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 pi-conjugated frameworks emitted strong fluorescence originating from the n-pi* 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 pi-pi 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.