Selective determination of mercury(II) by self-referenced surface-enhanced Raman scattering using dialkyne-modified silver nanoparticles

A novel surface-enhanced Raman scattering (SERS) probe was developed for selective determination of Hg(II) ion. It is based on the use of silver nanoparticles (Ag-NPs) modified with the dialkyne 1,4-diethynylbenzene (DEB). Hg(II) undergoes a very selective chemical reaction with the terminal ethynyl groups to form a –C ≡ C-Hg-C ≡ C– linkage which triggers the aggregation of Ag-NPs. This generates numerous hot spots that cause a substantial increase in the intensity of the SERS signal at 2,146 cm−1. This large effect was exploited for sensitive quantification of Hg(II) in aqueous solution by rationing the intensities of the (Hg-C ≡ C) peak at 2,146 cm−1 and the (C ≡ C) free peak at 2,109 cm−1. This self-referenced method is superior to the use of an internal standard. The method also displays excellent selectivity over other metal ions. Under optimal conditions, the rationed signal intensity is related to concentration of Hg(II) in the range between 1.1 nM and 61.2 nM, with a detection limit at 0.8 nM. The method was successfully applied to the determination of Hg(II) in spiked samples of river water.