Multi-enzyme activity of three layers FeO @ZnMnFeO @Fe-Mn organogel for colorimetric detection of antioxidants and norfloxacin with smartphone

In this study, the FeOx@ZnMnFeOy@Fe-Mn bimetallic organogel ([email protected]@FM-MOG) with three layers structure was synthesized. It presented outstanding multi-enzyme (peroxidase, oxidase and catalase) activities. The systematical characterization results showed that Zn and Mn on the surface of [email protected]@FM-MOG were nearly disappeared, and thus a large amount of Fe exposed as the active species. Accordingly, the high ratio of Fe2+/Fe3+ for [email protected]@FM-MOG was conductive to the electron transfer and enzyme activity. Moreover, the multiple detection platforms were constructed based on the different nanozyme activities. As for the peroxidase-mimetic activity, citric acid (CA) and norfloxacin (NOR) were monitored continuously on the basis of the turn on–off-on signal change due to the electron transfer abilities and hydroxyl radicals (•OH) formation. The linear range of 0.415–6.21 μM was obtained with a low detection limit of 79 nM, which was rarely detecting citric acid by nanozyme. And the low detection limit of 52 nM for NOR was superior to the most published NOR assays in nanozyme field. Furthermore, an oxidase platform for gallic acid (GA) was also established due to superoxide anions (O2•−) generation. It should be noted that the smartphone detection platforms for CA and NOR were established successfully for on-site analysis. This study provided multifunctional detection platform for valuating CA, NOR and GA in food quality and environment monitoring.