Porous surface MnO2 microspheres as oxidase mimetics for colorimetric detection of sulfite

Natural enzymes have been extensively studied and widely used for more than two centuries. The application of natural enzymes is limited due to their instability and high cost. Compared with natural enzymes, inorganic materials have the advantage of easy preparation, low cost and good stability for use as enzyme mimics. In this study, manganese dioxide (MnO2) microspheres with porous surfaces (PS-MnO2) were prepared by a facile one-pot hydrothermal method. The as-prepared PS-MnO2 showed intrinsic oxidase-like activity, it could catalyze the oxidation of typical peroxidase substrates, such as 3,3',5,5'-tetramethylbenzidine (TMB) and o-phenylenediamine, to form colored products by dissolved oxygen in the absence of H2O2. Furthermore, a simple colorimetric method for the detection of sulfite could be established based on the inhibition of sulfite on the TMB-O-2-MnO2 chromogenic system.