Dual-Emission COF-Based Platforms for Ratiometric Fluorescence Detection of Contaminants in Food Matrices: Mechanisms and Applications

Covalent organic frameworks (COFs), characterized by their high specific surface area, admirable stability, and tunable pore structures, offer ideal platforms for ratiometric fluorescence sensing systems. By measuring the intensity ratio between two emission signals, these sensors inherently provide built-in self-calibration capabilities. This approach addresses the limitations of single-signal probes, which are vulnerable to environmental interferences, thereby enhancing the reliability, sensitivity, and selectivity of contaminant detection in complex food matrices. This review systematically examines the design strategies employed in the progress of dual-emission COF-based ratiometric sensors for food safety applications. These strategies include intrinsic doping-induced dual emission, backbone dual emission, and heterostructure- or hybrid-induced dual emission mechanisms. For each approach, the associated advantages, limitations, and potential directions for future research are critically analyzed. Common structural challenges and their corresponding mitigation strategies are thoroughly explored to enhance the efficiency and reliability of these sensors. Furthermore, the application of these materials in detecting a wide range of food contaminants, such as pesticide residues, heavy metal ions, illegal additives, and antibiotics, is reviewed with emphasis on selectivity, sensitivity, and real-sample analysis. Relevant sensing principles, like excited-state intramolecular proton transfer (ESIPT) and Förster resonance energy transfer (FRET), as well as the interconnections among construction approaches, response modes, and detection procedures, have been discussed. Finally, future perspectives and current challenges are outlined to guide the rational design of advanced COF-based ratiometric sensors for ensuring food safety and public health.