Hengyan Ma,Mengya Li,Ting Yu,Hui Zhang,Minghua Xiong,Feng Li
In the present study, a magnetic mimic multi-enzyme system was developed by encapsulating the aryloxyphenoxypropionate (AOPP) herbicide hydrolase QpeH and alcohol oxidase (AOx) in zeolitic imidazolate framework (ZIF-8) nanocrystals with magnetic Fe3O4 nanoparticles (MNPs) to detect AOPP herbicides. The structural, protein loading capacity and loading ratio, porosity, and magnetic properties of QpeH/AOx@mZIF-8 were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen sorption, and vibrating sample magnetometry. An AOPP herbicide colorimetric biosensor made with QpeH/AOx@mZIF-8 had the highest sensitivity toward quizalofop-P-ethyl (QpE) with a limit of detection of 8.2 μM. This system was suitable to detect two other AOPP herbicides, including fenoxaprop-P-ethyl (FpE) and haloxyfop-P-methyl (HpE). The practical application of the biosensor was verified through quantitative analysis of QpE residues in industrial wastewater and field soils. Furthermore, QpeH/AOx@mZIF-8 exhibited excellent long-term storage stability (at least 50 days), easy separation by magnet, and reusability (at least 10 cycles), supporting its promising role in simple and low-cost detection of AOPP herbicides in real environmental samples.
Fengping Liu,Aiming Zhong,Qin Xu,Hongen Cao,Xiaoya Hu
The inhibition mechanism of 2,4-dichlorophenoxyacetic acid (2,4-D) to catalase was studied by a catalase biosensor in a flow-injection analysis (FIA) system. This system provides an ideal sensing platform to electrochemically evaluate the chemical mechanism of enzyme inhibition. Hierarchical porous calcium phosphate (hp-CaP), as a biocompatible nanomaterial, was used to immobilize catalase for repeat use. 2,4-D together with H2O2 was injected into the bioreactor of the immobilized catalase-FIA system during the experimental procedure. The activity of the immobilized catalase was inhibited, which caused a decrease of the catalase-catalyzed H2O2 reduction current. Lineweaver–Burk, Dixon, and Cornish–Bowden plots confirmed that the inhibition of catalase by 2,4-D followed an competitive mechanism with a inhibition constant of 4.78 × 10–7 M. Based on this inhibition characters, a biosensor for 2,4-D detection was constructed. This biosensor showed a linear range from 0.03 to 3.00 μM with a detection limit of 0.015 μM. It demonstrated good stability, acceptable reproducibility and low cost for 2,4-D screening. It has been successfully applied for the determination of 2,4-D in commercial bean sprouts samples. It is anticipated that a rapid evaluation of the chemical mechanism of catalase inhibition by the FIA system could pave the way to rationally designing biosensors.
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