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Latest Articles Include:

• Our choice from the recent literature
  - UNKNOWN 6(3):133 (2011)
  Nature Nanotechnology | Research Highlights Our choice from the recent literature Journal name:Nature NanotechnologyVolume: 6,Page:133Year published:(2011)DOI:doi:10.1038/nnano.2011.31Published online04 March 2011 Read the full article * Instant access to this article: US$32Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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. Nature469, 385–388 (2011) © 2011 NPG Surface-enhanced Raman spectroscopy (SERS) allows researchers to detect small numbers of molecules because the light scattered by the molecules can be enhanced by factors of up to a million. SERS relies on light being concentrated into hotspots by nanoscale features on the surface, but these hotspots — which are electromagnetic rather than material structures — are too small to be imaged with existing optical techniques. Now Xiang Zhang and co-workers at the University of California in Berkeley and the Lawrence Berkeley Lab have overcome this obstacle by using molecules to measure the electromagnetic field of individual hotspots. View full text Read the full article * Instant access to this article: US$32Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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
• Nanoelectronics: Flat transistors get off the ground
  - UNKNOWN 6(3):135-136 (2011)
  Nature Nanotechnology | News and Views Nanoelectronics: Flat transistors get off the ground * Frank Schwierz1Journal name:Nature NanotechnologyVolume: 6,Pages:135–136Year published:(2011)DOI:doi:10.1038/nnano.2011.26Published online04 March 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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. The presence of a large bandgap means that a single layer of molybdenum disulphide can be used to make field-effect transistors with high on/off ratios and reasonably high mobilities. View full text Subject terms: * Electronic properties and devices * Nanomaterials 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 Affiliations * Frank Schwierz is at the Technische Universität Ilmenau, 98684 Ilmenau, Germany. Corresponding author Correspondence to: * Frank Schwierz Author Details * Frank Schwierz Contact Frank Schwierz Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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
• Supramolecular structures: Robust materials from weak forces
  - UNKNOWN 6(3):136-137 (2011)
  Nature Nanotechnology | News and Views Supramolecular structures: Robust materials from weak forces * Carsten Schmuck1Journal name:Nature NanotechnologyVolume: 6,Pages:136–137Year published:(2011)DOI:doi:10.1038/nnano.2011.28Published online04 March 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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. Recyclable membranes that are capable of separating nanoparticles of different sizes can be prepared from supramolecular assemblies that are held together by non-covalent bonds. View full text Subject terms: * Molecular self-assembly * Nanoparticles 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 Affiliations * Carsten Schmuck is at the Institute of Organic Chemistry, University Duisburg-Essen, Universitätsstraße 7, 45117 Essen, Germany. Corresponding author Correspondence to: * Carsten Schmuck Author Details * Carsten Schmuck Contact Carsten Schmuck Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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
• Computational nanotoxicology: Predicting toxicity of nanoparticles
  - UNKNOWN 6(3):138-139 (2011)
  Nature Nanotechnology | News and Views Computational nanotoxicology: Predicting toxicity of nanoparticles * Enrico Burello1 * Andrew Worth1 * Affiliations * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:138–139Year published:(2011)DOI:doi:10.1038/nnano.2011.27Published online04 March 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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. A statistical model based on a quantitative structure–activity relationship accurately predicts the cytotoxicity of various metal oxide nanoparticles, thus offering a way to rapidly screen nanomaterials and prioritize testing. View full text Subject terms: * Nanoparticles * Environmental, health and safety issues 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 Affiliations * Enrico Burello and Andrew Worth are in the Systems Toxicology Unit, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Via Enrico Fermi 2749, Ispra (VA), Italy. Any views expressed in this article do not necessarily represent the official views of the JRC or the EC. Corresponding authors Correspondence to: * Enrico Burello or * Andrew Worth Author Details * Enrico Burello Contact Enrico Burello Search for this author in: * NPG journals * PubMed * Google Scholar * Andrew Worth Contact Andrew Worth Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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
• In vitro assays: Tracking nanoparticles inside cells
  - UNKNOWN 6(3):139-140 (2011)
  Nature Nanotechnology | News and Views In vitro assays: Tracking nanoparticles inside cells * Haruhisa Kato1Journal name:Nature NanotechnologyVolume: 6,Pages:139–140Year published:(2011)DOI:doi:10.1038/nnano.2011.25Published online04 March 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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. Statistical analysis of nanoparticle delivery shows that cells take up nanoparticles randomly and redistribute them to their daughter cells in a biased way. View full text Subject terms: * Nanomedicine * Nanoparticles * Environmental, health and safety issues 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 Affiliations * Haruhisa Kato is in the Polymer Standards Section Japan (PSSJ), National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, Higashi 1-1-1, Tsukuba, Ibaraki, 305-8565 Japan. Corresponding author Correspondence to: * Haruhisa Kato Author Details * Haruhisa Kato Contact Haruhisa Kato Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * 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
• A recyclable supramolecular membrane for size-selective separation of nanoparticles
  - UNKNOWN 6(3):141-146 (2011)
  Nature Nanotechnology | Letter A recyclable supramolecular membrane for size-selective separation of nanoparticles * Elisha Krieg1 * Haim Weissman1 * Elijah Shirman1 * Eyal Shimoni2 * Boris Rybtchinski1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:141–146Year published:(2011)DOI:doi:10.1038/nnano.2010.274Received26 August 2010Accepted09 December 2010Published online23 January 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 Most practical materials are held together by covalent bonds, which are irreversible. Materials based on noncovalent interactions can undergo reversible self-assembly, which offers advantages in terms of fabrication, processing and recyclability1, but the majority of noncovalent systems are too fragile to be competitive with covalent materials for practical applications, despite significant attempts to develop robust noncovalent arrays1, 2, 3, 4. Here, we report nanostructured supramolecular membranes prepared from fibrous assemblies5 in water. The membranes are robust due to strong hydrophobic interactions6, 7, allowing their application in the size-selective separation of both metal and semiconductor nanoparticles. A thin (12 µm) membrane is used for filtration (~5 nm cutoff), and a thicker (45 µm) membrane allows for size-selective chromatography in the sub-5 nm domain. Unlike conventional membranes, our supramolecular membranes can be disassembled using organic solvent! , cleaned, reassembled and reused multiple times. View full text Subject terms: * Molecular self-assembly * Nanoparticles Figures at a glance * Figure 1: Supramolecular filtration membrane. , Photograph showing the preparation of the membrane by filtration of a supramolecular solution of (5 × 10−4 M) in water over a CA filter (pore size, 0.45 µm). , Photograph of the supramolecular membrane deposited on top of the CA support in the commercial syringe filter. , Cryo-SEM image of the cross-section of a ~1 × 1 mm piece of the supramolecular membrane (0.65 mg cm−2) on the CA support. , Magnified image showing the sharp border between the coarse CA and the smooth layer (dashed line). , High-magnification image of the supramolecular layer. * Figure 2: Filtration of gold nanoparticles Au3. , Photograph of filtration experiment. ,, Representative