Stereoselective amino acid analysis has increasingly moved into the scope of interest of the scientific community. In this work, we report a study on the chiral recognition of d,l-Trp and d,l-His using l-Cys-capped gold nanoparticles (AuNPs) and copper(II) ion. In the l-Cys-capped AuNPs, the thiol group of the amino acid interacts with AuNPs through the formation of Au–S bond, whereas the α-amino and α-carboxyl groups of the surface-confined cysteine can coordinate the copper(II) ion, which in turn, binds the l- or d-amino acid present in solution forming diastereoisomeric complexes. The resulting systems have been characterized by UV–Vis spectra and dynamic light scattering measurements, obtaining different results for l- and d-Trp, as well as for l- and d-His. The knowledge of the solution equilibria of the investigated systems allowed us to accurately calculate in advance the concentrations of the species …