Chiroptical Study of Metal@semiconductor–Molecule Composites: Interaction between Cysteine and Ag@Ag3PO4 Core–Shell Hybrid Nanorods

The coupling between an inorganic nanostructure and a chiral molecule can give rise to a strong chiroptical response in a range from the UV to visible spectrum. In this work, novel plasmonic Ag@Ag3PO4 core–shell hybrid nanorods (CSHNRs) have been prepared via a wet chemical method. The cysteine molecules can adsorb on the surface of the plasmonic hybrid nanorods, leading to the appearance of new circular dichroism (CD) signals in the UV region. The Ag@Ag3PO4–cysteine CSHNRs show a similar CD spectrum to the Ag3PO4–cysteine polyhedral nanocrystals (PNCs), although they have different morphology and structure. The Ag@Ag3PO4–cysteine CSHNRs and Ag3PO4–cysteine PNCs have a stronger chiroptical response than the Ag–cysteine nanorods (NRs) attributed to the effect of phosphate groups. This indicates that the Ag+ ions on the surface of nanostructures can promote the formation of S–S bonds of oxidized cysteine under acidic conditions, rendering the uniformity of molecular conformation on the surface of nanostrucures, thus giving rise to the strong chiroptical response. Furthermore, the Ag@Ag3PO4 CSHNRs can spontaneously form a chiral liquid crystalline phase upon dispersion in the ethylene glycol solution owing to their large aspect ratio and the optimum solvating effect of ethylene glycol.