A Novel Paper-Based Electrochemical Biosensor Based on N,O-Rich Covalent Organic Frameworks for Carbaryl Detection

A new N,O-rich covalent organic framework (COF(DHNDA-BTH)) was synthesized by an amine-aldehyde condensation reaction between 2,6-dialdehyde-1,5-dihydroxynaphthalene (DHNDA) and 1,3,5-phenyltriformylhydrazine (BTH) for carbaryl detection. The free NH, OH, and C=O groups of COF(DHNDA-BTH) not only covalently couples with acetylcholinesterase (AChE) into the pores of COF(DHNDA-BTH), but also greatly improves the catalytic activity of AChE in the constrained environment of COF(DHNDA-BTH)’s pore. Under the catalysis of AChE, the acetylthiocholine (ATCl) was decomposed into positively charged thiocholine (TCl), which was captured on the COF(DHNDA-BTH) modified electrode. The positive charges of TCl can attract anionic probe [Fe(CN)(6)](3−/4−) on the COF(DHNDA-BTH)-modified electrode to show a good oxidation peak at 0.25 V (versus a saturated calomel electrode). The carbaryl detection can inhibit the activity of AChE, resulting in the decrease in the oxidation peak. Therefore, a turn-off electrochemical carbaryl biosensor based on a flexible carbon paper electrode loaded with COF(DHNDA-BTH) and AChE was constructed using the oxidation peak of an anionic probe [Fe(CN)(6)](3−/4−) as the detection signal. The detection limit was 0.16 μM (S/N = 3), and the linear range was 0.48~35.0 μM. The sensor has good selectivity, repeatability, and stability, and has a good application prospect in pesticide detection.