The Fabricaiton Of Electrochemical Sensors Based On Functional Graphene And Detection Of Organophosphorus Pesticides Residue

Pesticide has been playing an important role in agricultural productivity due totheir effective use in protecting agricultural crops from diseases. However, theircontamination existed in food, water and soil poses a serious risk to environment andhuman health. As one class of the most widely used pesticides, organophosphoruspesticides can inhibit the catalytic active sites of acetylcholinesterase （AChE） in thecentral and peripheral nervous-system, which leads to serious diseases and even todeath. Thus, it is considerably crucial and necessary to develop effective, sensitiveand practical analytical methods for the detection of organophosphorus pesticides.Due to the advantages of simple equipment, fast response, high sensitivity,instrument miniaturization and low cost, electrochemical biosensors have been widelyapplied in rapid online monitoring of organophosphorus pesticides. To achieve goodanalysis, improvements on the performance of the sensors have mainly focused on themodified materials. The properties of nanomaterials including excellent surface effect,small-size effect, good biocompatibility and high chemical activity make it promise ingreat improving the sensitivity, selectivity and response of the sensors. Therefore,three different electrochemical sensors were constructed based on new nanomaterialsfor the determination of organophosphorus pesticides and the main contents areoutlined as follows:（1） A novel poly（malachite green）/graphene nanosheets-nafion （PMG/GNs-NF）composite film-modi-fied glassy carbon electrode was developed to indirectly detectmethyl parathion （MP）. p-nitrophenol, the alkaline hydrolysis product of MP, wassuccessfully determined at a relatively lower potential using this modified electrodedue to the excellent electrocatalytic activity of PMG/GNs-NF composite film. Cyclicvoltammetry （CV）, linear sweep voltammetry （LSV） and chronoamperometry （CA）,were employed to investigate the electrochemical behaviors of p-nitrophenol on themodified electrodes. The presence of GNs in the composite film enhanced thestability of PMG and increased the electron transfer rate. The kinetic parameters ofmodified electrodes were studied. What is more, the optimum experimentalparameters affecting response were selected in terms of pH, accumulation potential,accumulation time, scanning cycles during polymerization of malachite green, andalkaline hydrolysis conditions. Under optimum conditions, the chronoamperometricresponse current was proportional to MP concentration over the range from0.02to 1.5l mol/L with a low-detection limit of2.0nmol/L. Finally, the sensor was appliedfor the determination of MP in real samples, and the results were satisfactory withrecoveries from97.20to104.53%.（2） A new nonenzymatic electrochemical sensor was developed for sensitivedetection of methyl parathion based on graphene nanosheets（GNs）/gadoliniumPrussian blue analogue （gadolinium hexacyanoferrate, GdHCF） modified glassycarbon electrode by a two-step electrochemical deposition method. Electrochemicalimpedance spectroscopy （EIS） was employed to characterize the modified electrodes.Cyclic voltammetry （CV） and differential pulse voltammograms （DPV） wereemployed to investigate the electrochemical behaviors of methyl parathion on themodified electrodes. Benefited from the synergistic effect of GNs and GdHCF, thesensor showed good electrocatalytic and adsorptive ability to methyl parathion. Underoptimum conditions, the reduction current was proportional to methyl parathionconcentration in the range of0.008to10mol/L with a detection limit of1nmol/L.The sensor displayed high sensitivity, acceptable stability and selectivity, and realizedthe reliable quantification of methyl parathion in practical environment samples.（3） A novel electrochemical immunosensor for highly sensitive detection ofchlorpyrifos was developed. The high sensitivity was achieved by triple signalamplification strategy. Firstly, toluidine blue and PAMAM functionalized graphene（Tb-GNs-PAMAM） used for the immunosensor platform not only enhanced theelectron transfer property but also loaded a large amount of chlorpyrifos primaryantibodies. Subsequently, the Au shell/Fe₃O₄core nanomaterials （Fe₃O₄@Au） withgood biocompatibility and catalytic property were used to capture plenty of secondaryantibodies and horseradish peroxidase （HRP）. Then, HRP catalyzed the oxidation ofTb in the presence of H₂O₂and the immunosensor produced an amplifiedelectrocatalytic response by the reduction of enzymatically oxidized Tb. Underoptimum condition, the reduction peak current was proportional to the chlorpyrifosconcentration over the range from0.08to300nmol/L with a low detection limit of0.06nmol/L. The immunosensor realized reliable quantification of chlorpyrifos inpractical environment samples.