A Raman chip for rapid and specific detection of trace mercury ions in seawater

Abstract

Mercury ions (Hg2+) in seawater even at trace level could continuously cause serious threats to marine fishes as well as to human health by food chain. In this work, a chip for sensing Hg2+ in seawater is constructed by dense decoration of glutathione (GSH) onto ITO-Au film, designated as ITO-Au-GSH. The chip avoids the serious aggregation of nanoparticles in seawater, exhibiting the superior surface enhanced Raman scattering (SERS) effect. The sensing strategy is due to GSH enriching Hg2+ ions by −COOH and then 4-mercaptopyridine as signal reporter selectively docking onto the GSH bound Hg2+ via formation of specific Hg-S bond, which is validated by SERS and DFT calculation. Under the optimized condition, ITO-Au-GSH-chip-based SERS protocol has a quick response to trace Hg2+ ions in water. The quantitative linear range is from 2 ng/L to 200 μg/L (R2 = 0.9871) and the limit of detection (LOD) of 1.76 ng/L is reached, which meets the limitation amount (2 μg/L) of Hg2+ ions in water set by USEPA and WHO. In this work, a portable Raman spectrometer and such Raman-chip are used to on-site monitor Hg2+ in seawater and a good linear relationship is in the range of 20 ng/L to 200 μg/L with the LOD of 4.77 ng/L. Clearly, the SERS-chip-based portable Raman strategy paves a path to realize seaside monitoring of marine environmental and early warning for mercury pollution.