TEM image of before filtration () and corresponding particle size histogram (). ,, TEM image of the filtrate () and corresponding histogram (). ,, TEM image of the retentate () and corresponding histogram (). Red lines in the histograms indicate the cutoff of the filter. Representative TEM images of larger areas are presented in Figs S22–S24. , UV/Vis spectra of the solution before filtration (black trace), retentate (red trace) and filtrate (blue trace). , Photographs showing the retrieval of and gold nanoparticles from the water/ethanol mixture. , Scheme of fabrication, use and recycling of the supramolecular membrane. * Figure 3: Retained nanoparticles in the supramolecular membrane. Backscattered electron cryo-SEM image of the supramolecular membrane used for filtering solution. Gold nanoparticles (appearing as bright spots) have sizes ranging from 10 to 20 nm. The crack in the membrane is a result of cryo-SEM sample preparation. * Figure 4: Filtration experiments of gold nanoparticles Au2 and Au8. , Filtration of : representative TEM image of particles before filtration () and particle size histogram (); representative TEM image of particles in the filtrate () and particle size histogram (); photograph of filtration (); UV/Vis spectra of an solution before filtration (black trace), after filtration over CA (control measurement, red trace), and after filtration over the supramolecular membrane (blue trace) (, OD, optical density). Filtration of over CA does not change any spectral features and the SPB at ~520 nm remains unchanged, indicating that all particles pass CA. In contrast, no SPB is visible in the sample filtered over the supramolecular membrane, indicating removal of particles larger than 5 nm. –, Filtration of : representative TEM image of particles before filtration () and particle size histogram (); representative TEM image of particles in the filtrate () and particle size histogram (); photograph of filtration (); UV/Vis spectra of an solution before fi! ltration (black trace), after filtration over CA (control measurement, dashed red trace), and after filtration over the membrane (blue trace) (). As even small (~2 nm) charge-neutral (PEG-SH stabilized) gold nanoparticles still exhibit a weak SPB32, 33, the SPB does not vanish completely in the filtrate but instead weakens and shifts from 512 to 502 nm. The spectra of the samples before filtration and filtered over CA overlap. Representative TEM images of larger areas are presented in Figs S25–S28. * Figure 5: Size-exclusion chromatography with quantum dots. ,, Normalized luminescence spectra (λex = 390 nm) of (orange trace), (green trace) and their mixture (black trace) (), and successive fractions 1–5 collected by filtering the mixture (). , Photograph of the mixture (top) and the collected fractions (bottom) under UV light (365 nm). Author information * Abstract * Author information * Supplementary information Affiliations * Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel * Elisha Krieg, * Haim Weissman, * Elijah Shirman & * Boris Rybtchinski * Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel * Eyal Shimoni Contributions B.R., H.W. and E.K. conceived the project and planned the experiments. E.K. performed the synthesis and filtration experiments. E. Shimoni and H.W. carried out electron microscopy studies and data analysis. E. Shirman synthesized nanoparticles , , and and participated in data analysis. E.K. and B.R. wrote the paper. All authors discussed the results and commented on the paper. All authors contributed extensively to the work presented in this paper. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Boris Rybtchinski Author Details * Elisha Krieg Search for this author in: * NPG journals * PubMed * Google Scholar * Haim Weissman Search for this author in: * NPG journals * PubMed * Google Scholar * Elijah Shirman Search for this author in: * NPG journals * PubMed * Google Scholar * Eyal Shimoni Search for this author in: * NPG journals * PubMed * Google Scholar * Boris Rybtchinski Contact Boris Rybtchinski Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information Movies * Supplementary information (5,328 KB) Supplementary movie PDF files * Supplementary information (5,328 KB) Supplementary information Additional data
• Single-layer MoS2 transistors
  - UNKNOWN 6(3):147-150 (2011)
  Nature Nanotechnology | Letter Single-layer MoS2 transistors * B. Radisavljevic1 * A. Radenovic2 * J. Brivio1 * V. Giacometti1 * A. Kis1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:147–150Year published:(2011)DOI:doi:10.1038/nnano.2010.279Received12 November 2010Accepted13 December 2010Published online30 January 2011Corrected online17 February 2011 Abstract * Abstract * Change history * 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 Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene1, 2, both because of its rich physics3, 4, 5 and its high mobility6. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors7. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films8, 9, 10, 11, 12, 13 or requires high voltages14, 15. Although single layers of MoS2 have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5–3 cm2 V−1 s−1 range17 are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS2 mobility of at least 200 cm2 V−1 s−1, similar to th! at of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 108 and ultralow standby power dissipation. Because monolayer MoS2 has a direct bandgap16, 18, it can be used to construct interband tunnel FETs19, which offer lower power consumption than classical transistors. Monolayer MoS2 could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting. View full text Subject terms: * Electronic properties and devices * Nanomaterials Figures at a glance * Figure 1: Structure and AFM imaging of monolayer MoS2. , Three-dimensional representation of the structure of MoS2. Single layers, 6.5 Å thick, can be extracted using scotch tape-based micromechanical cleavage. , Atomic force microscope image of a single layer of MoS2 deposited on a silicon substrate with a 270-nm-thick oxide layer. , Cross-sectional plot along the red line in . * Figure 2: Fabrication of MoS2 monolayer transistors. , Optical image of a single layer of MoS2 (thickness, 6.5 Å) deposited on top of a silicon substrate with a 270-nm-thick SiO2 layer. , Optical image of a device based on the flake shown in . The device consists of two field-effect transistors connected in series and defined by three gold leads that serve as source and drain electrodes for the two transistors. Monolayer MoS2 is covered by 30 nm of ALD-deposited HfO2 that acts both as a gate dielectric and a mobility booster. Scale bars (,), 10 µm. , Three-dimensional schematic view of one of the transistors shown in . * Figure 3: Characterization of MoS2 monolayer transistors. , Cross-sectional view of the structure of a monolayer MoS2 FET together with electrical connections used to characterize the device. A single layer of MoS2 (thickness, 6.5 Å) is deposited on a degenerately doped silicon substrate with 270-nm-thick SiO2. The substrate acts a back gate. One of the gold electrodes acts as drain and the other source electrode is grounded. The monolayer is separated from the top gate by 30 nm of ALD-grown HfO2. The top gate width for the device is 4 µm and the top gate length, source–gate and gate–drain spacing are each 500 nm. , Room-temperature transfer characteristic for the FET with 10 mV applied bias voltage Vds. Back-gate voltage Vbg is applied to the substrate and the top gate is disconnected. Inset: Ids–Vds curve acquired for Vbg values of 0, 1 and 5 V. * Figure 4: Local gate control of the MoS2 monolayer transistor. , Ids–Vtg curve recorded for a bias voltage ranging from 10 mV to 500 mV. Measurements are performed at room temperature with the back gate grounded. Top gate width, 4 µm; top gate length, 500 nm. The device can be completely turned off by changing the top gate bias from –2 to –4 V. For Vds = 10 mV, the Ion/Ioff ratio is >1 × 106. For Vds = 500 mV, the Ion/Ioff ratio is >1 × 108 in the measured range while the subthreshold swing S = 74 mV dec−1. Top and bottom gate leakage is negligible (Supplementary Fig. S3). Inset: Ids–Vtg for values of Vbg = –10, –5, 0, 5 and 10 V. , Ids–Vds curves recorded for different values of Vtg. The linear dependence of the current on bias voltage for small voltages indicates that the gold contacts are ohmic. Change history * Abstract * Change history * Author information * Supplementary informationCorrected online 17 February 2011In the version