Determination of mercury(II) by surface-enhanced Raman scattering spectroscopy based on thiol-functionalized silver nanoparticles

Silver nanoparticles (Ag NPs) modified with sodium 2-mercaptoethanesulfonate (mesna) exhibit strong surface-enhanced Raman scattering (SERS). Their specific and strong interaction with heavy metal ions led to a label-free assay for Hg(II). The covalent bond formed between mercury and sulfur is stronger than the one between silver and sulfur and thus prevents the adsorption of mesna on the surface of Ag NPs. This results in a decrease of the intensity of SERS in the presence of Hg(II) ions. The Raman peak at 795 cm(-1) can be used for quantification. The effect of the concentration of mesna, the concentration of sodium chloride, incubation time and pH value on SERS were optimized. Under the optimal conditions, the intensity of SERS decreases with increasing concentration of Hg(II). The decrease is linear in the 0.01 and 2 mu mol L-1 concentration range, with a correlation coefficient (R-2) of 0.996 and detection limit (S/N = 3) is 0.0024 mu mol L-1. The method was successfully applied to the determination of the Hg(II) in spiked water samples.