The fluorescence of ZnS quantum dots in colloidal water solution changes very slightly on addition of glutathione (GSH) but is strongly enhanced in the presence of Zn(II) even in concentrations as low as 10 μ M. The resulting Zn(II)-enhanced fluorescence is found to be quenched by GSH. In contrast to GSH, cysteine does not cause an effect. Response surface methodology was applied to optimize the experimental parameters. The best data can be obtained at 305/427 nm as excitation/emission wave- lengths. These findings were used to design an indirect method for the fluorometric determination of GSH that has a 0.9 μ M detection limit and a response that is linear in the 2.0 – 104.0 μ M GSH concentration range. The relative standard deviation at a level of 65 μ M of GSH (for n = 5) is 1.9%.
