Coal humus acid functionalized high stability fluorescent copper nanoclusters for tumor identification by sequential off-on-off monitoring tryptophan and Hg.

The abnormalities of Tryptophan (Trp) and mercury ions (Hg) 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 Hg 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 Hg due to the chelation interaction between Hg and pyrrole heterocycle in Trp. Moreover, this method is successfully applied in the analysis of Trp and Hg 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 Hg 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.