Specific detection of cysteine and homocysteine: recognizing one-methylene difference using fluorosurfactant-capped gold nanoparticles

Aggregation of fluorosurfactant-capped gold nanoparticles could be induced selectively by cysteine and homocysteine and, when solution ionic strength was low, the kinetics of homocysteine-induced aggregation of large size nanoparticles ( similar to 40 nm) was much faster than that induced by cysteine, leading to specific detection of homocysteine in the presence of excess cysteine.