Novel Hg2+-Specific "turn-on" fluorescence sensor: Applications in water samples and test strips via real-time colorimetric assay

Mercury pollution remains a global concern that causes harm to the environment and human health. Therefore, a rapid, sensitive, and effective method for detecting Hg2+ in the environment must be developed. This study successfully synthesized a new Hg2+-specific fluorescence sensor based on thiocarbonyl-functionalized rhodamine (TRS). The sensor exhibits drastic fluorescence enhancement and a chromogenic change toward Hg2+ in an aqueous methanol solution. Meanwhile, TRS can distinguish Hg2+ from other competing ions with a detection limit of 8.7 nM (1.7 ppb). The sensor recognizes Hg2+ with a 1:1 stoichiometric ratio, confirmed by Job's plot. Its sensing mechanism involves forming the Hg2+ complex and later desulfurization mechanism, as intensively proved by FTIR, 1H NMR, and 13C NMR spectral analysis. The efficacy of TRS in colorimetric and fluorometric assays for monitoring Hg2+ contents was validated using different real samples. A paper test strip developed from this sensor also demonstrated high selectivity for colorimetric Hg2+ detection.