Self-Cascade of the Cu/Ce-MOF-808 Nanozyme for One-Step Colorimetric Sensing

Natural enzyme cascades, including the same and different kinds of enzymes, have been widely used in biosensing. However, it is still a challenge for nanozymes, the mimics of natural enzymes, to achieve biosensing with different types of enzyme-like activities based on cascade reactions, such as hydrolase and oxidoreductase. Considering the characteristics of the multienzyme-like activity of some nanozymes, as a proof of concept, this study demonstrates a Cu/Ce-MOF-808 nanozyme as a self-cascade catalyst with hydrolase-like and catechol oxidase-like activities. Taking organophosphorus pesticides as an example, we constructed a self-cascade catalytic reaction for the one-step colorimetric detection of isocarbophos. Specifically, the hydrolase-like activity of Cu/Ce-MOF-808 can hydrolyze isocarbophos to produce colorless isopropyl salicylate, which is further oxidized by the catechol oxidase-like activity of Cu/Ce-MOF-808 and complexed with 4-aminoantipyrine (4-AAP) to produce red quinoneimine under neutral conditions with illumination. Thus, a colorimetric strategy for sensitive isocarbophos analysis is developed, with a linear range of 0.90-400.00 μg·mL^-1 and a detection limit of 0.42 μg·mL^-1. This research presents a new approach to the design and synthesis of nanozymes and has great application potential in the field of nanozyme cascade biosensing.