The Most Active Oxidase-Mimicking Mn₂ O₃ Nanozyme for Biosensor Signal Generation

Oxidase-mimicking nanozymes are more desirable than peroxidase-mimicking ones since H₂ O₂ can be omitted. However, only a few nanomaterials are known for oxidase-like activities. In this work, we compared the activity of Mn₂ O₃ , Mn₃ O₄ and MnO₂ and found that Mn₂ O₃ had the highest oxidase activity. Interestingly, the activity of Mn₂ O₃ was even inhibited by H₂ O₂ . The oxidase-like activity of Mn₂ O₃ was not much affected by the presence of proteins such as bovine serum albumin (BSA), but the physisorption of antibodies to Mn₂ O₃ was not strong enough to withstand the displacement by BSA. We then treated Mn₂ O₃ with 3-aminopropyltriethoxysilane to graft an amine group, which was used to conjugate antibodies using glutaraldehyde as a crosslinker. A one-step indirect competitive ELISA (icELISA) was developed for the detection of isocarbophos, and an IC₅₀ of 261.7 ng/mL was obtained, comparable with the results of the standard two-step assay using horseradish peroxidase (HRP)-labeled antibodies. This assay has the advantage of significant timesaving for rapid detection of large amounts of samples. This work has discovered a highly efficient oxidase-mimicking nanozyme useful for various nano- and analytical applications.