of this Letter originally published online, the label 'Vtg' was missing from Fig. 3a and the expression 'μ = 217 cm-2 Vs' should have read 'μ = 217 cm2 V-1 s-1' in Fig. 3b. These errors have now been corrected in all versions of the Letter. Author information * Abstract * Change history * Author information * Supplementary information Affiliations * Electrical Engineering Institute, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland * B. Radisavljevic, * J. Brivio, * V. Giacometti & * A. Kis * Institute of Biotechnology, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland * A. Radenovic Contributions B.R., J.B., V.G. and A.K. worked on device fabrication and contact optimization. A.R. built the system for atomic layer deposition of HfO2. B.R. and A.K. performed measurements and analysed the data presented in the paper and Supplementary Information. A.K. initiated the research and wrote the manuscript. All the authors read and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * A. Kis Author Details * B. Radisavljevic Search for this author in: * NPG journals * PubMed * Google Scholar * A. Radenovic Search for this author in: * NPG journals * PubMed * Google Scholar * J. Brivio Search for this author in: * NPG journals * PubMed * Google Scholar * V. Giacometti Search for this author in: * NPG journals * PubMed * Google Scholar * A. Kis Contact A. Kis Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Change history * Author information * Supplementary information PDF files * Supplementary information (679 KB) Additional data
• Plasmonic Luneburg and Eaton lenses
  - UNKNOWN 6(3):151-155 (2011)
  Nature Nanotechnology | Letter Plasmonic Luneburg and Eaton lenses * Thomas Zentgraf1, 4 * Yongmin Liu1, 4 * Maiken H. Mikkelsen1, 4 * Jason Valentine1, 2 * Xiang Zhang1, 3 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:151–155Year published:(2011)DOI:doi:10.1038/nnano.2010.282Received05 November 2010Accepted21 December 2010Published online23 January 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 Plasmonics takes advantage of the properties of surface plasmon polaritons, which are localized or propagating quasiparticles in which photons are coupled to the quasi-free electrons in metals. In particular, plasmonic devices can confine light in regions with dimensions that are smaller than the wavelength of the photons in free space, and this makes it possible to match the different length scales associated with photonics and electronics in a single nanoscale device1. Broad applications of plasmonics that have been demonstrated to date include biological sensing2, sub-diffraction-limit imaging, focusing and lithography3, 4, 5 and nano-optical circuitry6, 7, 8, 9, 10. Plasmonics-based optical elements such as waveguides, lenses, beamsplitters and reflectors have been implemented by structuring metal surfaces7, 8, 11, 12 or placing dielectric structures on metals6, 13, 14, 15 to manipulate the two-dimensional surface plasmon waves. However, the abrupt discontinuities in the! material properties or geometries of these elements lead to increased scattering of surface plasmon polaritons, which significantly reduces the efficiency of these components. Transformation optics provides an alternative approach to controlling the propagation of light by spatially varying the optical properties of a material16, 17. Here, motivated by this approach, we use grey-scale lithography to adiabatically tailor the topology of a dielectric layer adjacent to a metal surface to demonstrate a plasmonic Luneburg lens that can focus surface plasmon polaritons. We also make a plasmonic Eaton lens that can bend surface plasmon polaritons. Because the optical properties are changed gradually rather than abruptly in these lenses, losses due to scattering can be significantly reduced in comparison with previously reported plasmonic elements. View full text Subject terms: * Photonic structures and devices Figures at a glance * Figure 1: Plasmonic Luneburg lens. , SEM image of a Luneburg lens made of PMMA on top of a gold film (lens diameter, 13 µm). The grating for the SPPs (left) is made of air grooves fabricated by focused ion beam milling. , Mode index (vertical axis) for the Luneburg lens at a wavelength of 810 nm. , Relation between PMMA height and mode index for SPPs on a gold surface at a wavelength of 810 nm. , Cross-sections of the normalized magnetic field Hx (at the metal–dielectric interface in the x–z plane and for x = 0 in the y–z plane) for SPPs propagating through the Luneburg lens in the positive z-direction. The lens is designed to focus the SPPs to a point on the perimeter of the lens. * Figure 2: Fluorescence images of a plasmonic Luneburg lens. Fluorescence intensity for SPPs passing through the Luneburg lens (upper panels) and corresponding simulations (lower panels). Fluorescence intensity is colour-coded from black (low) to white (high). Positions of lenses are marked by the yellow dotted circle. SPPs have a Gaussian intensity distribution along the x axis with a full-width at half-maximum of 6 µm. The images show propagation of SPPs in the positive z-direction for three different launching positions in the x-direction, as indicated by the beam profile below the images (vertical dotted line marks the centre of the lens). * Figure 3: Broadband performance of a plasmonic Luneburg lens. , Intensity images obtained by leakage radiation microscopy for SPPs passing a Luneburg lens for wavelengths of 770 nm (), 800 nm () and 840 nm (). These images show focusing over a 70 nm bandwidth for the plasmonic Luneburg lens. SPPs are launched from a gold grating (dashed box) towards the Luneburg lens (dashed circle), which is 10 μm from the grating. , Corresponding surface profile cross-section along the propagation (z) direction measured by AFM, showing the height of the lens and the gratings. * Figure 4: Numerical simulations of a plasmonic Eaton lens. , Truncated mode index profile for an Eaton lens with a radius of 30 µm. Values larger than 1.54 in the centre are cut and set to 1.54 due to the finite range provided by the index of SPPs at the metal–PMMA interface. , Calculated magnitude of the electric surface field for a SPP launched in the positive z-direction. The solid line marks the outer diameter of the lens, and the dashed line marks the truncated index region with values set to 1.54. The SPPs bend to the right side when passing through the lens. , Calculated fluorescence intensity for , taking the height of the dye/PMMA layer into account, visualizing the expected intensity from the structure. In the colour scale in and , black represents low field amplitudes/intensities and yellow indicates high field amplitudes/intensities. * Figure 5: Demonstration of a plasmonic Eaton lens. , SEM image of an array of Eaton lenses on top of a gold film. , Height profile cross-section for the left side of the lens measured by AFM (solid line) compared to the model (dashed line). ,, Fluorescence microscopy image and corresponding simulation of the fluorescence intensity of the Eaton lens for SPPs propagating in the positive z-direction and bending to the right side when passing through the lens. Arrows indicate the launching position and direction of the SPPs. Solid lines mark the outer diameter of the lens and dashed lines the high index region, which was set to 1.54. In the colour scale, black represents low intensities and yellow high intensities. Author information * Abstract * Author information Primary authors * These authors contributed equally to this work * Thomas Zentgraf, * Yongmin Liu & * Maiken H. Mikkelsen Affiliations * NSF Nanoscale Science and Engineering Center (NSEC), 3112 Etcheverry Hall, University of California, Berkeley, California 94720, USA * Thomas Zentgraf, * Yongmin Liu, * Maiken H. Mikkelsen, * Jason Valentine & * Xiang Zhang * Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA * Jason Valentine * Materials Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA * Xiang Zhang Contributions T.Z., Y.L. and J.V. conceived and designed the experiments. T.Z. and M.H.M. performed the experiments and analysed the data. Y.L. designed the structures and performed the numerical simulations. J.V. and M.H.M. fabricated the samples. X.Z. guided the theoretical and experimental work. All authors discussed the results and co-wrote the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Xiang Zhang Author Details * Thomas Zentgraf Search for this author in: * NPG journals * PubMed * Google Scholar * Yongmin Liu Search for this author in: * NPG journals * PubMed * Google Scholar * Maiken H. Mikkelsen Search for this author in: * NPG journals * PubMed * Google Scholar * Jason Valentine Search for this author in: * NPG journals * PubMed * Google Scholar * Xiang Zhang Contact Xiang Zhang Search for this author in: * NPG journals * PubMed * Google Scholar Additional data
