Donor–Acceptor Engineering in Covalent Organic Frameworks Enabling Dual Fluorescence and Nanozyme Activity for On-Site Antibiotic Detection

The integration of distinct functionalities into single covalent organic frameworks (COFs) is highly desirable for advanced sensing, yet remains synthetically challenging. Herein, we address this by designing and synthesizing donor-acceptor COFs (named COF-Z) from tailored triazine and thiophene derivatives. COF-Z simultaneously exhibits strong intrinsic fluorescence and high peroxidase-like nanozyme activity, a dual functionality achieved through its precise π-conjugated and electron-rich porous structure. This unique combination enables the development of a sensitive dual-mode sensor for tetracycline (TC) detection. The sensing mechanism relies on the specific interaction between TC and the COFs, which enhances fluorescence while inhibiting nanozyme activity, thereby producing complementary optical and colorimetric signals. Furthermore, to facilitate practical application, COF-Z is embedded into an electrospun nanofibrous membrane, creating a portable solid-state sensor that allows for on-site visual detection of TC. When coupled with an artificial neural network for automated image analysis, this integrated platform achieves accurate and intelligent TC quantification. This work not only presents a rational design strategy for multifunctional COFs but also demonstrates a smart, device-ready sensing system for environmental antibiotic monitoring.