In this study, novel highly fluorescent sulfur, nitrogen, and oxygen co-doped carbon dots (S, N, O-CDs) were prepared from m-phenylenediamine and sulfamide by using the hydrothermal method. The prepared S, N, O-CDs show high doping rate and fluorescence yield as well as long-term fluorescence stability. In addition, S, N, O-CDs show good fluorescence response towards Cu2+ over a concentration range of 2-60 μM with a detection limit of 0.29 μM. Taking advantages of the properties of S, N, O-CDs including high selectivity and low cytotoxicity, S, N, O-CDs were successfully applied for Cu2+ sensing and imaging in the cells and O2˙--induced Cu2+ increase in the cells was observed. Furthermore, on account of strong complexation between Cu2+ and pyrophosphate ion (PPi) as well as specific hydrolysis ability of alkaline phosphatase (ALP) towards PPi, PPi and ALP were further detected with high selectivity based on S, N, O-CDs/Cu2+ system. The prepared S, N, O-CDs showed good detection results for PPi and ALP with detection limits of 0.44 μM and 1.03 U L-1, respectively. Moreover, the developed method also realized PPi and ALP detection in real samples.
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