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- Nat Nanotechnol 6(8):461 (2011)
Article preview View full access options Nature Nanotechnology | Research Highlights Our choice from the recent literature Journal name:Nature NanotechnologyVolume: 6,Page:461Year published:(2011)DOI:doi:10.1038/nnano.2011.133Published online04 August 2011 Environ. Sci. Technol. 10.1021/es201010f (2011) Quantum dots have applications in biomedical imaging, solar panels and various lighting technologies, and these semiconductor nanocrystals may eventually enter environmental compartments such as the soil column. Although the polymer coating around certain quantum dots is thought to be stable, Diana Aga and colleagues from the State University of New York in Buffalo now show that the integrity of quantum dots in soil will compromise over time depending on their formulation. Article preview Read the full article * Instant access to this article: US$32 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data - Nanomaterials: DNA brings quantum dots to order
- Nat Nanotechnol 6(8):463-464 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Nanomaterials: DNA brings quantum dots to order * Yan Liu1Journal name:Nature NanotechnologyVolume: 6,Pages:463–464Year published:(2011)DOI:doi:10.1038/nnano.2011.126Published online04 August 2011 Semiconductor quantum dots coated with strands of DNA can self-assemble into a variety of structures. Subject terms: * Molecular self-assembly * Photonic structures and devices Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Yan Liu is at the Biodesign Institute and in the Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA Corresponding author Correspondence to: * Yan Liu Author Details * Yan Liu Contact Yan Liu Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Graphene electronics: Thinking outside the silicon box
- Nat Nanotechnol 6(8):464-465 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Graphene electronics: Thinking outside the silicon box * Tomás Palacios1Journal name:Nature NanotechnologyVolume: 6,Pages:464–465Year published:(2011)DOI:doi:10.1038/nnano.2011.125Published online04 August 2011 The best applications of graphene will be those that exploit its basic characteristics, rather than try to change them. Subject terms: * Electronic properties and devices * Nanomaterials Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Tomás Palacios is in the Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Corresponding author Correspondence to: * Tomás Palacios Author Details * Tomás Palacios Contact Tomás Palacios Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Biocomputing: DNA computes a square root
- Nat Nanotechnol 6(8):465-467 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Biocomputing: DNA computes a square root * Yaakov Benenson1Journal name:Nature NanotechnologyVolume: 6,Pages:465–467Year published:(2011)DOI:doi:10.1038/nnano.2011.128Published online04 August 2011 Complex molecular circuits with reliable digital behaviour can be created using DNA strands. Subject terms: * Molecular machines and motors * Nanosensors and other devices Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Yaakov Benenson is in the Department of Biosystems Science and Engineering, Swiss Federal Institute of Technology (ETH Zurich), Basel 4058, Switzerland Corresponding author Correspondence to: * Yaakov Benenson Author Details * Yaakov Benenson Contact Yaakov Benenson Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Silicon nanoparticles: Isolation leads to change
- Nat Nanotechnol 6(8):467-468 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Silicon nanoparticles: Isolation leads to change * Graham L. W. Cross1Journal name:Nature NanotechnologyVolume: 6,Pages:467–468Year published:(2011)DOI:doi:10.1038/nnano.2011.124Published online04 August 2011 Nanoindentation experiments and atomistic modelling show that the nanoscale plasticity of silicon changes when the material is no longer connected to the bulk. Subject terms: * Computational nanotechnology * Nanoparticles Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Graham L. W. Cross is in the School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, Dublin 2, Ireland Corresponding author Correspondence to: * Graham L. W. Cross Author Details * Graham L. W. Cross Contact Graham L. W. Cross Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Nanomechanics of functional and pathological amyloid materials
- Nat Nanotechnol 6(8):469-479 (2011)
Nature Nanotechnology | Review Nanomechanics of functional and pathological amyloid materials * Tuomas P. J. Knowles1 * Markus J. Buehler2, 3, 4 * Affiliations * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:469–479Year published:(2011)DOI:doi:10.1038/nnano.2011.102Published online31 July 2011 Abstract * Abstract * Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Amyloid or amyloid-like fibrils represent a general class of nanomaterials that can be formed from many different peptides and proteins. Although these structures have an important role in neurodegenerative disorders, amyloid materials have also been exploited for functional purposes by organisms ranging from bacteria to mammals. Here we review the functional and pathological roles of amyloid materials and discuss how they can be linked back to their nanoscale origins in the structure and nanomechanics of these materials. We focus on insights both from experiments and simulations, and discuss how comparisons between functional protein filaments and structures that are assembled abnormally can shed light on the fundamental material selection criteria that lead to evolutionary bias in multiscale material design in nature. View full text Subject terms: * Molecular self-assembly * Nanomaterials Figures at a glance * Figure 1: The hierarchical structure of amyloid materials. Upper panel: Five different levels of hierarchy in the structure of amyloid materials. Second and third panels: Different experimental and computational analysis tools for studying the mechanical properties and structure of amyloid materials on the different length scales. Second panel: The image on the left shows an artificial amyloid film being tested in a DNA setup. The transmission electron micrograph represents an Alzheimer's amyloid β-fibril. The image on the right shows the diffraction pattern from amyloid-like nanocrystals formed from the peptide GNNQQNY from the N-terminal region of the yeast prion protein Sup35. Figures in the second panel reproduced with permission from: left, ref. 93, © 2010 NPG; middle, ref. 14, © 2008 NAS; right, ref. 102, © 2003 Elsevier. Third panel: The inlay above 'Continuum models' represents a large-scale atomistic model of an Alzheimer's β-amyloid fibril; the image above 'Coarse-grained models' shows a coarse-grained elastic network! model of an amyloid fibril52; the image above 'Molecular dynamics (MD)' depicts a molecular dynamics model52; the inlay above 'Density functional theory (DFT)' shows a snapshot of a molecular simulation of an Alzheimer's β-amyloid peptide oligomer (reproduced with permission from ref. 48, © 2002 NAS); and the image below 'Continuum models' shows a finite element model of an amyloid fibril (reproduced with permission from ref. 25, © 2005 ACS). Bottom panel: Hierarchical structure in linguistics as an analogy to demonstrate how functional properties emerge owing to the hierarchical assembly of simple building blocks. Figures in the bottom panel reproduced with permission from ref. 103, © 2007 Random House. * Figure 2: Classification of amyloid materials. Amyloid materials can be extracellular () or intracellular (), and functional () or pathological (). , Functional amyloid79 in biofilms produced by bacterial species such as E. coli and certain Salmonella spp. , Amyloid plaques as seen in a mouse model of Alzheimer's disease (scale bar, 20 μm). The large white arrow shows a newly formed plaque. , Transmission electron microscope image of Pmel17 scaffolds in melanosomes involved in the biosynthesis of melanin. , Lewy bodies, pathological protein aggregates that develop in neurons in Parkinson's disease (scale bar, 8 μm). Figures reproduced with permission from: , ref. 79, © 2007 NAS; , ref. 77, © 2008 NPG; , ref. 20, © 2009 ASBMB; , ref. 21, © 1997 NPG. * Figure 3: Mechanical properties of amyloid fibrils in comparison to biological and inorganic or non-biological materials. , Bending rigidity versus moment of inertia for covalent materials (blue region), strong non-covalent interactions (such as hydrogen bonds, orange region) and weak non-covalent interactions (green region). Blue points are amyloid fibrils (different symbols denote data from different studies) and grey symbols are other materials25, 31, 32, 33, 34, 36, 37, 38. Grey inverted triangles show the values for the response measured in the perpendicular direction to the fibril axis39. The upward triangles show data for one- and two-filament forms of bovine insulin, B-chain of bovine insulin, hen-egg-white lysozyme, bovine β-lactoglobulin, Alzheimer's amyloid β-peptide residues 1–42, GNNQQNY fragment of the yeast prion sup35, and human transthyretin residues 105–115 (all experimental)32. The pentagons show data for diphenylalanine (experimental)25, octagons for insulin (experimental)33, hexagons for ac-[RARADADA]2-am self-assembling peptide (simulation)36, stars for Alzheimer's a! myloid β-peptide residues 1–40 (simulation)37, and lozenges show data for β-lactoglobulin (experimental)31. The circles show data for the N-terminal domain of the hydrogenase maturation factor HypF (experimental)38, and squares show data for Alzheimer's amyloid β-peptide residues 1–40 (experimental)34. Figures reproduced with permission from: amyloid, ref. 104, © 2005 NPG; actin, ref. 105, © 2008 NAS; tubulin, ref. 106, © 2002 Elsevier. Images courtesy of: silicon wafer © istockphoto.com/photomick; elastic bands © istockphoto.com/shank/-ali. , E (which corresponds to stiffness) versus strength56, 57 for a range of different materials. Covalent and metallic bonding results in the stiffest and strongest materials, with diamond and single-wall carbon nanotubes (SWNTs) being the best performers. Silks are the strongest and stiffest protein materials, followed by amyloid and collagen; and significantly more-rigid materials (for