Tailoring dual-functional gold nanoplasmonic rods for colorimetric and SERS detection of mercury species in complex matrices

Mercury speciation is essential for ecological security and human health due to its accumulative, toxicity, and persistent feature in the environment and biota. Here, we present a bimodal detection strategy for discrimination of mercury ions (Hg2+) and methylmercury (CH3Hg+) by utilizing valence-states mediated morphology transi-tion of p-aminothiophenol (PATP) modified gold nanorods (GNRs@PATP). Hg2+ could be reduced by PATP to form Au-Hg amalgams on the surface of GNRs. The nanoalloy prevents GNRs aggregation, exhibiting a blue-shift of longitudinal surface plasmon resonance peak. Furthermore, the presence of Hg2+ triggers conversions of PATP to p, p '-dimercaptoazobenzene, which results in a distinctly surface enhanced Raman scattering (SERS) signals output. Conversely, CH3Hg+ reacts with the amino of the PATP and facilitates GNRs self-assembly due to the excellent affinity of CH3Hg+-NH2 interactions, leading to occurrence of an absorption peak at 930 nm. Based on the to-together-and-to-isolate interaction between GNRs@PATP and mercury species, a "turn-on" SERS method and colorimetric assay are developed for Hg2+ and CH3Hg+ detection, respectively, providing LOD of 3.2 fM for Hg2+ and 0.3 nM for CH3Hg+. This sensing system displays a high selective response towards Hg2+ and CH3Hg+. Its practical applications are further validated by mercury speciation in environmental water, food and human hair.