• Flexible high-performance carbon nanotube integrated circuits
  - UNKNOWN 6(3):156-161 (2011)
  Nature Nanotechnology | Letter Flexible high-performance carbon nanotube integrated circuits * Dong-ming Sun1 * Marina Y. Timmermans2, 3 * Ying Tian2 * Albert G. Nasibulin2 * Esko I. Kauppinen2 * Shigeru Kishimoto1 * Takashi Mizutani1 * Yutaka Ohno1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:156–161Year published:(2011)DOI:doi:10.1038/nnano.2011.1Received10 December 2010Accepted05 January 2011Published online06 February 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 Carbon nanotube thin-film transistors1 are expected to enable the fabrication of high-performance2, flexible3 and transparent4 devices using relatively simple techniques. However, as-grown nanotube networks usually contain both metallic and semiconducting nanotubes, which leads to a trade-off between charge-carrier mobility (which increases with greater metallic tube content) and on/off ratio (which decreases)5. Many approaches to separating metallic nanotubes from semiconducting nanotubes have been investigated6, 7, 8, 9, 10, 11, but most lead to contamination and shortening of the nanotubes, thus reducing performance. Here, we report the fabrication of high-performance thin-film transistors and integrated circuits on flexible and transparent substrates using floating-catalyst chemical vapour deposition followed by a simple gas-phase filtration and transfer process. The resulting nanotube network has a well-controlled density and a unique morphology, consisting of long (~10! µm) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm2 V–1 s–1 and an on/off ratio of 6 × 106. We also demonstrate flexible integrated circuits, including a 21-stage ring oscillator and master–slave delay flip-flops that are capable of sequential logic. Our fabrication procedure should prove to be scalable, for example, by using high-throughput printing techniques. View full text Subject terms: * Carbon nanotubes and fullerenes * Electronic properties and devices * Synthesis and processing Figures at a glance * Figure 1: Carbon nanotube growth and device fabrication. , Schematic of carbon nanotube growth, collection by filter, transfer and patterning. , SEM image of carbon nanotube film transferred onto a Si/SiO2 substrate. Carbon nanotube collection time, 2 s. Inset: magnified view of Y-junctions. The red and blue arrows indicate X- and Y-junctions, respectively. , Schematics of X- and Y-junctions. , Transfer (ID − VGS) characteristics at various VDS values ranging from −0.5 to −5 V. Lch = Wch = 100 µm. Inset: schematics of the bottom-gate carbon nanotube TFT on a Si/SiO2 substrate. , Output (ID − VDS) characteristics of the same device exhibiting saturation behaviour. * Figure 2: Mobility and on/off ratio. Comparison of 36 carbon nanotube TFTs with Lch = 100 µm and other representative TFTs based on carbon nanotube networks, amorphous silicon, polycrystalline silicon, ZnO-based semiconductors, and organic materials. Given that different methods were used for calculating the mobility of the carbon nanotube TFTs, the mobilities in refs 3 and 13 were re-evaluated. * Figure 3: Channel-length dependence and statistics of on/off ratio. , Plot of on-current, off-current and on/off ratio versus channel length at VDS = −0.5 V. VGS is swept from −10 to 10 V. Twenty TFTs are measured for each Lch. In the lower panel, solid circles and squares represent the median, and the upper and lower bands of the boxes correspond to the 75th and 25th percentiles, respectively, of the device population. In region I, metallic nanotubes may directly bridge the source and drain electrodes. Region II is described by percolation theory. In region III, Ioff is generated by thermally excited carriers. , Histograms of the distribution of the on/off ratio for Lch values ranging from 5 to 100 µm. Forty-six TFTs were considered for each value of Lch in the statistical analysis. Red curves are Gaussian fits. Blue and green lines indicate the separate groups of devices with and without metallic paths, respectively. * Figure 4: Carbon nanotube TFTs and integrated circuits on a flexible substrate. , Photograph of devices fabricated on a flexible and transparent PEN substrate. , Schematic cross-section of a bottom-gate TFT on a PEN substrate with an Al2O3 gate insulator. , Transfer characteristics of a typical TFT with Lch = 100 µm at VDS = −0.5 V, Wch = 100 µm. , Input–output and gain characteristics of an inverter. Insets: optical micrograph, circuit diagram and symbol of the inverter. ,, Optical micrograph and circuit diagram of a 21-stage ring oscillator. , Output characteristics of the ring oscillator with an oscillation frequency of 2.0 kHz at VDD = −4 V. * Figure 5: Logic gates and delay flip-flops on a flexible substrate. –, NOR gate. –, NAND gate. –, Master–slave delay flip-flop. Each panel includes an optical micrograph, circuit symbol, truth table and input–output characteristics of the device. In , 'X' denotes a 'don't care' condition and '*' denotes 'no change' in output. The master–slave delay flip-flop is triggered on the rising edge of the CLK signal. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan * Dong-ming Sun, * Shigeru Kishimoto, * Takashi Mizutani & * Yutaka Ohno * NanoMaterials Group, Department of Applied Physics and Center for New Materials, Aalto University, Finland * Marina Y. Timmermans, * Ying Tian, * Albert G. Nasibulin & * Esko I. Kauppinen * Previously published as Marina Y. Zavodchikova * Marina Y. Timmermans Contributions Y.O. and E.K. conceived and designed the experiments. D.S. performed device fabrication and characterization. M.T. and Y.O. performed the growth of nanotubes. Y.T. and M.T. performed absorption measurements. A.N. and E.K. developed the floating-catalyst growth technique. D.S. and Y.O. co-wrote the paper. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Yutaka Ohno Author Details * Dong-ming Sun Search for this author in: * NPG journals * PubMed * Google Scholar * Marina Y. Timmermans Search for this author in: * NPG journals * PubMed * Google Scholar * Ying Tian Search for this author in: * NPG journals * PubMed * Google Scholar * Albert G. Nasibulin Search for this author in: * NPG journals * PubMed * Google Scholar * Esko I. Kauppinen Search for this author in: * NPG journals * PubMed * Google Scholar * Shigeru Kishimoto Search for this author in: * NPG journals * PubMed * Google Scholar * Takashi Mizutani Search for this author in: * NPG journals * PubMed * Google Scholar * Yutaka Ohno Contact Yutaka Ohno Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,325 KB) Supplementary information Additional data
• Fast DNA sequencing with a graphene-based nanochannel device
  - UNKNOWN 6(3):162-165 (2011)
  Nature Nanotechnology | Letter Fast DNA sequencing with a graphene-based nanochannel device * Seung Kyu Min1, 3 * Woo Youn Kim1, 2, 3 * Yeonchoo Cho1 * Kwang S. Kim1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:162–165Year published:(2011)DOI:doi:10.1038/nnano.2010.283Received07 October 2010Accepted22 December 2010Published online06 February 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 Devices in which a single strand of DNA is threaded through a nanopore could be used to efficiently sequence DNA1, 2, 3, 4, 5, 6, 7, 8, 9. However, various issues will have to be resolved to make this approach practical, including controlling the DNA translocation rate, suppressing stochastic nucleobase motions, and resolving the signal overlap between different nucleobases4, 7. Here, we demonstrate theoretically the feasibility of DNA sequencing using a fluidic nanochannel functionalized with a graphene nanoribbon. This approach involves deciphering the changes that occur in the conductance of the nanoribbon10, 11 as a result of its interactions with the nucleobases via π–π stacking12, 13. We show that as a DNA strand passes through the nanochannel14, the distinct conductance characteristics of the nanoribbon15, 16, 17 (calculated using a method based on density functional theory coupled to non-equilibrium Green function theory18–20) allow the different nucleobases to! be distinguished using a data-mining technique and a two-dimensional transient autocorrelation analysis. This fast and