Manganese oxide functionalized silk fibers for enzyme mimic application

Abstract

The inorganic metal or metal-oxide nanoparticles (NPs) that mimic enzymes are of great interest due to improved physical and chemical properties compared with native enzymes. Here, we report that manganese dioxide (MnO2)-Silk exhibit catalase, oxidase, and peroxidase-like activities. The MnO2-Silk hybrid fibers effectively decomposed hydrogen peroxide (H2O2) and oxidized the typical horseradish peroxidase substrates, such as o-phenylenediamine (OPD), and 3,3′,5,5′- tetramethylbenzidine (TMB) in the presence or absence of H2O2. The oxidative properties of MnO2-Silk fiber hybrid showed an enzyme-like behavior for the catalase-like activity, oxidase-like activity, and peroxidase-like activity. The operational stability of the MnO2-Silk fiber hybrid over ten cycles showed a constant residual activity of about 25–30% after 2–3 cycles indicating that MnO2-Silk fiber hybrid could be used as a satisfactory oxidoreductase enzyme mimics. Potentiometric titration was used to determine the surface charges of the MnO2-Silk catalyst. Together, we identified the reactive species as Mn1−x4+Mnx3+O2−x(OH)x with a pK of approximately 5.2. Our results have implications on the understanding of the catalytic origin and interaction of metal oxides NP with various biomaterials.