Small-molecule-based fluorescent probes can generally detect and image one type of protein via specific binding while cross-reactive sensor arrays can discriminate among multiple different proteins via pattern-based recognition. David Margulies and colleagues developed a pattern-generating fluorescent molecular probe that combines the properties of both. This probe can produce unique fluorescence fingerprints for specific protein groups, allowing it to identify various members of these groups in biofluids and living cells, where comparable macroscopic analytical devices cannot access. The cover image is an artist's impression of the way proteins can be identified within cells via pattern-based detection.

Article p1161

IMAGE: TALI WIESEL (DESIGN, PHOTOGRAPHY AND PRINTING BRANCH, RESEARCH SERVICES DIVISION, WEIZMANN INSTITUTE OF SCIENCE)

COVER DESIGN: DAVID SHAND

Spin-orbit torques can nucleate skyrmions on magnetic racetracks - a key step towards the use of these spin textures as information carriers. Now, F. Büttner, I. Lemesh and co-workers use sub-nanosecond spin-orbit torque pulses to generate individual skyrmions within a geometrical constriction in an integrated magnetic device and to induce their subsequent propagation. No external in-plane magnetic fields are needed to make the process deterministic thanks to the strong Dzyaloshinskii-Moriya interaction characteristic of the considered device design. The cover image is an artistic depiction of the notch in the magnetic racetrack generating a bit sequence encoded in the presence or absence of skyrmions.

Letter p1040

COVER DESIGN: DAVID SHAND

IMAGE: MORITZ EISEBITT

Conventional sensors consume power continuously to monitor the environment, even when there is no relevant data to be detected, limiting their battery lifetime and increasing the cost of deployment and maintenance. Now, Rinaldi and co-workers have developed a digitizing sensor capable of detecting and discriminating an event of interest through its infrared spectral signature, while consuming zero power in standby. The cover image shows a false-colour scanning electron microscope image of this zero-power sensor, consisting of micromechanical photoswitch contacts and an infrared-absorbing plasmonic head.

Letter p969;

News & Views p940

IMAGE: VAGEESWAR RAJARAM, SUNGHO KANG, ZHENYUN QIAN AND MATTEO RINALDI, NORTHEASTERN UNIVERSITY

COVER DESIGN: DAVID SHAND

In solids, conduction of ions and electrons usually occurs in separate channels and therefore multiphase materials need to be engineered for applications, such as energy storage devices, where both particles need to be transported. Now J. Smet and co-workers have found that lithium ions diffuse within bilayer graphene faster than in graphite by an order of magnitude. In combination with the fast electronic conduction of graphene sheets, this system offers both ionic and electronic conductivity within the same single-phase solid material. The cover image is an artistic depiction of lithium ions intercalating and moving at speed within bilayer graphene.

Article p895

IMAGE: MATTHIAS KüHNE AND JURGEN H. SMET

COVER DESIGN: DAVID SHAND

Protein therapies face challenges including short half-lives, high cost, and dangerous side effects at concentrations required for efficacy. S. Stupp, S. Lee, T. Fyrner, W. Hsu, E. Hsu, and co-workers have now developed glycopeptide nanostructures that potentiate protein signalling to cells by mimicking the biological function of sulfated glycans. The concept was demonstrated using a model of spinal fusion in which bone regenerated with a growth factor dose that was 100-fold lower than required in the animal model. The cover image depicts a human spine covered with an artist's impression of the nanostructure surfaces that display hundreds of thousands of sulfated sugar molecules to activate proteins.

Article p821

IMAGE: MARK SENIW, SIMPSON QUERREY INSTITUTE, NORTHWESTERN UNIVERSITY

COVER DESIGN: DAVID SHAND

Iron-deficiency anaemia is a major global public health problem affecting over one billion people worldwide, for which affordable and viable solutions via food fortification still remain a challenge. Raffaele Mezzenga and colleagues have now developed a cost-effective strategy to deliver bioavailable iron via hybrids of milk-based amyloid fibrils and iron nanoparticles, bypassing most of the problems found in current technologies. The cover image is an artist's impression of the delivery of iron to blood cells using amyloid fibril shuttles.

