In this work, a highly sensitive and selective optical probe for cysteine was developed using unmodified gold nanoparticles. Quick visual detection depended on the distance-dependent optical properties of gold nanoparticles, the self-assembly of cysteine on the surface of gold nanoparticles, and the chelation in the presence of lead ions. The form of complex could rapidly induced the aggregation of gold nanoparticles, thereby resulting in red-to-blue (or purple) color change. The concentration of cysteine was determined with a limit of detectio...
