The LOD was determined from an additional experiment extending from previous serial dilutions (Figure ). The LOD for the OA nanozyme based histamine detection system, capable of differentiation via colorimetric assay, is 21.37 pgmL -1 (practically, at least 25 pgmL -1 ), which implies decent sensing performance compared to the conventional nanozyme-based sensor histamine detection . To prove this system's selective histamine detection capability, other biological and agricultural chemicals were tested in parallel with histamine in the colorimetric assay (Figure ). Some of these biological substances also possess net positively charged molecules (e.g., histidine), or neutral ions, but histamine has a higher affinity with OA nanozyme to inhibit the ABTS oxidation, providing evidence of selective histamine detection. For potential histamine detection in real samples, a mixture of chemical solutions containing up to 7 different bio/agrichemical with high concentrations (at least 1mgmL -1 ) was prepared to test the OA nanozyme's histamine detection capacity in a complex solution (Figure ). According to Figure , it was shown that the OA nanozyme selectively identifies the existence of histamine in the mixture, providing its potential for histamine detection in real-biological/agricultural samples.