Au/Ag2S dimeric nanostructures for highly specific plasmonic sensing of mercury(II)

Abstract

Although many plasmonic nanosenosrs have been established for the detection of mercury(II) (Hg2+), few of them is feasible for analyzing natural samples with very complex matrices because of insufficient method selectivity. To address this challenge, we propose an epitaxial and lattice-mismatch approach to the synthesis of a unique Au/Ag2S dimeric nanostructure, which consists of an Au segment with excellent plasmonic characteristics, and a highly stable Ag2S portion with minimum solubility product (Ksp(Ag2S) = 6.3 × 10−50). The detection relies on the chemical conversion of Ag2S to HgS when reacting with Hg2+, resulting in a red shift in the absorption band of the connecting Au NPs. The concurrent color changes of the solution from gray purple to dark green and finally to navy correlate well with Hg2+ concentration, thus enables UV–vis quantitation and a naked-eye readout of the Hg2+ concentration. This method exhibits superior selectivity towards Hg2+ over other interfering ions tested because Hg2+ is the only ion that can react with Ag2S to form HgS with even smaller solubility product (Ksp(HgS) = 4 × 10−53). The detection limit of this method is 1.21 µmol/L, calculated by the signal-to-noise of 3. The practicability of the method was verified by analyzing the Hg2+ in sewage water samples without sample pretreatment with satisfactory recoveries (93.1%-102.8%) and relative standard deviations (1.38%-2.89%). We believe this method holds great potential for on-the-spot detection of Hg2+ in environmental water samples with complex matrices.