The abnormalities of Tryptophan (Trp) and mercury ions (Hg2+) not only easily activate diseases, including mental illness and cancer, but also seriously affect human wellbeing. Fluorescent sensors are profoundly attractive options for identifying amino acids and ions; however, most sensors remain challenging due to the multipliable cost and deviation from the asynchronous quenching detection. In particular, fluorescent copper nanoclusters with high stability that quantitatively monitoring Trp and Hg2+ successively have seldom been reported. Herein, we employ coal humus acid (CHA) as a protective ligand and successfully construct weak cyan fluorescent copper nanoclusters (CHA-CuNCs) by a rapid, environmentally benign and cost-effective method. Significantly, the fluorescence of CHA-CuNCs is obviously improved by introducing Trp, because the indole group of Trp enhances the radiative recombination and aggregation-induced emissions. Interestingly, CHA-CuNCs not only realizes the highly selective and specific detection of Trp with a linear range of 25-200 μM and a detection limit of 0.043 μM based on the turn-on fluorescence strategy, but also quickly achieves the consecutive turn-off detection of Hg2+ due to the chelation interaction between Hg2+ and pyrrole heterocycle in Trp. Moreover, this method is successfully applied in the analysis of Trp and Hg2+ in real samples. Furthermore, the confocal fluorescent imaging of tumor cells demonstrates that CHA-CuNCs can be used for bioimaging and cancer cell recognition with Trp and Hg2+ abnormalities. These findings provide new guidance for the eco-friendly synthesis of CuNCs with eminent sequential off-on-off optical sensing property, indicating good prospects in biosensing and clinical medicine applications.
Keywords: Coal humus acid; Copper nanoclusters; Hg(2+); Sequential off-on-off sensing; Tryptophan; Tumor recognition.
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