Hot off the presses! Sep 01 Nat Nanotechnol

The Sep 01 issue of the Nat Nanotechnol is now up on Pubget (About Nat Nanotechnol): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• Recommended reading
  - Nat Nanotechnol 4(9):533 (2009)
  
• Where does nanotechnology belong in the map of science?
  - Nat Nanotechnol 4(9):534-536 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Science from the inside
  - Nat Nanotechnol 4(9):537-538 (2009)
  I want to purchase this article Register now Price: US$32 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Our choice from the recent literature
  - Nat Nanotechnol 4(9):540-541 (2009)
  I want to purchase this article Register now Price: US$32 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Top down bottom up: Digging deeper
  - Nat Nanotechnol 4(9):541 (2009)
  I want to purchase this article Register now Price: US$32 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• DNA nanotechnology: Geometric sorting boards
  - Nat Nanotechnol 4(9):543-544 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Nanomedicine: Silence the target
  - Nat Nanotechnol 4(9):544-545 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Carbon nanotubes: A simple approach to superlattices
  - Nat Nanotechnol 4(9):545-546 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Protein-nanoparticle interactions: What does the cell see?
  - Nat Nanotechnol 4(9):546-547 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Nanophotonics: Making the most of photons
  - Nat Nanotechnol 4(9):548-549 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Graphene: Surfing ripples towards new devices
  - Nat Nanotechnol 4(9):549-550 (2009)
  I want to purchase this article Register now Price: US$18 In order to purchase this article you must be a registered user. I want to subscribe to Nature Nanotechnology Select this option to purchase a personal subscription to Nature Nanotechnology.
• Molecular electronics with single molecules in solid-state devices
  - Nat Nanotechnol 4(9):551-556 (2009)
  The ultimate aim of molecular electronics is to understand and master single-molecule devices. Based on the latest results on electron transport in single molecules in solid-state devices, we focus here on new insights into the influence of metal electrodes on the energy spectrum of the molecule, and on how the electron transport properties of the molecule depend on the strength of the electronic coupling between it and the electrodes. A variety of phenomena are observed depending on whether this coupling is weak, intermediate or strong.
• Placement and orientation of individual DNA shapes on lithographically patterned surfaces
  - Nat Nanotechnol 4(9):557-561 (2009)
  Artificial DNA nanostructures1, 2 show promise for the organization of functional materials3, 4 to create nanoelectronic5 or nano-optical devices. DNA origami, in which a long single strand of DNA is folded into a shape using shorter 'staple strands'6, can display 6-nm-resolution patterns of binding sites, in principle allowing complex arrangements of carbon nanotubes, silicon nanowires, or quantum dots. However, DNA origami are synthesized in solution and uncontrolled deposition results in random arrangements; this makes it difficult to measure the properties of attached nanodevices or to integrate them with conventionally fabricated microcircuitry. Here we describe the use of electron-beam lithography and dry oxidative etching to create DNA origami-shaped binding sites on technologically useful materials, such as SiO2 and diamond-like carbon. In buffer with 100 mM MgCl2, DNA origami bind with high selectivity and good orientation: 70–95% of sites have individual or! igami aligned with an angular dispersion (1 s.d.) as low as 10° (on diamond-like carbon) or 20° (on SiO2).
• Controlled ripple texturing of suspended graphene and ultrathin graphite membranes
  - Nat Nanotechnol 4(9):562-566 (2009)
  Graphene is nature's thinnest elastic material and displays exceptional mechanical1, 2 and electronic properties3, 4, 5. Ripples are an intrinsic feature of graphene sheets6 and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials7, 8, 9, 10, 11, 12. The ability to control ripple structure in graphene could allow device design based on local strain13 and selective bandgap engineering14. Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains. We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite. These results elucidate the ripple formation process, which can be understood in te! rms of classical thin-film elasticity theory. This should lead to an improved understanding of suspended graphene devices15, 16, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene.
• Substrate-induced array of quantum dots in a single-walled carbon nanotube
  - Nat Nanotechnol 4(9):567-570 (2009)
  Single-walled carbon nanotubes are model one-dimensional structures1, 2, 3, 4, 5, 6. They can also be made into zero-dimensional structures; quantum wells can be created in nanotubes by inserting metallofullerenes7, by mechanical cutting8, 9, 10 or by the application of mechanical strain11. Here, we report that quantum dot arrays can be produced inside nanotubes simply by causing a misalignment between the nanotube and the 100 direction of a supporting silver substrate. This method does not require chemical or physical treatment of either the substrate or the nanotube. A short quantum dot confinement length of 6 nm results in large energy splittings.
• Plasmonic fluorescent quantum dots
  - Nat Nanotechnol 4(9):571-576 (2009)
  Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem1, 2. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence3, 4. So far, the combination of quantum dot fluorescence with plasmonically active gold has only been demonstrated on flat surfaces5. Here, we combine fluorescent and plasmonic activities in a single nanoparticle by controlling the spacing between a quantum dot core and an ultrathin gold shell with nanometre precision through layer-by-layer assembly. Our wet-chemistry approach provides a general route for the deposition of ultrathin gold layers onto virtually any discrete nanostructure or continuous surface, a! nd should prove useful for multimodal bioimaging6, interfacing with biological systems7, reducing nanotoxicity8, modulating electromagnetic fields5 and contacting nanostructures9, 10.
