removes the functional groups and converts the nanodiamonds into graphitic carbon nano-onions139, 140. A wide range of surface groups and functionalized nanodiamonds can also be produced using wet chemistry treatments. * Figure 6: Advanced atomic-level composite design with nanodiamond. , Three examples of the interfaces between nanodiamond and different matrices. Nanodiamond can bind to SiC through C–Si bonds between the surface of the nanodiamond and the Si atoms in the SiC to produce ND–SiC (left). Carboxylic groups present on the nanodiamond surface can form salts by ion exchange reactions with different metal ions, such as Cu2+ (middle; ref. 141). Metal ions can be later reduced, forming an atomically thin metal layer around the particle. These metallized particles can be used as a means to disperse nanodiamonds in metals that do not wet carbon, and also to produce wear-resistant ND–Cu sliding contacts. Nanodiamonds with surface carboxylic groups can be functionalized through covalent attachment of ODA by amide bond formation (right). , Stress–strain curves for six ND–ODA–PLLA composites that contain different amounts of ND–ODA11. The Young's modulus of a given composite is proportional to the slope of its stress–strain curve. , Aminate! d nanodiamond, produced through covalent attachment of ethylenediamine to carboxylic groups on the surface of the nanodiamond, can replace traditional epoxy curing agents (amines) in reaction with epoxy resin. This results in the covalent incorporation of the nanodiamond into the epoxy polymer network at a molecular level, improving the mechanical properties of the polymer matrix14. * Figure 7: Nanodiamonds and drug delivery. , DNA can be electrostatically attached to nanodiamonds by first covering negatively charged carboxylated nanodiamonds with positively charged PEI800 molecules. A similar electrostatic binding strategy has been used to attach siRNA and doxorubicin (Dox) to nanodiamond104. , Schematic representation of a proposed mechanism for ND–Dox complexes interacting with a cell. 1, Endocytosis of the ND–drug complexes. 2, Diffusion of free drug molecules across the cell membrane. 3, ABC transporter proteins efflux free drug molecules out of the cell, whereas ND–drug complexes are able to remain inside the cell and deliver a steady, lethal dose of the drug to the tumour. , Photographs of breast-cancer tumours after treatment with ND–Dox (top), Dox (middle) and a control (PBS; bottom). Two representative tumours are shown in each case. The large size of the tumours excised after long-term treatment with Dox or PBS illustrates a reduced ability of Dox to inhibit tumour growth owing! to the extreme resistance of the 4T1 breast cancer to chemotherapy. In contrast, treatment with ND–Dox clearly reduces the size of the tumours. Figure reproduced with permission from: , ref. 127, © 2009 ACS; , ref. 142, © 2011 AAAS; , ref. 104, © 2011 AAAS. Author information * Abstract * Author information Affiliations * Department of Materials Science and Engineering and A. J. Drexel Nanotechnology Institute, Drexel University, Philadelphia, Pennsylvania 19104, USA * Vadym N. Mochalin & * Yury Gogotsi * International Technology Center, Raleigh, North Carolina 27617, USA * Olga Shenderova * Departments of Biomedical and Mechanical Engineering, Northwestern University, Evanston, Illinois 60208, USA * Dean Ho * Institute for BioNanotechnology in Medicine (IBNAM) and Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, Illinois 60611, USA * Dean Ho Corresponding author Correspondence to: * Yury Gogotsi Author Details * Vadym N. Mochalin Search for this author in: * NPG journals * PubMed * Google Scholar * Olga Shenderova Search for this author in: * NPG journals * PubMed * Google Scholar * Dean Ho Search for this author in: * NPG journals * PubMed * Google Scholar * Yury Gogotsi Contact Yury Gogotsi Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Synthetically programmable nanoparticle superlattices using a hollow three-dimensional spacer approach
- Nat Nanotechnol 7(1):24-28 (2012)
Nature Nanotechnology | Letter Synthetically programmable nanoparticle superlattices using a hollow three-dimensional spacer approach * Evelyn Auyeung1, 2, 5 * Joshua I. Cutler2, 3, 5 * Robert J. Macfarlane2, 3 * Matthew R. Jones1, 2 * Jinsong Wu4 * George Liu4 * Ke Zhang2, 3 * Kyle D. Osberg1, 2 * Chad A. Mirkin1, 2, 3 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:24–28Year published:(2012)DOI:doi:10.1038/nnano.2011.222Received 14 July 2011 Accepted 14 November 2011 Published online 11 December 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Crystalline nanoparticle arrays and superlattices with well-defined geometries can be synthesized by using appropriate electrostatic1, 2, 3, hydrogen-bonding4, 5 or biological recognition interactions6, 7, 8, 9, 10, 11. Although superlattices with many distinct geometries can be produced using these approaches, the library of achievable lattices could be increased by developing a strategy that allows some of the nanoparticles within a binary lattice to be replaced with 'spacer' entities that are constructed to mimic the behaviour of the nanoparticles they replace, even though they do not contain an inorganic core. The inclusion of these spacer entities within a known binary superlattice would effectively delete one set of nanoparticles without affecting the positions of the other set. Here, we show how hollow DNA nanostructures can be used as 'three-dimensional spacers' within nanoparticle superlattices assembled through programmable DNA interactions7, 11, 12, 13, 14! , 15, 16. We show that this strategy can be used to form superlattices with five distinct symmetries, including one that has never before been observed in any crystalline material. View full text Subject terms: * Molecular self-assembly * Synthesis and processing Figures at a glance * Figure 1: Use of a three-dimensional spacer in DNA-programmable crystallization of gold nanoparticles. , Schematic of the synthesis of three-dimensional spacer particles by crosslinking alkyne-modified DNA on the gold nanoparticle surface and subsequent dissolution of the gold nanoparticle template to create hollow particles (shown in grey). ,, Assembly using a non-self-complementary binary DNA linker system (red and blue strands) results in a bcc lattice when only SNA–AuNPs are used (), and in a simple cubic lattice when a spacer particle is used (). The shaded region surrounding the gold nanoparticle and spacer particles denotes the crosslinked layer between the DNA binding region and the gold (or hollow) core. * Figure 2: SAXS data for seven distinct gold nanoparticle superlattices and 'lattice X'. –, One- and two-dimensional X-ray scattering patterns (left and bottom right of each panel) and schematic unit cell (top right; crosslinked shell omitted) showing the formation of the following superlattices: bcc (); simple cubic (); AB2 (isostructural with AlB2) (); simple hexagonal (); graphite-type (); AB6 (isostructural with Cs6C60) (); bcc (); 'lattice X' (). Five of the seven lattices (,,,,) are made using a mixture of gold and hollow SNA particles. Red traces are the experimentally obtained scattering patterns and the black peaks are the theoretical scattering for each respective lattice. Higher reflections were not indexed for the purpose of clarity. * Figure 3: SAXS data for cubic lattices made from nanoparticles of different sizes. SAXS data with indexed reflections corresponding to a simple cubic lattice made from 5 nm gold nanoparticles (grey line), 10 nm gold nanoparticles (black) and 20 nm gold nanoparticles (red). A hollow SNA particle is incorporated into the centre of each unit cell. Crosslinked shells in the schematic unit cells are omitted for clarity. Lines between particles denote edges of the unit cell, not direct connections between gold nanoparticles. * Figure 4: TEM images of the AB6-type lattices. , AB6-type lattice formed from 20 nm and 10 nm gold nanoparticles. , A bcc lattice formed from 20 nm gold nanoparticles and 10 nm hollow SNA spacers. , Lattice X structure formed from 20 nm hollow SNA spacers and 10 nm gold nanoparticles. All scale bars, 200 nm. Lattice projections shown in the insets are outlined in the TEM images. A three-dimensional reconstruction of a thin (~100 nm) section of the lattice in was obtained from electron tomography. , Representative snapshot of TEM images obtained in the tilt series, where the hole was used as a reference point for alignment (scale bar, 200 nm). ,, Snapshots from the reconstructed lattice along the [100] zone axis () and [111] zone axis () of a bcc lattice. Insets: perfect bcc lattice along each respective zone axis. A unit cell in each reconstructed lattice is outlined in red for clarity. