Colorimetric detection of cysteine based on dispersion–aggregation mechanism of chitosan stabilized gold nanoparticles

Abstract

A simple and selective colorimetric method for detection of cysteine using chitosan stabilized gold nanoparticles has been developed. L-cysteine is a sulfur containing amino acid. Cysteine binds with the gold nanoparticles through a sulfur group and induces aggregation of the nanoparticles, which leads to a visible colour change from pale red to blue. A good linearity was observed from 0.1 to 30 μmol/L (R = 0.9958) cysteine, and the limit of detection was found to be 0.1 μmol/L. The gold nanoparticles showed a high selectivity towards the detection of cysteine even in the presence of 10 000 fold higher concentration of common interferences such as glutathione, methionine, and homocysteine. A plausible mechanism for the selective detection of cysteine in presence of interferences based on a dispersion–aggregation mechanism has been proposed.