Quantum Dot-Based OFF/ON Probe for Detection of Glutathione

A simple strategy for detection of glutathione (GSH) in physiologically relevant concentrations is reported by manipulating the electron transfer pathways of surface-modified quantum dots. The probe consisted of fluorescent CdS:Mn/ZnS core/shell quantum dots (Qdot) properly conjugated to dopamine through CS2-assisted zero-length covalent coupling. Qdots exhibited bright yellow-orange emission at similar to 592 nm, which could be attributed to the T-4(1) --> (6)A(1) transition of Mn2+ ions in Qdot core. The fluorescently dark Qdots (OFF state) was obtained by modifying the Qdot surface with an electron rich dopamine molecule. The fluorescence of the probe was restored (ON state) when the disulfide bond was cleaved by the reducing GSH.