Spectrophotometric determination of cysteine based on self-assembly of gold nanoparticles

Due to the covalent combination with the SH group and the electrostatic binding with the NH3+ group of cysteine, gold nanoparticles can self-assemble and form a supermolecular network structure in the Britton-Robinson buffer solution (pH 4.56). As a result, absorption peak of the gold nanoparticles shifts from 520 nm to 660 nm. The mechanism of self-assembly of gold nanoparticles directed by cysteine was investigated. Based on the study, a simple and sensitive method for cysteine determination has been established. There is a good linear relationship between the absorbance at 660 nm and cysteine concentration in the range of 0.01 - 0.20 mg/L. The corresponding detection limit is 2.8 mu g/L (3 sigma, 2.3 x 10(-8) mol/L). Common amino acids and glutathione do not interfere with the determination.