Synthesis of Chiral Gold Nanostructures on Gold-Coral-Coated Transparent Conductive Oxide Substrates via [AuCl4]- and Cysteine Interactions for Enhanced Chiral Sensing.

Chirality appears in many molecules, crystals, and nanostructures and plays an important role in their physicochemical and biological functions. Because biological systems exhibit a chiral bias, they respond differently to each chiral enantiomer. Therefore, it is very important to develop methods or devices that can discriminate the enantiomers easily. Metallic nanostructures such as nanoparticles, nanorods, and mesoporous films exhibit significantly enhanced optical responses due to localized surface plasmon resonance. The optical properties of these nanostructures are highly dependent on their size, shape, and elemental composition, all of which can be precisely controlled through optimized chemical synthesis. In this study, we developed a hierarchical nanostructure of chiral Au nanostructures on Au coral structures, which were synthesized on transparent conductive oxide substrates using only electrochemical techniques. By considering both the substitution of chloride ions in [AuCl4]- with cysteine in the electrolyte solution and the subsequent reduction of the Au(III) complexes, we successfully controlled the morphology of the Au nanostructures, which exhibit circular dichroism. Furthermore, we explored the potential for chiral discrimination using these substrates. The hierarchical chiral Au nanostructures on Au coral structures enhanced the SERS intensity relative to Au corals alone and produced enantiomer-dependent SERS responses for L- and D-phenylalanine, demonstrating their potential for chiral discrimination.