SERS-based mercury ion "on-off" dual-mode sensor using a silver cavity array substrate

A SERS-based mercury ion (Hg²⁺) sensor has been developed that enables rapid, highly sensitive, and precise detection of Hg²⁺ on a single substrate surface through a turn-on/turn-off dual mode. The sensor employs a two-dimensional, highly ordered silver cavity array (SCA) as the substrate. Through the alloying reaction between mercury and the SCA substrate, a silver-mercury amalgam is formed, resulting in a substantial attenuation of the substrate's surface plasmon resonance effect, which establishes an effective turn-off detection mode for mercury ions. As for the turn-on mode, glutathione (GSH) molecules modified on the SCA substrate show selective recognition and binding affinity for mercury ions (Hg²⁺) through their amino and carboxyl functional groups, consequently forming stable chelates. These complexes act as key bridging molecules, effectively mediating the immobilization of probe molecules, sodium thiophenolate (TP), and ultimately creating an SCA/Hg/sandwich structure with enhanced signal amplification properties. In this analytical system, the SERS signal intensity of the probe molecule is positively correlated with the concentration of Hg²⁺. The detection limits were as low as 0.3 nM and 0.027 nM when using turn-on and turn-off detection modes, respectively. The rapidity, accuracy, and high sensitivity of this method were experimentally validated through spiked recovery assays of cultured clam and river water samples. This SERS-based detection approach is not only suitable for Hg²⁺ detection but also provides a practical analytical framework for other metal ions, showcasing considerable application prospects in environmental monitoring, food safety assessment, and pollution early warning fields.