Ratiometric sensing of α-glucosidase and its inhibitor based on MnO2 nanosheets promoted in-situ fluorescent reactions

Determination of alpha-glucosidase (alpha-Glu) activity and screening its inhibitors have great significance in disease diagnosis and biomedical research. In contrast to the flourishing development in fluorescent alpha-Glu assays, very few fluorescent ratiometric methods have been designed, especially the simplified one with two in-situ formed fluorescent signals derived from the same precursor. In this work, we have demonstrated that bovine serum albumin (BSA) templated MnO2 nanosheets (NSs) are robust oxidase mimics and oxidants that can switch o- phenylenediamine (OPD)-based fluorescent reactions in presence of ascorbic acid (AA). MnO2 NSs exert oxidase-like effects to simulate the oxidation of non-fluorescent OPD to orange fluorescent 2,3-diaminophenol (DAP) with fluorescence emission at 565 nm. In the presence of AA, MnO2 NSs as oxidants can effectively promote the dehydrogenation of AA and thus facilitate the fluorescent reaction between AA and OPD to generates fluorescent probe with emission at 425 nm. At the same time, generation of DAP is hindered due to OPD consuming and MnO2 NSs decomposition. AA-induced reversed fluorescence response at 425 and 565 nm lays the foundation for fluorescent ratiometric detection of alpha-Glu by using 2-O-alpha-D-glucopyranose-L-ascorbic acid (AAG) as substrate. This alpha-Glu assay features with the merits of strong anti-interference ability, easy operation and time-saving, and can be further used for inhibitor screening and inhibition efficiency evaluation.