We describe the peculiar conditions under which optically driven gold nanoparticles (NPs) can significantly increase temperature or even melt a surrounding matrix. The heating and melting processes occur under light illumination and involve the plasmon resonance. For the matrix, we consider water, ice, and polymer. Melting and heating the matrix becomes possible if a nanoparticle size is large enough. Significant enhancement of the heating effect can appear in ensembles of NPs due to an increase of a volume of metal and electric-field amplification.

Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here we report that covalent attachment of L/D-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the “crowded” edges. CD spectra of the GQDs revealed bands at ca 210-220 nm and 250-265 nm that changed their signs for different chirality of the cysteine edge-ligands. The high energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of aminoacid and atoms of graphene edges. Diverse experimental and modeling data including Density Functional Theory calculations of CD spectra with probabilistic distribution of GQD isomers indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveal their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics (MD) simulations demonstrated that D-GQDs has stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

Nanoparticles, Lightly Twisted: The helical structures that are widespread in natural macromolecules result from well-coordinated bonding interactions and affect their physical properties in striking ways. To obtain helical nanoparticles, Srivastava et al. (p. 1355 , published online 11 February) slowly oxidized cadmium-tellurium under visible light and assembled ribbons of nanostructure. The ribbons were persuaded to twist into helices because they were doped with cadmium sulfide nanoparticles, which underwent surface oxidation and caused localized stresses that could only be relieved by a conformational change. The pitch of the twisted ribbons that were produced could be controlled by the intensity of illumination applied. This behavior offers promise for application in the development of materials with interesting optical properties.