example, bone) contain minerals. Amyloi! d fibrils are shown in orange to distinguish them from other m! aterials. , Range of values of E for seven different classes of biological materials inside and outside the cell. The stiffest materials (such as collagen, bone, enamel and silk) are found outside the cell. Images courtesy of: actin © NIGMS/Torsten Wittmann; intermediate filaments © NIGMS/Evan Zamir; collagen © fei.com/Paul Gunning; silk © istockphoto.com/blackjack3d; bone © istockphoto.com/dwithers; enamel © istockphoto.com/shironosov. * Figure 4: Fragmentation, aggregation and the kinetics of amyloid growth. , Schematic illustrating the formation of amyloid fibrils from soluble monomers. On fragmentation, newly formed ends of amyloid fragments serve as seeds for further elongation, and the process repeats63. , Molecular mechanism of fragmentation of the cross-β core of amyloid fibrils65. Upper part: failure owing to tension, through the opening of a crack due to the breaking of hydrogen bonds. Lower part: failure under compression owing to fluid shear forces or thermal vibrations that excite bending or stretching modes. , Studies of the propagation of three strains of yeast prion (Sc4, Sc37 and SCS) show that there exists an intimate connection between mechanics and the growth kinetics of prion aggregates. These amyloid fibrils formed from the protein Sup35 propagate most effectively in yeast cells in cases where their intrinsic fragmentation rate was high and the mechanical strength correspondingly low. The gel electrophoretic analysis of prion particle size (, left) shows tha! t the greater frangibility of Sc4 fibrils results in a smaller size distribution of the aggregates, but more effective overall growth and sequestering of the monomer relative to the less frangible SCS fibrils. The [psi-] case represents a control system with no aggregates. The right panel shows the differences in the fibril breakage rates and growth rates. Reproduced from ref. 41, © 2006 NPG. , The tensile strength in GPa (red numbers, results from computational modelling) of amyloid fibrils of various lengths (black numbers): it can be seen that longer fibrils are weaker64. The plot also summarizes characteristic length scales of amyloid fibrils, including the layer spacing (distance between β-sheet layers in the core), the helical pitch in the twisted geometry of the fibrils, and the persistence length (data shown here are for Alzheimer's β-amyloid fibril). As the length of the amyloid fibrils that assemble into plaques is varied, the structure of the assembled plaques! changes from being highly organized and regular (green, right! ) to more entangled and randomized (red, left)14, 28, 35, 44, 65. This is because of the competition between bending and interfibril adhesion; in shorter fibrils the interfibril adhesion forces are strong enough to align fibrils in parallel, whereas for longer fibrils the entangled arrangement is stable. * Figure 5: Examples of functional synthetic amyloid materials. , Amyloid formation from a native protein results in universal building blocks that can be assembled and functionalized (for example, with fluorophores or metal particles) into larger and more diverse structures. Different structures can be achieved through changes in pH or other processing conditions. , AFM image of synthetic amyloid fibrils generated in vitro35. –, The fibrils can assemble to form conducting nanowires ()86, 88, surface coatings ()91 and nanostructured protein films ()93. , Schematic showing a light-harvesting nanostructure generated from amyloid fibrils95. Light harvesting occurs by means of absorption of a photon by the donor (1), followed by non-emissive transfer to an acceptor through resonance energy transfer (2). The energy is released by the acceptor as a photon (3). , Hollow nanotubes made from amyloid structures could be used to develop new nanoscale antenna96. , Optical image of active neuron synapses (labelled with a green fluorescent lipophili! c probe) whose growth was stimulated by β-sheet-rich scaffolds98. Figure reproduced with permission from: , ref. 35, © 2007 AAAS; , ref. 86, © 2006 ACS; , ref. 88, © 2003 NAS; , ref. 91, © 2009 NPG; , ref. 93, © 2010 NPG; , ref. 95, © 2009 ACS; , ref. 96, © 2008 RSC; , ref. 98, © 2000 NAS. Author information * Abstract * Author information Affiliations * Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK * Tuomas P. J. Knowles * Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave. Room 1-235A&B, Cambridge, Massachusetts, USA * Markus J. Buehler * Center for Computational Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts, USA * Markus J. Buehler * Center for Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts, USA * Markus J. Buehler Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Tuomas P. J. Knowles or * Markus J. Buehler Author Details * Tuomas P. J. Knowles Contact Tuomas P. J. Knowles Search for this author in: * NPG journals * PubMed * Google Scholar * Markus J. Buehler Contact Markus J. Buehler Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Deconfinement leads to changes in the nanoscale plasticity of silicon
- Nat Nanotechnol 6(8):480-484 (2011)
Nature Nanotechnology | Letter Deconfinement leads to changes in the nanoscale plasticity of silicon * Dariusz Chrobak1, 2, 5 * Natalia Tymiak1 * Aaron Beaber3 * Ozan Ugurlu3 * William W. Gerberich3 * Roman Nowak1, 4, 5 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:480–484Year published:(2011)DOI:doi:10.1038/nnano.2011.118Received04 January 2011Accepted17 June 2011Published online24 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Silicon crystals have an important role in the electronics industry, and silicon nanoparticles have applications in areas such as nanoelectromechanical systems, photonics and biotechnology1, 2. However, the elastic–plastic transition observed in silicon is not fully understood; in particular, it is not known if the plasticity of silicon is determined by dislocations or by transformations between phases. Here, based on compression experiments and molecular dynamics simulations, we show that the mechanical properties of bulk silicon3, 4, 5, 6 and silicon nanoparticles are significantly different. We find that bulk silicon exists in a state of relative constraint, with its plasticity dominated by phase transformations, whereas silicon nanoparticles are less constrained and display dislocation-driven plasticity. This transition, which we call deconfinement, can also explain the absence of phase transformations in deformed silicon nanowedges7, 8. Furthermore, the phenomenon is ! in agreement with effects observed in shape-memory alloy nanopillars9, and provides insight into the origin of incipient plasticity10, 11, 12, 13, 14, 15, 16, 17, 18, 19. View full text Subject terms: * Computational nanotechnology * Nanoparticles Figures at a glance * Figure 1: Mechanical response of nanodeformed silicon from bulk to nanoparticles. , P–δ response of silicon deduced from nanoindentation in bulk3, 4, 5, 6 and our nanocompression experiments on silicon nanospheres (Supplementary Fig. S1). A combination of PI during loading and PO during unloading is denoted the PI–PO effect. The sequence PO PI–PO PI indicates a transition from bulk to nanoparticle behaviour. , Results of nanocompression tests on silicon nanospheres with radii of 19–169 nm and bulk silicon nanoindentation data3, 4, 5. The PI-only (green) response is relevant to the smaller nanospheres (R ≤ 57 nm), and the PO-only (black) record is characteristic of bulk silicon (R ∞). Larger nanoparticles (R ≥ 67 nm) demonstrate the PI–PO effect (red), covering the transition area between bulk and pure PI response. As PO marks the Si-II Si-XII/III + α-Si phase transition, its gradual disappearance (PO PI–PO PI) with decreasing radius is in accordance with suppression of the reverse martensitic transformation reported for shape-memory al! loy nanopillars9. * Figure 2: Mechanical response of a compressed silicon nanoparticle. , MD simulations of silicon nanospheres compressed between two rigid plates. Displacement δ under applied load P is quantified in terms of ε = δ/R strain. , Contact pressure (pc = P/A, where A is contact area) versus strain relationship (pc–ε) demonstrates that the maximum value of pc reached in the nanoparticles (21.3–23.5 GPa) is nearly double that (~12 GPa) of bulk silicon18. Elastic deformation follows Hertzian theory25 (solid line). After the PI (onset of plasticity), multiple singularities reflect the nature of plasticity. , Slip vector (SV) analysis of the unstable dislocation structure of the silicon nanoparticle (R2 = 10 nm). Perfect dislocation loops (|SV| = 3.8 Å, b = |1/2[101]| = 3.84 Å, atoms marked in yellow) nucleate immediately after the PI (ε = 0.108), and terminate inside the nanosphere. After unloading, a majority of the dislocation loops vanish, whereas those at the nanoparticle surface stabilize, hence the nearly complete silicon particle shap! e recovery following a PI, referred to as 'reversible plasticity'15. * Figure 3: MD-simulated contrasting behaviour of confined (bulk) and deconfined (nanoparticle) silicon. , Initial plastic deformation of bulk silicon indented with a diamond sphere (R = 10 nm). As strain reaches ε = 0.101, the deformed volume under the indentation contact displays no evidence of dislocations. Coordination numbers ranging from 1 to 5 suggest an amorphous structure. , Plasticity initiation in a compressed silicon nanosphere. Despite similar levels of strain, the mechanisms of plasticity in the silicon nanoparticle and bulk are essentially different. Plastic deformation in a nanoparticle begins with perfect dislocation loops (atoms marked in turquoise) joined by stacking fault regions (atoms marked in green). Perfect dislocations to the left and right of the yellow arrow lie on the ( 11) and (11 ) planes, respectively, whereas the stacking fault joining them is positioned on the (10 ) plane. ,, Distribution of hydrostatic pressure (σh) in bulk silicon () and in the silicon nanosphere (R = 10 nm, ), both strained elastically up to ε = 0.0725. Atoms exposed to p! ressures higher than |σh| ≥ 1.5 GPa are marked in colours, indicating a higher stress concentration in confined silicon () than in the nanoparticle (). Note that both distributions are presented