An "on-off-on" fluorescent probe based on nitrogen-doped carbon quantum dots for the selective detection of glutathione.

Glutathione (GSH), an important biological sulfane sulfur compound, plays an integral role in a wide array of biological processes. Consequently, advancing highly sensitive and selective fluorescence-based analytical methods is crucial for research. This study successfully synthesized highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) using folic acid as a dual source of carbon and nitrogen through an economical and eco-friendly hydrothermal method. An "on-off-on" fluorescence probe was developed for detecting GSH. The fluorescence intensity of N-CQDs was significantly reduced due to effective quenching by Ag+. However, GSH exhibits a strong affinity for Ag+ and can induce aggregate formation via chelation, thereby restoring the fluorescence of N-CQDs. Under optimal conditions, the sensing method exhibited a detection limit of 0.39 μM for glutathione, with a good linear response in the concentration range of 10 to 50 μM; the detection limit in human serum was 1.731 μM, and the recovery rates ranged from 91.49% to 96.70%. The N-CQDs@Ag+ fluorescence probe was effectively utilized to detect GSH in various real samples, such as tomatoes, pears, lysates from three cancer cell lines, and human serum, highlighting its potential for analyzing complex biological samples.