Effective Peroxidase-Like Activity of Co-Aminoclay [CoAC] and Its Application for Glucose Detection

In this study, we describe a novel peroxidase-like activity of Co-aminoclay [CoAC] present at pH ~5.0 and its application to fluorescent biosensor for the determination of H₂O₂ and glucose. It is synthesized with aminoclays (ACs) entrapping cationic metals such as Fe, Cu, Al, Co., Ce, Ni, Mn, and Zn to find enzyme mimicking ACs by sol-gel ambient conditions. Through the screening of catalytic activities by the typical colorimetric reaction employing 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)diammonium salt (ABTS) as a substrate with or without H₂O₂, Fe, Cu, and CoACs are found to exhibit peroxidase-like activity, as well as oxidase-like activity was observed from Ce and MnACs. Among them, CoAC shows exceptionally high peroxidase-like activity, presumably due to its ability to induce electron transfer between substrates and H₂O₂. CoAC is then used to catalyze the oxidation of Amplex^® UltraRed (AUR) into a fluorescent end product, which enables a sensitive fluorescent detection of H₂O₂. Moreover, a highly sensitive and selective glucose biosensing strategy is developed, based on enzyme cascade reaction between glucose oxidase (GOx) and CoAC. Using this strategy, a highly linear fluorescence enhancement is verified when the concentration of glucose is increased in a wide range from 10 μM to 1 mM with a lower detection limit of 5 μM. The practical diagnostic capability of the assay system is also verified by its use to detect glucose in human blood serum. Based on these results, it is anticipated that CoAC can serve as potent peroxidase mimetics for the detection of clinically important target molecules.