Highly sensitive SERS sensor for mercury ions based on the catalytic reaction of mercury ion decorated Ag nanoparticles

A surface-enhanced Raman scattering (SERS) sensor of mercury ions based on the coordinated catalytic reaction of Hg²⁺–Ag nanoparticles (NPs) has been designed and constructed for water quality monitoring. We combined Ag NPs (average particle size is 49 nm) with mercury ions to form Hg²⁺–Ag NPs in aqueous phase by electrostatic interactions. The formed Hg²⁺–Ag particles can catalyze a redox reaction between o-phenylendiamine (OPD) and dissolved oxygen to form 2,3-diaminephenazine (DAP), which is Raman-active and possesses a strong SERS signal due to the adherence to Ag NPs. Therefore we can trace the SERS intensity of DAP to determine mercury ions and the lowest detectable concentration of mercury is 1.0 nM using this method. This sensor displays higher sensitivity and selectivity and it possesses a certain value in terms of water quality detection.