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Evelyn Auyeung & * Joshua I. Cutler Affiliations * Department of Materials Science and Engineering, Evanston, Illinois 60208-3113, USA * Evelyn Auyeung, * Matthew R. Jones, * Kyle D. Osberg & * Chad A. Mirkin * International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA * Evelyn Auyeung, * Joshua I. Cutler, * Robert J. Macfarlane, * Matthew R. Jones, * Ke Zhang, * Kyle D. Osberg & * Chad A. Mirkin * Department of Chemistry, Evanston, Illinois 60208-3113, USA * Joshua I. Cutler, * Robert J. Macfarlane, * Ke Zhang & * Chad A. Mirkin * Electron Probe Instrumentation Center, Northwestern University, Evanston, Illinois 60208-3113, USA * Jinsong Wu & * George Liu Contributions E.A. and J.I.C. designed the experiments, prepared the materials, collected and analysed the data, and wrote the manuscript. R.J.M. designed the experiments and collected and analysed the data. M.R.J. collected and analysed the data. J.W. and G.L. analysed data for the tomography experiments. K.Z. and K.D.O. designed the experiments. C.A.M. designed the experiments and wrote the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Chad A. Mirkin Author Details * Evelyn Auyeung Search for this author in: * NPG journals * PubMed * Google Scholar * Joshua I. Cutler Search for this author in: * NPG journals * PubMed * Google Scholar * Robert J. Macfarlane Search for this author in: * NPG journals * PubMed * Google Scholar * Matthew R. Jones Search for this author in: * NPG journals * PubMed * Google Scholar * Jinsong Wu Search for this author in: * NPG journals * PubMed * Google Scholar * George Liu Search for this author in: * NPG journals * PubMed * Google Scholar * Ke Zhang Search for this author in: * NPG journals * PubMed * Google Scholar * Kyle D. Osberg Search for this author in: * NPG journals * PubMed * Google Scholar * Chad A. Mirkin Contact Chad A. Mirkin Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (3,504 KB) Supplementary information Movies * Supplementary information (2,399 KB) Supplementary movie 1 * Supplementary information (2,308 KB) Supplementary movie 2 * Supplementary information (3,189 KB) Supplementary movie 3 Additional data - Direct visualization of large-area graphene domains and boundaries by optical birefringency
- Nat Nanotechnol 7(1):29-34 (2012)
Nature Nanotechnology | Letter Direct visualization of large-area graphene domains and boundaries by optical birefringency * Dae Woo Kim1, 3 * Yun Ho Kim1, 2, 3 * Hyeon Su Jeong1 * Hee-Tae Jung1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:29–34Year published:(2012)DOI:doi:10.1038/nnano.2011.198Received 12 September 2011 Accepted 13 October 2011 Published online 20 November 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The boundaries between domains in single-layer graphene1, 2, 3, 4 strongly influence its electronic properties5, 6, 7, 8, 9, 10, 11, 12. However, existing approaches for domain visualization, which are based on microscopy and spectroscopy2, 12, 13, 14, 15, 16, are only effective for domains that are less than a few micrometres in size. Here, we report a simple method for the visualization of arbitrarily large graphene domains by imaging the birefringence of a graphene surface covered with nematic liquid crystals. The method relies on a correspondence between the orientation of the liquid crystals and that of the underlying graphene, which we use to determine the boundaries of macroscopic domains. View full text Subject terms: * Electronic properties and devices * Molecular self-assembly * Nanometrology and instrumentation * Structural properties * Surface patterning and imaging * Synthesis and processing Figures at a glance * Figure 1: Schematic of 4-n-alkyl-4′-cyanobiphenyl (nCB) liquid crystals on graphene and TEM image of the graphene film and its domain boundary. , Liquid-crystal film on graphene transferred to various substrates. Graphene was transferred onto glass or SiO2/Si substrates. Bottom: Schematic of liquid crystal film, graphene and substrate, and molecular structure of nematic () liquid-crystal materials and the thermal transition temperature. , The graphene film was transferred on a holey carbon grid (optical microscopy (OM) image) and SAED patterns were taken from square regions; these indicate good long-range order. , Magnified image of the graphene film; a sharp and single hexagonal SAED pattern was obtained from the bright region. * Figure 2: Optical visibility of the domain boundaries of graphene using aligned liquid-crystal material (5CB) and birefringent colour transition while rotating the sample. , POM images of liquid crystal-coated graphene films on a SiO2/Si substrate. Although the domains or boundaries of the graphene are not observable without liquid crystal (inset, optical microscopy), the POM image shows graphene domains and boundaries on the SiO2/Si substrate. was spin-coated on the same sample, which was then heated to 40 °C and subsequently cooled to room temperature. , Liquid-crystal molecules have different orientations depending on the graphene domain, resulting in various birefringent colours. , When the sample in was rotated 30° in a clockwise direction, the greenish region (indicated by the red dashed circle) became dark, because the optical axis of the liquid-crystal molecules anchored on the graphene domain were now parallel to the polarizer direction. Reddish regions in (indicated by the yellow dashed circle) became white as the sample was rotated. ,, Schematic illustrations of and as liquid-crystal molecules are rotated (by rotation of the samp! le stage), resulting in a colour change. P, polarizer; A, analyser. * Figure 3: Schematic of liquid crystal alignment on the surface of the graphene. The alkyl chains of occupy alternate positions on the hexagons within the graphene surface. Graphene grown on the surface of the copper foil has multiple domains with different lattice orientations. The alignment directions of liquid-crystal molecules differ in accordance with the graphene domains. Red arrows indicate the aligned director field of the liquid crystal. Short yellow lines indicate liquid-crystal molecules lying (or planar anchoring) on the graphene film. * Figure 4: Thermal and electric-field recovery of liquid-crystal molecules (5CB) on graphene. , Liquid-crystal molecules aligned on the graphene. , Above the isotropic transition temperature (40 °C), the transmitted intensity of the polarized light is quite low, with the dark colour therefore representing the isotropic state. , As the sample is cooled, liquid-crystal molecules become re-aligned. , In an electric field (2 V µm−1), liquid-crystal molecules undergo a transition that results in a vertically aligned structure of the molecules. When the electric field is removed, the liquid-crystal molecules again become aligned. The inset in Fig. 4e shows a conoscopic interference pattern. * Figure 5: Relationships between copper domains and graphene domains. , Optical image of copper domains after graphene growth. To mark the selected region, gold (40 nm) was evaporated using an electron-beam evaporator. , POM image of graphene with liquid crystals; graphene has been transferred from the copper region of to the glass substrate. , Extracted boundaries of copper domains in overlapped on the POM image of . The shape and size of the graphene domains match those of the copper domains relatively well. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Dae Woo Kim & * Yun Ho Kim Affiliations * National Research Lab, for Organic Opto-Electronic Materials, Department of Chemical and Biomolecular Eng. (BK-21), Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea * Dae Woo Kim, * Yun Ho Kim, * Hyeon Su Jeong & * Hee-Tae Jung * Department of Biomedical Engineering, Washington University in St Louis, 1 Brookings Drive, St Louis, Missouri 63130, USA * Yun Ho Kim Contributions D.W.K., Y.H.K., H.S.J. and H-T.J. wrote the paper. D.W.K., Y.H.K. and H-T.J. conceived and directed the research. D.W.K. prepared graphene and carried out characterization using electron microscopy. D.W.K., Y.H.K. and H.S.J. carried out liquid-crystal cell experiments and interpreted liquid-crystal alignment on the graphene. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Hee-Tae Jung Author Details * Dae Woo Kim Search for this author in: * NPG journals * PubMed * Google Scholar * Yun Ho Kim Search for this author in: * NPG journals * PubMed * Google Scholar * Hyeon Su Jeong Search for this author in: * NPG journals * PubMed * Google Scholar * Hee-Tae Jung Contact Hee-Tae Jung Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (955 KB) Supplementary information Additional data - Mechanically controlled molecular orbital alignment in single molecule junctions
