Oxidase mimicking of CuMnO2 nanoflowers and the application in colorimetric detection of ascorbic acid

As a novel artificial enzyme, CuMnO2 nanoflowers (CuMnO2 NFs) were synthesized by a hydrothermal reaction, and the morphology could be obtained by adjusting the temperature and time of reaction. CuMnO2 NFs was a new type of artificial enzyme with oxidase-like properties. Compared with traditional copper-based artificial enzymes, CuMnO2 NFs were simple to prepare and did not require the assistance of other active substances. Due to the large number of active sites on the surface of CuMnO2 NFs and the synergistic reaction of Cu+/Cu2+ and Mn3+/Mn4+ redox couples in CuMnO2 NFs, CuMnO2 NFs could catalyze 3,3´,5,5´-tetramethylbenzidine (TMB, colorless) to oxidized TMB (ox-TMB, blue) without hydrogen peroxide. When ascorbic acid (AA) bound to ox-TMB, ox-TMB (blue) was reduced to TMB (colorless). Based on the oxidase-like ability of CuMnO2 NFs, the reaction system composed of CuMnO2 NFs and TMB had the ability to detect AA content with a large detection range of 1–105 µM and the limit of detection (LOD) was 0.39 µM. This assay could detect the AA concentration in fruit and vegetable juices effectively. The spiked experimental results of TMB-CuMnO2 NFs system showed that the recoveries were between 95.1% and 104.8%, and the RSDs were no more than 2.87%. Comparison with the HPLC method, the TMB-CuMnO2 NFs colorimetric detection method was effective and accurate for the detection of AA in fruit and vegetable juices.