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. Plasmonic reporter: Discrete Au@Ag core–shell nanocuboids capped with cysteine molecules exhibit two bisignate circular dichroism (CD) resonances in the UV region. One corresponds to the molecular electronic CD of cysteine, the other is an induced, unusual CD band originating from the formation of extended helical networks among neighboring cysteine molecules, which is dramatically amplified by the interband absorption of Ag.