Mn/Ce Mofs Nanoenzyme-Based Freeze-Dried Bioactive Capsules Integrated Visualization/Electrochemical Dual-Mode Sensor for the Detection of Organophosphorus Pesticide Malathion in Water

Abstract

Pesticide remnants threaten ecosystems and public health. Here, we reported an electrochemical and colorimetric dual-mode method for the determination of organophosphate pesticides malathion based on the color and current changes of 3,3,5,5-tetramethylbenzidine (TMB) solution. Mn/Ce MOFs nanoenzyme with high oxidase activity and acid phosphatase (ACP) were put into a visual capsule by freeze-drying method, and integrated with electrochemical workstation to construct a portable dual-mode biosensor. The acid phosphatase (ACP) reacted with the L-ascorbic acid-2-phosphate trisodium salt (AAP) to form ascorbic acid, which inhibited the activity of Mn/Ce MOFs oxidase, in turn inhibiting the TMB oxidation. In the presence of malathion, Mn/Ce MOFs oxidase activity was inhibited, restoring the oxidase activity and catalyzed the colorless TMB solution to blue oxTMB. Meanwhile, the addition of the terminating reagent H2SO4 oxidized the blue oxTMB to a yellow diimide, and its oxidation current could be obtained by chronoamperometry. The changes of TMB solution color and current of diimide enabled sensitive dual-mode detection of malathion in the concentration range of 1-2,000 nM (R2=0.9987), with the detection limit (3σ/k) was 0.06 nM. Successfully applied to real water samples with 91%-103% recovery, demonstrating potential for rapid malathion detection.

Keywords: Mn/Ce MOFs nanoenzyme, Bioactive capsules, Enzyme-based biosensor, Dual-mode detection, Organophosphate pesticides