OA nanozyme and HRP, at a concentration of at least 3.77 × 10 -14 M and 0.001mg mL -1 were dissolved in a range of pH buffers (0.1M sodium acetate, pH 2, approximately). After allowing for a maximum incubation period of 3 hours at 37°C, both OA nanozyme and HRP were re-collected via centrifugation (maximum 4000 rpm, 10 minutes) and resuspended in a pH 4 buffer (NaAc, 0.1M) for further colorimetric assay. An ABTS-based colorimetric assay was carried out following the previously described endpoint procedure to determine the relative stability based on the absorbance peak values. Each measurement was replicated three times (N=3).