- Nat Nanotechnol 7(1):35-40 (2012)
Nature Nanotechnology | Letter Mechanically controlled molecular orbital alignment in single molecule junctions * Christopher Bruot1 * Joshua Hihath1, 2 * Nongjian Tao1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:35–40Year published:(2012)DOI:doi:10.1038/nnano.2011.212Received 20 September 2011 Accepted 31 October 2011 Published online 04 December 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Research in molecular electronics often involves the demonstration of devices that are analogous to conventional semiconductor devices, such as transistors and diodes1, but it is also possible to perform experiments that have no parallels in conventional electronics. For example, by applying a mechanical force to a molecule bridged between two electrodes, a device known as a molecular junction, it is possible to exploit the interplay between the electrical and mechanical properties of the molecule to control charge transport through the junction2, 3, 4, 5, 6, 7, 8. 1,4′-Benzenedithiol is the most widely studied molecule in molecular electronics9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and it was shown recently that the molecular orbitals can be gated by an applied electric field11. Here, we report how the electromechanical properties of a 1,4′-benzenedithiol molecular junction change as the junction is stretched and compressed. Counterintuitively, the conductance increases ! by more than an order of magnitude during stretching, and then decreases again as the junction is compressed. Based on simultaneously recorded current–voltage and conductance–voltage characteristics, and inelastic electron tunnelling spectroscopy, we attribute this finding to a strain-induced shift of the highest occupied molecular orbital towards the Fermi level of the electrodes, leading to a resonant enhancement of the conductance. These results, which are in agreement with the predictions of theoretical models14, 15, 16, 17, 19, 20, also clarify the origins of the long-standing discrepancy between the calculated and measured conductance values of 1,4′-benzenedithiol, which often differ by orders of magnitude21. View full text Subject terms: * Electronic properties and devices Figures at a glance * Figure 1: Changes in conductance of BDT due to stretching. , Schematic of a molecular junction (top). Schematic energy diagram (bottom) showing how the energy of the HOMO changes relative to EF of the electrodes as electrode separation increases. , Characteristic conductance histograms at room temperature (black) and 4.2 K (red). Histograms offset for clarity. ,, Plots of conductance (in units of G0) versus electrode displacement measured at 4.2 K. For some junctions the conductance increases with displacement (), whereas for others the conductance–displacement curves are either flat or bowl-shaped (). Different colours in and represent different junctions, and the traces have been offset for clarity. * Figure 2: Differential conductance and IETS of BDT junctions as a result of stretching and compressing. , Plot of conductance G versus electrode displacement for a junction during repeated stretching and compressing at 4.2 K. , Differential conductance curves (G versus V) for positions 1–8 in . The curves show clear, reversible changes in asymmetry as the mechanical force changes. , IET spectra (d2I/dV2 versus V) also show reversible changes. Both the G–V curves and the IET spectra are offset for clarity. ,, Plots of rectification ratio at V = 0.2 V () and peak height ratio for the ±14 mV mode () versus electrode displacement. Red curves are fits to guide the eye. See Supplementary Information for all G–V curves and IET spectra for this junction, including the assignment of vibration modes to the observed peaks. * Figure 3: Conductance switching behaviour of two BDT junctions. , Plot of conductance G versus electrode displacement showing switching and increasing conductance behaviour. , Differential conductance (G–V) curves at the four different positions indicated in : the curve at position 3 is clearly more symmetric than at position 2. ,, IET spectra at positions 1 and 2 () and 3 and 4 () in , showing that changes in the conductance lead to changes in the intensity and shape of the peaks. IET spectra are plotted on the same scale and are offset for clarity. , Plot of conductance versus displacement for a different junction, showing the conductance first decreasing and then increasing after a switching event. , G–V curves from positions 1 and 2 in . All measurements performed at 4.2 K. * Figure 4: Exploring the energy levels of a molecular junction. , Plot of conductance versus electrode displacement of a BDT junction at 4.2 K recorded with the junction being stretched and compressed much faster than the plots shown in Figs 2 and 3. The conductance decreases when the junction is compressed, and then increases to a relatively high value when the junction is stretched. , Plots of current I versus bias voltage V at the three positions indicated in , recorded with V being swept much faster than the plots shown in Figs 2 and 3. Thin lines are fits to the data. , Plots of ln(I/V2) versus 1/V for three different values of the displacement (based on fits to the I–V curves in ). The height of the barrier that electrons have to tunnel through is determined by the transition voltage, which is the voltage corresponding to the minimum of each plot (indicated by arrows). The height of the barrier decreases as the molecule is stretched. Author information * Abstract * Author information * Supplementary information Affiliations * Center for Bioelectronics and Biosensors, Biodesign Institute, School of Electrical, Energy and Computer Engineering, Arizona State University; Tempe, Arizona 85287-5801, USA * Christopher Bruot, * Joshua Hihath & * Nongjian Tao * Department of Electrical and Computer Engineering, University of California Davis, Davis, California 95616, USA * Joshua Hihath Contributions N.J.T. conceived the experiment. C.B. and J.H. performed the experiment and analysed the data. C.B., J.H. and N.J.T. co-wrote the paper. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Nongjian Tao Author Details * Christopher Bruot Search for this author in: * NPG journals * PubMed * Google Scholar * Joshua Hihath Search for this author in: * NPG journals * PubMed * Google Scholar * Nongjian Tao Contact Nongjian Tao Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,746 KB) Supplementary information Additional data - A surface-anchored molecular four-level conductance switch based on single proton transfer
- Nat Nanotechnol 7(1):41-46 (2012)
Nature Nanotechnology | Letter A surface-anchored molecular four-level conductance switch based on single proton transfer * Willi Auwärter1, 2 * Knud Seufert1, 2 * Felix Bischoff1 * David Ecija1 * Saranyan Vijayaraghavan1 * Sushobhan Joshi1 * Florian Klappenberger1 * Niveditha Samudrala1 * Johannes V. Barth1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:41–46Year published:(2012)DOI:doi:10.1038/nnano.2011.211Received 13 June 2011 Accepted 31 October 2011 Published online 11 December 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The development of a variety of nanoscale applications1, 2 requires the fabrication and control of atomic3, 4, 5 or molecular switches6, 7 that can be reversibly operated by light8, a short-range force9, 10, electric current11, 12 or other external stimuli13, 14, 15. For such molecules to be used as electronic components, they should be directly coupled to a metallic support and the switching unit should be easily connected to other molecular species without suppressing switching performance. Here, we show that a free-base tetraphenyl-porphyrin molecule, which is anchored to a silver surface, can function as a molecular conductance switch. The saddle-shaped molecule has two hydrogen atoms in its inner cavity that can be flipped between two states with different local conductance levels using the electron current through the tip of a scanning tunnelling microscope. Moreover, by deliberately removing one of the hydrogens, a four-level conductance switch can be created. The res! ulting device, which could be controllably integrated into the surrounding nanoscale environment, relies on the transfer of a single proton and therefore contains the smallest possible atomistic switching unit. View full text Subject terms: * Molecular machines and motors * Surface patterning and imaging Figures at a glance * Figure 1: Double proton transfer in 2H-TPP on Ag(111). , Pseudo three-dimensional rendering of a high-resolution STM image of 2H-TPP adsorbed on Ag(111). , Corresponding model consistent with the NEXAFS data (cf. Supplementary