Determination of Hg(II) based on the inhibited catalytic growth of surface-enhanced Raman scattering-active gold nanoparticles on a patterned hydrophobic paper substrate

Anthropogenic mercury (Hg) presents serious risks to the surroundings and public health due to its toxicity and bioaccumulation. In this study, a new assay was developed to combat mercury-related issues, and it is based on surface-enhanced Raman scattering (SERS) on an active paper substrate for rapid Hg(II) determination. The sensing principle is based on the hindering effect of Hg(II) on the catalytic growth of SERS-active gold nanoparticles (AuNPs) on a hydrophobically patterned paper substrate. 4-mercaptobenzonic acid (4-MBA) was chosen as an effective Raman reporter molecule, and its Raman signal was enhanced by surface plasmonic 2-[4-(2-hydroxyethel) piperazine-1-yl]ethanesulfonic acid-stabilized gold nanostars (HEPES-AuNSs) on a piece of paper with a hydrophobic surface. After adding a Hg(II) analyte solution to this SERS substrate, an amalgam formed at the solid-liquid interface of the HEPES-AuNSs. The formation of the AuHg amalgam resulted in the dissolution of the branches of the HEPES-AuNSs. In the presence of a growth solution (mixture of Au(III), HCl, and H2O2), the remaining HEPES-AuNSs and the AuHg amalgams acted as seeds to form small AuNPs, resulting in a weak SERS signal of 4-MBA (Raman shift at 1590 cm(-1)). Solution concentration, temperature, and treatment time were optimized to realize a significant decrease in the Raman intensity of 4-MBA when the paper sensor was exposed to Hg(II). The Raman intensity decreased with the increasing concentration of Hg(II) ions in the range of 0.1 nM-1.0 mu M (R-2 = 0.98), with a limit of detection (S/N = 3.0) of 0.03 nM. For practicality, the proposed paper substrate was examined by estimating Hg(II) concentrations in environmental water samples (i.e., seawater and pond water) and the certified standard of SRM 1641d through standard addition and a recovery study. The promising selectivity, sensitivity, and reproducibility of the proposed paper sensor constitute substantial progress toward the portable detecting mercury in real water samples, which can facilitate crucial surrounding monitoring.