Enhancing the Reactivity of Nanozymes by Asymmetric Structural Oxygen Vacancy Electron Transfer for Colorimetric Sensing and TAC Analysis

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By regulating the electron density of atoms within the reaction active center, the catalytic activity of nanozymes can be precisely controlled, thereby enhancing their reactivity and sensitivity in applications such as colorimetric sensing. In this study, we synthesized metal oxide Fe-MMO ov nanozymes, enriched with doping defects and oxygen vacancy defects, by Fe-doped LDH with an ultrathin 2D structure through roasting-induced topological transformation. This process tunes the electron density distribution within the active center atoms of the nanozymes through its intrinsic asymmetric Zn-O v -Fe doping structure, resulting in excellent POD-like and OXD-like multienzyme activities. This enhancement contributes to the overall effectiveness of nanozymes in applications such as colorimetry. These improvements facilitated its successful application in the total antioxidant capacity (TAC) detection of various fruit juices and commercial beverages. Density functional theory (DFT) calculations revealed that the d-band center of the Fe active center is enhanced by the O v microenvironment within the Fe-MMO ov nanozyme, leading to improved catalytic activity. Based on this, a Fe-MMO ov /TMB visual colorimetric system was established and successfully validated for colorimetric detection of analytes such as ascorbic acid, cysteine, and glutathione. It was further integrated with a mobile platform for on-site TAC detection in food samples. This study introduces an approach for nanozyme design in colorimetric sensing while also presenting a rapid, cost-effective, and dependable strategy for the miniaturization, convenience, and widespread applicability of TAC detection. We demonstrate how the introduction of oxygen vacancies into Fe-MMO ov nanozymes enhances their catalytic activity, paving the way for the development of more efficient catalysts in colorimetric detection.

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