Fig. S1) highlights the saddle-shaped deformation resulting in two inequivalent pairs of pyrrole rings (α-pyr, marked in orange, and κ-pyr) , STM image of configuration Hα (I = 0.1 nA, U = −0.2 V). , Model highlighting the saddle-shaped deformation and the position of the hydrogen pair in configuration Hα. , STM image of configuration Hκ (I = 0.1 nA, U = −0.2 V). , Model of configuration Hκ. , Spatial dependence of the switching rate displayed with colour-coded dots (recorded at −1.6 V and 2 nA). The highest rates (yellow markers) are observed above the α-pyr. , Current versus time trace recorded at −1.9 V at the position indicated in . A switching between two current levels representing the high (h) and low (l) conductance states is clearly discernible. * Figure 2: Sequential deprotonation of 2H-TPP on Ag(111). , STM image of 2H-TPP (I = 0.2 nA, U = −0.2 V). , STM image of 1H-TPP. , STM image of 0-TPP. –, Tentative models illustrating the 2H-TPP, singly deprotonated 1H-TPP and fully deprotonated 0H-TPP species. , I(t) trace recorded at the centre of 2H-TPP at 1.9 V. The sudden decrease in current represents the single deprotonation to 1H-TPP. * Figure 3: Visualization of the four proton positions in 1H-TPP on Ag(111). –, STM images (–) of the same 1H-TPP molecule in four configurations representing the hydrogen positions schematically shown in corresponding models – (I = 0.2 nA, U = −0.2 V). , Current trace recorded in a slightly asymmetric position on a κ-pyr position (marked by the dot in ). The four conductance levels are clearly discernible (I = 0.4 nA, U = −1.6 V). * Figure 4: Current dependence of switching rate S for 2H-TPP and 1H-TPP recorded on an α-pyr position. , S increases linearly with tunnelling current I, pointing to a one-electron process driving proton transfer. Every single data point represents one I(t) spectrum where the current is averaged over the whole spectrum. The absolute rate depends on tip geometry (see Supplementary Information). The tip used for this experiment yields a rate S2H-TPP of 3.0 ± 0.1 s−1 nA−1 at a constant voltage of −1.6 V. , Comparison of S for 2H-TPP and 1H-TPP for five molecules. The blue line represents the normalized fits for the 2H-TPP species. Normalization to one average rate for 2H-TPP was performed to ease the comparison to 1H-TPP as the absolute rates for 2H-TPP vary from molecule to molecule. The green and red lines show the corresponding rates for the same molecules measured with an identical tip after the first deprotonation. Although the rates are generally similar for 2H-TPP and 1H-TPP, the ratio S1H-TPP/S2H-TPP varies between 0.76 (dark green) and 1.36 (dark red). * Figure 5: Voltage dependence of the switching rate S for 2H-TPP and 1H-TPP excited on an α-pyr position. , Voltage dependences measured at constant currents of 0.5, 2 and 4 nA, respectively, showing a threshold for switching of ~500 mV followed by a sharp increase with similar slope for both polarities (all data points were normalized to 1 at −1.5 V using scaling factors of 0.28 and 0.13, respectively). , Characteristic scanning tunnelling spectra recorded above an α-pyr position of 2H-TPP representing the local density of states, which is clearly asymmetric for both polarities. The broad feature around 700 mV is identified as the LUMO, whereas no occupied resonance is observed at negative bias voltages. The discontinuities observed at elevated voltages of both polarities are effects of proton transfer. , Scheme sketching the stepwise proton transfer via a cis-like intermediate state for 2H-TPP (the phenyl groups are omitted for clarity; see text for discussion). The macrocycle deformation on adsorption potentially lifts the degeneracy of both trans-configurations. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Willi Auwärter & * Knud Seufert Affiliations * Physik Department E20, Technische Universität München, D-85748 Garching, Germany * Willi Auwärter, * Knud Seufert, * Felix Bischoff, * David Ecija, * Saranyan Vijayaraghavan, * Sushobhan Joshi, * Florian Klappenberger, * Niveditha Samudrala & * Johannes V. Barth Contributions K.S., W.A., F.B., D.E., S.V., S.J. and N.S. performed the STM experiments and analysed and interpreted the experimental data. F.K. supported the data analysis and contributed to the NEXAFS experiments. W.A., K.S. and J.V.B conceived the studies and co-wrote the paper. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Willi Auwärter Author Details * Willi Auwärter Contact Willi Auwärter Search for this author in: * NPG journals * PubMed * Google Scholar * Knud Seufert Search for this author in: * NPG journals * PubMed * Google Scholar * Felix Bischoff Search for this author in: * NPG journals * PubMed * Google Scholar * David Ecija Search for this author in: * NPG journals * PubMed * Google Scholar * Saranyan Vijayaraghavan Search for this author in: * NPG journals * PubMed * Google Scholar * Sushobhan Joshi Search for this author in: * NPG journals * PubMed * Google Scholar * Florian Klappenberger Search for this author in: * NPG journals * PubMed * Google Scholar * Niveditha Samudrala Search for this author in: * NPG journals * PubMed * Google Scholar * Johannes V. Barth Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,179 KB) Supplementary information Additional data - Hole spin relaxation in Ge–Si core–shell nanowire qubits
- Nat Nanotechnol 7(1):47-50 (2012)
Nature Nanotechnology | Letter Hole spin relaxation in Ge–Si core–shell nanowire qubits * Yongjie Hu1, 2, 4 * Ferdinand Kuemmeth2 * Charles M. Lieber1, 3 * Charles M. Marcus2 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 7,Pages:47–50Year published:(2012)DOI:doi:10.1038/nnano.2011.234Received 30 September 2011 Accepted 21 November 2011 Published online 18 December 2011 Abstract * Abstract * Author information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Controlling decoherence is the biggest challenge in efforts to develop quantum information hardware1, 2, 3. Single electron spins in gallium arsenide are a leading candidate among implementations of solid-state quantum bits, but their strong coupling to nuclear spins produces high decoherence rates4, 5, 6. Group IV semiconductors, on the other hand, have relatively low nuclear spin densities, making them an attractive platform for spin quantum bits. However, device fabrication remains a challenge, particularly with respect to the control of materials and interfaces7. Here, we demonstrate state preparation, pulsed gate control and charge-sensing spin readout of hole spins confined in a Ge–Si core–shell nanowire. With fast gating, we measure T1 spin relaxation times of up to 0.6 ms in coupled quantum dots at zero magnetic field. Relaxation time increases as the magnetic field is reduced, which is consistent with a spin–orbit mechanism that is usually masked by hyperfine ! contributions. View full text Subject terms: * Electronic properties and devices * Quantum information Figures at a glance * Figure 1: Spin qubit device based on a Ge–Si heterostructure nanowire. Scanning electron micrograph (with false colour) of a Ge–Si nanowire (horizontal) contacted by four palladium contacts (Sdd, Ddd, Ss, Ds, grey) and covered by a HfO2 gate dielectric layer. Top gates L, M and R (blue) induce a double quantum dot on the left device. Plunger gates LP and RP (orange) change the chemical potential of each dot independently, and side gates EL and ER (purple) improve electrical contact to the nanowire. A single quantum dot on the right half of the nanowire (isolated by chemical etching between Ddd and Ds) is capacitively coupled to a floating gate (green) and a tuning gate (yellow), and senses the charge state of the double dot. Inset: transmission electron microscope image of a typical nanowire with a single-crystal germanium core and an epitaxial silicon shell. * Figure 2: Zeeman splitting of confined holes in a single quantum dot. , Differential conductance gdd as a function of source–drain bias VSD and gate voltage VLP. Bright features with VSD > 0 correspond to discrete quantum states of N + 1 holes (N = even) in a single dot formed between gates L and M. , Slices of gdd along dashed lines in (VLP ≈ 655 mV) reveals Zeeman splitting of the N + 1 ground state for a magnetic field of B = 5 T. , Zeeman splitting ΔEZ versus B and a linear fit (dashed line) yield a g-factor of 1.02 ± 0.05. * Figure 3: Hole-spin doublets in a Ge–Si double dot. , Differential conductance dgs/dVL through the sensor dot versus B in the absence of current through the double quantum dot (source–drain bias = 0). Peaks in dgs/dVL versus VL indicate ground-state transitions when holes are removed from the left dot. , B dependence of reduced Coulomb spacings, , where VN are the peak ordinates (emphasized