on a common scale. * Figure 4: Effect of deconfinement of silicon from bulk to nanosphere viewed in terms of stress analysis. Averaged ratio of hydrostatic (σh) and von Mises stresses (σm) determined using MD calculations during consecutive steps of elastic deformation. The σh/σm values calculated for the nanoparticle (green) are systematically lower than those obtained for the bulk state (black), which suggests that the silicon particle is prone to undergo non-dilatational strain rather than the volumetric strain dominant in bulk. * Figure 5: Schematic of silicon deconfinement process scaled with the pressure of the Si-II Si-XII/III + α-Si phase transition. General relationship determined by means of nanocompression experiments (green and red solid lines) for highly deconfined silicon (nanoparticles) appears to extrapolate for larger nanoparticles (red broken line) towards the data obtained for bulk silicon deformed by nanoindentation (black area). When the entire free surface of the bulk is under external high pressure, it is possible to imagine such a material as being 'confined to a higher degree' (with virtually no free surface). This is exactly what happens to silicon deformed in pressure cell experiments33, in which the characteristic pressure of the Si-II Si-XII/III transformation (magenta point) is certainly higher than for the nanoindented bulk crystal (black area). Note that in the deconfined state, silicon deforms with the contribution of phase transformation, but for higher degrees of deconfinement, there is no transformation at all (green solid line). The schematic thus constitutes a roadmap for a range of mate! rials deconfined from their bulk state to nanoparticle, nanowire, nanowedge or nanopillar (cf. ref. 9). Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Dariusz Chrobak & * Roman Nowak Affiliations * Nordic Hysitron Laboratory, School of Chemical Technology, Aalto University, Vuorimiehentie 2A, Espoo, 00076 Aalto, Finland * Dariusz Chrobak, * Natalia Tymiak & * Roman Nowak * Institute of Materials Science, University of Silesia, Bankowa 12, 40-007 Katowice, Poland * Dariusz Chrobak * Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA * Aaron Beaber, * Ozan Ugurlu & * William W. Gerberich * Extreme Energy-Density Research Institute, Nagaoka University of Technology, Nagaoka, Niigata, 940-2188 Japan * Roman Nowak Contributions D.C. carried out the calculations and analysed the compatibility of the theoretical and experimental data. R.N. conceived the concept of deconfinement-driven transition and designed the research project. N.T. analysed the data. W.W.G. designed and supervised the experimental part, and A.B. and O.U. performed nanocompression tests and analysed the output. R.N. and D.C. wrote the paper. All authors discussed the results. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Roman Nowak Author Details * Dariusz Chrobak Search for this author in: * NPG journals * PubMed * Google Scholar * Natalia Tymiak Search for this author in: * NPG journals * PubMed * Google Scholar * Aaron Beaber Search for this author in: * NPG journals * PubMed * Google Scholar * Ozan Ugurlu Search for this author in: * NPG journals * PubMed * Google Scholar * William W. Gerberich Search for this author in: * NPG journals * PubMed * Google Scholar * Roman Nowak Contact Roman Nowak Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information Movies * Supplementary information (2,637 KB) Supplementary movie 1 * Supplementary information (3,535 KB) Supplementary movie 2 PDF files * Supplementary information (1,485 KB) Supplementary information Additional data - DNA-based programming of quantum dot valency, self-assembly and luminescence
- Nat Nanotechnol 6(8):485-490 (2011)
Nature Nanotechnology | Letter DNA-based programming of quantum dot valency, self-assembly and luminescence * Grigory Tikhomirov1, 4 * Sjoerd Hoogland2, 4 * P. E. Lee1 * Armin Fischer2 * Edward H. Sargent2 * Shana O. Kelley1, 3 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:485–490Year published:(2011)DOI:doi:10.1038/nnano.2011.100Received21 February 2011Accepted31 May 2011Published online10 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The electronic and optical properties of colloidal quantum dots, including the wavelengths of light that they can absorb and emit, depend on the size of the quantum dots. These properties have been exploited in a number of applications including optical detection1, 2, 3, solar energy harvesting4, 5 and biological research6, 7. Here, we report the self-assembly of quantum dot complexes using cadmium telluride nanocrystals capped with specific sequences of DNA. Quantum dots with between one and five DNA-based binding sites are synthesized and then used as building blocks to create a variety of rationally designed assemblies, including cross-shaped complexes containing three different types of dots. The structure of the complexes is confirmed with transmission electron microscopy, and photophysical studies are used to quantify energy transfer among the constituent components. Through changes in pH, the conformation of the complexes can also be reversibly switched, turning on an! d off the transfer of energy between the constituent quantum dots. View full text Subject terms: * Molecular self-assembly * Photonic structures and devices Figures at a glance * Figure 1: Synthetic strategy for the development of quantum dots exhibiting strong luminescence, tunable emission spectrum, programmable valency and highly controllable binding energy. , Schematic depicting control over (i) photoluminescence efficiency, conducive to efficient energy transfer and the realization of highly luminescent quantum dots; (ii) spectral tunability, to generate quantum dots with specific optical properties and allow for efficient energy transfer inside the complexes by matching donor emission and acceptor absorption; (iii) valency, to control the number of binding sites on each quantum dot and therefore to control the assembly of higher-order complexes; and (iv) programmable bonding, to allow selective bonding between specific different quantum dots to generate desired assemblies. , Schematic representation of the synthesis of DNA-capped CdTe quantum dots. , Chemical structure of phosphate and phosphorothioate fragments and the schematic design of DNA strands. QD, quantum dot. * Figure 2: Experimental results showing control over DNA-programmed quantum dots. , Luminescence: photoluminescence quantum efficiency of CdTe quantum dots capped with phosphorothioate DNA pentamers containing A, G, T or C residues, showing that dots capped with G-residue pentamers yield the highest luminescence efficiency. The excitation wavelength was 375 nm in all cases. All photoluminescence measurements were carried out on solutions at room temperature. , Quantum dot size/emission wavelength: photoluminescence spectrum as a function of quantum dot synthesis reaction time. After 10, 65 and 145 min of reaction, green-, orange- and red-emitting quantum dots are generated, respectively. Photoluminescence (coloured) and absorption (black) spectra are shown for the three different materials. The sequence used in this trial is G1 (see Supplementary Information for further sequence information). , Valency: size exclusion chromatography results on titration of complementary sequences, showcasing the control over the number of equivalents of complementary DNA ! which has a direct correlation to the number of available binding sites (see Supplementary Information for sequences and experimental procedures). * Figure 3: Representative high-resolution TEM images of DNA-programmed quantum dot complexes. , Quantum dot assemblies built using red dots with valencies of 1–5 and green dots. , Symmetric binary system made from the same green dots (top); complex structure made from three different dots: linear ternary complex (middle) and cross-shaped ternary complex (bottom). See Supplementary Information for sequences. Scale bar, 10 nm. * Figure 4: Optical characteristics of DNA-programmed quantum dot complexes. –, Photoluminescence spectra of the constituent green, orange and red quantum dots used as building blocks for higher-order complexes (), the linear ternary complex solution after purification () (the complex exhibits pure red luminescence and is substantially devoid of the green and orange luminescence that was present before hybridization), and the linear ternary complex after cleavage by DNase, displaying the reversibility of complexation () (the green curve represents a fit wherein the spectra of the constituents were summed, using weighting coefficients, in an attempt to reproduce the cleaved photoluminescence spectrum). , Photoluminescence spectra at neutral and basic pH. At neutral pH, the complex acts as a coupled entity with all energy transferred to the red dot, whereas at basic pH values, the complex behaves as an ensemble of uncoupled quantum dots. , Photoluminescence intensity at 577 nm as a function of pH cycle number, showing the reversible switching of the ! complex between the on and off states. , Hydrodynamic diameter (from DLS) and relative energy transfer efficiency (from photoluminescence spectra) as a function of pH for the linear ternary complex solution as measured by DLS. With increasing pH, the complex size increases and the energy transfer efficiency decreases. This change is completely reversible when pH is readjusted to neutral. In all photoluminescence studies, the excitation wavelength was 375 nm. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Grigory Tikhomirov & * Sjoerd Hoogland Affiliations * Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, Ontario M5S 3M2, Canada * Grigory Tikhomirov, * P. E. Lee & * Shana O. Kelley * Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada * Sjoerd Hoogland, * Armin Fischer & * Edward H. Sargent * Department of Biochemistry, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada * Shana O. Kelley Contributions G.T. and S.O.K. designed the protocols for the synthesis of the nanoparticles and complexes. S.H., G.T. and E.H.S. designed and interpreted the energy transfer studies. G.T., P.E.L. and A.F. carried out materials analysis, and worked with E.H.S. and S.O.K. in their interpretation. E.H.S. and S.O.K. co-wrote the paper with contributions from G.T., S.H., A.F. and P.E.L. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Edward H. Sargent or * Shana O. Kelley Author Details * Grigory Tikhomirov Search for this author in: * NPG journals * PubMed * Google Scholar * Sjoerd Hoogland Search for this author in: * NPG journals * PubMed * Google Scholar * P. E. Lee Search for this author in: * NPG journals * PubMed * Google Scholar * Armin Fischer Search for this author in: * NPG journals * PubMed * Google Scholar * Edward H. Sargent Contact Edward H. Sargent Search for this author in: * NPG journals * PubMed * Google Scholar * Shana O. Kelley Contact Shana O. Kelley Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (2,451 KB) Supplementary information Additional data - Thick lead-free ferroelectric films with high Curie temperatures through nanocomposite-induced strain
