shown, the expected catalytic activity is the peroxidase-like (POD) activity, which catalyzes the H2O2 to produce byproduct including H2O and oxidized substrates. To understand its catalytic activity, coloring-substrate dependent colorimetric assay and EPR analysis were conducted (Figure ). ABTS and OPD were used as target coloring substrates for POD activity-dependent colorimetric assay (Figure ) The EPR signal indicated that OA nanozyme selectively consumes H2O2 as the substrate, generating hydroxyl (or hydroxyl-like) radical. Four major peaks (semi-symmetric around 3510 G) were observed with the OA nanozyme+H2O2+DMPO in the magnetic field range between 3450 -3550G (Figure ). The reference group, containing the OA nanozyme and DMPO but H2O2, did not show these four peaks, assuring OA nanozyme's POD activity . A coloring substrate-based colorimetric assay using OA nanozyme was conducted to verify its POD activity (Figure ). Absorbance scanning was performed in the range of wavelength 400-500 nm, providing peak ranges at the λmax of each coloring substrate (e.g., λmax ABTS = 417nm, λmax OPD = 450 nm), demonstrating successful oxidization of those substrates, accelerated by OA nanozyme's POD activity. The control groups, which have neither H2O2(2, orange line) nor the OA nanozyme (3, blue line), did not show significant color change reaching the peak endpoint at the λmax point of the substrates(Figure C, D), indicating OA nanozyme is the only elements to exhibit enzyme-like catalytic activity and it cannot exhibit oxidase-like activity, but POD activity selectively, consistent with previous EPR analysis(Figure , Figure ).