A turn-on fluorescent sulfide probe prepared from carbon dots and MnO.sub.2 nanosheets

A turn-on fluorescent sulfide probe was prepared from carbon dots (CDs; synthesized using an environmentally friendly method) and MnO.sub.2 nanosheets. In this composite probe, the fluorescence of the CDs (with excitation/emission peaks at 330/430 nm) is quenched by the MnO.sub.2 nanosheets through an inner filter effect. Introducing sulfide causes the MnO.sub.2 nanosheets to be disintegrated through a redox reaction between sulfide and MnO.sub.2. Hence, the blue fluorescence of the CDs is restored. Under the optimum conditions, fluorescence increases linearly in the 2-25 [mu]M sulfide concentration range. The detection limit is 0.8 [mu]M. The method was used to analyze spiked real water samples, and satisfactory results were achieved.