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.

A plasmon-assisted fluoro-immunoassay (PAFI) was developed for the detection of the influenza virus by using Au nanoparticle (Au NP)-decorated carbon nanotubes (AuCNTs) that were synthesized using phytochemical composites at room temperature in deionized water. Specific antibodies (Abs) against the influenza virus were conjugated onto the surface of AuCNTs and cadmium telluride quantum dots (QDs), which had a photoluminescence intensity that varied as a function of virus concentration and a detection limit of 0.1 pg/mL for all three types of influenza viruses examined. The clinically isolated influenza viruses (A/Yokohama/110/2009 (H3N2)) were detected in the range of 50-10,000 PFU/mL, with a detection limit of 50 PFU/mL. From a series of proof-of-concept and clinical experiments, the developed PAFI biosensing system provided robust signal production and enhancement, as well as an excellent selectivity and sensitivity for influenza viruses. This nanoparticle-based technique could be potentially developed as an efficient detection platform for the influenza virus.

Green chemical synthesis of Au nanoparticles (NPs) has been of great interest because of its potential biomedical applications. In this study, we successfully produced phytochemical-induced Au NPs cofunctionalized with gallic acid, protocatechuic acid, and isoflavone. They have a strong antioxidant effect and serve as effective reducing agents, inducing the immediate passivation of Au NPs. The properties of these green chemical Au NPs were characterized by TEM, UV/Vis and FT-IR spectroscopy, and ζ-potential measurements, and the Au NPs exhibited excellent homogeneity with an average diameter of 20 nm and high dispersity at all pH ranges, with long-term stability as well as excellent cytocompatibility. Molecular dynamics (MD) simulations were also carried out in order to reveal the surface stability of the Au NPs. The computational results indicate that there are strong interactions between the phytochemicals and Au NPs, especially in the Au/protocatechuic acid–isoflavone model. Phytochemical-stabilized Au NPs allowed about 40% H₂O₂ to be removed at an NP concentration of 50 μg mL⁻¹; this removal rate is the same as that achieved by 3000 units per mg catalase. Therefore, this novel synthesis route for Au NPs using phytochemical reducing agents may be effectively exploited for nonthermal-assisted reactions and one-pot processes of biological applications.