- Nat Nanotechnol 6(8):491-495 (2011)
Nature Nanotechnology | Letter Thick lead-free ferroelectric films with high Curie temperatures through nanocomposite-induced strain * Sophie A. Harrington1 * Junyi Zhai2 * Sava Denev3 * Venkatraman Gopalan3 * Haiyan Wang4 * Zhenxing Bi4 * Simon A. T. Redfern5 * Seung-Hyub Baek6 * Chung W. Bark6 * Chang-Beom Eom6 * Quanxi Jia2 * Mary E. Vickers1 * Judith L. MacManus-Driscoll1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:491–495Year published:(2011)DOI:doi:10.1038/nnano.2011.98Received28 April 2011Accepted24 May 2011Published online03 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Ferroelectric materials are used in applications ranging from energy harvesting to high-power electronic transducers1. However, industry-standard ferroelectric materials contain lead, which is toxic and environmentally unfriendly2. The preferred alternative, BaTiO3, is non-toxic and has excellent ferroelectric properties, but its Curie temperature of ~130 °C is too low to be practical3. Strain has been used to enhance the Curie temperature of BaTiO3 (ref. 4) and SrTiO3 (ref. 5) films, but only for thicknesses of tens of nanometres, which is not thick enough for many device applications. Here, we increase the Curie temperature of micrometre-thick films of BaTiO3 to at least 330 °C, and the tetragonal-to-cubic structural transition temperature to beyond 800 °C, by interspersing stiff, self-assembled vertical columns of Sm2O3 throughout the film thickness. The columns, which are 10 nm in diameter, strain the BaTiO3 matrix by 2.35%, forcing it to maintain its tetragonal struc! ture and resulting in the highest BaTiO3 transition temperatures so far. View full text Subject terms: * Electronic properties and devices * Nanomaterials * Synthesis and processing Figures at a glance * Figure 1: Self-assembled vertical nanostructure. , TEM images of a 600-nm-thick BaTiO3:Sm2O3 film on SrTiO3: cross-section () near the film–substrate interface; plan view (); cross-section () revealing structure still present near the film-free surface. Sm2O3 shows a darker contrast compared with BaTiO3. Yellow arrow represents c-axis direction. , Crystallographic model of interface matching. * Figure 2: Enhanced tetragonality at elevated temperature. ,, X-ray reciprocal space maps about the (3) of the STO substrate for a pure BTO film () and a composite film (), both with a thickness of 1 µm. , Temperature dependence of lattice parameters comparing a single crystal and a substrate-controlled pure BTO film (50 nm) (reproduced from ref. 4) with BTO:SmO composite films (150 and 600 nm). Closed symbols: out-of plane lattice parameter calculated from the (002) X-ray peak; open symbols: in-plane lattice parameter calculated from the (101) X-ray peak. , Dependence of SHG signal on temperature for a 600 nm film (purple, heating; orange, cooling) and a 1.25 µm film (red, heating; blue, cooling). Inset: SHG signal (radial distance) versus fundamental polarization (azimuthal angle) at room temperature (25 °C) and 795 °C for p (signal polarized in the incidence plane). Black lines are a fit from equation (1) (see Methods). * Figure 3: Direct electrical measurements. Polarization versus electric field hysteresis loops of 1 µm BTO:SmO thin-film capacitors at room temperature and 330 °C. Upper inset: dependence of dielectric constant on temperature for pure and composite films with a thickness of 1 µm, at 10, 25, 50 and 100 kHz. Lower inset: leakage current as a function of applied field for the same thickness (600 nm) of pure BTO and BTO:SmO thin films. The Pt top electrode was positively biased. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Materials Science, University of Cambridge, Cambridge, CB2 3QZ, UK * Sophie A. Harrington, * Mary E. Vickers & * Judith L. MacManus-Driscoll * Center for Integrated Nanotechnologies, MS K771, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA * Junyi Zhai & * Quanxi Jia * Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, USA * Sava Denev & * Venkatraman Gopalan * Department of Electrical and Computer Engineering, Texas A and M University, 3128 TAMU, College Station, Texas 778433128, USA * Haiyan Wang & * Zhenxing Bi * Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK * Simon A. T. Redfern * Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, 53706, Wisconsin, USA * Seung-Hyub Baek, * Chung W. Bark & * Chang-Beom Eom Contributions H.W. and Z.B. collected and analysed TEM images. V.G. and S.D. were responsible for SHG data. C.B.E., S.A.T.R., S.H.B. and C.W.B. were responsible for high-temperature XRD measurements. J.Z. advised on direct electrical measurements. M.E.V. and Q.J. discussed the results and commented on the manuscript. S.A.H. prepared films, collected room-temperature XRD data, performed direct electrical measurements and analysed data. S.A.H. and J.L.M. co-wrote the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Sophie A. Harrington Author Details * Sophie A. Harrington Contact Sophie A. Harrington Search for this author in: * NPG journals * PubMed * Google Scholar * Junyi Zhai Search for this author in: * NPG journals * PubMed * Google Scholar * Sava Denev Search for this author in: * NPG journals * PubMed * Google Scholar * Venkatraman Gopalan Search for this author in: * NPG journals * PubMed * Google Scholar * Haiyan Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Zhenxing Bi Search for this author in: * NPG journals * PubMed * Google Scholar * Simon A. T. Redfern Search for this author in: * NPG journals * PubMed * Google Scholar * Seung-Hyub Baek Search for this author in: * NPG journals * PubMed * Google Scholar * Chung W. Bark Search for this author in: * NPG journals * PubMed * Google Scholar * Chang-Beom Eom Search for this author in: * NPG journals * PubMed * Google Scholar * Quanxi Jia Search for this author in: * NPG journals * PubMed * Google Scholar * Mary E. Vickers Search for this author in: * NPG journals * PubMed * Google Scholar * Judith L. MacManus-Driscoll Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (480 KB) Supplementary information Additional data - Direct laser writing of micro-supercapacitors on hydrated graphite oxide films
- Nat Nanotechnol 6(8):496-500 (2011)
Nature Nanotechnology | Letter Direct laser writing of micro-supercapacitors on hydrated graphite oxide films * Wei Gao1 * Neelam Singh2 * Li Song2 * Zheng Liu2 * Arava Leela Mohana Reddy2 * Lijie Ci2 * Robert Vajtai2 * Qing Zhang3 * Bingqing Wei3 * Pulickel M. Ajayan1, 2 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:496–500Year published:(2011)DOI:doi:10.1038/nnano.2011.110Received26 April 2011Accepted14 June 2011Published online31 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Microscale supercapacitors provide an important complement to batteries in a variety of applications, including portable electronics. Although they can be manufactured using a number of printing and lithography techniques1, 2, 3, continued improvements in cost, scalability and form factor are required to realize their full potential. Here, we demonstrate the scalable fabrication of a new type of all-carbon, monolithic supercapacitor by laser reduction and patterning of graphite oxide films. We pattern both in-plane and conventional electrodes consisting of reduced graphite oxide with micrometre resolution, between which graphite oxide serves as a solid electrolyte4, 5, 6, 7, 8, 9. The substantial amounts of trapped water in the graphite oxide makes it simultaneously a good ionic conductor and an electrical insulator, allowing it to serve as both an electrolyte and an electrode separator with ion transport characteristics similar to that observed for Nafion membranes10, 11. T! he resulting micro-supercapacitor devices show good cyclic stability, and energy storage capacities comparable to existing thin-film supercapacitors1. View full text Subject terms: * Electronic properties and devices * Synthesis and processing Figures at a glance * Figure 1: Schematics of CO2 laser-patterning of free-standing hydrated GO films to fabricate RGO–GO–RGO devices with in-plane and sandwich geometries. The black contrast in the top schematics corresponds to RGO, and the light contrast to unmodified hydrated GO. For in-plane devices, three different geometries were used, and the concentric circular pattern gives the highest capacitance density. The bottom row shows photographs of patterned films. Typical dimensions of these devices are mentioned in the caption to Supplementary Fig. S1. * Figure 2: Comparisons of CV and impedance behaviour of in-plane and sandwich devices. , CV curves of in-plane circular and sandwich devices at a scan rate of 40 mV s−1. The in-plane circular structure gives a specific capacitance twice that of the sandwich structure. , Impedance spectra from 1 MHz to 10 mHz at 10 mV sinusoidal signal, zoomed in at the high-frequency region, demonstrating a much higher ESR value (the intercept of the slanted straight line with the Z′ axis) for the in-plane device than for the sandwich device, leading to a lower power density for the in-plane device. Z′, real part of impedance; Z′′, imaginary part of impedance. * Figure 3: Characterization of the water effect on GO ionic conductivity. , Stepwise change in impedance spectra versus exposure time to vacuum (0.08 MPa) at 25 °C. Cell structure: a pristine GO film coated with silver on both sides, and sandwiched between two pieces of stainless steel foil (1 cm × 1.2 cm); frequency