reliable DNA sequencing device should be experimentally feasible in the near future. View full text Subject terms: * Computational nanotechnology * Nanobiotechnology Figures at a glance * Figure 1: DNA base stacking on a graphene nanodevice during its passage through a fluidic nanochannel. , Schematic of a nanochannel device with an armchair GNR (AGNR) through which a ssDNA passes. The water molecules and counterions in the nanochannel are not depicted. , Instantaneous snapshot from a simulation (d, stacking distance; θ, tilt angle). * Figure 2: Electronic and transport properties of a GNR device stacked optimally with DNA bases. , Transmission curves (in G0). , Density of states. ,, MOs of a GNR with stacked Cyt at energies (E − EF) of −0.9 eV () and −1.4 eV (). The sharp dip in transmission of Cyt at −1.4 eV occurs due to the strong Fano resonance between its MO and graphene (). * Figure 3: Simulation results of the transport properties of 5′-GCATCGCT-3′. , Time-dependent histogram of the transmission peak positions (red, maximal values; blue, minimal values). The histogram shows features of Cyt (SC), Gua (SG), Ade/Cyt (SA/C) and Gua/Thy (SG/T) corresponding to the band centred around E − EF = Es = 1.8, −0.65, −1.2 and −1.65 eV, respectively. The height of each box to the right of the histogram represents the energy range of integration for each Sbase. , Plots of Sbase(t) versus time as an ssDNA passes. The sequence GCATCGCT can be inferred from the four curves. , Resolving of the sequence by Pbase(t), as a function of Sbase(t). , Plot of two-dimensional TACF, C(t, t0; τ = 0.025 ns). The black dotted lines each indicate an instant at which a (subsequent) DNA base passes out; white dashed lines each indicate an instant at which a (subsequent) DNA base comes in. , Final base sequence obtained from analysis of and . Colours and heights are given in relative intensity. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Seung Kyu Min & * Woo Youn Kim Affiliations * Center for Superfunctional Materials, Department of Chemistry and Department of Physics, Pohang University of Science and Technology, Hyojadong, Namgu, Pohang 790-784, Korea * Seung Kyu Min, * Woo Youn Kim, * Yeonchoo Cho & * Kwang S. Kim * Present address: Department of Chemistry, KAIST, Daejeon 305-701, Korea * Woo Youn Kim Contributions S.K.M. and W.Y.K. worked together. Y.C. assisted in the calculations and analysis. K.S.K. supervised the project. S.K.M., W.Y.K. and K.S.K. wrote the paper together. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Kwang S. Kim Author Details * Seung Kyu Min Search for this author in: * NPG journals * PubMed * Google Scholar * Woo Youn Kim Search for this author in: * NPG journals * PubMed * Google Scholar * Yeonchoo Cho Search for this author in: * NPG journals * PubMed * Google Scholar * Kwang S. Kim Contact Kwang S. Kim Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information Movies * Supplementary information (9,192 KB) Supplementary movie PDF files * Supplementary information (947 KB) Supplementary information Additional data
• Direct observation of stepwise movement of a synthetic molecular transporter
  - UNKNOWN 6(3):166-169 (2011)
  Nature Nanotechnology | Letter Direct observation of stepwise movement of a synthetic molecular transporter * Shelley F. J. Wickham1 * Masayuki Endo2, 3 * Yousuke Katsuda4 * Kumi Hidaka4 * Jonathan Bath1 * Hiroshi Sugiyama2, 3, 4 * Andrew J. Turberfield1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:166–169Year published:(2011)DOI:doi:10.1038/nnano.2010.284Received02 November 2010Accepted22 December 2010Published online06 February 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 Controlled motion at the nanoscale can be achieved by using Watson–Crick base-pairing to direct the assembly and operation of a molecular transport system consisting of a track, a motor1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and fuel13, 14, 15, all made from DNA. Here, we assemble a 100-nm-long DNA track on a two-dimensional scaffold16, and show that a DNA motor loaded at one end of the track moves autonomously and at a constant average speed along the full length of the track, a journey comprising 16 consecutive steps for the motor. Real-time atomic force microscopy allows direct observation of individual steps of a single motor, revealing mechanistic details of its operation. This precisely controlled, long-range transport could lead to the development of systems that could be programmed and routed by instructions encoded in the nucleotide sequences of the track and motor. Such systems might be used to create molecular assembly lines modelled on the ribosome. View full text Subject terms: * Molecular machines and motors * Nanobiotechnology Figures at a glance * Figure 1: DNA motor and track. , Layout of the DNA origami tile, bearing the single-stranded stators of the track (green) and two rows of hairpin loops (blue) on opposite surfaces. , Motor mechanism: a nicking enzyme cuts the motor-bound stator revealing a toehold at the 3′ end of the motor (magenta) that facilitates transfer of the motor to the adjacent intact stator by branch migration. , AFM image of track with all stators decorated with motor. ,, Motor can be precisely positioned on the track by omitting the first stator during tile assembly () then repairing the tile by addition of the missing stator hybridized to the motor (). * Figure 2: Fluorescence measurements of movement on intact and broken tracks. , Designed operating sequence. A motor carrying a quencher (Q) is loaded at position S1 of an eight-stator track. Blocking strands occupy stators S2–S8, preventing movement of the motor. (i) Addition of release strand removes the blockade (ii). Active motion (iii) is triggered by addition of enzyme. Motor position is reported by quenching of fluorophores F1, F2, F3, F4 and F8 by the motor. , Tracks labelled at F1 and F3 or F1 and F4 mixed with tracks labelled at F2. , Fluorescence from tracks labelled at F2, F8. The quenching of F8 that reports the arrival of motor at the end of an intact track is greatly reduced on tracks where stator S4 is omitted. * Figure 3: Observation of motor movement by AFM. Seventeen-stator tracks with motor loaded at position S1 were incubated with nicking enzyme at 23 °C. The distribution of motor positions before addition of enzyme and after 1, 2 and 3 h were determined by AFM. Representative images and histograms of motor positions are shown for each time point. Inset: motor distributions predicted by a simple kinetic model (Supplementary Fig. S5) using rate constants one-quarter of those deduced from fluorescence measurements on a short test track (the motor is slowed by the lower temperature and different buffer conditions required for AFM measurements, Supplementary Fig. S6). Scale bars, 20 nm. * Figure 4: AFM observation of discrete steps of a single motor molecule. The main panel shows a kymograph, a stack of slices from successive frames, collected at 0.1 Hz, that correspond to the height profile along the track (3 of the 65 frames are shown on the right). The highest point on each profile, interpreted as the motor position, is marked; the histogram shows motor position relative to the first position observed. The motor steps between four stators (blue lines). Periods of rapid movement between adjacent stators are followed by slower transitions (*) in which the motor advances a single step. Scale bars, 50 nm. Timescale for the kymograph is in seconds. Author information * Abstract * Author information * Supplementary information Affiliations * University of Oxford, Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK * Shelley F. J. Wickham, * Jonathan Bath & * Andrew J. Turberfield * Institute for Integrated Cell–Material Sciences (iCeMS), Kyoto University, Yoshida-ushinomiyacho, Sakyo-ku, Kyoto 606-8501, Japan * Masayuki Endo & * Hiroshi Sugiyama * Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan * Masayuki Endo & * Hiroshi Sugiyama * Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa-oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan * Yousuke Katsuda, * Kumi Hidaka & * Hiroshi Sugiyama Contributions Experiments were designed by S.W. with input from J.B. and A.J.T. Ensemble fluorescence experiments were carried out by S.W in the laboratory of A.J.T. Real-time AFM experiments were done by S.W., M.E., Y.K. and K.H in the laboratory of H.S. The manuscript was written by S.W., J.B., H.S. and A.J.T. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Hiroshi Sugiyama or * Andrew J. Turberfield Author Details * Shelley F. J. Wickham Search for this author in: * NPG journals * PubMed * Google Scholar * Masayuki Endo Search for this author in: * NPG journals * PubMed * Google Scholar * Yousuke Katsuda Search for this author in: * NPG journals * PubMed * Google Scholar * Kumi Hidaka Search for this author in: * NPG journals * PubMed * Google Scholar * Jonathan Bath Search for this author in: * NPG journals * PubMed * Google Scholar * Hiroshi Sugiyama Contact Hiroshi Sugiyama Search for this author in: * NPG journals * PubMed * Google Scholar * Andrew J. Turberfield Contact Andrew J. Turberfield Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information Movies * Supplementary information (4,548 KB) Supplementary movie 1 * Supplementary information (389 KB) Supplementary movie 2 PDF files * Supplementary information (4,318 KB) Supplementary information Additional data
