Rapid and selective detection of cysteine based on its induced aggregates of cetyltrimethylammonium bromide capped gold nanoparticles

A detection method of cysteine is reported in this contribution with water-soluble positively charged gold nanoparticles (Au-NPs) that were prepared by seed-mediated method and capped with cetyltrimethylammonium bromide (CTAB). In aqueous medium of pH 4.2, the CTAB-capped Au-NPs display greatly different features from those of generally prepared citrate-coated Au-NPs. It was found that in a medium of high salt concentration, the presence of cysteine could induce aggregation of CTAB-capped Au-NPs, while citrate-coated Au-NPs could get aggregation soon even if without the presence of cysteine. The cysteine-induced aggregates of CTAB-capped Au-NPs display strong plasmon resonance light scattering (PRLS) signals characterized at 566.0 nm when excited by a light beam, and the PRLS intensities of the aggregates are in proportion to the concentration of cysteine in the range of 0.01–0.40 μg mL−1 with the limit of detection (3σ) being 2.9 ng mL−1. No amino acids in the samples interfere with the detection, and cysteine in artificial samples could be detected with the recovery between 95.3% and 105.9%, and R.S.D. is less than 3.6%.