Stabilizer-free MnO2 nanozyme with singlet-oxygen conducted high oxidase-like activity and fast catalysis capability for improving alkaline phosphatase assay

Oxidase (OXD) nanozyme is a type of artificial enzyme that can directly oxidize reducible substrates. By virtue of enzyme catalysis, it is often designed as a sensor for alkaline phosphatase (ALP) assays. MnO2 nanozymes have received extensive attention due to their low cost and ease of preparation. To enhance its sensing capability, further development of MnO2-based OXD nanozyme with higher activity and faster catalysis is necessary. In this study, we synthesized Fe3O4 @polydopamine supported MnO2 (IOPM) nanoparticles, which exhibited excellent OXD activity with a Vmax of 19.67 × 10-8 M·s-1 and a catalysis balance period of less than 1 min. Further investigation confirms that IOPM's good performance is associated with its stabilizer-free interface, magnetic purification method, and singlet-oxygen-conducted catalysis mechanism. More importantly, IOPM is demonstrated to possess the ability of improving ALP assay, with lower limit of detection (0.045 U/L) and wider linear range (0.05 – 40 U/L). Finally, it is successfully used to evaluate ALP activity in clinical blood samples. This study aims to develop a more efficient MnO2-based OXD nanozyme. It emphasizes the positive impact of magnetic purification and a stabilizer-free interface in enhancing OXD activity and improving the ALP detection capability of the nanozyme.