Establishment Of Electrochemical Aptasensors For Detection Of Organophosphorus Pesticides Residues In Vegetables

The problem of excessive organophosphorus pesticide residues has become one of the major hidden dangers of vegetable safety in China.At present,the main method of pesticide residues detection is instrumental analysis,which has high sensitivity and stability.But most of them have the shortcomings of expensive equipment,high solvent consumption,and inability to meet the on-site detection.Therefore,it is of great practical significance to study the rapid detection method of organophosphorus pesticide residues in vegetables with high efficiency and reliability.Due to the advantages of easy synthesis,easy labeling,and good biostability,aptamer-based sensing technology has been rapidly developed and combined with various analytical techniques?electrochemistry,fluorescence,colorimetry,etc.?.It is widely used in the field of analysis of harmful substances in agricultural products.In this paper,the related research and exploration were carried out for the construction of electrochemical aptamer sensors with high sensitivity,simple preparation process and reusable.It was used to detect four organophosphorus pesticides residues?profenofos,phorate,isocarbophos and omethoate?in vegetables,and laid a foundation for the development of portable rapid detection device for pesticide residues.The main contents are as follows:?1?A novel ultra-sensitive aptamer sensor for the detection of organophosphorus pesticides residues was developed by using ferrocene?Fc?labeled hairpin aptamer as electrochemical signal donor and graphene oxide-chitosan?GO-CS?nanocomposite modified screen printed carbon electrode?SPCE?.In this experiment,the organophosphorus pesticide aptamer was designed as a hairpin structure,which labeled with amino?-NH₂?and Fc as redox signal switch.GO-CS was used to fix the amino aptamer,and its good conductivity also made the electrochemical reaction easier to monitor,thus realizing the sensitive detection of organophosphorus pesticides residues.The electrochemical behaviors of four organophosphorus pesticides on the aptasensor were studied.The minimum detection limit was0.003 nM,and the recoveries of vegetable samples were 79.66%-136.90%.?2?We used a one-step electrodeposition technique to immobilize the organophosphorus pesticide aptamer?Apt?,graphene oxide?GO?and copper nanoparticles?CuNPs?,preparing a stable electrochemical aptasensor.In the preparation of electrodeposition solution,GO was first combined with Apt,and then we introduced CuNPs to improve the conductivity of electrodeposition film.In addition,GO was reduced to reduced graphene oxide?rGO?in electrodeposition process,which provides better electrochemical performance.The morphology and electrochemical characterization of Apt/rGO-CuNPs composite coatings were carried out by scanning electron microscopy and cyclic voltammetry.The linear correlation coefficient between the sensor and the four organophosphorus pesticides ranged from0.928-0.99174,and the recoveries were between 94.99%and 121.3%in the standard addition recovery experiments of several vegetable samples.?3?Self-cleaning SPCE and graphene oxide-ferric oxide?GO-Fe₃O₄?magnetic nanomaterials were prepared and used for the construction of renewable electrochemical aptasensor.In this work,SPCE was modified with polydimethylsiloxane?PDMS?to achieve self-cleaning of the electrode,allowing the sensor to be used multiple times.The prepared GO-Fe₃O₄ magnetic material was combined with Apt to form an organophosphorus pesticide magnetic trap for the capture and enrichment of specific targets.The magnetic trap and the magnetic trap-pesticide complex were immobilized on the surface of the self-cleaning electrode under the action of a magnetic field for electrochemical detection.The experimental results show that the aptasensor could be reused twice.In addition,the difference of current response signal between standard solution and baby cabbage was as low as 0.018?A.