black dotted lines in ). , Data of plotted with guide lines g = 1.0 assuming a gate coupling efficiency α = 0.37 extracted from the single dot device in Fig. 2. * Figure 4: Pulsed gate measurements of spin relaxation times. , Sensor conductance gS near a spin-blocked charge transition between the left and right dot. Spin-to-charge conversion results in pulse triangles that fade away with increasing measurement time τM. Here, N and M indicate an odd number of holes in the left and right dots (denoted (1,1) in the main text). , Visibility I(τM) measured at the centre of the pulse triangle versus τM at different magnetic fields. The fitting curves (solid lines) give T1 = 0.6, 0.3 and 0.2 ms at B = 0 (red), 0.1 (blue) and 1 T (green), respectively. Inset: blue arrows visualize the T1 pulse sequence in gate voltage space when the measurement point is held in the centre of the pulse triangle. Author information * Abstract * Author information Affiliations * Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA * Yongjie Hu & * Charles M. Lieber * Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA * Yongjie Hu, * Ferdinand Kuemmeth & * Charles M. Marcus * School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA * Charles M. Lieber * Present address: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139, USA * Yongjie Hu Contributions Y.H. and F.K. performed the experiments. Y.H. prepared the materials and fabricated the devices. Y.H., F.K., C.M.L. and C.M.M. analysed the data and co-wrote the paper. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Charles M. Lieber or * Charles M. Marcus Author Details * Yongjie Hu Search for this author in: * NPG journals * PubMed * Google Scholar * Ferdinand Kuemmeth Search for this author in: * NPG journals * PubMed * Google Scholar * Charles M. Lieber Contact Charles M. Lieber Search for this author in: * NPG journals * PubMed * Google Scholar * Charles M. Marcus Contact Charles M. Marcus Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Mixing subattolitre volumes in a quantitative and highly parallel manner with soft matter nanofluidics
- Nat Nanotechnol 7(1):51-55 (2012)
Nature Nanotechnology | Letter Mixing subattolitre volumes in a quantitative and highly parallel manner with soft matter nanofluidics * Sune M. Christensen1, 2, 3, 4 * Pierre-Yves Bolinger1, 2, 4 * Nikos S. Hatzakis1, 2, 3 * Michael W. Mortensen1, 2 * Dimitrios Stamou1, 2, 3 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:51–55Year published:(2012)DOI:doi:10.1038/nnano.2011.185Received 01 August 2011 Accepted 27 September 2011 Published online 30 October 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Handling and mixing ultrasmall volumes of reactants in parallel can increase the throughput1, 2 and complexity3 of screening assays while simultaneously reducing reagent consumption1. Microfabricated silicon and plastic can provide reliable fluidic devices4, 5, 6, 7, 8, but cannot typically handle total volumes smaller than ~1 × 10–12 l. Self-assembled soft matter nanocontainers9, 10, 11, 12, 13, 14, 15, 16 can in principle significantly improve miniaturization and biocompatibility, but exploiting their full potential is a challenge due to their small dimensions17. Here, we show that small unilamellar lipid vesicles can be used to mix volumes as small as 1 × 10–19 l in a reproducible and highly parallelized fashion. The self-enclosed nanoreactors are functionalized with lipids of opposite charge to achieve reliable fusion. Single vesicles encapsulating one set of reactants are immobilized on a glass surface and then fused with diffusing vesicles of opposite charge that! carry a complementary set of reactants. We find that ~85% of the ~1 × 106 cm–2 surface-tethered nanoreactors undergo non-deterministic fusion, which is leakage-free in all cases, and the system allows up to three to four consecutive mixing events per nanoreactor. View full text Subject terms: * Nanofluidics * Nanomaterials Figures at a glance * Figure 1: Mixing of subattolitre volumes by fusion of SUVs of opposite charge. , Target SUV reactors containing alkaline phosphatase were immobilized at a PLL-g-PEG/PLL-g-PEG-biotin functionalized glass surface via biotin–neutravidin coupling. Fusion of cargo SUV reactors carrying FDP with the targets caused mixing of enzyme and substrate, thus triggering a biochemical reaction within the confined volumes of the surface-tethered reactors. , Histograms of reactor volumes for populations extruded with 50 nm and 400 nm filters, respectively. , The scheme in monitored by confocal microscopy of Texas Red-DHPE in the target reactor membrane (top), DiD in the cargo reactor membrane (middle) and fluorescein produced from the enzymatic reaction (bottom). Scale bar, 5 µm. A threshold was applied to the images to improve visualization. , Fusion monitored by FRET following lipid mixing. In this experiment target reactors were labelled with DiI (energy acceptor) and cargo reactors with DiO (energy donor). Lipid mixing upon fusion of a reactor pair gave rise to a! n abrupt increase in acceptor fluorescence with a corresponding FRET efficiency above the threshold for lipid mixing (dashed line). , Enzymatic production of fluorescein on fusion of a single reactor pair. Traces show the fluorescence intensity of the cargo reactor membrane label (DiD) and fluorescein. * Figure 2: Characterization of operational performance of the platform. , Scheme showing delivery of FDP to target reactors loaded with alkaline phosphatase (AP). , Volume histograms of all target reactors (N = 1,972) and reactors exhibiting product formation (on average 88%) for the AP–FDP system after 10 min incubation with cargo reactors. The black curve shows the percentage of successful product formation events as a function of reactor volume. The graph includes data from two independent experiments. , Scheme showing reaction experiment with membrane-activated lipase TLL. , Average density of reaction events for three enzyme–substrate systems. AR, Amplex Red. The numbers of fusion events used to calculate reaction densities were 1,676 (AP–FDP), 134 (TLL–CFDA), 42 (HRP–AR). , Leakage assay. , Time traces of the three labels corresponding to a single fusion event characterized by quenching of the donor (target reactor, DiI) and simultaneous increase in acceptor (cargo reactor, DiD) fluorescence. The steady signal of the lumen report! er, A488, demonstrates that the reactor remained sealed during the fusion process. , FRET efficiency trace corresponding to the fusion event in . , Histogram of retained A488 fluorescence quantified from single fusion events such as the one shown in . The retained percentage of A488 was obtained from the average A488 intensity before and after reactor fusion. Fitting the data with a normal distribution showed that the reactors retained 100 ± 1% (s.d.) of the encapsulated fluorophores. * Figure 3: Consecutive mixing events triggered in single target reactors. , Scheme showing repetitive fusion of cargo reactors to a single target. , Time course demonstrating two consecutive product formation events in a single target reactor (horizontal bars have been added to guide the eye). , Lipid mixing traces of cargo and target reactor fluorescence for a target accepting several events. The spikes in donor fluorescence between the labelled events correspond to cargo reactors diffusing in the vicinity of the target without fusing. , Accumulated fusion counts for all target reactors on the surface. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Sune M. Christensen & * Pierre-Yves Bolinger Affiliations * Bionanotechnology and Nanomedicine Laboratory, Department of Neuroscience and Pharmacology, University of Copenhagen, 2100 Copenhagen, Denmark * Sune M. Christensen, * Pierre-Yves Bolinger, * Nikos S. Hatzakis, * Michael W. Mortensen & * Dimitrios Stamou * Nano-Science Center, University of Copenhagen, 2100 Copenhagen, Denmark * Sune M. Christensen, * Pierre-Yves Bolinger, * Nikos S. Hatzakis, * Michael W. Mortensen & * Dimitrios Stamou * Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, 2100 Copenhagen, Denmark * Sune M. Christensen, * Nikos S. Hatzakis & * Dimitrios Stamou Contributions D.S. designed and supervised the project. S.M.C. and P-Y.B. conducted most experiments and data analysis and contributed equally to this work. S.M.C. and D.S. wrote the paper. All authors helped design experiments, discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Dimitrios Stamou Author Details * Sune M. Christensen Search for this author in: * NPG journals * PubMed * Google Scholar * Pierre-Yves Bolinger Search for this author in: * NPG journals * PubMed * Google Scholar * Nikos S. Hatzakis Search for this author in: * NPG journals * PubMed * Google Scholar * Michael W. Mortensen Search for this author in: * NPG journals * PubMed * Google Scholar * Dimitrios Stamou Contact Dimitrios Stamou Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (767 KB) Supplementary information Additional data - Label-free imaging of semiconducting and metallic carbon nanotubes in cells and mice using transient absorption microscopy
