Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simply mimicking these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Huisheng Peng and colleagues have now created actuating fibres, formed through the hierarchical and helical assembly of aligned carbon nanotubes, that respond to solvent and vapour stimuli. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and the micrometre-scale gaps between the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The artist’s impression on the cover shows a helical actuating fibre with compact coils that allow it to rotate reversibly.

Article p1077

IMAGE: PENG RESEARCH GROUP AT FUDAN UNIVERSITY

COVER DESIGN: BETHANY VUKOMANOVIC

Unlike DNA, the use of proteins as building blocks for engineering biological devices has remained largely unexplored. Philip Dannhauser and colleagues have now formed regular two-dimensional lattices of clathrin, a three-legged protein complex, on a variety of solid supports. The lattices can be dehydrated and rehydrated without the loss of function, and can be stored for months, offering potential applications in biosensing. The cover shows an electron micrograph of an irregular aluminium surface coated with regular clathrin lattices (magnification: 165,000×). The surface was prepared by critical point drying and subsequent shadowing with platinum and carbon.

Letter p954

IMAGE: PHILIP DANNHAUSER (MEDICAL SCHOOL HANNOVER)

COVER DESIGN: KAREN MOORE

The ability to reliably handle individual polymer chains could lead to the fabrication of miniaturized electronic and optical wires. To this end, Kurt Gothelf, Mingdong Dong and colleagues have now developed a method to control the shape individual polymer molecules adopt. They synthesized a polymer with short single-stranded DNA extending from the backbone enabling the polymer to self-assemble into predesigned routings using the complementary DNA strands extending from 2- and 3D DNA origami structures. The artist’s impression on the cover shows the DNA-functionalized polymer assembling on a U-shaped track on a rectangular DNA origami template.

Article p892; News & Views p829

IMAGE: JAKOB BACH KNUDSEN

COVER DESIGN: KAREN MOORE

The DNA origami technique — in which a long strand of DNA is folded into a desired shape with the help of numerous short staple strands — has been used to create a range of 2D and 3D nanostructures. These structures are, however, typically made up of tightly packed parallel DNA helices. Hao Yan, Yan Liu and colleagues have now developed a design strategy for engineering wireframe DNA origami nanostructures that uses multi-arm junction vertices. The technique can be used to construct a variety of complex structures including quasicrystalline 2D patterns and reconfigurable 3D Archimedean solids. The artist’s impression on the cover illustrates some of the 3D wireframe Archimedean solid structures that were created.

Letter p779; News & Views p733

IMAGE: MICHAEL NORTHROP

COVER DESIGN: ALEX WING

In rod-shaped Escherichia coli cells, Min proteins oscillate back and forth between poles to assist cell division. Cees Dekker and colleagues have now been able to explore how these proteins adapt to different cellular geometries by using nanofabricated chambers to ‘sculpt’ living bacterial cells into a variety of shapes and sizes. The cells are shaped into squares, rectangles, circles and triangles, and the Min proteins exhibit a range of versatile oscillation patterns that include rotational, longitudinal, diagonal, stripe and transversal modes. The data demonstrate how a Turing reaction–diffusion process achieves adaptation within the cell boundary. The artist’s impression on the cover shows bacterial cells sculpted into a variety of shapes, and highlights the oscillating patterns of Min proteins experimentally observed within such shaped cells.

Article p719; News & Views p655

IMAGE: CEES DEKKER LAB, TU DELFT / TREMANI

COVER DESIGN: KAREN MOORE

Flexible electronic components can conform to corrugated surfaces such as biological tissues and can therefore be used in biosensing devices. However, it is challenging to deliver such components to internal regions, whether artificial or biological, in a targeted manner. In this issue, Charles Lieber and colleagues report the injection of an ultraflexible electronic mesh into polymer cavities and murine brains using a syringe needle. The cover image depicts the injection and unfolding of the electronic mesh. The diameter of the needle is smaller than the size of the mesh, which reshapes to its original size once injected into the targeted region.

Article p629; News & Views p570

IMAGE: LIEBER RESEARCH GROUP, HARVARD UNIV.

