Detection Of Neonicotinoid Pesticides Based On Molecular Imprinting And Surface-enhanced Raman Spectroscopy

Neonicotinoid insecticides（NEOs）have been widely used in agricultural production because of their high water solubility,high insecticidal activity and broad spectrum.With the extensive use of neonicotinoid pesticides,many ecological and food safety problems have been brought about:these pesticides will disturb the behavior of bees,resulting in bee population collapse;It enters the human body through the environment and food chain and has potential toxicity（reproductive toxicity,genetic toxicity and neurotoxicity）,so it is particularly important to monitor its residues in the environment and agricultural products.Due to the shortcomings of traditional detection methods such as complex,time-consuming and laborious pre-treatment process,this paper aims to develop a rapid and efficient detection method for neonicotinoid pesticides through the preparation of molecularly imprinted polymer with specific recognition effect and SERS technology.The research content of this paper is as follows:（1）Gold nanosol was prepared by sodium citrate reduction method and applied in SERS detection of acetamidine and thiamethloprid solution.The influence of different amounts of sodium citrate on SERS signal intensity of the target was explored,and the signal characteristic peak(629 cm^-1)of acetamidine and thiacloprid was determined.The optimal detection conditions were as follows:the volume ratio of gold nanosol to pesticide was 10:1,and the coagulants of acetamidine and thiacidprid were sodium chloride and calcium chloride（10μL,1 mol/L）,respectively.Under these conditions,five concentrations of solution were used for detection.The results showed that the R² of acetamidine and thiacloprid were 0.9978 and 0.9999,respectively,in the range of 0.5～10μg/g,which proved the application potential of SERS technology in the rapid detection of neonicotinoid pesticides.（2）A precipitation-polymerization method was used to prepare molecular imprinted polymers（MIPs）with acetamidine as template molecule,MAA as functional monomer,EGDMA as crosslinking agent and acetonitrile as pore-causing agent.MIP-SERS method was established for detection of acetamidine and thiamethloprid in environmental water samples and agricultural products.The microstructure of MIPs was characterized by SEM and FT-IR,and it was proved that the MIPS were synthesized successfully.The MIPS were uniform spherical with rough surface and obvious fold.The adsorption performance of MIPs was evaluated by dynamic and static tests.The adsorption rate of MIPs was fast and the adsorption performance was good（up to 108.89 mg/g）.MIPs was used as solid phase extractant to optimize the adsorption and desorption conditions of solid phase extraction.The optimal conditions were determined（water sample:30 mg material,40 m L loading sample,water eluent,2 m L methanol eluent;Fruit:30 mg material,1 m L loading,loading solvent was water,p H of solution was 5,eluent was 1 m L 10%methanol aqueous solution,2 m L methanol elution）.Combining MIPs and SERS,a MIP-SERS method was established for the detection of acetamidine and thiacloprid in environmental water samples and agricultural products（pear and peach）.By adding three different concentrations（50,80 and 100 ng/m L for water and 1,2 and 4μg/g for fruit）to agricultural products,the recoveries were 63.8%～101.4%and RSDs were1.3%～6.7%.Furthermore,HPLC-UV confirmation method was used to detect acetamidine and thiacloprid in the same samples,which proved that the established MIP-SERS method had the advantages of high accuracy and good reproducibility.This study proved that the prepared MIPs had a highly specific recognition ability,and the established MIP-SERS method provided a reference for the detection of trace acetamidine and thiacloprid residues in complex substrates.（3）Magnetic nanoparticles（Fe₃O₄）were prepared by co-precipitation method,and the surface was modified by vinyl modification.On this basis,magnetic molecular-imprinted polymers（MMIPs）were prepared by surface imprinting technology.SEM and TEM characterization showed that MMIPs showed a typical core-shell microsphere structure with rough surface.Compared with magnetic nanoparticles（diameter of 60 nm）,the diameter of magnetic imprinted polymer was significantly larger（about 700 nm）.The chemical composition and magnetic strength of the material were investigated by FT-IR and VSM,which showed that the magnetic imprinted material was successfully synthesized and had excellent magnetic strength and separation effect.The adsorption performance of MMIPs was evaluated by dynamic and static adsorption tests.The results showed that MMIPs had specific adsorption capacity of neonicotinoid pesticide,and the maximum adsorption capacity reached 33.35 mg/g.Using MMIPs as magnetic solid phase extraction agent,under the optimal conditions（8 m L sample matrix,60 mg adsorption material,loading solvent as water,solution p H 5,eluent as 1 m L 10%methanol aqueous solution,1 m L acetonitrile solution as vortex elution twice,oscillating adsorption for 1 min）,A method of MMIP-SERS for enrichment and detection of acetamidine and thiacloprid in agricultural products was established.The recoveries were 73.5%～108.2%and RSDs were 0.4%～7.0%when three different concentrations（1,2 and 4μg/g）were added to pears and peaches.Through the accuracy of HPLC-UV verification method,it was proved that the established MMIP-SERS method had the advantages of simple operation and good reproducibility,which provided a new detection technology for the rapid enrichment and detection of acetamidine and thiacloprid in complex substrates of agricultural products.