An “ON–OFF–ON” Fluorescent Sensor Based on N,S,F-Doped Carbon Dots for Selective Detection of MnO4− and Dopamine Hydrochloride

Dopamine hydrochloride (DPH) is a key neurotransmitter, and its dysregulated concentration has been linked to various neurological disorders. Meanwhile, potassium permanganate (MnO 4 − ), a potent oxidant, poses significant environmental risks when discharged in excess. Therefore, sensitive detection of MnO 4 − and DPH is essential. In this work, nitrogen, sulfur, and fluorine tridoped carbon dots (N,S,F-CDs) were prepared through a hydrothermal route using Aconitum pendulum Busch extract as a biomass-derived carbon source, with thiourea and sodium fluoride serving as heteroatom dopants. The obtained N,S,F-CDs exhibited bright blue emission, good aqueous dispersibility, and a fluorescence quantum yield of 43.16%, with strong emission at 408 nm under 345-nm excitation. Upon addition of MnO 4 − , the fluorescence was efficiently suppressed owing to the combined contribution of inner-filter effect and dynamic quenching. Subsequent introduction of DPH reduced MnO 4 − and recovered the fluorescence signal, enabling the construction of an “ON–OFF–ON” sensing platform. Under optimized conditions, the sensor displayed linear responses of 5.03–275.23 μM for MnO 4 − and 6.11–371.02 μM for DPH, with detection limits of 0.25 and 0.68 μM, respectively. The method was further applied to tap water, serum, and orange juice samples with satisfactory recoveries, indicating its potential for environmental and bioanalytical detection.