- Nat Nanotechnol 7(1):56-61 (2012)
Nature Nanotechnology | Letter Label-free imaging of semiconducting and metallic carbon nanotubes in cells and mice using transient absorption microscopy * Ling Tong1 * Yuxiang Liu2 * Bridget D. Dolash3 * Yookyung Jung4 * Mikhail N. Slipchenko2 * Donald E. Bergstrom3, 5 * Ji-Xin Cheng1, 2, 5 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:56–61Year published:(2012)DOI:doi:10.1038/nnano.2011.210Received 02 September 2011 Accepted 31 October 2011 Published online 04 December 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg As interest in the potential biomedical applications of carbon nanotubes increases1, there is a need for methods that can image nanotubes in live cells, tissues and animals. Although techniques such as Raman2, 3, 4, photoacoustic5 and near-infrared photoluminescence imaging6, 7, 8, 9, 10 have been used to visualize nanotubes in biological environments, these techniques are limited because nanotubes provide only weak photoluminescence and low Raman scattering and it remains difficult to image both semiconducting and metallic nanotubes at the same time. Here, we show that transient absorption microscopy offers a label-free method to image both semiconducting and metallic single-walled carbon nanotubes in vitro and in vivo, in real time, with submicrometre resolution. By using appropriate near-infrared excitation wavelengths, we detect strong transient absorption signals with opposite phases from semiconducting and metallic nanotubes. Our method separates background signals gen! erated by red blood cells and this allows us to follow the movement of both types of nanotubes inside cells and in the blood circulation and organs of mice without any significant damaging effects. View full text Subject terms: * Surface patterning and imaging Figures at a glance * Figure 1: Semiconducting and metallic nanotubes exhibit strong transient absorption signals with opposite phases. , Extinction spectra of pure S-SWNT (left), pure M-SWNT (middle) and DNA-wrapped nanotubes (DNA-SWNT) (right) solutions. E11M, first optical transition of M-SWNTs; E22S, second optical transition of S-SWNTs. , Transient absorption images of pure S-SWNTs (left), pure M-SWNTs (middle) and DNA-SWNTs (right) in the in-phase channel. S-SWNTs and M-SWNTs showed positive and negative contrast, respectively. Scale bars, 2 µm. For all transient absorption images, pump and probe beams were at 707 nm and 885 nm, respectively. The laser power after the objective was 0.7 mW for the pump beam and 1.3 mW for the probe beam. , Raman spectra from pure S-SWNTs (left), pure M-SWNTs (middle) and DNA-SWNTs (right). * Figure 2: Comparison of transient absorption and AFM images of the same nanotube sample show that transient absorption microscopy can detect M-SWNTs and S-SWNTs in a chirality-insensitive manner. –, Transient absorption image (,) and AFM image () of pure S-SWNTs in the same area. –, Transient absorption image (,) and AFM image () of pure M-SWNTs in the same area. The pump and probe polarization directions are vertical in and and horizontal in and , as indicated by two-headed arrows above the transient absorption images. Nanotubes that are detected by transient absorption images are labelled with arrows on both the transient absorption and AFM images. In total, 21 of 25 S-SWNTs (84%) and 15 of 17 M-SWNTs (88%) seen in the AFM image were shown in the transient absorption image, respectively. Scale bars, 1 µm. Laser power post-objective was 0.7 mW for the pump beam and 1.3 mW for the probe beam. ,, Height analyses along the blue dotted lines in and , respectively, show individual nanotubes, not bundles. * Figure 3: Cellular uptake and intracellular trafficking of DNA-SWNTs monitored in real time by transient absorption microscopy. , Transient absorption image of DNA-SWNTs internalized by CHO cells after 24 h incubation. , Time-lapse images showing the fusion process for two nanotubes (indicated by white circle). , Time-lapse images showing the transport of a nanotube (indicated by white circle) back to the cell surface. The yellow line outlines the cell. Grey, transmission of cells; green, S-SWNTs; red, M-SWNTs. Scale bars, 5 µm. Pump, 707 nm; probe, 885 nm. The laser power post-objective was 1 mW for the pump beam and 1.6 mW for the probe beam. * Figure 4: Imaging of RBCs and F127-wrapped SWNTs (F127-SWNTs) circulating in the blood vessels of a mouse earlobe. , Thermal lens signals from isolated RBCs at different z-positions with z = 0 µm as the middle plane of a RBC. Pump, 707 nm; probe, 885 nm. , Phase of thermal lens signals from a RBC as a function of focus position. , In-phase channel signal (X), quadrature channel signal (Y) and amplitude of the thermal lens signal (R = (X2 + Y2)1/2) from a RBC as a function of focus position. ,, Intravital thermal lens imaging of RBCs in the blood vessel inside the earlobe of a mouse injected with pure saline when the pump beam is at 707 nm () and 790 nm (). The probe beam was fixed at 885 nm for both cases. Images were taken by line scanning (x–t scanning, 132 pixels per line). , Intravital imaging of F127-SWNTs in the blood vessel inside the earlobe of a mouse by line scanning (x–t scanning, 105 pixels per line). In-phase channel: transient absorption signals from F127-SWNTs. Quadrature channel: thermal lens signals from RBCs. Pump and probe beams were at 790 nm and 885 nm, respecti! vely. Laser power post-objective was 16 mW for both beams. Scale bars (–), 3 µm. , Intensity profile showing three peaks corresponding to the three dots in . * Figure 5: F127-SWNTs in different organs of treated mice are visualized by transient absorption microscopy at the cellular level. , Image of F127-SWNTs in liver tissue with Kupffer cells labelled with ED-1 antibody. Green, S-SWNTs; red, M-SWNTs; blue, two-photon fluorescent signal from antibody. , A zoom-in image of nanotubes in a Kupffer cell in the liver. , Image of normal liver tissue without nanotubes. , Image of nanotubes in spleen tissue. Grey, transmission of tissue. Scale bars, 5 µm. Pump, 707 nm; probe, 885 nm. Laser power post-objective was 1.0 mW for the pump beam and 1.6 mW for the probe beam. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA * Ling Tong & * Ji-Xin Cheng * Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, USA * Yuxiang Liu, * Mikhail N. Slipchenko & * Ji-Xin Cheng * Department of Medical Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA * Bridget D. Dolash & * Donald E. Bergstrom * Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA * Yookyung Jung * Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA * Donald E. Bergstrom & * Ji-Xin Cheng Contributions L.T. and J.X.C. conceived and designed the experiments. L.T. and Y.L. performed the experiments. L.T. and Y.L. analysed the data. B.D.D., Y.J., M.N.S. and D.E.B. contributed materials and analysis tools. L.T. and J.X.C. co-wrote the paper. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Ji-Xin Cheng Author Details * Ling Tong Search for this author in: * NPG journals * PubMed * Google Scholar * Yuxiang Liu Search for this author in: * NPG journals * PubMed * Google Scholar * Bridget D. Dolash Search for this author in: * NPG journals * PubMed * Google Scholar * Yookyung Jung Search for this author in: * NPG journals * PubMed * Google Scholar * Mikhail N. Slipchenko Search for this author in: * NPG journals * PubMed * Google Scholar * Donald E. Bergstrom Search for this author in: * NPG journals * PubMed * Google Scholar * Ji-Xin Cheng Contact Ji-Xin Cheng Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (4,809 KB) Supplementary information Movies * Supplementary information (1,017 KB) Supplementary movie 1 * Supplementary information (457 KB) Supplementary movie 2 * Supplementary information (1,442 KB) Supplementary movie 3 Additional data - Role of cell cycle on the cellular uptake and dilution of nanoparticles in a cell population
- Nat Nanotechnol 7(1):62-68 (2012)