COVER DESIGN: KAREN MOORE

Single-photon sources are essential elements of quantum communication devices. In the past, single-photon emission has been observed in a variety of systems, including semiconductor quantum dots, nitrogen–vacancy centres and single molecules. Now, four papers published in this issue report single-photon emission from defects in the two-dimensional semiconductor WSe2. The versatility of the material and the simplicity with which it can be isolated make the results promising for future development. The cover image depicts the results by Nick Vamivakas and colleagues, who showed that the optical properties of the defects can also be controlled through the application of an electrical voltage.

Letters p491, p497, p503 and p507; News & Views p485; Editorial p481

IMAGE: MICHAEL OSADCIW/UNIV. OF ROCHESTER

COVER DESIGN: KAREN MOORE

Techniques for visualizing light–matter interactions with nanometre-scale resolution have generally been limited to producing two-dimensional images. Ashwin Atre and colleagues now describe a tomographic approach that extends this capability to three dimensions. First, two-dimensional cathodoluminescence images of a crescent-shaped nanoparticle were acquired using an electron microscope at various tilt angles. Then, tomographic reconstruction algorithms were used to generate a three-dimensional map of the radiative optical properties of the nanostructure with nanometre-scale spatial and spectral resolution. The cover image shows an artist's rendition of this technique.

Article p429; News & Views p386

IMAGE: STANFORD/AMOLF/TREMANI

COVER DESIGN: KAREN MOORE

Peptide self-assembly and structural DNA nanotechnology are two important but distinct branches of bionanotechnology. Ehud Gazit and colleagues have now looked to combine these two fields by exploring the assembly of peptide nucleic acids (PNAs) — short DNA mimics that have an amide backbone. Three guanine-containing di-PNAs — CG, GC and GG — were found to form ordered assemblies, and the crystal structure of GC di-PNA revealed the occurrence of both stacking interactions and Watson–Crick base pairing. The computer-generated image on the cover shows a perspective view of this crystal structure.

Article p353; News & Views p295

CREDIT: ELLA MARUSHCHENKO, SCIENTIFIC ILLUSTRATIONS

COVER DESIGN: KAREN MOORE

Controlling the emission from a light-responsive material to produce any desirable colour(s) on demand is essential for display technology, but it is challenging in terms of materials design. Xiaogang Liu and colleagues now describe a concept for tuning emission in the full colour spectrum by varying the shape and intensity of pulsed laser excitations. The utilization of the pulse-modulation technique with rationally designed lanthanide-doped core–shell upconversion multilayer nanocrystals has enabled volumetric 3D displays with high spatial resolution and locally addressable colour gamut. The cover image shows the additive colours that can be displayed in a transparent 3D matrix.

Letter p237; News & Views p203; In The Classroom p284

IMAGE: RENREN DENG

COVER DESIGN: ALEX WING

On the nanometre length scale, the non-radiative energy transfer process has an efficiency close to unity. Brenneis and colleagues now describe how this type of energy transfer can be used to electronically read-out the spin of nitrogen–vacancy centres in diamond, which are considered to play a fundamental role in new quantum information technologies. The diamond is placed only a few nanometres away from a graphene layer. Through non-radiative energy transfer additional charge carriers are generated in the graphene. These charges are detected as a current signal and provide information on the electron spin in the nitrogen–vacancy centre. The experiment was performed on a picosecond timescale, where the transfer efficiency is highest.

Letter p135

IMAGE: CHRISTOPH HOHMANN, NANOSYSTEMS INITIATIVE MUNICH

COVER DESIGN: ALEX WING

A vortex is a macroscopic system that exists far from equilibrium: it requires a constant supply of energy that is continuously dissipated to sustain its structure. Analogously, dissipative systems at the nanoscale can take energy from a source, potentially to do useful work on the surroundings, but it is challenging to devise them. Now, Credi and colleagues describe a self-assembly system that consists of an asymmetric axle molecule transiting through a macrocycle. Under thermal equilibrium, the transit of the axle would be random, but when a constant source of energy is supplied (in the form of light) the transit is unidirectional as a result of a continuous dissipation of energy that keeps the self-assembly system far from equilibrium.

Article p70; News & Views p18

IMAGE: STRUCTURE, GIULIO RAGAZZON; VORTEX © AMANA IMAGES INC./ALAMY

COVER DESIGN: ALEX WING