Herein, we demonstrated a simple and efficient method to detect Cu2+ based on amplified optical activity in the chiral nanoassemblies of gold nanorods (Au NRs). L-Cysteine can induce side-by-side or end-to-end assembly of Au NRs with an evident plasmonic circular dichroism (PCD) response due to coupling between surface plasmon resonances (SPR) of Au NRs and the chiral signal of L-Cys. Because of the obvious stronger plasmonic circular dichrosim (CD) response of the side-by-side assembly compared with the end-to-end assemblies, SS assembled Au NRs was selected as a sensitive platform and used for Cu2+ detection. In the presence of Cu2+, Cu2+ can catalyze O2 oxidation of cysteine to cystine. With an increase in Cu2+ concentration, the L-Cysteine-mediated assembly of Au NRs decreased because of decrease in the free cysteine thiol groups, and the PCD signal decreased. Taking advantage of this method, Cu2+ could be detected in the concentration range of 20 pM– 5 nM. Under optimal conditions, the calculated detection limit was found to be 7 pM.
