The active sites of the OA nanozymes are located within the nanozyme framework. Once covered with histamine due to electrostatic bonding, the possibility of these sites encountering the designated substrates decreases, which reduces the substrate amount per active site for enzymelike catalytic activity. Thus, it will reduce the H2O2-dependent catalyzing activity, resulting in a reduced generation of byproducts that contributes to ABTS oxidization, leading to a decrease in absorbance signal. The interference at the active site is relatively correlated to the initial histamine concentration; thus, these mechanisms are applied for OA-nanozyme based, histamine detection.