• Statistical analysis of nanoparticle dosing in a dynamic cellular system
  - UNKNOWN 6(3):170-174 (2011)
  Nature Nanotechnology | Letter Statistical analysis of nanoparticle dosing in a dynamic cellular system * Huw D. Summers1 * Paul Rees1 * Mark D. Holton1 * M. Rowan Brown1 * Sally C. Chappell2 * Paul J. Smith2 * Rachel J. Errington2 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:170–174Year published:(2011)DOI:doi:10.1038/nnano.2010.277Received06 September 2010Accepted13 December 2010Published online23 January 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 delivery of nanoparticles into cells is important in therapeutic applications1, 2, 3 and in nanotoxicology4. Nanoparticles are generally targeted to receptors on the surfaces of cells and internalized into endosomes by endocytosis5, 6, 7, 8, 9, but the kinetics of the process and the way in which cell division redistributes the particles remain unclear. Here we show that the chance of success or failure of nanoparticle uptake and inheritance is random. Statistical analysis of nanoparticle-loaded endosomes indicates that particle capture is described by an over-dispersed Poisson probability distribution that is consistent with heterogeneous adsorption and internalization. Partitioning of nanoparticles in cell division is random and asymmetric, following a binomial distribution with mean probability of 0.52–0.72. These results show that cellular targeting of nanoparticles is inherently imprecise due to the randomness of nature at the molecular scale, and the statistical ! framework offers a way to predict nanoparticle dosage for therapy and for the study of nanotoxins. View full text Subject terms: * Nanomedicine * Nanoparticles * Environmental, health and safety issues Figures at a glance * Figure 1: Schematic of nanoparticle delivery and loading into cells. The administered dose is in particulate form and undergoes diffusion before and after attaching to the cell membrane (and sedimentation in the case of larger particles). The NLVs represent the delivered dose, which undergoes further dilution and dispersion during cell mitosis as the NLVs are stochastically partitioned into daughter cells (the different stages of dose evolution are highlighted by blue shading). * Figure 2: Optical tracking using photonic nanoparticles. , Electron micrograph of the CdTe/ZnS core/shell quantum dots (left) and a bright-field optical image of a U2-OS cell overlaid with the epifluorescent image of quantum dot-loaded vesicles (24 h post loading) (right). , Fluorescence intensity histogram from 5,000 cells, measured immediately following a 1 h loading period at 4 °C with a 10 nM quantum dot concentration. Low-temperature loading inhibits endosome internalization, ensuring that measured distributions reflect the statistics of initial nanoparticle adhesion rather than internalization and dilution. Below the histogram are sample images from the cytometer, corresponding to specific intensity bins. The signal heterogeneity per cell is clearly due to variation in the number of NLVs. * Figure 3: Nanoparticle delivery to cells. , NLV histogram of the data shown in Fig. 2b. Inset: typical fluorescence bright-field image (top) and a cluster identification mask overlay (bottom). NLVs per cell counts are obtained by implementing a peak count on the image mask. Line curves show fits to the data using a Poisson distribution (symbols, λ = 21 h−1) and an over-dispersed Poisson distribution (solid line, α = 7, αβ = λ, see equations in Methods). The over-dispersed Poisson distribution provides a >95% confidence level fit (Kolmogorov–Smirnov goodness-of-fit, D-stat = 0.0192). , Gamma function distribution of NLV formation rate λ, mean = 21 h−1, variance = 44 h−1. , Correlation plot of fluorescence intensity versus NLV number (Pearson correlation coefficient = 0.73). * Figure 4: Nanoparticle dose inheritance. , Normalized NLV dose dilution curve obtained from mean NLV number (red circles) and cell density measurements (black points show inverse of cell density). The solid line is a mono-exponential fit corresponding to a mean cell division time of 20.5 h. This confirms intergenerational conservation of NLVs. , Evolution of the NLV histogram over three cell generations. , Data fitting using a binomial transfer function. The predicted final distribution, obtained from a binomial convolution of the initial 48 h data set, is shown (red) together with the 72 h data set (green). , Variation in the goodness-of-fit between measured and predicted final distributions. A Kolmogorov–Smirnov fit statistic indicates a minimum, below the 95% confidence level (solid line), for a binomial probability of P = 0.7. Author information * Abstract * Author information * Supplementary information Affiliations * Centre for Nanohealth, College of Engineering, Swansea University, Swansea, SA2 8PP, UK * Huw D. Summers, * Paul Rees, * Mark D. Holton & * M. Rowan Brown * School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK * Sally C. Chappell, * Paul J. Smith & * Rachel J. Errington Contributions H.D.S., P.R., R.J.E. and P.J.S. designed the experiments. H.D.S., P.R. and M.R.B. analysed the data. H.D.S. and P.R. wrote the manuscript in close collaboration with the other authors. M.D.H and S.C. performed cell culture and nanoparticle loading. M.D.H. performed flow cytometry measurements. All authors discussed the results and approved the final version of the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Huw D. Summers Author Details * Huw D. Summers Contact Huw D. Summers Search for this author in: * NPG journals * PubMed * Google Scholar * Paul Rees Search for this author in: * NPG journals * PubMed * Google Scholar * Mark D. Holton Search for this author in: * NPG journals * PubMed * Google Scholar * M. Rowan Brown Search for this author in: * NPG journals * PubMed * Google Scholar * Sally C. Chappell Search for this author in: * NPG journals * PubMed * Google Scholar * Paul J. Smith Search for this author in: * NPG journals * PubMed * Google Scholar * Rachel J. Errington Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information Movies * Supplementary information (2,710 KB) Supplementary movie PDF files * Supplementary information (1,530 KB) Supplementary information * Supplementary information (315 KB) Supplementary information Additional data
• Using nano-QSAR to predict the cytotoxicity of metal oxide nanoparticles
  - UNKNOWN 6(3):175-178 (2011)