range, 1 MHz to 100 Hz at 10 mV sinusoidal signal. Water is slowly evaporated out of the film under vacuum, leading to an increase in the arc diameter in the high-frequency range, which indicates a decrease in ionic conductivity. , Dependence of ionic conductivity on exposure time to vacuum and air. Conductivity data were obtained from Z view fitting of the impedance spectra. The hydrated GO film became less conductive under vacuum, but recovered its full conductivity after 3 h of re-exposure to air. Four-probe electrical measurement on a single piece of pristine GO film also showed at least three orders of magnitude decrease in conductance under vacuum (Supplementary methods), indicating that in GO the major contribution to measure! d conductivity is ionic. , Schematic of GO chemical structure, and table of measured physical properties of GO in an ambient environment. A sandwich geometry with well-defined cross-sectional area offered an accurate conductivity value of 1.1 × 10−5 S cm−1, and the in-plane structure with an estimated cross-sectional area showed a higher ionic conductivity of 2.8 × 10−3 S cm−1. We believe, due to the lamella structure of GO, its ionic conductivity is anisotropic. Upon hydration, the ionic conductivity further increases (Supplementary Fig. S4a,b), and becomes comparable to Nafion10. * Figure 4: Morphology and performance characterization of laser written micro-supercapacitors. , Photograph of an array of concentric circular patterns fabricated on a free-standing hydrated GO film. , SEM image of the interface between GO and RGO (scale bar, 100 µm), with yellow arrows indicating a long-range pseudo-ordered structure generated by laser-beam scanning. , Long cyclability tests of the as-prepared sandwich and concentric circular devices, showing a less than 35% drop in capacitance after 10,000 cycles. , Histogram comparison of area-based capacitance density of a sandwich device as-prepared (dark yellow), with excess DI water (navy), aqueous electrolyte (1.0 M Na2SO4, purple) and organic electrolyte (1.0 M TEABF4, burgundy). Inset: volumetric energy density versus power density data of the corresponding devices (shown in the same colours). Error bars represent the standard error of the mean of five independent experiments. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Chemistry, Rice University, Houston, Texas 77005, USA * Wei Gao & * Pulickel M. Ajayan * Mechanical Engineering and Materials Science Department, Rice University, Houston, Texas 77005, USA * Neelam Singh, * Li Song, * Zheng Liu, * Arava Leela Mohana Reddy, * Lijie Ci, * Robert Vajtai & * Pulickel M. Ajayan * Department of Mechanical Engineering, University of Delaware, Newark, Delaware 19716, USA * Qing Zhang & * Bingqing Wei Contributions W.G. prepared the GO, fabricated devices and collected characterization data. A.L.M.R., N.S. and W.G. conducted ionic conductivity testing and data analysis. Z.L., L.S. and W.G. conducted conductivity measurements and analysed the data. L.C. and R.V. were involved in study design. P.M.A., W.G. and L.C. designed the study. P.M.A., W.G. and N.S. wrote the paper. Q.Z. and B.W. conducted self-discharge measurements and analysed the relevant data. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Pulickel M. Ajayan Author Details * Wei Gao Search for this author in: * NPG journals * PubMed * Google Scholar * Neelam Singh Search for this author in: * NPG journals * PubMed * Google Scholar * Li Song Search for this author in: * NPG journals * PubMed * Google Scholar * Zheng Liu Search for this author in: * NPG journals * PubMed * Google Scholar * Arava Leela Mohana Reddy Search for this author in: * NPG journals * PubMed * Google Scholar * Lijie Ci Search for this author in: * NPG journals * PubMed * Google Scholar * Robert Vajtai Search for this author in: * NPG journals * PubMed * Google Scholar * Qing Zhang Search for this author in: * NPG journals * PubMed * Google Scholar * Bingqing Wei Search for this author in: * NPG journals * PubMed * Google Scholar * Pulickel M. Ajayan Contact Pulickel M. Ajayan Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,371 KB) Supplementary information Additional data - Interfacial phase-change memory
- Nat Nanotechnol 6(8):501-505 (2011)
Nature Nanotechnology | Letter Interfacial phase-change memory * R. E. Simpson1 * P. Fons1, 2 * A. V. Kolobov1, 2 * T. Fukaya1 * M. Krbal1 * T. Yagi3 * J. Tominaga1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:501–505Year published:(2011)DOI:doi:10.1038/nnano.2011.96Received25 March 2011Accepted23 May 2011Published online03 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating1 or some other excitation process2, 3, 4, 5. For example, switching the composite Ge2Sb2Te5 (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude6, and also increases reflectivity across the visible spectrum7, 8. Moreover, phase-change memory based on GST is scalable9, 10, 11, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses1, 6. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimen! sion, thus substantially reducing the entropic losses associated with the phase-change process12, 13. In particular, aligning the c-axis of a hexagonal Sb2Te3 layer and the 111 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb2Te3 interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds. View full text Subject terms: * Electronic properties and devices * Nanomaterials Figures at a glance * Figure 1: Optical pump–probe testing of IPCM switching behaviour. , High-resolution transmission electron micrograph TEM image of a typical as-grown (GeTe)2(Sb2Te3)4 interfacial phase-change material on silicon. The (GeTe)2 layers are 1 nm thick, and the (Sb2Te3)4 layers are 4 nm thick. , Time-resolved pump–probe static tester measurement for the RESET to SET transition process of a 400-nm-radius laser RESET mark in the IPCM film. The RESET mark was created with a laser pulse with a duration of 40 ns and a power of 32 mW. The normalized optical transmission of a 100 µW probe beam through the RESET mark is plotted as a function of time during and after the 100 ns laser pump pulse for varying incident optical powers. Four regions can be discerned: (i) no change in transmission, (ii) a reduction in transmission (indicative of a transition from the RESET state to the SET state), (iii) a slight increase followed by a reduction in transmission (indicative of melting then subsequent crystallization into the SET state), and (iv) an increase in ! transmission (indicative of melting then partial ablation). , Re-crystallized fraction of the 400-nm-radius RESET mark (created with a 40 ns, 32 mW laser pre-pulse) as a function of time for GST (100 ns, 9.5 mW pump pulses; black); IPCM (100 ns, 9.5 mW pump pulses; red); IPCM (25 ns, 16.5 mW pump pulses; blue), respectively. * Figure 2: Electrical switching characteristics of IPCM devices. , Plots of resistance versus current for PCRAM devices in the first cycle (upper panel) and after 1 × 106 cycles (lower panel). Filled squares are from a device fabricated from a single GST target, and filled circles are for a device containing a (GeTe)4(Sb2Te3)2 IPCM. The SET pulse lengths were 50 ns and 100 ns for the IPCM and GST materials, respectively. The RESET pulse length was fixed at 50 ns for both the IPCM- and GST- based devices. , Maximum number of SET–RESET cycles plotted as a function of phase-change material thickness. The cyclability of phase-change memory cells based on the GST material shows a strong dependence on film thickness (black circles), whereas the cyclability of the IPCM (red triangles) based on repeated blocks of (GeTe)2(Sb2Te3)2 shows little sensitivity to total film thickness. Dashed lines have been included to guide the eye. * Figure 3: Analysis of the RESET state. , TEM images of a (GeTe)2(Sb2Te3)4 IPCM structure in the RESET state after 1 × 103 SET–RESET cycles. In contrast to GST, the TEM image shows that there is no amorphous region surrounding the TiN heating electrode. –, High-resolution TEM images (top) and SAD patterns (bottom) for the four regions inside the coloured squares in . The layered IPCM structure and associated superlattice diffraction spots are clearly visible in all images. , Selective area electron diffraction pattern of the whole IPCM structure. The white concentric rings originate from the TiN electrodes. , DFT calculations of the inter-planar distances in (GeTe)2(Sb2Te3)4 (left column) are in good agreement with the distances determined from the diffraction pattern. , Model used in DFT calculations: Ge, Sb and Te atoms are coloured green, purple and orange, respectively. , An IPCM device that was deliberately RESET with the same high-power pulse conditions required by GST. As with GST, a melt-amorphized do! me is formed above the TiN heater, resulting in destruction of the superlattice structure and irreversible damage to the IPCM device. Author information * Abstract * Author information * Supplementary information Affiliations * Nanoelectronics Research Institute, National Institute of Applied Industrial Science and Technology, Tsukuba Central 4, 1-1-1 Higashi, Tsukuba 305-8562, Japan * R. E. Simpson, * P. Fons, * A. V. Kolobov, * T. Fukaya, * M. Krbal & * J. Tominaga * SPring-8, Japan Synchrotron Radiation Research Institute (JASRI), Mikazuki Hyogo 679-5198, Japan * P. Fons & * A. V. Kolobov * National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 3, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan * T. Yagi Contributions J.T. conceived and designed the entropy controlled interfacial phase-change memory structures. J.T., R.E.S. and T.Y. performed the experiments. R.E.S. wrote the paper. All authors analysed the results and contributed to the discussion presented in the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * R. E. Simpson or * J. Tominaga Author Details * R. E. Simpson Contact R. E. Simpson Search for this author in: * NPG journals * PubMed * Google Scholar * P. Fons Search for this author in: * NPG journals * PubMed * Google Scholar * A. V. Kolobov Search for this author in: * NPG journals * PubMed * Google Scholar * T. Fukaya Search for this author in: * NPG journals * PubMed * Google Scholar * M. Krbal Search for this author in: * NPG journals * PubMed * Google Scholar * T. Yagi Search for this author in: * NPG journals * PubMed * Google Scholar * J. Tominaga Contact J. Tominaga Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,080 KB) Supplementary information Additional data - Electrically pumped waveguide lasing from ZnO nanowires
