The “off–on” phosphorescent switch of Mn-doped ZnS quantum dots for detection of glutathione in food, wine, and biological samples

The phosphorescent 3-mercaptopropionic acid (MPA) capped Mn-doped ZnS quantum dots (MPA-Mn:ZnS QDs)-KMnO 4 hybrid system was developed to be an “off–on” phosphorescent switch based on chemical redox mechanism for detection of glutathione (GSH) in food, wine, and biological samples. By employing KMnO 4 as the quencher to the phosphorescence of MPA-Mn:ZnS QDs, GSH recovered the emission for its determination by the use of its reducibility. The possible mechanism for the restored phosphorescence was elucidated that SO 4 2− oxidized by KMnO 4 on the surface of the Mn:ZnS QDs was reduced to S 2− with the addition of GSH. The phosphorescent hybrid system allowed highly sensitive detection of GSH in aqueous solution with a detection limit of 97   nM and a wide linear range of 0.3–280   μM. The precision for 11 replicate detection of 200   μM GSH was 3.5% (relative standard deviation, RSD). The developed method was applied for the detection of GSH in food, wine, and biological samples with the quantitative spike recoveries from 95% to 104%.