L-Cysteine modified gold nanoparticles for tube-based fluorometric determination of mercury(II) ions

A fluorescent probe is described for detection of mercury(II) ion by using L-cysteine-modified gold nanoparticles (Cys-AuNP). These were fabricated by a tube-based redox reaction where Cys acts as both the reducing reagent and capping ligand. The Cys-AuNP display red fluorescence, with excitation/emission peaks at 373/625 nm. Owing to the high-affinity of the Hg(II)–Au(I) interaction and the Hg(II)/carboxy or amino group interaction, the presence of Hg(II) cause selective quenching the fluorescence, while other metal ions do not give such an effect. Based on these findings, a method was designed for the determination of Hg(II) that has attractive figures of merit. These include a low limit of detection (1.3 nM), a wide detection range (from 2 nM to 30µM), and excellent specificity. The method was applied to Hg(II) screening in (spiked) tap and river water, and it gave satisfactory results. Schematic representation of the application of L-cysteine modified gold nanoparticles (Cys-AuNP) for qualitative and quantitative detection of mercury(II) ions. Based on the interaction between Cys-AuNP and mercury(II) ion to quench the red fluorescence of Cys-AuNP, the target mercury(II) can in turn be determined by a fluorometric method.