High quantum yield sulfur quantum dots for folic acid detection in food samples and living cells imaging

Monitoring folic acid (FA) levels in food is essential for nutritional regulation and cancer risk prevention, as FA deficiency is closely associated with increased cancer incidence. Despite the availability of various detection methods, challenges remain in achieving a combination of high sensitivity, environmental sustainability, and biocompatibility. To address this gap, we report a green and efficient synthesis of sulfur quantum dots (SQDs) with a high fluorescence quantum yield of 0.352, using K 2 FeO 4 and H 2 O 2 as eco-friendly etching agents. The as-prepared SQDs exhibit excellent hydrophilicity, stability, and selective response to FA through the synergistic effects of the inner filter effect (IFE) and static quenching effect (SQE). The proposed fluorescent probe enables FA detection with a low detection limit of 0.18 μM and demonstrates high recovery rates from 99 to 103% in real food samples. Furthermore, this quantum dot has been successfully applied to the imaging of H22 cells rich in folic acid, highlighting their potential for biomedical diagnostics. This work provides a sustainable and high-performance fluorescent nanoprobe for FA sensing, with significant implications for food safety and early cancer screening. • Sulfur quantum dots (SQDs) achieve a high fluorescence quantum yield of 35.24% through the use via coprecipitation and etching processes. • By leveraging the fluorescence inner filter effect (IFE) and static quenching effect (SQE), SQDs act as sensitive probes for the selective detection of folic acid (FA) with a detection limit of 0.18 μM. • SQDs can be used for cellular imaging and FA content determination of H22 cells.