- Nat Nanotechnol 6(8):506-510 (2011)
Nature Nanotechnology | Letter Electrically pumped waveguide lasing from ZnO nanowires * Sheng Chu1, 5 * Guoping Wang1, 5 * Weihang Zhou2 * Yuqing Lin3 * Leonid Chernyak3 * Jianze Zhao1, 4 * Jieying Kong1 * Lin Li1 * Jingjian Ren1 * Jianlin Liu1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:506–510Year published:(2011)DOI:doi:10.1038/nnano.2011.97Received30 March 2011Accepted24 May 2011Published online03 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Ultraviolet semiconductor lasers are widely used for applications in photonics, information storage, biology and medical therapeutics. Although the performance of gallium nitride ultraviolet lasers has improved significantly over the past decade, demand for lower costs, higher powers and shorter wavelengths has motivated interest in zinc oxide (ZnO), which has a wide direct bandgap and a large exciton binding energy1, 2, 3, 4, 5, 6. ZnO-based random lasing has been demonstrated with both optical and electrical pumping7, 8, 9, 10, but random lasers suffer from reduced output powers, unstable emission spectra and beam divergence. Here, we demonstrate electrically pumped Fabry–Perot type waveguide lasing from laser diodes that consist of Sb-doped p-type ZnO nanowires and n-type ZnO thin films. The diodes exhibit highly stable lasing at room temperature, and can be modelled with finite-difference time-domain methods. View full text Subject terms: * Nanoparticles * Photonic structures and devices Figures at a glance * Figure 1: Structure and material properties of the ZnO nanowire/film laser device. , Schematic of the laser device, which consists of an n-type ZnO thin film on a c-sapphire substrate, p-type vertically aligned ZnO nanowires, ITO contact and Au/Ti contact. , Photo-image of the device. , Side-view SEM image of the device structure showing the ZnO thin film and nanowires. Scale bar, 1 µm. , XPS spectrum of the Sb-doped ZnO nanowires array. , Room-temperature optically pumped lasing spectra from 46 kW cm−2 to 403 kW cm−2 with average steps of ~20 kW cm−2. Solid arrows denote equidistant lasing peaks, and a spacing of 2.4 nm is extracted. Inset: integrated spectra intensity as a function of pumping power density. Solid lines represent threshold Pth (~180 kW cm−2). * Figure 2: I–V properties and evidence of the formation of a ZnO nanowire/film p-n junction. , I–V characteristic of the ITO/ZnO nanowire/ZnO film laser device. Positive bias is applied on the ITO side. , EBIC profile superimposed on the side-view SEM image of the cleaved device. * Figure 3: Laser emission characterizations. , Electroluminescence spectra of the laser device operated between 20 mA and 70 mA. Above 50 mA, lasing characteristics are clearly observed. Arrows in the 70 mA spectrum represent quasi-equidistant peaks. , Side-view optical microscope images of the lasing device, corresponding to the electroluminescence spectra in . The first image was taken with lamp illumination and without current injection. * Figure 4: Lasing threshold gain/feedback properties. , Integrated spectrum intensity as a function of injection current. Dashed line is a guide to the eye. Inset: camera images corresponding to the emission pattern along the nanowire length direction at each injection current. , Gain feedback diagram of the ZnO nanowire/thin-film laser cavity. The laser gain area (red) is defined by the diffusion length Ln and Lp. * Figure 5: Far-field pattern of light emission. , Schematic of the FDTD simulation/measurement environment (area, 9 × 10 µm2). , Simulated spatial distribution of the light (385 nm) intensity. , Angle distribution of the far-field emission patterns (the x-axis represents the emission angle θ with respect to the nanowire growth direction and the y-axis represents the normalized emission intensity). Orange curve, simulation results; blue squares, results from electroluminescence measurements when rotating the device with respect to the nanowire length direction. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Sheng Chu & * Guoping Wang Affiliations * Quantum Structures Laboratory, Department of Electrical Engineering, University of California at Riverside, Riverside, CA 92521 USA * Sheng Chu, * Guoping Wang, * Jianze Zhao, * Jieying Kong, * Lin Li, * Jingjian Ren & * Jianlin Liu * Laboratory of Advanced Materials, Department of Physics, Fudan University, Shanghai, 200433 China * Weihang Zhou * Department of Physics, University of Central Florida, Orlando, FL 32816 USA * Yuqing Lin & * Leonid Chernyak * School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian, 116024 China * Jianze Zhao Contributions S.C., G.W. and J.L. conceived and designed the experiments. S.C., G.W. and J.Z. carried out the experiments. Y.L. and L.C. performed and analysed the EBIC experiment. W.Z. performed the lasing measurement by optical pumping. S.C. and J.K. carried out theoretical simulations. J.R. and L.L. contributed material analysis. S.C., G.W. and J.L. co-wrote the paper. J.L. supervised the project. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Jianlin Liu Author Details * Sheng Chu Search for this author in: * NPG journals * PubMed * Google Scholar * Guoping Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Weihang Zhou Search for this author in: * NPG journals * PubMed * Google Scholar * Yuqing Lin Search for this author in: * NPG journals * PubMed * Google Scholar * Leonid Chernyak Search for this author in: * NPG journals * PubMed * Google Scholar * Jianze Zhao Search for this author in: * NPG journals * PubMed * Google Scholar * Jieying Kong Search for this author in: * NPG journals * PubMed * Google Scholar * Lin Li Search for this author in: * NPG journals * PubMed * Google Scholar * Jingjian Ren Search for this author in: * NPG journals * PubMed * Google Scholar * Jianlin Liu Contact Jianlin Liu Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,905 KB) Supplementary information Additional data - Electrically tuned spin–orbit interaction in an InAs self-assembled quantum dot
- Nat Nanotechnol 6(8):511-516 (2011)
Nature Nanotechnology | Article Electrically tuned spin–orbit interaction in an InAs self-assembled quantum dot * Y. Kanai1, 7 * R. S. Deacon1, 2, 7 * S. Takahashi1 * A. Oiwa1, 2 * K. Yoshida1 * K. Shibata3 * K. Hirakawa2, 3, 4 * Y. Tokura5 * S. Tarucha1, 4, 6 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:511–516Year published:(2011)DOI:doi:10.1038/nnano.2011.103Received20 January 2011Accepted02 June 2011Published online24 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Electrical control over electron spin is a prerequisite for spintronics spin-based quantum information processing. In particular, control over the interaction between the orbital motion and the spin state of electrons would be valuable, because this interaction influences spin relaxation and dephasing. Electric fields have been used to tune the strength of the spin–orbit interaction in two-dimensional electron gases, but not, so far, in quantum dots. Here, we demonstrate that electrical gating can be used to vary the energy of the spin–orbit interaction in the range 50–150 µeV while maintaining the electron occupation of a single self-assembled InAs quantum dot. We determine the spin–orbit interaction energy by observing the splitting of Kondo effect features at high magnetic fields. View full text Subject terms: * Electronic properties and devices * Nanomagnetism and spintronics * Nanoparticles Figures at a glance * Figure 1: Magnetic evolution of system ground states. , False-colour plot of differential conductance (G = dI/dVsd), showing the magnetic evolution of the Coulomb charging peaks for Vsd = 0 V and Vsg = −0.5 V. The external magnetic field is applied out-of-plane, ext‖z. Solid lines are a guide to the eye indicating spin-up (↑) and spin-down (↓) electron states that create the crossings in regions I, II and III. , Schematic representation of the energy levels for two crossings (equivalent to II and III). In each case, two single-particle energy levels with different orbital and opposite spin states are tuned to a degeneracy at which the SOI hybridization occurs. The resulting avoided crossing may be detected as a splitting of the high B-field Kondo feature, which is possible wherever there is a degeneracy of two opposite spin states. Green arrows indicate a fourth-order tunnelling process, which is representative of the high-order processes that generate the Kondo feature. The Kondo peak at the Fermi energy is split due t! o the hybridization of the crossing levels. , False-colour plot of G(VG, B) about region II with Vsd = 0 mV and Vsg = −0.5 V. , Differential conductance at the centre of region II (half-filling condition) for Vsd = 0 mV as a function of temperature. The red line indicates a best fit using the empirical expression discussed in the text. * Figure 2: Hybridization of the orbital states. , False-colour G(VG, B) plot focusing on region II, with Vsd = 0 V and Vsg = 0 V. Solid and dashed lines indicate the ranges of VG and B swept in measurements – and , respectively. All measurements are plotted with the same colour scale (units of e2/h) as in . Dashed lines in – indicate the split Kondo feature. * Figure 3: Action of the side-gate. , Positions of the Coulomb charging resonances for Vsd = 0 V. Dashed lines indicate the position of the degenerated crossing/anti-crossing point. –, False-colour plots of differential conductance collected by sweeping Vsd while simultaneously stepping both B and VG to follow the dashed lines in . , G(Vsd) traces at the half-filling condition in the centre of region II for a range of Vsg. Traces are offset for clarity. * Figure 4: Electrical control of SOI. Plot of SOI hybridization energy evaluated in the centre of regions II, IV and V for a range of Vsg. Bars indicate a quarter of the full-width at half-maximum of the peaks for comparison. Inset: schematic of the device with relevant axes indicated. Source and drain electrodes are indicated in blue, with the QD drawn in red as an elongated semi-ellipsoid. The external magnetic field is applied out-of-plane, ext‖z. * Figure 5: Azimuthal B-field rotation. , False-colour plot of G(VG, B) for Vsd = 0 V, Vsg = −0.5 V and θ = −20°. , Schematic of the device with relevant axes indicated. The external field ext is applied in-plane with angle θ measured from the y-axis. , SOI energy Δ as a function of θ for Vsg = −0.5 V and Vsg = 1.0 V. Bars indicate a quarter of the full-width at half-maximum of the split peaks for comparison. The solid (dashed) blue line indicates an absolute cosine function fit to the Vsg = 0 V (−0.5 V) data, as described in the main text. The blue dashed arrow shows the approximate in-plane direction of the real vector SOI/i indicated by the offset angle of the cosine fit, θ0. