On–Off–On Fluorescent Chemosensors Based on N/P-Codoped Carbon Dots for Detection of Microcystin-LR

The sensing of microcystin-LR (MC-LR) as a nonfluorescent species is still challenging since it has a negligible influence on the emission of fluorescent nanomaterials. Herein, a well-defined “on–off–on” indirect chemosensing strategy is developed by means of nitrogen/phosphorus-codoped carbon dots (N/P CDs) for highly sensitive and selective MC-LR determination. The nanoscale N/P CDs were conveniently synthesized by one-step hydrothermal carbonization of adenosine 5′-triphosphate (ATP) in aqueous media. The fluorescence intensity of the N/P CDs was quenched in the presence of Fe3+ due to the formation of Fe–O–P bonds between Fe3+ and the phosphate groups of the N/P CDs. The resulting N/P CD-Fe3+ system was sensitive to MC-LR, and its fluorescence intensity recovered dramatically and quickly since the MC-LR cavity competitively coordinated with Fe3+. Under optimized conditions, the proposed chemosensor exhibited a wide linear response for MC-LR in the range of 0.05–3 μg/L, with a detection limit down to 17.1 ng/L. Moreover, the chemosensor was successfully applied to accurately detect MC-LR in real water samples and achieved high recoveries in the range of 95.0–109.3%, with relative standard deviations within 1.8–4.7%. By relying on the benefits of fluorescent chemosensors, such as simple operation, low production cost, fast response time, selectivity, and sensitivity, the proposed sensing platform possesses promising applicability for MC-LR determination in complex environmental water samples.