Interband Absorption Enhanced Optical Activity in Discrete Au@Ag Core–Shell Nanocuboids : Probing Extended Helical Conformation of Chemisorbed Cysteine Molecules

Detailed understanding of the interaction between a chiral molecule and a noble metal surface is essential to rationalize and advance interfacial self-assembly of amino acids and metal-mediated anchoring of proteins. Here we demonstrate that individual Au@Ag core–shell nanocuboids can serve as a plasmonic reporter of an extended helical network formed among chemisorbed cysteine molecules, through generating an interband absorption enhanced, Ag-surface-exclusive circular dichroism (CD) band in the UV region. The observed unusual, strong CD response in the hybrid Au@Ag–cysteine system can be used to probe in real time conformational evolution and structural rearrangement of biomolecules in general and also monitor the interfacial interaction between a metal surface and an adsorbed molecule, opening up the possibility of using Ag nanostructures as promising stereochemically attuned nanosensors.