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The cover image illustrates a simulation assembly composed of a boron nitride nanotube 6.9 Å in diameter, a 14-Å-thick silicon nitride membrane (shaded), water molecules, and sodium (yellow) and chloride (blue) ions. Molecular dynamics simulations are conducted to determine the force experienced by ions and water molecules as they attempt to move through the nanotube. In response to the pressure applied across the membrane, water ions flow rapidly across the tube, while sodium and chloride ions are effectively rejected, even when the ionic concentrations in the reservoir are increased to twice that of seawater. The speed of water flow across the nanotube is comparable to that of biological water channels or aquaporins. For more information, please read the Full Paper “Salt Rejection and Water Transport Through Boron Nitride Nanotubes” by T. A. Hilder et al., beginning on page 2183. The image was created by Rhys Hawkins of the ANUSF.

The cover picture shows fluorescence micrographs of 4-µm particles taken in optically coated mirror-embedded microchannels. At 45 degrees the mirror ideally reflects the side views of the channels and enables the positional information of microparticles in three dimensions to be easily obtained without any calibration by directly observing the in-focus side and top views. With this method, the principle of hydrophoresis that has spatially varying characteristics in three dimensions is revealed. For more information, please read the Full Paper “Optically Coated Mirror-Embedded Microchannel to Measure Hydrophoretic Particle Ordering in Three Dimensions” by S. Choi and J.-K. Park, beginning on page 2205.

The absorption and emission polarization of single semiconductor nanowire quantum dots is studied. The polarization of light absorbed or emitted by such dots strongly depends on the orientation of the nanowire with respect to the directions along which light is incident or emitted (see image). This result is vital for photonic applications based on quantum dots, such as generation of entangled photons.

The power-conversion efficiency of an organic photovoltaic cell composed of poly(3-hexylthiophene) and (6,6)-phenyl-C₆₁-butyric acid methyl ester is enhanced significantly by controlling the surface morphology of the photoactive layer. The hierarchical micro-/nanostructures of the active-layer surface are fabricated by nanoimprinting the active layer with a commercially available, anodic aluminum oxide (AAO) membrane filter (see image).

A multiscale architecture with interlaced submicrometer ridges and nanoprotrusions is built on a polydimethylsiloxane (PDMS) surface by a combination of self-assembly, soft lithography, and physical treatment (see picture). The multiscale structure reduces activated-platelet adhesion under flow conditions, which is significant for the development of blood-contacting materials.

A new nanomaterial conjugation technique is presented to effectively bind semiconductor quantum dots (QDs) onto single-walled carbon nanotubes (SWCNTs) via covalent amidation, employing single-stranded DNA oligonucleotides as linkers (see schematic and AFM image). This technique provides a measurement platform for the study of their interactions involving photoinduced charge transfer between QDs and SWCNTs at the nanoscale.

Nanoparticles that assemble into core/shell aggregate structures comprising thermally addressable, phase-separated DNA binding domains are designed. Since the strength of the DNA binding in these domains differs, these aggregate systems exhibit two distinct melting transitions upon dehybridization (see image) resulting from the stepwise disassociation of the entire structure. These materials are ideal for probing the structure–function relationship of DNA-linked nanoparticle aggregates.

Nanoparticles in a wireless form are employed to overcome the extremely low efficiency of electroenzymatic synthesis reactions. The nanoparticle-mediated electrochemical regeneration of cofactor (NADH) is used in the enzymatic conversion of α-ketoglutarate to L-glutamate (see picture). The use of colloidal nanoparticles in electrolyte provides a new strategy for electroenzymatic catalysis.

The frontispiece shows schematically (following the arrows) the introduction of polymer microcapsules filled with fluorescently labeled peptides into a cell, the controlled opening of the intracellular capsule with an infrared laser beam, the release of the peptides from the microcapsules into the cytoplasm, the transport of peptides into the endoplasmic reticulum, the binding of the peptides to major histocompatibility complex (MHC) class I molecules, and the peptide-induced surface transport of the MHC class I molecules. For more information, please read the Full Paper “Controlled Intracellular Release of Peptides from Microcapsules Enhances Antigen Presentation on MHC Class I Molecules” by S. Springer et al., beginning on page 2168.

Microcapsules can be used to introduce hydrophilic substances into live cells. Such capsules are opened at a defined time point with an infrared laser pulse (see image) and demonstrate that the peptide they contain is released into the cytosol and subsequently becomes presented at the cell surface by a major histocompatibility complex class I molecule.

Molecular self-assembly on an ultrathin insulating film of NaCl grown on a Au(111) surface is investigated using scanning tunneling microscopy (see image). Strong intermolecular forces resulting from complementary triple hydrogen bonds between melamine and cyanuric acid make it possible to grow 2D bimolecular networks that are stable at a relatively high temperature and below saturation coverage.

A (5, 5) boron nitride nanotube embedded in a silicon nitride membrane (see image) can, in principle, obtain 100% salt rejection while conducting water molecules at a rate between 1.6 and 10.7 water molecules per nanosecond. Moreover, when the nanotube radius is increased to 4.14 Å the tube becomes cation-selective, mimicking the function of the gramicidin channel.

A simple model based on hydrophobic and hydrophilic forces is used to investigate the molecular dynamics that lead to the supramolecular self-assembly of surfactants around carbon nanotubes (CNTs). The effects of the concentration and the structure of surfactants are explored. The bead-based mesoscopic description spontaneously develops the several micellar morphologies that are known to wrap and solvate CNTs (see image).

Crosslinked hyperbranched polyglycerol nanocapsules possessing o-nitrobenzyl linkers bind ionic guest molecules. These nanocarriers show high capacity and selectivity in guest binding, which can be achieved by the variation of the counterion of guest molecules. Light-induced cleavage results in rapid release of the guest molecules (see image). Modification of the polymer's outer shell allows control over the host–guest complex stability and release.

The 3D measurement of particle ordering is used to characterize hydrophoresis through the use of a mirror-embedded microchannel. The mirror, ideally at 45, reflects the side view of the channel and allows positional information to be obtained from two different orthogonal-axis images (see picture). It is shown that hydrophoresis is governed by convective vortices and steric hindrance.

Graphene oxide sheets are found to be promising nanoscale substrates for the formation of nanoparticle films. The flexible silver-nanoparticle films assembled on likewise flexible graphene oxide sheets can be dispersed in water solution to form a stable suspension, which can be facilely processed into macroscopic films with high reflectivity (see image).

Recent experiments have identified a specific molecular wire, bipyridyl-dinitro oligophenylene-ethynylene dithiol, that can be operated as a molecular memory element. Here, theoretical work explains the mechanism by which the memory is conserved. At its heart it is a two-axis rotation of the molecule's functional unit (see image). The theoretical current–voltage characteristics reproduce the experimental observations.