  Nature Nanotechnology | Letter Using nano-QSAR to predict the cytotoxicity of metal oxide nanoparticles * Tomasz Puzyn1, 2 * Bakhtiyor Rasulev1 * Agnieszka Gajewicz1, 2 * Xiaoke Hu3 * Thabitha P. Dasari3 * Andrea Michalkova1 * Huey-Min Hwang3 * Andrey Toropov4 * Danuta Leszczynska5 * Jerzy Leszczynski1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:175–178Year published:(2011)DOI:doi:10.1038/nnano.2011.10Received04 August 2010Accepted14 January 2011Published online13 February 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 It is expected that the number and variety of engineered nanoparticles will increase rapidly over the next few years1, and there is a need for new methods to quickly test the potential toxicity of these materials2. Because experimental evaluation of the safety of chemicals is expensive and time-consuming, computational methods have been found to be efficient alternatives for predicting the potential toxicity and environmental impact of new nanomaterials before mass production. Here, we show that the quantitative structure–activity relationship (QSAR) method commonly used to predict the physicochemical properties of chemical compounds can be applied to predict the toxicity of various metal oxides. Based on experimental testing, we have developed a model to describe the cytotoxicity of 17 different types of metal oxide nanoparticles to bacteria Escherichia coli. The model reliably predicts the toxicity of all considered compounds, and the methodology is expected to provide g! uidance for the future design of safe nanomaterials. View full text Subject terms: * Nanoparticles * Environmental, health and safety issues Author information * Abstract * Author information * Supplementary information Affiliations * Interdisciplinary Nanotoxicity Center, Department of Chemistry and Biochemistry, Jackson State University 1400 Lynch Street, Jackson, Mississippi 39217-0510, USA * Tomasz Puzyn, * Bakhtiyor Rasulev, * Agnieszka Gajewicz, * Andrea Michalkova & * Jerzy Leszczynski * Laboratory of Environmental Chemometrics, Faculty of Chemistry, University of Gdańsk, Sobieskiego 18, 80-952 Gdańsk, Poland * Tomasz Puzyn & * Agnieszka Gajewicz * Interdisciplinary Nanotoxicity Center, Department of Biology, Jackson State University, 1400 Lynch Street, Jackson, Mississippi 39217-0940, USA * Xiaoke Hu, * Thabitha P. Dasari & * Huey-Min Hwang * Instituto di Ricerche Farmacologiche Mario Negri, 20156, Via La Masa 19, Milano, Italy * Andrey Toropov * Interdisciplinary Nanotoxicity Center, Department of Civil and Environmental Engineering, Jackson State University, 1325 Lynch Street, Jackson, Mississippi 39217-0510, USA * Danuta Leszczynska Contributions X.H., T.P.D. and H-M.H. carried out empirical testing of the cytotoxicity of the metal oxides to E. coli. A.M. designed molecular clusters for calculations. T.P., B.R., A.G., A.M., A.T., D.L. and J.L. performed quantum-mechanical calculations, selected the optimal structural descriptors, developed and validated the nano-QSAR model and discussed the results. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Jerzy Leszczynski Author Details * Tomasz Puzyn Search for this author in: * NPG journals * PubMed * Google Scholar * Bakhtiyor Rasulev Search for this author in: * NPG journals * PubMed * Google Scholar * Agnieszka Gajewicz Search for this author in: * NPG journals * PubMed * Google Scholar * Xiaoke Hu Search for this author in: * NPG journals * PubMed * Google Scholar * Thabitha P. Dasari Search for this author in: * NPG journals * PubMed * Google Scholar * Andrea Michalkova Search for this author in: * NPG journals * PubMed * Google Scholar * Huey-Min Hwang Search for this author in: * NPG journals * PubMed * Google Scholar * Andrey Toropov Search for this author in: * NPG journals * PubMed * Google Scholar * Danuta Leszczynska Search for this author in: * NPG journals * PubMed * Google Scholar * Jerzy Leszczynski Contact Jerzy Leszczynski Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (647 KB) Supplementary information Additional data
• The origins and limits of metal–graphene junction resistance
  - UNKNOWN 6(3):179-184 (2011)
  Nature Nanotechnology | Article The origins and limits of metal–graphene junction resistance * Fengnian Xia1, 2 * Vasili Perebeinos1, 2 * Yu-ming Lin1 * Yanqing Wu1 * Phaedon Avouris1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:179–184Year published:(2011)DOI:doi:10.1038/nnano.2011.6Received19 November 2010Accepted07 January 2011Published online06 February 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 A high-quality junction between graphene and metallic contacts is crucial in the creation of high-performance graphene transistors. In an ideal metal–graphene junction, the contact resistance is determined solely by the number of conduction modes in graphene. However, as yet, measurements of contact resistance have been inconsistent, and the factors that determine the contact resistance remain unclear. Here, we report that the contact resistance in a palladium–graphene junction exhibits an anomalous temperature dependence, dropping significantly as temperature decreases to a value of just 110 ± 20 Ω µm at 6 K, which is two to three times the minimum achievable resistance. Using a combination of experiment and theory we show that this behaviour results from carrier transport in graphene under the palladium contact. At low temperature, the carrier mean free path exceeds the palladium–graphene coupling length, leading to nearly ballistic transport with a transfer effi! ciency of ~75%. As the temperature increases, this carrier transport becomes less ballistic, resulting in a considerable reduction in efficiency. View full text Subject terms: * Carbon nanotubes and fullerenes * Electronic properties and devices Figures at a glance * Figure 1: Determination of palladium–graphene contact resistance using the transfer length method (TLM). , Total resistance (Rtotal) between source and drain in a graphene FET array as a function of back-gate bias. Inset: scanning electron micrograph of a graphene FET array consisting of six devices with channel lengths varying from 1 to 6 µm, in steps of 1 µm. , Deriving contact resistance using the TLM at gate biases of −10 V (p-doped) and 23 V (Dirac point voltage), respectively. Black squares, measured total resistance; black line, linear fitting curve. Red and green lines, upper and lower 90% confidence limits, respectively, from which the error bars are inferred. , Contact resistance as a function of gate bias. Red and grey squares, measured contact resistance from FET arrays A and B, respectively. * Figure 2: Temperature dependence of contact resistance. , Transfer characteristics of a graphene FET with a 2-μm-wide and 1-μm-long graphene channel at temperatures ranging from 6 to 300 K. Inset: measured electron and hole mobilities as a function of temperature at a carrier density of ~6 × 1012 cm−2. , Grey squares, measured palladium–graphene contact resistance at 6 K as a function of gate bias. Grey and green solid lines denote the calculated contact resistance, assuming TMG of 0.75 and 1, respectively. Values used in the calculation: η = 5 meV, t1 = 300 meV, d1 = 1 Å. Red line, contact resistance in an ideal metal–graphene contact on 90 nm oxide. , Measured palladium–graphene contact resistance as a function of temperature at gate biases of VDirac − 30 V and VDirac + 30 V. * Figure 3: Carrier transport processes at the palladium–graphene junction and gate dependence of Dirac-point energies in graphene under palladium and in the channel. , Schematic view of two cascaded carrier transport processes at the metal–graphene junction, with transmission efficiencies TMG and TK, respectively. , Schematic view of the band profile and dipole formation at the metal–graphene interface. φM is the palladium work function, φG represents the work function of monolayer graphene, ΔEFM (ΔEFG) is the difference between the Dirac-point and Fermi-level energies in the metal-doped graphene (graphene channel), ΔV is the total built-in potential difference, deq is the equilibrium distance, and d1 is the effective distance between the charge sheets in the graphene and metal. The red cross represents the Dirac cone, and thick red lines are used to denote the broadening of electronic states. , Calculated ΔEFG (grey line) and ΔEFM (red, green, and blue lines for different d1) as a function of gate bias. Inset: calculated contact resistance RC as a function of gate bias for different broadening energy t1 from 100 to 300 meV wi! th d1 = 1 Å and perfect TMG and TK. * Figure 4: Transmission efficiency TMG, determined using Matthiessen's rule. Calculated transmission efficiency from metal to metal-doped graphene, TMG, as a function of the ratio of the mean free path (λ) and metal–graphene coupling length (λm). Inset: palladium–graphene contact, showing transfer length LT. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Fengnian Xia & * Vasili Perebeinos Affiliations * IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA * Fengnian Xia, * Vasili Perebeinos, * Yu-ming Lin, * Yanqing Wu & * Phaedon Avouris Contributions All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Fengnian Xia or * Phaedon Avouris Author Details * Fengnian Xia Contact Fengnian Xia Search for this author in: * NPG journals * PubMed * Google Scholar * Vasili Perebeinos Search for this author in: * NPG journals * PubMed * Google Scholar * Yu-ming Lin Search for this author in: * NPG journals * PubMed * Google Scholar * Yanqing Wu Search for this author in: * NPG journals * PubMed * Google Scholar * Phaedon Avouris Contact Phaedon Avouris Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (618 KB) Supplementary information Additional data
• Giant magnetoresistance through a single molecule
  - UNKNOWN 6(3):185-189 (2011)
