The QDs-based fluorescence chemosensing could be performed by different strategies. In many analytical sensing procedures, handling the surface chemistry of quantum dots (QDs) has been utilized to achieving the goal, according to the interaction between the mediator and QDs surface as well as the analyte and mediator [1,2]. In this study, an indirect turn-off fluorescence sensing strategy was proposed for the determination of reduced glutathione (GSH), utilizing the zinc sulfide quantum dots. The quantum dots were prepared by precipitation method using mercaptopropionic acid as stabilizer (MPA-ZnS QDs). The fluorescence of the water soluble ZnS QDs, changed very slightly with the direct addition of GSH. Interestingly, the emission of ZnS QDs can be strongly ameliorated in the presence of Zn 2+ and subsequently, this fluorescence intensity was efficiently quenched by different concentrations of GSH. The fluorescent Zn 2+ -MPA-ZnS QDs hybrid system was developed for the detection of GSH with a LOD of 0.920 µM and a linear range of 2.0-104.0 µM. The RSD for five replicate measurements of 65 µM GSH was 1.9%. To examine the selectivity of Zn 2+ - MPA-ZnS QDs set for GSH, the effect of some substances, including amino acids, dopamine, urea, uric acid, ascorbic acid, glucose, sucrose and fructose was studied. The quenching effect of GSH on this hybrid system was significantly higher than all of the investigated species. The fluorescence spectra were recorded by a Perkin-Elmer luminescence spectrometer (model LS-50B, 3.5 cm × 1.0 cm × 1.0 cm quartz cell, excitation and emission wavelength were 305 and 425 nm, respectively)
