Ratiometric fluorescence monitoring of α-glucosidase activity based on oxidase-like property of MnO2 nanosheet and its application for inhibitor screening

Abstract In recent years, α-glucosidase (α-Glu) inhibitor has been widely used in clinic for diabetic and HIV therapy. Although different systems have been constructed for sensitive and selective detection of α-Glu and screening its inhibitor, the method based on ratiometric fluorescence for α-glucosidase inhibitor screening remains poorly investigated. Herein, we constructed a new MnO2 nanosheet (NS)-based ratiometric fluorescent sensor for α-glucosidase activity assay and its inhibitor screening. MnO2 NS as an oxidase-mimicking nanomaterial directly oxidized o-phenylenediamine (OPD) into 2,3-diaminophenazine (DAP) which had a strong fluorescence emission at 575 nm, whereas the fluorescence of Ag nanoclusters (NCs) at 450 nm was then quenched by the generated DAP through inner filter effect (IFE). When 2-O-α- d -glucopyranosyl- l -ascorbic acid (AAG) as α-Glu substrate and α-Glu were introduced into the above system, MnO2 NS would be reduced to Mn2+ and lose the oxidase-like property since ascorbic acids (AA) were released with the hydrolysis of AAG by α-Glu. Thus, DAP would not be produced and IFE was stopped accompanying with the fluorescence decrease of DAP and fluorescence increase of AgNCs. A ratiometric fluorescent α-Glu nanosensor was thus developed. The fluorescence intensity ratio of DAP to AgNCs linearly decreased with the increasing of α-Glu concentrations in the range of 0.2–8 U mL−1, and limit of detection was 0.03 U mL−1. This proposed sensing approach was also expanded to α-Glu inhibitor screening and showed excellent applicability. As a typical α-Glu inhibitor, acarbose was investigated with a low detection limit of 10−8 M. The constructed sensor platform was proven to be sensitive and selective as well as simple, label-free and low-cost, making it promising for the accurate diagnosis of relevant disease and discovery of potential drugs.