Eu(III)-functionalized iCOF hybrids by “tandem post-synthetic modifications” for fluorescent detection of folic acid and trimethoprim: A logical judgment by combination of neural networks and logic gates

A universal strategy called “tandem post-synthetic modifications” is applied to combine lanthanide ions with cationic covalent organic frameworks by using anionic carboxylate ligand as “molecular bridge”. In the first step, anionic carboxylate ligand is introduced into cationic COFs by ion exchange, which is then coordinated to Eu3+ ions in the second step. Herein, 2,2-biquinoline-4,4-dicarboxylic acid disodium (BCA) is selected to verify the feasibility of this strategy and successfully introduce Eu3+ to EB-TFP, resulting in the hybrid system Eu3+@BCA@EB-TFP. Based on the “turn-off” mechanism, Eu3+@BCA@EB-TFP can be used as a probe for the detection of folic acid (FA) and trimethoprim (TMP). The limits of detection (LOD) for FA and TMP in ethanol solution can reach to 0.142 and 0.139 μM at 282 nm respectively. The fluorescence properties are then explored to uncover the potential of the probe for detection of FA and TMP in serum. Interestingly, FA remains the quenching ability under excitation at 342 nm, while TMP has no response, which provides great convenience in distinguishing between them. In addition, according to the experimental results and through the combination of neural networks and logic gates, a theoretical scenario for determining the tolerance of bacteria to TMP is also presented for reference.