A Study On A Ratio-based Electrochemical Sensor For Organophosphorus Pesticides Determination In Fruits And Vegetables

As important agricultural products,garden stuff plays a positive role in developing the economy and increasing income.However,pesticide residues in agricultural products have seriously restricted the garden stuff industry.Therefore,it is very important to establish the detection method of agricultural residues in garden stuff.Electrochemical sensors have shown broad application prospects in the field of pesticide residue detection due to their advantages of low cost,accuracy,and rapid response.This study is based on ratiometric to construct electrochemical sensor,and focuses on immunoassay technology,electric-field driven devices,and molecular imprinting technology to achieve specific detection of common organophosphorus pesticides in fruits and vegetables,including chlorpyrifos,methyl parathion,and glyphosate.Specific content is developed in the following three parts:（1）Ratiometric electrochemical sensor with DNA tetrahedron nanostructure as high-performance carrier of reference signal and its applications in phoxim determination for vegetablesA ratiometric electrochemical sensor,based on DNA tetrahedron nanostructure（DTNS）,is designed for vegetable phoxim（PHO）detection.DTNS spontaneously adheres onto gold-nanoparticle-modified electrode and forms stable three-dimensional structure,providing plenty of binding sites to the built-in reference,methylene blue（MB）.Monoclonal antibody（m-Ab）is vertically linked onto DTNS vertex,selectively responses antigenic PHO,and promotes the target signal of I_PHO.Thus,the target signal(I_PHO)and the reference signal(I_MB)sensibly established a ratiometric indicator I_PHO/I_MB.Ratiometric signal presents better performance than solo system in repeatability and long-time stability.As-fabricated sensor presents wide dynamic range as 0.1～30 ng/m L,and limit of detection is well-defined as 0.003 ng/m L.Finally,this method is verified with real-vegetable-sample,certified HPLC and recovery test,with a relative error of less than 5.13%.（2）Programmable dual-electric-field immunosensor using MXene-Au-based competitive signal probe for natural parathion-methyl detectionA dual-electric-field parathion-methyl（PTM）immunosensor on highly-compatible screen-printed electrode is presented.MXene-Au is the product of in-situ gold nanoparticle growth on MXene,provides considerable binding sites for PTM antigen（ATG）and methylene blue（MB）.During sensing,MXene-Au-MB-ATG probe competitively binds PTM antibody,composing a ratiometric immune-system.With DC-biased sine excitations from complementary waveforms,on-chip electric field couple improves immunoreactions among PTM,probe,and antibody.Electric field distribution is programmed by trimming bypass resistors to pursue optimal performance.This method brings less consumption of immune time,and simultaneously provides more powerful ratiometric signal than the rivals.Log-linear relationship,between PTM level and sensor readout,is established in 0.02～38 ng/m L,and limit of detection is found as 0.01 ng/m L.This method is applied in laboratorial and natural PTM analyses,and the readouts are consistent with HPLC,the relative error is approximately 4.0～6.1%（2）An indirect ratiometric molecular imprinting electrochemical sensor based on metal ion reoxidation for glyphosate detection in fruitA low-cost and highly sensitive molecular imprinting（MIP）electrochemical sensor is proposed for the indirect detection of glyphosate（GLY）in fruit.MIP/MWCTNS-Au/GCE is formed by modifying carbon nanotubes（MWCTNs）and gold nanoparticles（Au NPs）on glassy carbon electrode surface,and imprinting MIP with reference signal（MB）and template molecule GLY.GLY can be coordinated with metal ions to form a complex,and the metal ions can be enriched and reoxidized by differential pulse voltammetry.At this time,metal ions can be used as the signal probe of MIP,and the ratio signal I_Cu/I_MB is recognized as the index for the quantitative determination of GLY.Under optimal conditions,the sensor presents a high sensitivity to GLY in the range of 1.23～400 ng/m L,and the detection limit is 0.24 ng/m L.The sensor performs well in selectivity and long-term stability exploration,and is finally used to detect GLY in real fruit samples.The reading of the sensor is consistent with HPLC,with a relative error of 3.4%to 6.7%.The ratiometric electrochemical sensor designed and developed in this study has been successfully used for the detection of organophosphorus pesticides in fruits and vegetables,which has reference significance for the subsequent detection research of pesticide residues in food and agricultural products.