Chiara Pastore

Sensing cellular cues

Two-dimensional (2D) Ruddlesden–Popper metal halide perovskites (MHPs) offer a promising solution to the notorious moisture sensitivity of bulk perovskites. However, in devices with vertical architecture, the insulating bulky ammonium cations that separate 2D perovskites slabs impede efficient out-of-plane charge transport. Now, Chen et al. have devised a strategy to enhance optoelectronic properties of 2D MHPs by controlling the alignment of vertically oriented layers. The researchers used a two-step fabrication procedure involving solution processing and low-temperature annealing to achieve thin films with various degrees of molecular orientation. X-ray measurements reveal that nucleation and growth of 2D perovskites occur at the precursor liquid–air interface. The assumed orientation stems from the tendency of the aliphatic chain of butylammonium molecules to remain in the solution environment. By tuning the crystallization conditions, specifically by adding a pre-crystallization annealing step, Chen and co-workers were able to obtain thin films of vertically oriented 2D perovskites with near 100% degree of the out-of-plane preferential alignment. When made into a solar cell, such optimized 2D MHPs show a strong short-circuit current increase and an overall efficiency improvement in comparison with randomly oriented crystals. OB

Inhibiting collective cell migration

Metal nanoporous structures combine good electrical and mass transport with high surface area to volume ratio, which makes them promising for supercapacitors and catalysis applications. Such structures can be obtained by de-alloying binary metallic alloys. For example, nanoporous gold is often created by dissolution of silver from a silver–gold alloy. Despite encouraging results obtained in the past, a limitation of nanoporous gold is that the pore structure is usually fairly random and generates considerable resistance to mass flow. Now, Cheng Zhu et al. have fabricated hierarchical nanoporous gold by the combination of 3D printing with alloying and de-alloying. Large macroscopic pores, of the order of micrometres or even tens of micrometres, can be used as preferential channels for mass transport, while a finer structure of pores in the tens of nanometres range ensures a high surface to volume ratio. Credit: AAAS The first step of the fabrication process is the 3D printing of a porous macrostructure of gold and silver microparticles, which is then annealed to form a homogeneous Au–Ag alloy. Eventually, the alloy is immersed in an etching agent that removes the silver, leaving a porous nanostructure with typical features in the 10–100 nm range. The hierarchical non-porous structure substantially outperforms its non-hierarchical analogue in terms of electrochemical, mass-transport and catalytic properties. FP

Gold nanoparticles: A warm-up for muscle cells.

To grow artificial muscles or mend natural tissues it is necessary to stimulate muscle cell contraction and differentiation. In vitro, this is typically achieved by electrical stimulation, mechanical stretching or light pulses. Each method, however, presents challenges in terms of generation of toxic by-products, invasiveness or limited applicability. A. Marino et al. now show that mild photothermal stimulation can also activate myotube contraction (ACS Nano http://doi.org/bznk; 2017). To do so they use silica–gold core–shell nanoparticles that absorb in the nearinfrared (the ability to penetrate through deep layers of tissues makes the nearinfrared the spectral region of choice for nanomedical applications). When they incubate the myotubes with the nanoparticles and irradiate with nearinfrared light pulses, the authors measure a 5 °C increase in the local temperature. Concomitantly, they observe a large increase in myotube contraction compared with control cells subjected to irradiation but with no nanoparticles. In line with previous reports, they demonstrate that the enhanced contraction is related to an increase in the interaction between the two major protein filaments in the myotubes, A warm-up for muscle cells GOLD NANOPARTICLES