Superlubricity occurs when friction between two sliding surfaces almost vanishes. This phenomenon has been observed so far only for small specimens that are a few micrometres wide at most. Yingying Zhang and colleagues have now observed superlubricity between centimetre-long concentric carbon nanotubes (schematically shown on the cover), which was made possible by a synthesis method that allows the production of pure carbon nanotubes that are several centimetres long.

Letter p912; News & Views p893

IMAGE: FEI WEI

COVER DESIGN: ALEX WING

The hunt for Majorana fermions continues as condensed-matter physicists try to prove that Majorana modes, in superconductor- semiconductor hybrid devices, obey non-Abelian exchange statistics. To test this, an exchange operation in which two Majorana fermions are moved around one another is needed, and this requires a network of nanowires. Single crystalline InSb nanocrosses — shown in a scanning electron microscope image on the cover — synthesized by Sebastien Plissard, Ilse van Weperen and colleagues are among the most promising material systems for the exchange of Majorana fermions.

Article p859

IMAGE: I. VAN WEPEREN AND S. R. PLISSARD

COVER DESIGN: ALEX WING

The identity of a nanoparticle in a living system can be affected by the protein coat, or corona, that forms on its surface when it is exposed to a biological fluid. Using label-free snapshot proteomics, Stefan Tenzer, Dominic Docter, Roland Stauber and colleagues have profiled the rapid evolution of protein corona formation on silica and polystyrene nanoparticles and investigated its influence on the nanoparticle/biological interface. The cover illustrates a clustering analysis of the relative abundance of proteins from a blood plasma sample bound to silica nanoparticles.

Article p772; News & Views p701

IMAGE: JÖRG KUHAREV AND SHIRLEY K. KNAUER

COVER DESIGN: ALEX WING

The chemistry of molecules that form a self-assembled monolayer depends on the curvature of the surface onto which they are tethered. Bartosz Grzybowski and colleagues coat dumbbell-shaped nanoparticles (yellow in the artistic representation on the cover) with a monolayer of 1-mercaptoundecanoid acid (red) and observe that the acidic properties of the molecule depend on where it is attached on the nanoparticle. The researchers take advantage of this effect and induce the dumbbell-shaped nanoparticles to self-assemble in different ways by changing the pH of the solution.

Article p676; News & Views p620

IMAGE: DAVID A. WALKER

COVER DESIGN: ALEX WING

Artificial cell-like chemical systems can be used as models for fundamental studies of natural biological systems and could potentially be used to develop new biotechnological applications. Such systems do not, however, typically take into account the high concentration of macromolecules that can be present in living cells. Russell Schwartz, Philip LeDuc and colleagues have now used artificial cellular systems with an integrated synthetic biology approach to show that this molecular crowding can increase the robustness of gene expression. The fluorescence microscopy image on the cover shows an artificial cell that is made from a phospholipid membrane and measures approximately 10 âμm across.

Article p602; News & Views p545

IMAGE: CHEEMENG TAN AND KRISTEN McCONNELL

COVER DESIGN: ALEX WING

The development of sophisticated devices to monitor, and eventually interfere with, essential cellular processes is an ongoing challenge. Now, Jos A. Plaza and colleagues have fabricated silicon chips that are small enough to be internalized inside cells and detect intracellular pressure changes. These devices can be considered the first step towards achieving a broad range of intracellular nanochips. A pseudocoloured scanning microscopy image (on the cover) shows a HeLa cell interacting with a silicon chip pressure sensor.

Letter p517

IMAGE: MARTA DUCH AND JOS A. PLAZA

COVER DESIGN: ALEX WING

Novel memory devices have been proposed in which the information is stored and transferred by magnetic domain walls that move along magnetic nanoscale tracks. However, one of the main challenges for practical implementation is the difficulty in stopping the domain walls at precise locations in a dynamically controlled way. Now, Bauer and colleagues have demonstrated that a voltage applied to a top electrode can trap and release, on demand, domain walls moving in a magnetic film beneath the electrode (the cover image is a composite of four magneto-optical Kerr effect images taken over a period of 9.8 ms and shows a single domain wall moving from right to left). This all-electrical method to bring fast moving domain walls to a standstill with nanoscale precision allows realization of a three-bit domain-wall memory.