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Y. Kanai & * R. S. Deacon Affiliations * Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8656, Japan * Y. Kanai, * R. S. Deacon, * S. Takahashi, * A. Oiwa, * K. Yoshida & * S. Tarucha * JST CREST, 4-1-8 Hon-cho, Kawaguchi-shi, Saitama 332-0012, Japan * R. S. Deacon, * A. Oiwa & * K. Hirakawa * Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan * K. Shibata & * K. Hirakawa * INQIE, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan * K. Hirakawa & * S. Tarucha * NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa, 243-0198, Japan * Y. Tokura * QPEC, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan * S. Tarucha Contributions Y.K. and R.S.D. performed measurements, analysed the results and wrote the manuscript. S. Takahashi contributed to interpretation of the data. K.Y. contributed to device fabrication. K.S. and K.H. grew the self-assembled InAs quantum dot samples. Y.T. performed simulations of the system, which were crucial to interpretation of data. A.O. and S. Tarucha directed the research. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * R. S. Deacon Author Details * Y. Kanai Search for this author in: * NPG journals * PubMed * Google Scholar * R. S. Deacon Contact 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 Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (16,832 KB) Supplementary information Additional data - Long-range electron tunnelling in oligo-porphyrin molecular wires
- Nat Nanotechnol 6(8):517-523 (2011)
Nature Nanotechnology | Article Long-range electron tunnelling in oligo-porphyrin molecular wires * Gita Sedghi1 * Víctor M. García-Suárez2, 3 * Louisa J. Esdaile4 * Harry L. Anderson4 * Colin J. Lambert2 * Santiago Martín1, 5 * Donald Bethell1 * Simon J. Higgins1 * Martin Elliott6 * Neil Bennett6 * J. Emyr Macdonald6 * Richard J. Nichols1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:517–523Year published:(2011)DOI:doi:10.1038/nnano.2011.111Received17 May 2011Accepted15 June 2011Published online31 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Short chains of porphyrin molecules can mediate electron transport over distances as long as 5–10 nm with low attenuation. This means that porphyrin-based molecular wires could be useful in nanoelectronic and photovoltaic devices, but the mechanisms responsible for charge transport in single oligo-porphyrin wires have not yet been established. Here, based on electrical measurements of single-molecule junctions, we show that the conductance of the oligo-porphyrin wires has a strong dependence on temperature, and a weak dependence on the length of the wire. Although it is widely accepted that such behaviour is a signature of a thermally assisted incoherent (hopping) mechanism, density functional theory calculations and an accompanying analytical model strongly suggest that the observed temperature and length dependence is consistent with phase-coherent tunnelling through the whole molecular junction. View full text Subject terms: * Electronic properties and devices Figures at a glance * Figure 1: Structure of the oligo-porphyrins. , Compounds n = 1 (monomer), n = 2 (dimer) and n = 3 (trimer). The C8H17O pendent side chains in compounds are replaced by H3CO– side chains in the structural model. , Schematic representation of the butadiyne-linked trimer between gold leads, when the porphyrin rings lie in one plane. Axial ligands (pyridine) binding to the Zn centres are also not shown (these inhibit aggregation of the molecules and are observed to promote the formation of Au | oligoporphyrin | Au junctions in the STM experiments). The terminal N atoms are bonded to gold adatoms on each electrode surface (A–A configuration). Atom colouring: C, dark grey; H, light grey; N, blue; O, red; Zn, pink; Au, yellow. * Figure 2: Single-molecule conductance data for the dimer. , Conductance histogram and I(s) curves (inset) for porphyrin recorded by an STM at room temperature, with Vbias = 0.6 V and a set point current of 6 nA. A total of 285 I(s) curves are included in the histogram. , Conductance histograms for porphyrin dimer at five different temperatures. Inset: Arrhenius-type plot of the single-molecule conductance σ. The red line is the best fit to the data points, and error bars refer to one standard deviation of the data points forming the histogram peak (from its mean value). * Figure 3: Dependence of conductance of oligo-porphyrins on length. Conductance data at 25 °C for the monomer, dimer and trimer (open circles). Theoretical data are also shown for when the dihedral angle between the rings is 0° (squares) and 15° (triangles). The theoretical values were calculated with a single-zeta basis set in the leads and a double-zeta polarized basis set in the molecule. The coupling nitrogen atoms at each end of the molecular bridge were located on top of a gold adatom and the leads were grown along the (001) direction of fcc gold, with 49 atoms per slice. The conductance values were evaluated by taking the transmission near the HOMO resonance (see text). The y-scale is logarithmic. Straight lines are plotted to connect points. * Figure 4: Dependence of electron transmission on dihedral angle. ,, DFT-computed transmission coefficient T (on a logarithmic scale) versus electron energy for the butadiyne-linked monomer (solid black line), dimer (grey line) and trimer (dashed line) when the angle between the rings of the oligomers is 0° () and 90° (). (Note that the curves for the monomer are the same in and .) EF0 is the value of the Fermi energy predicted by DFT. Other parameters are the same as those used in Fig. 3. * Figure 5: Dependence of conductance on temperature. DFT-computed conductance (on a logarithmic scale) versus EF − EF0, where EF is the true Fermi energy and EF0 is given by DFT without adjustment, for the monomer at temperatures of 25 °C (grey line) and 100 °C (dashed line); the black line shows the limit of zero temperature and voltage, which corresponds to the zero-bias transmission T. Inset: conductance in the region near EF − EF0 = −1.27 eV in more detail (on a linear scale). Other parameters are the same as those used in Fig. 3. Author information * Abstract * Author information * Supplementary information Affiliations * Chemistry Department, University of Liverpool, Liverpool L69 7ZD, UK * Gita Sedghi, * Santiago Martín, * Donald Bethell, * Simon J. Higgins & * Richard J. Nichols * Department of Physics, Lancaster University, Lancaster LA1 4YB, UK * Víctor M. García-Suárez & * Colin J. Lambert * Departamento de Física, Universidad de Oviedo & CINN, 33007 Oviedo, Spain * Víctor M. García-Suárez * Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK * Louisa J. Esdaile & * Harry L. Anderson * Departamento de Química Física, Universidad de Zaragoza & INA, 50009 Zaragoza, Spain * Santiago Martín * School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK * Martin Elliott, * Neil Bennett & * J. Emyr Macdonald Contributions G.S. performed experimental conductance measurements and analysed the data, in part with the assistance of S.M. V.G-S. performed DFT computations and analysed computational data. L.J.E. synthesized and chemically characterized the compounds. M.E. originated the analytical model and further developed it in consultation with C.J.L. N.B. performed supporting STM characterization measurements and contributed to numerical calculations of the Lorentzian model. G.S., V.G-S., H.L.A., C.J.L., S.J.H., M.E. and R.J.N. were involved in writing the manuscript and supporting information. H.L.A., C.J.L., D.B., S.J.H., M.E., E.M. and R.J.N. provided supervision at the different sites. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Richard J. Nichols or * Harry L. Anderson or * Colin J. Lambert Author Details * Gita Sedghi Search for this author in: * NPG journals * PubMed * Google Scholar * Víctor M. García-Suárez Search for this author in: * NPG journals * PubMed * Google Scholar * Louisa J. Esdaile Search for this author in: * NPG journals * PubMed * Google Scholar * Harry L. Anderson Contact Harry L. Anderson Search for this author in: * NPG journals * PubMed * Google Scholar * Colin J. Lambert Contact Colin J. Lambert Search for this author in: * NPG journals * PubMed * Google Scholar * Santiago Martín Search for this author in: * NPG journals * PubMed * Google Scholar * Donald Bethell Search for this author in: * NPG journals * PubMed * Google Scholar * Simon J. Higgins Search for this author in: * NPG journals * PubMed * Google Scholar * Martin Elliott Search for this author in: * NPG journals * PubMed * Google Scholar * Neil Bennett Search for this author in: * NPG journals * PubMed * Google Scholar * J. Emyr Macdonald Search for this author in: * NPG journals * PubMed * Google Scholar * Richard J. Nichols Contact Richard J. Nichols Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (5,434 KB) Supplementary information Additional data - Cell-surface sensors for real-time probing of cellular environments
- Nat Nanotechnol 6(8):524-531 (2011)