• A quantitative fluorescence study of protein monolayer formation on colloidal nanoparticles
  - Nat Nanotechnol 4(9):577-580 (2009)
  It is now known that nanoparticles, when exposed to biological fluid, become coated with proteins and other biomolecules to form a 'protein corona'1. Recent systematic studies have identified various proteins that can make up this corona, but these nanoparticle–protein interactions are still poorly understood, and quantitative studies to characterize them are few in number. Here, we have quantitatively analysed the adsorption of human serum albumin onto small (10–20 nm in diameter) polymer-coated FePt and CdSe/ZnS nanoparticles by using fluorescence correlation spectroscopy. The protein corona forms a monolayer with a thickness of 3.3 nm. Proteins bind to the negatively charged nanoparticles with micromolar affinity, and time-resolved fluorescence quenching experiments show that they reside on the particle for 100 s. These new findings deepen our quantitative understanding of the protein corona, which is of utmost importance in the safe application of nanoscale obj! ects in living organisms.
• Single europium-doped nanoparticles measure temporal pattern of reactive oxygen species production inside cells
  - Nat Nanotechnol 4(9):581-585 (2009)
  Low concentrations of reactive oxygen species, notably hydrogen peroxide (H2O2), mediate various signalling processes in the cell1, 2. Production of these signals is highly regulated3 and a suitable probe is needed to measure these events. Here, we show that a probe based on a single nanoparticle can quantitatively measure transient H2O2 generation in living cells. The Y0.6Eu0.4VO4 nanoparticles undergo photoreduction under laser irradiation but re-oxidize in the presence of oxidants, leading to a recovery in luminescence. Our probe can be regenerated and reliably detects intracellular H2O2 with a 30-s temporal resolution and a dynamic range of 1–45 M. The differences in the timing of intracellular H2O2 production triggered by different signals were also measured using these nanoparticles. Although the probe is not selective towards H2O2, in many signalling processes H2O2 is, however, the dominant oxidant3, 4, 5, 6. In conjunction with appropriate controls, this prob! e is a powerful tool for unravelling pathways that involve reactive oxygen species.
• Dynamic superlubricity and the elimination of wear on the nanoscale
  - Nat Nanotechnol 4(9):586-591 (2009)
  One approach to ultrahigh-density data storage involves the use of arrays of atomic force microscope probes to read and write data on a thin polymer film, but damage to the ultrasharp silicon probe tips caused by mechanical wear has proved problematic. Here, we demonstrate the effective elimination of wear on a tip sliding on a polymer surface over a distance of 750 m by modulating the force acting on the tip–sample contact. Friction measurements as a function of modulation frequency and amplitude indicate that a reduction of friction is responsible for the reduction in wear to below our detection limit. In addition to its relevance to data storage, this approach could also reduce wear in micro- and nanoelectromechanical systems and other applications of scanning probe microscopes.
• Long vertically aligned titania nanotubes on transparent conducting oxide for highly efficient solar cells
  - Nat Nanotechnol 4(9):592-597 (2009)
  Dye-sensitized solar cells consist of a random network of titania nanoparticles that serve both as a high-surface-area support for dye molecules and as an electron-transporting medium. Despite achieving high power conversion efficiencies, their performance is limited by electron trapping in the nanoparticle film. Electron diffusion lengths can be increased by transporting charge through highly ordered nanostructures such as titania nanotube arrays. Although titania nanotube array films have been shown to enhance the efficiencies of both charge collection and light harvesting, it has not been possible to grow them on transparent conducting oxide glass with the lengths needed for high-efficiency device applications (tens of micrometres). Here, we report the fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 m using a novel electrochemistry approach. Dye-sensitized solar cells containing these ar! rays yielded a power conversion efficiency of 6.9%. The incident photon-to-current conversion efficiency ranged from 70 to 80% for wavelengths between 450 and 650 nm.
• A novel magnetic crystal–lipid nanostructure for magnetically guided in vivo gene delivery
  - Nat Nanotechnol 4(9):598-606 (2009)
  Cancer gene therapy requires a safe and effective gene delivery system. Polymer- and lipid-coated magnetic nanocrystals have been used to deliver silencing RNA, but synthesizing these magnetic vectors is difficult. Here, we show that a new nanoparticle formulation can be magnetically guided to deliver and silence genes in cells and tumours in mice. This formulation, termed LipoMag, consists of an oleic acid-coated magnetic nanocrystal core and a cationic lipid shell. When compared with the commercially available PolyMag formulation, LipoMag displayed more efficient gene silencing in 9 of 13 cell lines, and better anti-tumour effects when systemically administered to mice bearing gastric tumours. By delivering an optimized sequence of a silencing RNA that targets the epidermal growth factor receptor of tumour vessels, the intended therapeutic benefit was achieved with no evident adverse immune reaction or untoward side effects.