A colorimetric and NIR fluorescent dual-mode probe based on xanthene-quinoline conjugate for detecting mercury ion in water/soil/seafood samples, living cells and mice.

Mercury ions (Hg2+), as a highly toxic heavy metal pollutant, pose severe threats to environmental safety and human health. To address the urgent need for reliable Hg2+ monitoring, we developed a novel near-infrared (NIR) xanthene-quinoline-based fluorescence probe (XQ-SCN) incorporating phenyl isothiocyanate as the recognition unit. XQ-SCN offers many benefits，such as NIR emission (730 nm), a remarkable fluorescence enhancement (227-fold), rapid response (10 s), a large Stokes shift (170 nm), a low detection limit (12.3 nM) and high selectivity, along with distinct visual colorimetric changes. The recognition mechanism has been suggested to result from Hg2+-induced spirolactam ring opening followed by 1,3,4-oxadiazole formation, which was verified by HRMS, IR analysis and density functional theory (DFT) computations. Benefiting from superior photophysical properties, XQ-SCN has been effectively utilized for the quantification of Hg2+ in water, soil and seafood samples. Specially, a smartphone-based RGB analysis method was established for on-site Hg2+ screening, creating a cost-effective and portable detection platform. Furthermore, the outstanding biocompatibility enables the probe to be applied for monitoring Hg2+ via fluorescence imaging in living cells and animals. This study not only achieves reliable Hg2+ tracking in multifunctional applications, but also offers a feasible strategy for rapid field detection of hazardous substances.