Nature Nanotechnology | Article Cell-surface sensors for real-time probing of cellular environments * Weian Zhao1, 2, 3, 4 * Sebastian Schafer1, 2, 3, 4 * Jonghoon Choi5 * Yvonne J. Yamanaka5, 6 * Maria L. Lombardi7 * Suman Bose8 * Alicia L. Carlson2, 9 * Joseph A. Phillips1, 2, 3, 4 * Weisuong Teo1, 2, 3, 4 * Ilia A. Droujinine1, 2, 3, 4 * Cheryl H. Cui1, 2, 3, 4 * Rakesh K. Jain10 * Jan Lammerding7 * J. Christopher Love5 * Charles P. Lin2, 3, 9 * Debanjan Sarkar1, 2, 3, 4 * Rohit Karnik8 * Jeffrey M. Karp1, 2, 3, 4 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:524–531Year published:(2011)DOI:doi:10.1038/nnano.2011.101Received03 December 2010Accepted02 June 2011Published online17 July 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell biology and developing effective therapeutics. However, it is not yet possible to monitor the interaction of cells with their environments in real time. Here, we show that a fluorescent sensor attached to a cell membrane can detect signalling molecules in the cellular environment. The sensor is an aptamer (a short length of single-stranded DNA) that binds to platelet-derived growth factor (PDGF) and contains a pair of fluorescent dyes. When bound to PDGF, the aptamer changes conformation and the dyes come closer to each other, producing a signal. The sensor, which is covalently attached to the membranes of mesenchymal stem cells, can quantitatively detect with high spatial and temporal resolution PDGF that is added in cell culture medium or secreted by neighbouring cells. The engineered stem cells retain their ability to find their way to the bone marrow and can be monit! ored in vivo at the single-cell level using intravital microscopy. View full text Subject terms: * Nanobiotechnology * Nanosensors and other devices Figures at a glance * Scheme 1: Probing the cellular niche environment and signalling using cells engineered with an aptamer sensor. Aptamer sensors that bind to signalling molecules (PDGF in this case) are covalently attached to the surface of cells (mesenchymal stem cells in this case). Signalling molecules secreted by niche cells are detected by the sensor cells, and the fluorescent signal generated is measured. * Figure 1: Mechanism of PDGF aptamer sensors in solution. , Original PDGF sensor described in ref. 28. When bound to PDGF, the aptamer changes from an open structure to a complex with paired bases in the stem region. The two dyes are located closer to one another and yield a fluorescent signal. , Non-specific folding of the original sensor at elevated ionic strength in the presence of divalent metal ions. ,, Engineered sensors. The terminal C–G base pair (blue) is mutated to an A–G pair (red–blue) for less non-specific folding in the aptamer. Biotin moieties allow immobilization on the cell surface. In the quench sensor (), fluorescence of the FAM dye is quenched by a quencher molecule (Dabcyl) in the presence of 10 nM PDGF in PBS–/–. In the FRET sensor (), donor dye (Cy3) fluorescence decreases and acceptor dye (Cy5) fluorescence increases upon addition of 10 nM PDGF in PBS. Spectra in and were recorded at room temperature. * Figure 2: Anchoring the engineered aptamer sensor to the cell surface. , Schematic showing the chemistry approach used to attach sensors to MSCs. –, Flow cytometry data using the Cy3 signal of the FRET sensor show successful conjugation of the aptamer sensor on the cell surface. * Figure 3: Aptamer sensor functions on the cell surface. , Representative sensor performance data, examined using flow cytometry, for the quench sensor immobilized on the MSC surface before and immediately after addition of 10 nM PDGF (GM, geometric mean). , Sensor signal (defined as the ratio of GM before and after addition of PDGF) versus concentration of PDGF in PBS–/–. ,, Representative fluorescent microscopy images of sensor cell before and immediately after addition of 10 nM PDGF in PBS–/–, respectively. , PDGF (2 µM) was added to sensor-modified MSCs from the top/left corner (arrow shows direction) using a pipette tip, and the image was recorded immediately. , The PDGF gradient was separated into five regions using image analysis, and the fluorescent intensities of 10 representative cells from each region were averaged and plotted. The sensor signal in region 1 is defined as 1; other regions are normalized accordingly. * Figure 4: Spatial-temporal imaging of a single MSC functionalized with the quench sensor demonstrates that PDGF sensing correlates with data generated from a computational model. , PDGF (2 µM) was injected 30 µm from the cell using a microneedle, as indicated by the orange arrow (Supplementary Fig. S5 includes a representative light microscope image showing the microneedle juxtaposed to the cell surface). The signal was quenched as PDGF engaged the sensor while moving across the cell surface as a function of time, as observed by fluorescent microscopy. , Concentration of PDGF on the cell surface as predicted from a three-dimensional computational mass transport model (described in Supplementary Information). Scale bar, 10 µm. * Figure 5: Real-time sensing of PDGF secretion from neighbouring MDA-MB-231 cells by sensor-engineered MSCs. Left panel: representative images of microwells containing different numbers of PDGF-producing MDA-MB-231 cells (green) in the same well with sensor MSC (red) at time t = 0 (n is the number of MSCs used in the analysis). MDA-MB-231 is genetically engineered to secrete PDGF that is fused with a GFP tag. To be distinguishable, the quench sensor in this set of experiments is labelled with a red dye (Cy5), and with Iowa Black RQ as a quencher. Cy5/Iowa Black RQ and FAM/Dabcyl perform similarly (Supplementary Fig. S9). Right panel: fluorescence of sensor MSC declining during the course of PDGF production. The signal, which is defined as the percentage of MSCs that have fluorescence intensity less than 50% of their initial value at the indicated time, correlates with the number of PDGF-producing MDA-MB-231 cells in the same well as a sensor MSC. * Figure 6: Bone marrow homing and transmigration of aptamer-labelled MSCs. , Large-area map of right parietal bone marrow compartments in an eight-week-old Balb/c mouse 24 h after injection of MSC and aptamer-MSC. Several image stacks were acquired in the right parietal bone ~200 µm to the right of the sagittal suture. , Zoomed-in image of the area in the white box in , shows a similar distribution of MSC (green) and aptamer-MSC (blue) in the vicinity of a large venule (red). , Quantification of the average number of cells per z-stack. , Quantification of percentage of cells positioned outside blood vessels shows no difference between MSC and aptamer-MSC (P-value = 0.116). MSC, green; aptamer-MSC, blue; blood vessels, red; bone, white. Scale bar, 100 µm. Author information * Abstract * Author information * Supplementary information Affiliations * Center for Regenerative Therapeutics & Department of Medicine, Brigham & Women's Hospital, 65 Landsdowne Street, Cambridge, Massachusetts 02139, USA * Weian Zhao, * Sebastian Schafer, * Joseph A. Phillips, * Weisuong Teo, * Ilia A. Droujinine, * Cheryl H. Cui, * Debanjan Sarkar & * Jeffrey M. Karp * Harvard Medical School, 65 Landsdowne Street, Cambridge, Massachusetts 02139, USA * Weian Zhao, * Sebastian Schafer, * Alicia L. Carlson, * Joseph A. Phillips, * Weisuong Teo, * Ilia A. Droujinine, * Cheryl H. Cui, * Charles P. Lin, * Debanjan Sarkar & * Jeffrey M. Karp * Harvard Stem Cell Institute, 65 Landsdowne Street, Cambridge, Massachusetts 02139, USA * Weian Zhao, * Sebastian Schafer, * Joseph A. Phillips, * Weisuong Teo, * Ilia A. Droujinine, * Cheryl H. Cui, * Charles P. Lin, * Debanjan Sarkar & * Jeffrey M. Karp * Harvard-MIT Division of Health Science and Technology, 65 Landsdowne Street, Cambridge, Massachusetts 02139, USA * Weian Zhao, * Sebastian Schafer, * Joseph A. Phillips, * Weisuong Teo, * Ilia A. Droujinine, * Cheryl H. Cui, * Debanjan Sarkar & * Jeffrey M. Karp * Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA * Jonghoon Choi, * Yvonne J. Yamanaka & * J. Christopher Love * Department of Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA * Yvonne J. Yamanaka * Department of Medicine, Brigham and Women's Hospital/Harvard Medical School, 65 Landsdowne Street, Cambridge, Massachusetts 02139, USA * Maria L. Lombardi & * Jan Lammerding * Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA * Suman Bose & * Rohit Karnik * Wellman Center for Photomedicine and Center for Systems Biology, Massachusetts General Hospital/Harvard Medical School, 40 Blossom Street, Boston, Massachusetts 02114, USA * Alicia L. Carlson & * Charles P. Lin * Edwin L. Steele Laboratory, Department of Radiation Oncology, Massachusetts General Hospital/Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, USA * Rakesh K. Jain Contributions W.Z. and J.M.K. are responsible for study concept and design. W.Z., J.M.K., J.L., J.C.L., C.P.L., D.S. and R.K. prepared the manuscript. W.Z., S.S., J.C., Y.J.Y., M.L.L., S.B., A.L.C., J.A.P, W.T., I.A.D. and C.C. carried out experiments and performed data analysis. R.K.J. provided genetically engineered cells. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Jeffrey M. Karp Author Details * Weian Zhao Search for this author in: * NPG journals * PubMed * Google Scholar * Sebastian Schafer Search for this author in: * NPG journals * PubMed * Google Scholar * Jonghoon Choi Search for this author in: * NPG journals * PubMed * Google Scholar * Yvonne J. Yamanaka Search for this author in: * NPG journals * PubMed * Google Scholar * Maria L. Lombardi Search for this author in: * NPG journals * PubMed * Google Scholar * Suman Bose Search for this author in: * NPG journals * PubMed * Google Scholar * Alicia L. Carlson Search for this author in: * NPG journals * PubMed * Google Scholar * Joseph A. Phillips Search for this author in: * NPG journals * PubMed * Google Scholar * Weisuong Teo Search for this author in: * NPG journals * PubMed * Google Scholar * Ilia A. Droujinine Search for this author in: * NPG journals * PubMed * Google Scholar * Cheryl H. Cui Search for this author in: * NPG journals * PubMed * Google Scholar * Rakesh K. Jain Search for this author in: * NPG journals * PubMed * Google Scholar * Jan Lammerding Search for this author in: * NPG journals * PubMed * Google Scholar * J. Christopher Love Search for this author in: * NPG journals * PubMed * Google Scholar * Charles P. Lin Search for this author in: * NPG journals * PubMed * Google Scholar * Debanjan Sarkar Search for this author in: * NPG journals * PubMed * Google Scholar * Rohit Karnik Search for this author in: * NPG journals * PubMed * Google Scholar * Jeffrey M. Karp Contact Jeffrey M. Karp Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (875 KB) Supplementary information Additional data
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