N, S-co-doped carbon quantum dots as a versatile platform for monitoring hydrogen sulfide and nitrite based on Fe2+/Fe3+ redox cycle: Applications in food safety and bioimaging

Food safety is a key public concern, making the detection of harmful substances in food increasingly urgent. Herein, a multifunctional fluorescence sensing platform was designed utilizing glutathione-derived N, S-co-doped carbon quantum dots (N, S-CDs), capable of sensitively monitoring nitrite (NO 2 - ) and hydrogen sulfide (H 2 S) in both food and living biological cells. The detection relies on Fe 3+ -induced fluorescence quenching of N, S-CDs through inner filter effect and static quenching, combined with the redox reactions of NO 2 - with Fe 2+ and H 2 S with Fe 3+ . The linear ranges and limits of detection (LOD) were as follows: NO 2 - , 1-1000 μM and 0.164 μM; H 2 S, 25-425 μM and 0.114 μM. Thanks to its ideal biocompatibility, N, S-CDs enabled visualization of NO 2 - and H 2 S in living cells. Meanwhile, N, S-CDs paper-based fluorescent sensor was constructed to detect NO 2 - in pickled meat and H 2 S in spoiled meat, demonstrating great potential for biological tracking and portable sensor development.