Biomimetic cascade intelligent paper chip sensor based on bimetallic porphyrin-based covalent organic framework with triple-enzyme mimetic activities

Enzyme-induced biological cascade catalysis can achieve selective and efficient transformations of substrates in vivo. Thus, the biomimetic cascade systems have attracted much attention in biological detection on account of their ingenious strategies for signal conduction and amplification. In this study, a porphyrin-based covalent organic framework (COFFe/CoP-Ph) with bimetal-nitrogen-coordinate centers (M − N4) were constructed via Schiff base reaction. The synergistic effect of the highly exposed M − N4 bimetallic active sites and the unique topology overcame the self-limitation of nanozyme, resulting in a significant enhancement of the triple-enzyme mimetic activities of COFFe/CoP-Ph, namely oxidase (OXD)-, peroxidase (POD)-, and catalase (CAT)-like activities. Simultaneously, a multiple enzyme-driven cascade catalysis strategy for signal amplification was proposed utilizing the OXD- and POD-like mimetic mechanisms of COFFe/CoP-Ph, enabling the colorimetric determination of malathion without the addition exogenous H2O2. The established colorimetric sensor exhibited an exceptional linear relationship within the range of 1–18 μM and a low detection limit of 11 nM. Subsequently, a portable smartphone platform was developed by integrating paper chip, facilitating successful malathion point-of-care testing (POCT) in real samples. This work not only creates a bimetallic COF nanozyme and establishes an efficient cascade amplification strategy, but also introduces a novel design approach for development of a low-cost and user-friendly POCT method.