Preparation And Application Of Thiamethoxam Molecularly Imprinted Electrochemical Sensor Which Based On Graphene

Now,neonicotinoid pesticides are one of the most widely used pesticides in the world.Thiamethoxazole is a representative compound of neonicotinoid insecticides.Thiamethoxam is the main insecticide for the control of rice suckingpests,it is used in at least 64 countries including China.Rice is the main food product of our country,in order to improve its production through blind,excessive use of thiamethoxam.Thus,the resulting residual problem is more of a concern.Chromatography as a commonly used detection method,with high sensitivity,good specificity.But instruments are expensive,professional personnel,mainly use in the laboratory.It is not suitable for on-site rapid screening of farmland and market.Therefore,it is of great significance to construct a fast,efficient,sensitive,low-cost and easy-to-use in quick inspection technology for thiamethoxam field.In this study,we report a facile method for the preparation of molecularly imprinted polymers based graphene for electrochemical detection of thiamethoxam residues in rice.The main research contents are as follows:(1)Preparation and characterization of graphene-based molecularly imprinted electrochemical sensors(MIPs-GN/GCE)A molecular imprinted electrochemical sensor based on graphene was prepared.Thiamethoxam was used as the template molecule,we chose p-vinylbenzoic acid as functional monomer,it could be immobilized onto graphene surface and form a uniform imprinting layer via ?-? interaction in just one step,effectively simplify the reaction process.The optimal parameters of the molecularly imprinted polymerization system are then optimized.And the molecularly imprinted electrochemical sensors were successfully prepared by using the synthesized molecularly imprinted reaction solution.Chitosan(acetic acid,0.01%)solution was used as a protective film to improve the stability of the sensor.Due to the characteristic of irreversible electrochemical reduction of thiamethoxam,the template can be removed easily by Cyclic Voltammetry scanning,without the need for organic solvent.The characterization of glassy carbon electrode modified by molecularly imprinted polymers which based on graphene(MIPs-GN/GCE)(scanning electron microscopy,atomic force microscopy and electrochemical impedance spectroscopy)showed that the homogeneous molecular imprinted membrane was successfully loaded on the surface of graphene.And the imprinted film is much lower than the molecular imprinted film thickness(17 nm)reported on the graphene surface in the literature,only 2 nm.(2)Adsorption performance and adsorption mechanism of graphene-based molecular imprinted electrochemical sensor(MIPs-GN/GCE).The adsorption performance of the graphene-based molecular imprinted electrochemical sensor was evaluated.The adsorption mechanism was studied by the adsorption thermodynamics model and the adsorption kinetic model.The results showed that MIPs-GN/GCE has a higher specificity to TMX and the binding of thiamethoxam was rapidly balanced.MIPs-GN/GCE has good selectivity for thiamethoxam in the presence of structural analogues,imprinted factor is 2.36.Adsorption thermodynamics model and adsorption kinetic model showed that MIPs-GN/GCE is a uniform,ultra-thin,chemically adsorbed,adsorption combined with faster of molecular imprinted sensitive film.(3)Electrochemical analysis of graphene-based molecular imprinted electrochemical sensors.The results showed that the MIPs-GN/GCE had good detection sensitivity,strong anti-interference ability and good reproducibility and stability.The linear range of MIPs-GN/GCE to thiamethoxam was 0.5 ?mol/L ~ 20 ?mol/L,the detection limit is 0.1?mol/L,the prepared MIPs-GN/GCE sensitivity has improved significantly compared with the literature reported.(4)Determination of graphene-based Molecularly Imprinted Electrochemical Sensors in Rice SamplesFirst,the four rice samples of indica rice,japonica rice,glutinous rice and brown rice were purchased from market,then the pretreatment method was simplified and the spike recovery experiment was carried out.The results showed that the average recoveries of MIPs-GN/GCE for thiamethoxam in indica rice,japonica rice,glutinous rice and brown rice were 80% ~ 94%,81% ~ 91%,85% ~ 92%,88% ~ 94%.There was no significant difference between the proposed sensors and HPLC analysis method.And the satisfactory results were obtained at the minimum added concentration of 5 ?mol/L(equal to 0.001 mg / kg sample weight)to meet the trace amount of pesticide residues analysis.The results indicate the practicability of our method can be used for the determination of thiamethoxam residues in indica rice,japonica rice,glutinous rice and brown rice samples.It also shows that MIPs-GN/GCE has great application prospect in other rice samples.