A Study On The Detection Method And Instrument For Rapid Monitoring Organophosphorus Pesticides In Vegetables

Organophosphorus pesticides(OPs)play a critical role in agricultures.But,with the use of these pesticides in a long term and in a large volume,OPs residues in food, water and environment are increasing,leading to the contamination and the poisoning of the environment,animals and human bodies.The incidences caused by OPs happen more frequently and more seriously than any other pesticides.Due to the high toxicity of OPs,analyzing and monitoring OPs rapidly,precisely and sensitively become increasingly important and urgent.The detection of OPs residues is a comprehensive and complicated task.Up till now,there are several analytical techniques for the detection of OPs including spectrum analysis,GC/LC chromatography,immunity analysis,chemical luminescence and biosensor etc..This dissertation is focused on the stury of detection method and instrument for rapid monitoring OPs in vegetables. Biochemistry,nanomaterials and sensing technology are combined to establish novel OPs biosensors modified with nano materials.The enzymic reactions and electrochemical characteristics of the biosensors are also discussed;on the other hand,a portable OPs detector is designed and fabricated according to the principle of UV-vis spectrophotometer.The dissertation is divided into four parts:Chapter one:PrefaceFirst of all,basic knowledge of pesticide is introduced including the use and production of pesticide in our country,the sorts of pesticide,the harm caused by pesticide residues etc..Then,the analytical techniques for OPs detection are presented especially the application of biosensor technology which is revolutionized by the nanotechnology.Finally,the work and significance of this dissertation are brought forward.Chapter two:Au-doped Fe₃O₄ Nanoparticles Immobilized Acetylcholinesterase Sensor for the Detection of Organophosphorus Pesticides Au-doped magnetic Fe₃O₄ nanoparticles were synthesized and used for fabrication of acetylcholinesterase(ACHE)immobilized electrochemical sensor for the detection of organophosphorus pesticides(OPs),such as dichlorvos.The degree of inhibition of the AChE enzyme by OPs compounds was investigated by measuring the electrooxidation current of the thiocholine generated by the AChE catalyzed hydrolysis of acetylthiocholine(ATCh).The Au-Fe₃O₄ modified electrode showed significant stabilization and sensitivity with the detection limit of 4.0×10^-13 mol/L.A value of 10.3 mmol/L for the apparent Michaelis-Menten constant(K_M^app) was also obtained in this work.Chapter three:Electrochemical sensor based on Au-doped TiO₂ nanoparticles for the direct detection of parathionIn this study,Au-doped TiO₂ nanoparticles(NPs)were synthesized and used for fabrication of electrochemical sensor with Chitosan as a conjunct.The sensor exhibits excellent electrocatelytic activities for the detection of parathion,which is one of the nitroaromatic organophosphorus pestcides.The electrochemical characterization and cathodal stripping voltammetric performance of parathion were evaluated using Cyclic Voltammetric(CV)and Differential Pulse Voltammetric(DPV).Experimental parameters,including the amount of nanoparticles and pH of the electrolyte have been optimized in this work.Under the optimum conditions,electrochemical sensor modified with Au-TiO₂ NPs exhibited promising voltammetric performances.The current response to parathion was highly linear in the range of 1.0 to 7.0×10³ ng/mL,with a detection limit of 0.5 ng/mL(S/N=3).Chapter four:The manufacture of a portable detector for organophosphorus pesticidesA protable detector for the rapid detection of OPs is designed and manufactured based on the inhibition of acetylcholinesterase(AChE).Compared with other existing detectors,this one bears a much smaller size which is convenient to carry.A compensated electrocircuit is introduced to the whole circuitry which excludes the influence of light from outside,improving the stability and accuracy of the detector. When applied to the detection of OPs residues in water and vegetable,the detector shows its reliability in result and simplicity in operation.