Toward selective, sensitive, and discriminative detection of Hg2+ and Cd2+via pH-modulated surface chemistry of glutathione-capped gold nanoclusters

Abstract

Heavy metal pollution can exert severe effects on the environment and human health. Simple, selective, and sensitive detection of heavy metal ions, especially two or more, using a single probe, is thereby of great importance. In this study, we report a new and facile strategy for discriminative detection of Hg²⁺ and Cd²⁺ with high selectivity and sensitivity via pH-modulated surface chemistry of the glutathione-capped gold NCs (GSH-Au NCs). By simply adjusting pH values of the colloidal solution of the NCs, Hg²⁺ could specifically turn off the fluorescence under acidic pH, however, Cd²⁺ could exclusively turn on the fluorescence under alkaline pH. This enables the NCs to serve as a dual fluorescent sensor for Hg²⁺ and Cd²⁺. We demonstrate that these two opposing sensing modes are presumably due to different interaction mechanisms: Hg²⁺ induces aggregation by dissociating GSH from the Au surface via robust coordination and, Cd²⁺ could passivate the Au surface by forming a Cd-GSH complex with a compact structure. Finally, the present strategy is successfully exploited to separately determine Hg²⁺ and Cd²⁺ in environmental water samples.