Degradable metal-organic framework/methylene blue composites-based homogeneous electrochemical strategy for pesticide assay

Precise screening of organophosphate (OP) and carbamate pesticides is of significant importance for safeguarding the environment and food resources. Herein, a facile immobilization-free homogeneous electrochemical sensing strategy was developed for sensitively detecting pesticides by using acetylcholinesterase (AChE) as a recognition component and zeolitic imidazolate framework-8 (ZIF-8) as a degradable carrier for encapsulating methylene blue (MB, an electroactive molecule). The pH-responsive ZIF-8/MB composites were synthesized by a simple one-pot self-assembly method and then directly used for pesticide detection. The sensing strategy is based on the dissolution of ZIF-8/MB composite in acidic condition induced by the AChE-catalyzed hydrolytic reaction, which then resulted in the release of numerous MB molecules for generating strong diffusion current. Therefore, OPs and carbamates, as AChE inhibitors, would be monitored by the decrease of the electrochemical signals. Benefitting from the large number of MB molecules entrapped in ZIF-8/MB nanoparticles, this sensing platform achieved high analytical performance for the detection of paraoxon with a detection limit of 1.7 ng/mL. Moreover, this strategy was versatile for other OP and carbamate pesticides and worked well in real samples, indicating that the proposed strategy offered an alternative approach for the sensitive assessment of pesticides in the food and environmental fields.