Letter p642

IMAGE: ELLA MARUSHCHENKO

COVER DESIGN: DAVID SHAND

Graphene-oxide membranes have been used to realize sieves that filter out small nanoparticles, organic molecules and even larger salts. To be used in desalination technologies they should also be able to sieve common salts, which require ångström-size capillaries. Jijo Abraham and co-workers have developed a strategy to fabricate graphene-oxide membranes with controllable ångström-size capillaries. Ion permeation rates through these capillaries are found to decrease exponentially with decreasing capillary size whereas water transport is only weakly affected. The cover image illustrates water and ion transport through ångström-size capillaries in graphene-oxide-based membranes.

Letter p546; News & Views p500

IMAGE: ELLA MARU STUDIO

COVER DESIGN: DAVID SHAND

Crude oil spills represent a major source of marine and coastal pollution. A promising way to clean up spills is the use of sponges that can selectively absorb oil and not water. This can be achieved for example by coating the surface of polymer foams with nanostructures that render the foams more hydrophobic and more oleophilic simultaneously. Shu-Hong Yu and co-workers have now shown the right choice of coating nanomaterial can provide additional advantages. They have coated polymer foams with graphene nanostructures and shown that applying an electric voltage to the graphene produced enough local heating to reduce the oil viscosity and increase the absorption speed substantially. The conceptual image on the cover illustrates the idea of using graphene to aid oil spill remediation.

Letter p434; News & Views p406

IMAGE: DAVID HUNTER/ALAMY STOCK PHOTO

COVER DESIGN: LAUREN HESLOP

Triangulene is a triangular segment of graphene, but any attempt to draw alternating single and double bonds for the whole molecule leaves two electrons unpaired. Those two electrons make this molecule extremely reactive and challenging to isolate. Now, Niko Pavliček and co-workers have overcome the difficulties by using atomic manipulation techniques and succeeded in synthesizing triangulene on various surfaces. The cover shows a pattern realized with an atomic force microscope image of a single triangulene molecule.

Letter p308; News & Views p292

IMAGE: NIKO PAVLIčEK, IBM RESEARCH–ZURICH

COVER DESIGN: BETHANY VUKOMANOVIC

Many self-organized systems in nature exploit a sophisticated blend of deterministic and random processes. In contrast, engineering seldom takes advantage of the power of randomness for fabricating complex structures. Now, Tikhomirov, Petersen and Qian have demonstrated that randomness in molecular self-assembly can be combined with deterministic rules to produce complex nanostructures out of DNA. The cover image is a coloured atomic force microscopy image of self-assembled random maze structures on the surface of DNA tile arrays.

Article p251; News & Views p189; In the Classroom p284

IMAGE: GRIGORY TIKHOMIROV, PHILIP PETERSEN AND LULU QIAN, CALIFORNIA INSTITUTE OF TECHNOLOGY

COVER DESIGN: BETHANY VUKOMANOVIC

Helical 1D electronic systems, where the electron spin is locked to its momentum, offer a promising route towards realizing circuits of topological quantum states. Javier Sanchez-Yamagishi, Jason Luo, Pablo Jarillo-Herrero, and colleagues have demonstrated a new method to create helical 1D states from quantum Hall edge states by applying magnetic and electric fields to a twisted bilayer graphene device. The advantage of this approach is the ability to build new types of 1D systems that incorporate fractional quantum Hall edge states. The cover image shows a measurement of the resistance of their graphene device at high magnetic fields as a function of electric field and charge density, where the effects of both helical and fractional edge states are observed.

Letter p118

IMAGE: JAVIER SANCHEZ-YAMAGISHI AND JASON LUO, MASSACHUSETTS INSTITUTE OF TECHNOLOGY

COVER DESIGN: BETHANY VUKOMANOVIC

The motion of electrons across interfaces is at the heart of semiconductor-device technology. Bringing together the temporal resolution of femtosecond light pulses with the spatial resolution of electron microscopy, Keshav Dani and colleagues image the highly non-equilibrium distribution of photoexcited electrons in space at the instant of photoexcitation. Then they make a movie as the photoexcited electrons equilibrate by flowing from high-energy states of one material to the low-energy states of another, thus capturing the fundamental operating process in a solar cell. The cover is an artists rendition of femtosecond light pulses exciting and emitting electrons from a semiconductor heterostructure, which are subsequently imaged at different time delays to make the movie.

Letter p36; News & Views p3

IMAGE: MIWAKO YAMADA, DUKATTI DESIGN STUDIO

COVER DESIGN: BETHANY VUKOMANOVIC