Letter p411 ; News & Views p391

IMAGE: UWE BAUER

COVER DESIGN: ALEX WING

Laser-cooled atoms are central to modern precision measurements and enable a wide variety of quantum technologies to be realized. Although significant progress has been made in miniaturizing room-temperature atomic sources, simplifying the optical set-up for atomic cooling and loading using technology capable of scalable production has proved difficult. Now, Arnold and colleagues have utilized microfabrication technology to create specialized semiconductor wafers (pictured), which diffract a single incoming laser beam into four appropriately polarized beams, creating a beam-overlap zone ideal for the trapping and cooling of atoms. These gratings — similar to miniaturized Lego boards — could be mass produced and require only a single alignment.

Letter p321 ; News & Views p317

IMAGE: ANDREW BROOKES, NPL

COVER DESIGN: ALEX WING

An abiding goal in solar-energy conversion is the fabrication of a small, artificial photosynthetic device that is able to carry out photocatalytic redox chemistry autonomously to create useful products such as fuel or fine chemicals. This artist's impression shows a plasmonic water-splitting device based on a gold nanorod array. On illumination with visible light all of the hydrogen is produced as a result of the reduction of water by hot electrons derived from surface plasmons.

Letter p247; News & Views p229

IMAGE: PETER ALLEN

COVER DESIGN: ALEX WING

Nitrogen-vacancy (NV) centres in diamond have the potential to act as qubits for quantum information as well as ultrasensitive probes of both magnetic and electric fields. To fully exploit the capabilities of NV centres, techniques to manipulate them with nanometere accuracy are required. The Letter by Geiselmann et al. describes how optical tweezers are used to achieve both translational and angular control of single NV centres in solution. The cover image is an artists view of one of the experiments that was performed in which a single NV was trapped at the focus of a near-infrared laser beam and was raster scanned to map the distribution of the optical modes around an ensemble of gold nanoislands. Because the technique may be used in a biological environment, it could open new possibilities for the use of colour centres for spin-based cell interrogation.

Letter p175

IMAGE: MATHIEU L. JUAN AND ROMAIN QUIDANT

COVER DESIGN: ALEX WING

Although the use of extracellular microelectrode arrays (MEAs) permits simultaneous, cell-non-invasive, long-term recordings of extracellular field potentials generated by action potentials, they are 'blind' to subthreshold synaptic potentials generated by the individual neurons. On the other hand, intracellular recordings of the full electrophysiological repertoire are, at present, only obtained by sharp or patch microelectrodes. These, however, are limited to single cells at a time and for short durations. New techniques are arising that merge the advantages of extracellular MEAs and intracellular microelectrodes (like the nanowires depicted in the image). The Review by Spira and Hai describes these approaches, identifying their strengths and limitations.

Review Article p83

IMAGE: AVIAD HAI, ARIEL CHAI AND MICHA SPIRA

COVER DESIGN: ALEX WING

Binary nanoparticle superlattices are periodic nanostructures that are typically made from two different types of synthetic material. Such superlattices can, for example, be self-assembled using nanoparticles covered with complementary strands of DNA, but incorporating biological building blocks remains challenging. Mauri Kostiainen and colleagues have now shown that protein cages can be used to form three-dimensional binary superlattices. They are formed through tunable electrostatic interactions between negatively charged patches on the proteins and positively charged gold nanoparticles. This computer generated image shows a superlattice with a AB8 face-centred cubic crystal structure, which was formed from cowpea chlorotic mottle virus (blue) and gold nanoparticlesâ (yellow).

Letter p52; News & Views p5

IMAGE: MAURI KOSTIAINEN AND PANU HIEKKATAIPALE

COVER DESIGN: ALEX WING