Nature Nanotechnology | Letter Role of cell cycle on the cellular uptake and dilution of nanoparticles in a cell population * Jong Ah Kim1 * Christoffer Åberg1 * Anna Salvati1 * Kenneth A. Dawson1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 7,Pages:62–68Year published:(2012)DOI:doi:10.1038/nnano.2011.191Received 07 July 2011 Accepted 04 October 2011 Published online 06 November 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Nanoparticles are considered a primary vehicle for targeted therapies because they can pass biological barriers and enter and distribute within cells by energy-dependent pathways1, 2, 3. So far, most studies have shown that nanoparticle properties, such as size4, 5, 6 and surface7, 8, can influence how cells internalize nanoparticles. Here, we show that uptake of nanoparticles by cells is also influenced by their cell cycle phase. Although cells in different phases of the cell cycle were found to internalize nanoparticles at similar rates, after 24 h the concentration of nanoparticles in the cells could be ranked according to the different phases: G2/M > S > G0/G1. Nanoparticles that are internalized by cells are not exported from cells but are split between daughter cells when the parent cell divides. Our results suggest that future studies on nanoparticle uptake should consider the cell cycle, because, in a cell population, the dose of internalized nanoparticles in each ce! ll varies as the cell advances through the cell cycle. View full text Subject terms: * Nanoparticles * Nanomedicine * Environmental, health and safety issues Figures at a glance * Figure 1: The cell cycle and its role in nanoparticle uptake. , The cell cycle, which is a series of events that lead to cell division and replication, consists of four phases: G1, S, G2 and M. Cells in the different phases are distinguished by blue, pink and green nuclei for the G1, S and G2/M phases, respectively. The cell cycle commences with the G1 phase, during which the cell increases its size. During the S phase the cell synthesizes DNA, and in the G2 phase it prepares for cell division, which occurs during the M phase. The two daughter cells then enter the G1 phase. , A cell culture contains a mixture of cells in different phases of their cell cycle, simultaneously undergoing progression and cell division. , Nanoparticle uptake in a cycling cell. The yellow-green circles represent the nanoparticles, which, inside cells, accumulate in the lysosomes, represented by the oval compartment. When the cell divides, the internalized nanoparticles are split between the two daughter cells. Figure not to scale. * Figure 2: Internalization of nanoparticles and ranking of the concentration of nanoparticles in the cells. A549 cells were exposed to 40 nm yellow-green PS-COOH (25 µg ml−1 in cMEM) for up to 72 h before imaging and flow cytometry measurements. , Confocal images after 5, 24 and 72 h of exposure show nanoparticles accumulated in the lysosomes. Blue, nuclei (DAPI); red, lysosomes (LAMP1 antibody); green, nanoparticles. , Mean cell fluorescence intensity obtained by flow cytometry as a function of time shows a linear increase due to particle uptake, but plateaus after one day due to cell division. Error bars are standard deviation over three replicates. ,, A549 cells were exposed to similar nanoparticles for up to 28 h before flow cytometry measurements. Mean fluorescence intensity as a function of exposure time () and flow cytometry distributions of cell fluorescence intensity after 2, 12 and 28 h of exposure to nanoparticles () for all cells and cells in the G0/G1, S and G2/M phases (defined in Supplementary Fig. S5). The results and the scheme show that the intracellular conce! ntration of nanoparticles is ranked according to the cell cycle phases: G2/M > S > G0/G1. ,, Numerical simulation corresponding to data in and , respectively, showing good agreement with experimental results. * Figure 3: Nanoparticle export is negligible. A549 cells were exposed to 40 nm yellow-green PS-COOH (25 µg ml−1 in cMEM) for 4 h, then the S-phase cells were EdU-labelled for 30 min and cells grown further in nanoparticle-free media, before cell fluorescence measurement by flow cytometry. , EdU–DNA double-scatter plots 0, 5 and 8 h after EdU-labelling. (For full time course see Supplementary Fig. S10.) The indicated regions show EdU-labelled cells after division ('After division') and all other cells ('Complement'). , Fraction of divided EdU-labelled cells, showing excellent agreement with the prediction from the corresponding numerical simulation (solid line). , Mean cell fluorescence of all cells, divided EdU-labelled cells and their complement. The solid line is a fit to the result expected due to cell division alone. Dashed lines are horizontal fits. The good agreement indicates that export is negligible and the internalized nanoparticle load decreases only as a result of cell division. * Figure 4: Nanoparticle uptake rates during the different phases of the cell cycle. Independent uptake experiments of 40 nm yellow-green PS-COOH nanoparticles (25 µg ml−1 in cMEM) were performed on A549 cells 2, 6 and 12 h after EdU-labelling, at which times many EdU-positive cells are in the S, G2/M and G0/G1 phases, respectively (Supplementary Fig. S12). The presented values are the means of the cell fluorescence intensity of cells in the S, G2/M and G0/G1 phases (as defined in Supplementary Fig. S13) obtained by flow cytometry. Error bars represent the standard deviation of three replicates. Solid lines are linear fits performed to determine the uptake rates. The results show that the uptake rate is comparable for all phases of the cell cycle. * Figure 5: Nanoparticle uptake in synchronized cell cultures. , DNA histograms (obtained by propidium iodide staining) of non-synchronized A549 cells, a population enriched in G0/G1 phase by serum deprivation ('synchronized'), and populations synchronized by the same procedure and subsequently exposed to nanoparticle-free cMEM (for 6 and 24 h) to revert the synchronization and restart cell cycle progression ('restarted'). , Mean cell fluorescence intensity obtained by flow cytometry after exposure to nanoparticles (40 nm yellow-green PS-COOH 25 µg ml−1 in cMEM) in synchronized and non-synchronized A549 cells (with the same starting cell number). Error bars represent standard deviation of three independent replicates. The results show similar nanoparticle uptake during the first 5 h of exposure, but over 24 h the synchronized cells accumulate more nanoparticles. Author information * Abstract * Author information * Supplementary information Affiliations * Centre for BioNano Interactions, School of Chemistry and Chemical Biology and Conway Institute for Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland * Jong Ah Kim, * Christoffer Åberg, * Anna Salvati & * Kenneth A. Dawson Contributions J.A.K. performed experiments, analysed and interpreted data, and wrote the paper. C.Å. developed the numerical simulations and analytical tools, analysed and interpreted data, and wrote the paper. A.S. supervised the experimental work, analysed and interpreted data, and wrote the paper. K.A.D. interpreted data and wrote the paper. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Kenneth A. Dawson or * Anna Salvati Author Details * Jong Ah Kim Search for this author in: * NPG journals * PubMed * Google Scholar * Christoffer Åberg Search for this author in: * NPG journals * PubMed * Google Scholar * Anna Salvati Contact Anna Salvati Search for this author in: * NPG journals * PubMed * Google Scholar * Kenneth A. Dawson Contact Kenneth A. Dawson Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (3,852 KB) Supplementary information Other * Supplementary information (368 KB) Supplementary information Additional data - One- and two-dimensional photonic crystal microcavities in single crystal diamond
- Nat Nanotechnol 7(1):69-74 (2012)
