On-off-on fluorescent sensor for glutathione based on bifunctional vanadium oxide quantum dots induced spontaneous...

Fluorescence sensing of glutathione by tailor-made chemical sensors is a prospective technique, which could provide simple, fast, and visual detection. Herein, a fluorescence sensor based on vanadium oxide quantum dots (VO_x QDs) and permanganate (MnO₄^-) has been designed for monitoring glutathione. The bifunctional VO_x QDs, possessing rich redox chemistry and robust fluorescence (exhibiting fluorescence near 505 nm upon excitation at 450 nm), were synthesized via cryogenic-mediated liquid-phase exfoliation. In the presence of MnO₄^-, VO_x QDs induced the spontaneous formation of MnO₂ nanosheets which caused the fluorescence quenching. However, the subsequent introduction of glutathione could trigger MnO₂ reduction to Mn²⁺, and the fluorescence was recovered. Based on this phenomenon, an "on-off-on" fluorescence sensor for glutathione detection was established. Under the optimal conditions, this sensor allowed detection of glutathione in the linear range of 0.5-100 μM with a detection limit of 0.254 μM. Additionally, the proposed strategy revealed the selectivity toward glutathione and the potential of practical application in the analysis of human serum, vegetable, and fruit samples.