When a spin-polarized current passes from a ferromagnet into a non-magnetic material, the spins of the itinerant electrons are 'flipped' at the interface between the two materials, producing a mechanical torque. Pritiraj Mohanty and co-workers have now made a nanoscale torsion oscillator that can measure this torque in a metal nanowire with unprecedented sensitivity. The oscillator is made of silicon and the metal nanowire runs from top left to bottom right in the scanning electron micrograph on the cover. The left half of this wire is a 50-nm-thick layer of cobalt (which is ferromagnetic) and the right half is a 50-nm-thick layer of gold (which is not magnetic). This highly sensitive approach to measuring torque could have applications in spintronics and fundamental physics, chemistry and biology.

Cover design by Karen Moore

Letter p720; News & Views p710

Nanoparticle superlattices are promising for many applications, but conventional patterning methods are not suited to producing these structures. Dan Luo and co-workers have now overcome this problem with a process that involves moulding liquid microdroplets containing DNA-capped gold nanoparticles. They use a combination of moulding pressure and mould geometry to spatially control the de-wetting process that is central to the formation of the superlattices. The image on the cover is based on false-colour SEM micrographs of circular and hexagonal double-corral superlattice structures. The lines in the micrographs are about 70 nm wide.

Cover design by Karen Moore

Article p682

Nanoscale particles have an important role in the chemical and biological sciences, but efforts to make nanoparticles from borosilicate glass which exhibits high tolerance to chemicals and solvents, combined with excellent mechanical and thermal stability have proved unsuccessful so far. Now Martin Gijs and co-workers have shown that borosilicate nanoparticles (100 - 500 nm in size) can be synthesized by simply mixing a silicon-boron binary oxide solution with water to induce a vigorous exothermic phase separation in which the borosilicate nanoparticles burst out of a silica phase. In addition to potential applications in the life sciences, the nanoparticles could also be useful in ultrasonic microscopy, optics and chemical filtration membranes.

Cover design by Karen Moore

Letter p589

Nanoscale mechanical resonators can make precision measurements of force, position and mass. Atomic resolution in mass sensing at room temperature has now been demonstrated with a carbon nanotube-based resonator that essentially operates as a mass spectrometer. Kenny Jensen and co-workers demonstrated that their device had a sensitivity of 0.40 gold atoms per root hertz. They also detected the atomic equivalent of shot noise (image from Getty).

Cover design by Karen Moore

Letter p533; News & Views p525

The electrical, optical and mechanical properties of nanowires depend on their morphology. Nanowires that possess both chirality and a branched structure should therefore exhibit new material properties. Such nanowires can be formed by vapour-liquid-solid branching from a central lead selenide nanowire with an axial screw dislocation, as demonstrated by Yi Cui and co-workers. These nanostructures also provide a direct visualization of the Eshelby Twist a phenomenon that was first predicted in the 1950s.

Cover design by Karen Moore

Letter p477; News & Views p457

Two main challenges must be overcome before nanoscale electronic devices can be made on a large scale precise engineering of the building blocks, and assembly of these building blocks into working circuits. In attempts to achieve these goals, graphene has emerged as an attractive alternative to nanotubes, nanowires and other approaches to nanoscale electronics. Now, Levente Tapaszt and co-workers have made graphene nanoribbons with welldefined widths and crystallographic orientations using scanning tunnelling microscope lithography. The nanometre precision offered by this technique makes it possible to engineer the electronic properties of the nanoribbons in a way that could ultimately lead to ballistic electronic devices operating at room temperature. The cover image shows a 30 junction in an 8-nm-wide nanoribbon (the yellow region between the two red lines).

Cover design by Karen Moore

Letter p397

Aggregates of fullerene molecules are able to enter cells and alter various cell functions, but the details of this process are poorly understood. Luca Monticelli and co-workers have used computer simulations to explore the movement of fullerene clusters through a model lipid membrane made of DOPC molecules (which are shown in blue on the cover). They find that high concentrations of fullerene molecules (shown in red) induce changes in the structural and elastic properties of the lipid bilayer, but not enough to mechanically damage the membrane. The simulations suggest that mechanical damage is an unlikely cause of membrane disruption and fullerene toxicity.

Cover design by Karen Moore

Article p363

Individual carbon nanotubes have been widely used as microelectromechanical systems (MEMS) such as oscillators, actuators, sensors, memory devices and even radios. However, there is also a demand for similar devices made from large numbers of nanotubes. Now Kenji Hata and co-workers have fabricated well-defined three-dimensional structures such as the threedimensional nanotube relay shown here from highly ligned carbon nanotube wafers using a lithography-based approach in which every fabrication step is both parallel and scalable. This technique opens up new ways to make devices with unprecedented structural complexity and functionality. Image width: 10 m. Letter p289

The unique mechanical, electronic, optical and thermal properties of carbon nanotubes make them attractive building blocks for nanotechnology, but integrating them into functional nanosystems remains a challenge. Although there has been considerable progress in patterning surfaces with nanotubes, most of these methods have relied on the assembly of pre-formed nanotubes using templates or aligned growth. Now Noam Geblinger, Ariel Ismach and Ernesto Joselevich have shown that it is possible to create structures that are notably more complex than before such as the serpentines shown on the cover by using the flow of gas across a stepped surface to control the shape of a nanotube grown from a catalyst nanoparticle. The nanotube in this image has a diameter of 1.2 nanometres. Letter p195

Nanocarriers for drug-delivery applications are often functionalized with biological recognition molecules that guide them to their target. However, nanocarriers are often repelled by the body's natural mechanisms for capturing and eliminating foreign material. Now, Mauro Ferrari and colleagues have developed a multistage delivery system based on mesoporous silicon particles that can carry, release over time and deliver two types of nanoparticles into cells. In the new approach, rather than functionalizing every single nanoparticle, they are all loaded into one biocompatible carrier that unloads them at the target, opening up new ways to deliver multiple payloads while avoiding biological barriers. Letter p151

Although DNA is best known as the molecule that encodes genetic information, it is also an incredibly versatile and 'intelligent' building material at the nanoscale. Many examples of DNA nanostructures have been reported, but potential uses are somewhat limited by their static nature. Now, Andrew Turberfield and co–workers have made DNA tetrahedra (shown on the cover) containing edges that can be expanded and contracted to reconfigure the overall shape of the assembly. These dynamic structures may prove useful for the fabrication of nanomechanical devices or for controlled drugrelease applications.

Cover design by Karen Moore.

Letter by Kapanidis et al.

The magnetization of a magnetic material often prefers to lie along an 'easy' axis. This magnetic anisotropy is weak in bulk samples of transition metals, but it becomes much stronger in nanowires. Now Erio Tosatti and colleagues have predicted that platinum nanowires should exhibit a novel phenomenon called colossal magnetic anisotropy, in which the magnetization is finite in directions along the nanowire, and zero at right angles to this direction. The cover image is based on contour plots of the anisotropy energy as a function of magnetic moment (see Fig. 2c on page 23).

Cover design by Karen Moore.

Letter by Smogunov et al.