A dithioacetal-based NIR fluorescent chemosensor for Hg²⁺ detection in biological and environmental samples

The widespread occurrence, high toxicity, and bioaccumulative nature of mercury (Hg²⁺) render its pollution a critical concern for ecosystems and human well-being. Hence, a novel near-infrared (NIR) fluorescent chemosensor (DHDM) was constructed through a naphthyl-substituted dicyanoisophorone dye and a 1,2-ethanedithiol recognition unit, which responds via a Hg²⁺-induced specific cleavage reaction and an ICT mechanism. DHDM exhibits excellent analytical performance, including a large stokes shift (192 nm), ultrafast reaction time (<1 min), sensitive detection limit (0.93 μg/L), which is significantly lower than the requirements of the U.S. Environmental Protection Agency's drinking water guideline standards. DHDM also exhibits high selectivity and robust anti-interference capability when challenged with various competing metal ions and amino acids. Such performance originates from the Hg²⁺-promoted deprotection of the dithioacetal moiety, which reinstates the conjugated fluorophore. The proposed reaction pathway has been corroborated by ¹H NMR, HRMS, and DFT calculations. Meanwhile, DHDM successfully enabled in situ imaging of Hg²⁺ in HeLa cells, zebrafish, and germinating plant seeds, demonstrating good biocompatibility and tissue penetration, and yielding reliable recovery rates (89-109%) in spiked environmental water samples. Overall, the study establishes a reliable tool for mercury monitoring and constructs a multifunctional molecular scaffold, providing new perspectives for the rational design of advanced fluorescent chemosensors to address various challenges in the environmental and biomedical fields.