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.

Complex chiral particles: Synthetic colloids are usually smooth, but nature can produce micrometer-scale particles with intricate structure and shape, such as the coccoliths produced by algae. Jiang et al. controlled the self-assembly of gold–cysteine nanoplatelets into a variety of chiral, hierarchically organized colloidal particles by changing the chiral fraction of cysteine and the nucleation temperature. Organic cations created electrostatic repulsions that favored edge assembly of the nanoplatelets, which in turn could create surfaces bearing twisted spikes. Science , this issue p. 642

3-Aminobenzeneboronic acid functionalized graphene quantum dots (APBA-GQDs) were synthesized and used as a selective and sensitive sensing system for glucose. Combined with microdialysis, glucose was monitored successfully in vivo in the striatum of rat.

Semiconductors with chiral geometries at the nanoscale and mesoscale provide a rich materials platform for polarization optics, photocatalysis, and biomimetics. Unlike metallic and organic optical materials, the relationship between the geometry of chiral semiconductors and their chiroptical properties remains, however, vague. Homochiral ensembles of semiconductor helices with defined geometries open the road to understanding complex relationships between geometrical parameters and chiroptical properties of semiconductor materials. We show that semiconductor helices can be prepared with an absolute yield of ca 0.1% and an enantiomeric excess (e.e.) of 98% or above from cysteine-stabilized cadmium telluride nanoparticles (CdTe NPs) dispersed in methanol. This high e.e. for a spontaneously occurring chemical process is attributed to chiral self-sorting based on the thermodynamic preference of NPs to assemble with those of the same handedness. The dispersions of homochiral self-assembled helices display broadband visible and near-infrared (Vis-NIR) polarization rotation with anisotropy (g) factors approaching 0.01. Calculated circular dichroism (CD) spectra accurately reproduced experimental CD spectra and gave experimentally validated spectral predictions for different geometrical parameters enabling de novo design of chiroptical semiconductor materials. Unlike metallic, ceramic, and polymeric helices that serve predominantly as scatterers, chiroptical properties of semiconductor helices have nearly equal contribution of light absorption and scattering, which is essential for device-oriented, field-driven light modulation. Deconstruction of a helix into a series of nanorods provides a simple model for the light-matter interaction and chiroptical activity of helices. This study creates a framework for further development of polarization-based optics toward biomedical applications, telecommunications, and hyperspectral imaging.