A nanohybrid composed of MoS2 quantum dots and MnO2 nanosheets with dual-emission and peroxidase mimicking properties for use in ratiometric fluorometric detection and cellular imaging of glutathione

A nanohybrid probe was fabricated from manganese dioxide nanosheets (MnO2 NSs), molybdenum disulfide quantum dots (MoS2 QDs) and o-phenylenediamine (OPD) for ratiometric detection of glutathione (GSH) in aqueous solutions and living cells. The MoS2 QDs act as the fluorescent “turn off-on” units. The MnO2 NSs have 3 functions, viz. (a) as fluorescence quencher, (b) as fluorescence initiator for oxidized OPD (ox OPD) and (c) as selective recognizer of GSH. The quenched blue fluorescence of the MoS2 QDs can be restored by introducing GSH that reduces the MnO2 NSs. However, the green fluorescence of ox OPD is decreased through the loss of peroxidase activity of MnO2 NSs in the presence of GSH. Therefore, the ratio of the fluorescence intensities at 560 and 400 nm (from ox OPD and MoS2 QDs, respectively) linearly decreases with increasing concentrations of GSH. Under the optimal conditions, the detection limit for GSH is as low as 90 nM. The method was successfully applied to the determination of GSH in human serum samples. This nanohybrid also is shown to be membrane-permeable and to have low cytotoxicity. This paved the way to intracellular sensing of GSH in living normal HFF and cancerous HeLa cells. Additionally, by combining with logic gate, this assay was successfully applied to visually discriminate changes in the intracellular GSH. The combination of ratiometric fluorometry and peroxidase mimicking can provide a wide range of application in bioanalysis and intracellular imaging.