A label-free fluorescence turn-on assay for glutathione detection by using MnO2 nanosheets assisted aggregation-induced emission-silica nanospheres

Glutathione (GSH) serves several vital biological functions and its abnormal levels are associated with many diseases. Simple and sensitive methods capable of detecting GSH are desired for better understanding the mechanism of diseases. In this work, a label-free MnO2 nanosheets assisted aggregation-induced emission (ME)-silica nanospheres (SiO2 NPs) nanoprobe for fluorescent turn-on detection of GSH with high sensitivity was reported for the first time. The anionic tetraphenylethylene derivative 3 (TPE3) was synthesized and employed as the ME-active probe, which can be aggregated on the uncoated amino-functionalived SiO2 NPs to form AIE-SiO2 NPs and emitted strong fluorescence. Negatively charged MnO2 nanosheets were employed as both positive charge protectors for amino-functionalized SiO2 NPs and recognition units for GSH. The presence of GSH could selectively reduce MnO2 nanosheets to Mn2+, thus releasing the amino-functionalized SiO2 NPs and exposure its positive charges. Accordingly, the TPE3 could be aggregated on the exposured amino-functionalized SiO2 NPs to form AIE-SiO2 NPs and emitted strong fluorescence. The proposed assay is simple, fast, low cost, and highly sensitive with a detection limit of 200 nM for GSH. The assay was further applied in human serum samples for the detection of GSH with satisfactory results, demonstrating its promising application in practical biological samples.