Research On Novel Electrochemical Sonsors For Neonicotinoid Insectide Detection Based On Functionalized Graphene

Food safety is a major problem of the human's livelihood,and the chemical pesticide pollutant is the main source of food safety problem.Neonicotinoid insecticides have been widely used in modern agricultural production to result in serious residue issues.It threatens human's health and caused a great political and economic loss.Accordingly,rapid,accurate,sensitive and cost-efficient detection technologies should be proposed.Electrochemical sensor has become the most potential proposal because of the advantages including simple operation,high integration and low lost.With the fast development of supermolecular recognition,molecularly imprinted technique,and three-dimentional materials,their combination with graphene to improve the sensentivity and selective of neonictinoid pesticide detection becomes the important research directi on of residue determination and huge challenges to anlysis researchers.B ased on this purpose,the main research contents have been accomplished as following:Simple wet synthetic route was used to synthesize?-CD-r GO.Strong oxidant was used to deal with graphite,providing the rich oxygen containing functional groups(e.g.epoxy group,hydroxyl and carbonyl)to make graphene oxide dissolve in water.Compared with the bare glassy carbon electrode(GCE),the reduction peak currents of paichongding(IPP)on the r GO modified GCE(r GO/GCE)and the ?-CD-rGO/GCE were increased.The experimental conditions influencing the voltammetric determination of thiamethoxam,such as the amount of ?-CD-r GO,temperature and accumulation time,were optimized.We also discussed the reduction mechanism and binding affinity of this material.To characterize?-CDr GO composite,UV spectrum,infrared spectroscopic spectra,atomic force microscopy,scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were carried out.In conclusion,?-CD-rGO was prepared to highly improve the peak current of IPP,besides,incubation of the proposed electrode at low temperature could further improve the signal.Molecularly imprinted polymers(MIPs)films loaded on graphene provi de recognition function and high electrocatalytic activity,which could be applied to improve the selectivity and sensitivity of neonictinoid insecticides detection.Vinyl benzoic acid(VBA,which provides recognition group to interact with template molecule and alkenyl units to connect cross linking agent)was applied to form uniform molecular imprinting(MIPs)film on the surface of graphene.Then electrochemical methods in blank PBS was applied to elute template molecules.The imprinting factor of imidacloprid(IDP)on the proposed GN/MIPs/GCE is 2.3,which is much higher than other neonictinoid insecticides,indicating good specificity.In conclusion,surface molecularly imprinted polymer films on graphene using VBA as functional monomer could improve the selectivity and stability of IDP detection.Oligochitosanmodified three dimentional graphene was synthesized using water thermal method.Firstly,the important factors effecting three dimentional graphenewere studied,including ultrasonic frequency,ultras onic time and size of graphene oxide.Secondly,positive charged oligosaccharides were applied to interact with negative charged graphene to make graphene layersassembled regularly and form porous structure.Aerogel OCS-GF was formed by freeze-drying of hydrogel OCS-GF.Compared with unmodified GF,the cyclic voltammetry(CV)curves of OCS-GF in PBS were much more continuous and smooth,andthe peak current of IDP on OCS-GF was increased significantly,showing that OCS-GF has strong adsorption ability and continuous electron transfer properties to IDP,which is an ideal sensor electrode.The three proposed electrodes,including?-CD-r GO/GCE,GN/MIPs/GCE,and OCS-GF,were used as the working electrode to apply into real samples detection.?-CD-rGO/GCEwas available in five kinds of neonictinoid detection,with the Limit of Detection(LOD)between 0.10 and 0.11 ?M.GN/MIPs/GCEwas proved to not only improve the selectivity of IDP,but also the sensitivity of IDP,with LOD of 0.10 ?M.OCS-GF widened the limit of linear range from 0.5~15?M to 1.0~50.0?M.All of the linear relationship of standard curve is good and the correlation coefficients reach 0.99 and above.Based on individual characteristic of neonictinoid insecticides,effective pretreatment were established to detect residuals in brown rice samples,together with the proposed electrochemical methods.The recoveries were 70% ~ 120%,which are consistent with the testing results of High Performance Liquid Chromatography(HPLC),indicating the feasibility of real samples.