Easy Green Construction of a Universal Sensing Platform Based on Crystalline Polyimide Covalent Organic Frameworks with Sensitive Fluorescence Response to Metal Ions and Antibiotics

It is of great significance to establish a simple method for sensitively detecting metal ions and antibiotics for food safety. Herein, two crystalline polyimide covalent organic frameworks (COFs) were constructed via a green method, in which no organic solvents were used. Results suggested that both COF-1 and COF-2 with π-conjugated frameworks emitted strong fluorescence originating from the n−π* transition in N,N-dimethylformamide and the alkaline aqueous solution. More interestingly, both COF-1 and COF-2 showed excellent sensing performance for various metal ions and typical antibiotics. Taking COF-1 as the specific research object, the as-synthesized COF-1 exhibited noticeable turn-off fluorescence behaviors for 10 metal ions and 2 antibiotics. A high linear correlation coefficient, a wide linear range, and a low detection limit were achieved in real samples. The aggregation effect and π–π reaction were the possible fluorescence quenching mechanisms. In short, this work provides insights into the synthesis and application of fluorescent sensors based on COFs in food detection fields.