Fluorescent Sensing Platform Based on Nitrogen‐Doped Carbon Dots for Selective Detection of Sulfite

Nitrogen‐doped carbon dots (d‐CDs) were prepared and refined through a solvothermal approach, employing malonic acid and barbituric acid as the carbon and nitrogen sources, respectively, in N, N‐dimethylformamide. Single‐factor experiments established the optimal synthesis conditions: reaction time of 18 h, barbituric acid dosage of 1.5 g, and temperature of 180 °C. Under these optimized conditions, the resulting d‐CDs exhibited a quantum yield of 23.2%. In a phosphate buffer (pH 7.0), the d‐CDs demonstrated specific fluorescence recognition for sulfite ions (SO 3 2− ), achieving a quenching efficiency of 64.6%. Notably, the sensor exhibited strong anti‐interference capability against 17 common anions (e.g., F − , Cl − , Br − , I − , CH 3 COO − , NO 3 − , SO 4 2− , HPO 4 2− , CN − , S 2− , CO 3 2− , PO 4 3− , C 2 O 4 2− , K + , Ca 2+ , Mg 2+ , and Zn 2+ ). Kinetic studies revealed an ultrafast response, with quenching equilibrium reached within 10 s. Quantitative analysis yielded a low detection limit of 0.22 μmol·L −1 for SO 3 2− . The Stern–Volmer equation and fluorescence lifetime measurements demonstrate that this highly sensitive recognition is governed by a static quenching mechanism. Application to real water samples (lake water and river water) showed excellent recovery rates (98.0%–100.7%) and low coefficient of variation (CV < 4.04%) in spike‐and‐recovery tests.