Luigi Martiradonna

Riddles in perovskite research

Claudine Katan, Aditya D. Mohite and Jacky Even discuss the possible impact of various entropy contributions (stochastic structural fluctuations, anharmonicity and lattice softness) on the optoelectronic properties of halide perovskite materials and devices.

Hybrid perovskites: Cationic vibrations

When it comes to the reconstitution of the multicellular architecture of 3D tissues, most culture methods provide limited control over long-range tissue organization. 3D-printing and cell-patterning techniques, such as dielectrophoresis and micromoulding, often have low cell viability and resolution, or suffer from limitations in the solvent conditions and type of extracellularmatrix formulations that can be used. Zev Gartner and colleagues now show how cells and template substrates patterned with complementary DNA can be used to program specific and reversible cell adhesion layer by layer to rapidly build organoid-like microtissues with pre-defined size (up to a few centimetres long), shape and composition, and with control over the tissue’s 3D structure with single-cell resolution. Using this modular platform, the researchers built microtissues that combined various cell types with high viability to study the effects of spatial heterogeneity, composition of the extracellular matrix, and tissue shape and size on collective cell behaviour. PP CATALYSIS Pinpointing platinum Science 350, 189–192 (2015)

Getting more from photons

The phoenician ivory carvings found at Arslan Tash in northern Syria date back to the end of the ninth century bc, and are renowned for their artistic quality. For archaeological conservationists, they also represented something of a conundrum. The carvings were originally covered with a thin layer of gold foil, and over the centuries this has reacted with the ivory to give rise to distinctive purple stains. Detailed chemical analyses carried out at the Louvre museum in Paris revealed that these stains consist of gold nanoparticles (AuNPs) with a relatively uniform size distribution. Ivory is, in essence, a collagen-based mineralized tissue with a high specific surface area arising from the presence of hydroxyapatite nanocrystals, and it is known that AuNPs can be made by photoreducing collagen–HAuCl4 complexes in solution. But their formation in archaeological finds had not been examined. Now, Ina Reiche and colleagues demonstrate that the collagen can indeed act as a stabilizer for AuNP formation in a simple reaction that occurs at ambient burial conditions. With the origin of the stains established, the authors propose they can be used as a marker of authenticity for other gold-plated ivory artefacts found in the future. AT