Development of Sulfur and Nitrogen-Doped Fluorescent Carbon Quantum Dots for Hydroquinone Sensing

This study reports a facile hydrothermal synthesis of fluorescent sulfur- and nitrogen-doped carbon quantum dots (S-N-CQDs) using cost-effective solid precursors such as L-methionine, malonic acid, and ethylenediamine. The S-N-CQDs exhibited a high quantum yield of 43%, measured with quinine sulfate as the reference standard. Various characterizations using HRTEM, XRD, XPS, zeta potential analysis, UV-Vis spectroscopy, and fluorescence lifetime measurements. The S-N-CQD particles have a size range of 2-3.5 nm and a zeta potential of -24.4 mV. The fluorescence of S-N-CQDs remained stable across a broad range of pH and under continuous UV irradiation (365 nm). Further S-N-CQDs were successfully employed as a fluorescent probe for hydroquinone (HQ) detection, showing concentration-dependent fluorescence quenching. The probe demonstrated a detection limit of 75 nM, with a linear response in the range 10-40 μM (R² = 0.998), and exhibited excellent selectivity toward HQ. The application and reliability associated with fluorescent probes were demonstrated for the examination of HQ in real water samples. The results found that the one-pot hydrothermal synthesis method shows high sensitivity, selectivity, and accuracy for the detection of HQ, highlighting its potential for environmental monitoring and practical applications.