Nature Nanotechnology | Article One- and two-dimensional photonic crystal microcavities in single crystal diamond * Janine Riedrich-Möller1 * Laura Kipfstuhl1 * Christian Hepp1 * Elke Neu1 * Christoph Pauly2 * Frank Mücklich2 * Armin Baur3 * Michael Wandt3 * Sandra Wolff4 * Martin Fischer5 * Stefan Gsell5 * Matthias Schreck5 * Christoph Becher1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 7,Pages:69–74Year published:(2012)DOI:doi:10.1038/nnano.2011.190Received 09 August 2011 Accepted 30 September 2011 Published online 13 November 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Diamond is an attractive material for photonic quantum technologies because its colour centres have a number of outstanding properties, including bright single photon emission and long spin coherence times. To take advantage of these properties it is favourable to directly fabricate optical microcavities in high-quality diamond samples. Such microcavities could be used to control the photons emitted by the colour centres or to couple widely separated spins. Here, we present a method for the fabrication of one- and two-dimensional photonic crystal microcavities with quality factors of up to 700 in single crystal diamond. Using a post-processing etching technique, we tune the cavity modes into resonance with the zero phonon line of an ensemble of silicon-vacancy colour centres, and we measure an intensity enhancement factor of 2.8. The controlled coupling of colour centres to photonic crystal microcavities could pave the way to larger-scale photonic quantum devices based on si! ngle crystal diamond. View full text Subject terms: * Photonic structures and devices * Synthesis and processing Figures at a glance * Figure 1: SEM images of two-dimensional and one-dimensional fabricated PhC cavities. , SEM image of the fabricated M7 cavity with lattice constant a ≈ 275 nm and radii R ≈ 85 nm. , Close-up of the cavity centre. , Cross-sectional image (tilt angle, 52°). A thin platinum layer was deposited on the PhC to allow for a straight cut through the diamond membrane using FIB. From the cross-sectional image, a diamond film thickness of 300 nm can be inferred. The sidewalls of the milled air holes exhibit a tilt angle of ~6°. ,, Top () and side () views of the fabricated one-dimensional nanobeam cavity with a pitch:width:height ratio of 2:3:3 (a ≈ 200 nm). The hole radii monotonically decrease from R ≈ 83 nm at the cavity centre to R ≈ 72 nm at the waveguide edge. , Close-up of the one-dimensional waveguide–cavity. * Figure 2: Photoluminescence spectra. ,, Experimental photoluminescence spectra of an M7 cavity () and a nanobeam cavity () are shown in black, and the reference spectra of the unstructured membrane are shown in grey. The intensity of the reference spectra is scaled to account for the smaller collection efficiency from unpatterned areas of the sample (see Supplementary Information). Coloured curves show the simulated cavity modes for different symmetric boundary conditions. Ex and Ey mode profiles for fundamental mode e1 and various higher-order modes are shown above. The spectrum of the M7 cavity () shows several cavity modes close to the SiV centre zero phonon line at λ = 738 nm (yellow area). The simulated spectrum (coloured curves, arbitrary amplitude) of an ideal M7 cavity with R = 0.31a and h = 1.1a matches the experimental results very well. The spectrum of the nanobeam cavity () shows three cavity modes close to the design wavelength λ = 637 nm of the NV− centre zero phonon line. The calculated modes! (coloured curves, arbitrary amplitude) of an ideal nanobeam cavity with h = w = 1.5a and radii that decrease from R = 0.42a at the cavity centre to R = 0.37a at the structure edge, agree very well with the experimental measurement. ,, Polarization analysis of an M7 cavity () and a nanobeam cavity (). Photoluminescence spectra taken without a polarizer are shown in black. The even modes are pronounced for a polarizer oriented in the y-direction (red curves), whereas the odd modes are prominent for polarizer oriented along the x-axis (blue curves). * Figure 3: Cavity tuning. , Cavity spectrum taken before the first oxidation step (black) and after one, two, three and four oxidation steps (coloured curves). When the cavity mode o2 (marked by *) is tuned into resonance with the emission line of SiV centres, the intensity of the zero phonon line (the peak in the yellow region) is clearly enhanced. , Wavelengths for various cavity modes are blueshifted by 3 nm on average per oxidation step. The four lines at the bottom show higher-order modes (e4, o3, o4, o5; not labelled for clarity). In total, the cavity modes are tuned up to 15 nm. , Quality factors of the fundamental cavity modes show no significant degradation following tuning. Author information * Abstract * Author information * Supplementary information Affiliations * Universität des Saarlandes, Fachrichtung 7.2 (Experimentalphysik), 66123 Saarbrücken, Germany * Janine Riedrich-Möller, * Laura Kipfstuhl, * Christian Hepp, * Elke Neu & * Christoph Becher * Universität des Saarlandes, Fachrichtung 8.4 (Materialwissenschaft und Werkstofftechnik), 66123 Saarbrücken, Germany * Christoph Pauly & * Frank Mücklich * University of Freiburg, Department of Microsystems Engineering (IMTEK), Cleanroom Service Center, 79110 Freiburg, Germany * Armin Baur & * Michael Wandt * TU Kaiserslautern, Nano + Bio Center, 67653 Kaiserslautern, Germany * Sandra Wolff * Universität Augsburg, Lehrstuhl für Experimentalphysik IV, 86159 Augsburg, Germany * Martin Fischer, * Stefan Gsell & * Matthias Schreck Contributions J.R-M. and L.K. fabricated the photonic crystals, performed the experiments and carried out the numerical modelling of the structures. M.F., S.G. and M.S. developed the CVD growth process for the diamond films on iridium buffer layers. A.B. and M.W. prepared the diamond membrane. J.R-M. and S.W. thinned the diamond film. C.P., J.R-M., L.K. and F.M. performed FIB milling. C.H. and E.N. contributed experimental tools and helped with the photoluminescence measurements and interpretation of data. C.B. conceived and designed the experiments. J.R-M. and C.B. wrote the manuscript. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Christoph Becher Author Details * Janine Riedrich-Möller Search for this author in: * NPG journals * PubMed * Google Scholar * Laura Kipfstuhl Search for this author in: * NPG journals * PubMed * Google Scholar * Christian Hepp Search for this author in: * NPG journals * PubMed * Google Scholar * Elke Neu Search for this author in: * NPG journals * PubMed * Google Scholar * Christoph Pauly Search for this author in: * NPG journals * PubMed * Google Scholar * Frank Mücklich Search for this author in: * NPG journals * PubMed * Google Scholar * Armin Baur Search for this author in: * NPG journals * PubMed * Google Scholar * Michael Wandt Search for this author in: * NPG journals * PubMed * Google Scholar * Sandra Wolff Search for this author in: * NPG journals * PubMed * Google Scholar * Martin Fischer Search for this author in: * NPG journals * PubMed * Google Scholar * Stefan Gsell Search for this author in: * NPG journals * PubMed * Google Scholar * Matthias Schreck Search for this author in: * NPG journals * PubMed * Google Scholar * Christoph Becher Contact Christoph Becher Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (3,964 KB) Supplementary information Additional data - Electrically tuned spin–orbit interaction in an InAs self-assembled quantum dot
- Nat Nanotechnol 7(1):75 (2012)
Nature Nanotechnology | Corrigendum Electrically tuned spin–orbit interaction in an InAs self-assembled quantum dot * Y. Kanai * R. S. Deacon * S. Takahashi * A. Oiwa * K. Yoshida * K. Shibata * K. Hirakawa * Y. Tokura * S. TaruchaJournal name:Nature NanotechnologyVolume: 7,Page:75Year published:(2012)DOI:doi:10.1038/nnano.2011.228Published online 28 December 2011 Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Nature Nanotechnology6, 511–516 (2011); published online 24 July 2011; corrected after print 22 November 2011. In the version of this Letter originally published, in the discussion of Fig. 5c on page 514, the fitting function should have been Δ = A|cos(θ − θ0 ± π/2)| + B, and the offsets of θ0 should have been −30 ± 4° and −39 ± 5° for Vsg = −0.5 V and 1.0 V, respectively. These errors have been corrected in the HTML and PDF versions of the Letter. Author information Author Details * Y. Kanai Search for this author in: * NPG journals * PubMed * Google Scholar * R. S. Deacon Search for this author in: * NPG journals * PubMed * Google Scholar * S. Takahashi Search for this author in: * NPG journals * PubMed * Google Scholar * A. Oiwa Search for this author in: * NPG journals * PubMed * Google Scholar * K. Yoshida Search for this author in: * NPG journals * PubMed * Google Scholar * K. Shibata Search for this author in: * NPG journals * PubMed * Google Scholar * K. Hirakawa Search for this author in: * NPG journals * PubMed * Google Scholar * Y. Tokura Search for this author in: * NPG journals * PubMed * Google Scholar * S. Tarucha Search for this author in: * NPG journals * PubMed * Google Scholar Additional data Author Details * Y. Kanai Search for this author in: * NPG journals * PubMed * Google Scholar * R. S. Deacon Search for this author in: * NPG journals * PubMed * Google Scholar * S. Takahashi Search for this author in: * NPG journals * PubMed * Google Scholar * A. Oiwa Search for this author in: * NPG journals * PubMed * Google Scholar * K. Yoshida Search for this author in: * NPG journals * PubMed * Google Scholar * K. Shibata Search for this author in: * NPG journals * PubMed * Google Scholar * K. Hirakawa Search for this author in: * NPG journals * PubMed * Google Scholar * Y. Tokura Search for this author in: * NPG journals * PubMed * Google Scholar * S. Tarucha Search for this author in: * NPG journals * PubMed * Google Scholar
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