  Nature Nanotechnology | Article Giant magnetoresistance through a single molecule * Stefan Schmaus1, 2 * Alexei Bagrets2, 3 * Yasmine Nahas1, 2 * Toyo K. Yamada1, 4 * Annika Bork1 * Martin Bowen5 * Eric Beaurepaire5 * Ferdinand Evers3, 6 * Wulf Wulfhekel1, 2 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:185–189Year published:(2011)DOI:doi:10.1038/nnano.2011.11Received22 November 2010Accepted14 January 2011Published online20 February 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 Magnetoresistance is a change in the resistance of a material system caused by an applied magnetic field. Giant magnetoresistance occurs in structures containing ferromagnetic contacts separated by a metallic non-magnetic spacer, and is now the basis of read heads for hard drives and for new forms of random access memory. Using an insulator (for example, a molecular thin film) rather than a metal as the spacer gives rise to tunnelling magnetoresistance, which typically produces a larger change in resistance for a given magnetic field strength, but also yields higher resistances, which are a disadvantage for real device operation. Here, we demonstrate giant magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope. We measure the magnetoresistance to be 60% and the conductance to be 0.26G0, where G0 is the quantum of conductance. Theoretical analysis identifies spin-dependent hybridi! zation of molecular and electrode orbitals as the cause of the large magnetoresistance. View full text Subject terms: * Electronic properties and devices * Nanomagnetism and spintronics Figures at a glance * Figure 1: H2Pc molecules adsorbed on cobalt islands with different out-of-plane magnetic orientations. , Topographic image of H2Pc molecules adsorbed onto two cobalt islands on the Cu(111) surface. Colour code: measured dI/dV at −310 mV. The two island species can be distinguished by the magnetization parallel (in yellow) and antiparallel (in red) to the tip magnetization. , Typical dI/dV spectra taken on parallel and antiparallel oriented cobalt islands (marked by red and blue crosses in ) clearly reveal spin-polarized density of states below the Fermi edge. , Energy dependence of the optimistic TMR ratio calculated from the dI/dV spectra. The highest value is measured at approximately −350 meV, and is used to distinguish between the magnetic orientation of the islands. * Figure 2: Current–distance traces and magnetoresistance measured across single H2Pc molecules. , Typical set of conductance-distance curves measured on top of a H2Pc molecule adsorbed onto parallel and antiparallel magnetized islands with a constant tunnelling voltage of 10 mV (G0 = (2e2/h)). , As the tip approaches the molecule, the tunnel barrier width decreases, so the conductance increases exponentially. , Below a certain tip-to-surface separation (typically 3–4 Å) the conductance abruptly increases as the molecule jumps into contact, and then varies only slightly upon further reducing the distance. Transport across the contacted molecule reflects both tip-to-surface tunnelling and conduction across the molecule. , Histogram of corrected molecular conductances (381 parallel and 366 antiparallel). A Gaussian fit is used to determine the statistical conductance in the parallel and antiparallel configurations, and thus the GMR ratio. Error bars indicate statistical errors in the conductance distribution. * Figure 3: Ab initio simulations of current–distance traces and the magnetoresistance effect across a H2Pc molecule. ,, Contact geometry used in the transport calculation: for a H2Pc molecule adsorbed on the Cobalt island (), and in simultaneous contact with the tip and the cobalt surface through a lifting of the aromatic group (). Cobalt sites, grey; hydrogen, white; carbon, green; nitrogen, cyan. , Conductance of H2Pc sandwiched between two parallel or antiparallel aligned Co(111) surfaces in the tunnelling (before contact) and ballistic (after contact) junction geometries. * Figure 4: Molecular orbitals and transmission curves reveal the spin-selective LUMO broadening and the impact on GMR across the H2Pc molecule. , Transmission probability T(E) of an electron with energy E through a parallel oriented molecular junction for the majority (red) and minority (orange) spin channels and the current-carrying (LUMO) orbitals of the molecular junction at the Fermi energy. Hybridization of the LUMO orbitals with the cobalt states is weak in the majority channel and strong in the minority channel. , Corresponding data for an antiparallel oriented junction. Majority spin electrons are injected from the cobalt surface to the minority spin band of the cobalt tip (violet), and minority spin electrons are injected from the cobalt surface to the majority spin band of the cobalt tip (blue). In this configuration, the LUMO orbitals are hybridized in an asymmetric way between the cobalt surface and the tip, thus accounting for the conductance decrease relative to that found for parallel oriented junctions. Author information * Abstract * Author information * Supplementary information Affiliations * Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76128 Karlsruhe, Germany * Stefan Schmaus, * Yasmine Nahas, * Toyo K. Yamada, * Annika Bork & * Wulf Wulfhekel * DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT), 76128 Karlsruhe, Germany * Stefan Schmaus, * Alexei Bagrets, * Yasmine Nahas & * Wulf Wulfhekel * Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), 76128 Karlsruhe, Germany * Alexei Bagrets & * Ferdinand Evers * Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan * Toyo K. Yamada * Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 UdS-CNRS, 67034 Strasbourg Cedex 2, France * Martin Bowen & * Eric Beaurepaire * Institut Für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology (KIT), D-76128 Karlsruhe, Germany * Ferdinand Evers Contributions S.S. and W.W. conceived and designed the experiments. S.S., Y.N., T.K.Y. and An.B. performed the experiments. S.S., Y.N. and An.B. analysed the data. Al.B. and F.E. designed and performed the calculations. M.B. and E.B. provided purified molecules. S.S., Al.B., T.K.Y., F.E., M.B., E.B. and W.W. co-wrote the paper. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Wulf Wulfhekel Author Details * Stefan Schmaus Search for this author in: * NPG journals * PubMed * Google Scholar * Alexei Bagrets Search for this author in: * NPG journals * PubMed * Google Scholar * Yasmine Nahas Search for this author in: * NPG journals * PubMed * Google Scholar * Toyo K. Yamada Search for this author in: * NPG journals * PubMed * Google Scholar * Annika Bork Search for this author in: * NPG journals * PubMed * Google Scholar * Martin Bowen Search for this author in: * NPG journals * PubMed * Google Scholar * Eric Beaurepaire Search for this author in: * NPG journals * PubMed * Google Scholar * Ferdinand Evers Search for this author in: * NPG journals * PubMed * Google Scholar * Wulf Wulfhekel Contact Wulf Wulfhekel Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (498 KB) Supplementary information Additional data
• DNA computing circuits using libraries of DNAzyme subunits
  - UNKNOWN 6(3):190 (2011)
  Nature Nanotechnology | Corrigendum DNA computing circuits using libraries of DNAzyme subunits * Johann Elbaz * Oleg Lioubashevski * Fuan Wang * Françoise Remacle * Raphael D. Levine * Itamar WillnerJournal name:Nature NanotechnologyVolume: 6,Page:190Year published:(2011)DOI:doi:10.1038/nnano.2011.23Published online09 February 2011 Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Nature Nanotechnology5, 417–422 (2010); published online: 30 May 2010; corrected after print: 9 February 2011. In the version of this Letter originally published, components of the systems illustrated in Figs 3a–d, 4a and 4d were incorrectly labelled. In the Supplementary Information, components of the systems illustrated in Figs S7a, S9a–c and S10 were also incorrectly labelled. These errors have now been corrected in the HTML and PDF versions of the text, and in the Supplementary Information. Additional data Author Details * Johann Elbaz Search for this author in: * NPG journals * PubMed * Google Scholar * Oleg Lioubashevski Search for this author in: * NPG journals * PubMed * Google Scholar * Fuan Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Françoise Remacle Search for this author in: * NPG journals * PubMed * Google Scholar * Raphael D. Levine Search for this author in: * NPG journals * PubMed * Google Scholar * Itamar Willner Search for this author in: * NPG journals * PubMed * Google Scholar