The selectivity of the carboxylate groups terminated carbon dots switched by buffer solutions for the detection of multi-metal ions

•The carboxylate groups terminated carbon dots (−OOC-C-dots) were synthesized.•The carbon dots exhibited switchable selectivity to metal ions in different buffers.•Potential detection of multi-metal ions using one carbon-dot-based chemosensor. In this work, the carboxylate groups terminated carbon dots (−OOC-C-dots) were synthesized by the thermal pyrolysis of citric acid at 180°C for 40h under air. The −OOC-C-dots with excellent water solubility showed bright blue emission under excitation at 360nm. The blue emission fluorescence of the −OOC-C-dots can be quenched by Al3+, Hg2+, Pb2+, Ni2+, Cu2+, Cr3+, Co2+, and Fe3+ ions in HNO3 solution at pH=5.0. Most interestingly, the −OOC-C-dots exhibited highly selective response to Fe3+ in NaAc-HAc buffer solution, to Pb2+ in Britton-Robinson buffer solution, and to Hg2+ in PBS buffer solution at pH=5.0, respectively. Moreover, good linear relationships were found between (F0-F)/F0 and the concentrations of Fe3+, Pb2+, and Hg2+ in the corresponding buffer solutions. As a result, the −OOC-C-dots can be explored as a chemosensor for the label-free detection of Fe3+, Pb2+, and Hg2+ with selectivity being switched by different buffer systems. By the proposed method, the selective detection of Fe3+, Pb2+, and Hg2+ in real water samples (mineral and tap), even in the presence of high concentration of interfering ions, was accurately achieved. Hence, a new method for the potential detection of multi-metal ions can be developed by using one carbon-dot-based chemosensor with switchable selectivity in different buffer solutions.