Electrochemical Sensor Based On Oxime Group-functionalized Nitrogen-doped Graphene Composites For Determination Organophosphorus Pesticides

Organophosphorus pesticides?OPs?are widely used to eradicate insect pests and increase agricultural production.However,OPs trigger off an unacceptable threat on the environment and human health because of their ability to irreversibly inhibit acetylcholinesterase?AChE?.So,accurate,sensitive and selective detection methods should be developed to screen OP residues.OPs have been identified and quantified through traditional analytical methods based on gas chromatography?GC?,mass spectrometry?MS?,they exhibit disadvantages such as expensive instruments,time-consuming and complicated pretreatments,and on-field monitoring requirement,which limit their applications for rapid analyses under urgent conditions.Thus,sensitive,rapid,and simple sensors should be developed to detect OPs.Electrochemical analytical systems have been widely used in analytical science and have been considered as promising tools because of their high sensitivity,low cost,and portability.For example,enzymes and antibodies are frequently modified on electrodes for OPs identification,and this approach exhibits high sensitivity and specificity.However,the use of enzymes and antibodies is also limited by various factors,such as high temperature,acidic conditions,or organic solvents.To detect OPs in various media effectively,researchers employed the electrochemical redox of analytes in the field of trace sensing including methyl parathion,paraoxon,and fenitrothion.However,the use of this approach has been limited to the detection of OPs without intrinsic redox activity.Therefore,the application of electrochemical methods to other OPs without electrochemical redox activity,such as fenthion,dimethoate and so on,should be investigated.Some approaches for OPs assay based on oxime compounds have aroused much interest recently.Oximes are employed as antidotes against OP poison.As a super nucleophilic group,oxime serves as a reactivating agent of OP-inhibited AChE because of the excellent reactivity between oximes and OPs.Considering these features,researchers developed a series of oxime-based sensors to detect OPs.Most of these sensors are based on spectral change.Surprisingly,oxime-based electrochemical detection methods have been rarely explored,despite of their excellent properties,such as high sensitivity,simplicity,and low costs.Hence,effective oxime-based electrochemical sensor systems should be established.First of all,nitrogen-doped graphene is introduced to the surface area of a GCE to enhance electrical conductivity and to provide a substrate for AuNPs.After that,three kinds of nanoparticles with different morphologies were designed and synthesized,including MNO/Au/Ag?MNO/AuNPs and MNO/AuNPs/Co₃O₄ nanoparticles.After mixed with nitrogen-doped graphene,MNO/Au/Ag/NG,MNO/AuNPs/NG and MNO/AuNPs/ Co₃O₄/ NG composites were prepared.Secondly,the above suspension of synthesis of composites were dropped onto the surface of GCE.Afterwards,NG/Au NPs was immersed in an ethanol solution containing 0.1 mM of MNO for 2 min forming GCE.And then air dried.After dried,the electrodes were immersed into the MNO solution to prepare the MNO/Au/Ag/NG/GCE,MNO/AuNPs/NG/GCE and MNO/AuNPs/Co₃O₄/NG/GCE electrochemical sensors.Finally,It's found that the nitrogen-doped graphene/metal nanoparticles functionalized with MNO have a best electrochemical signal.Besides,each of the single-factor variables were studied by differential pulse method?DPV?such as adsorption time;the pH value;the amount of composites modified electrodes;the selective of different pesticides;anti-interference and other studies.Furthermore,MNO/AuNPs/Co₃O₄/NG/GCE electrochemical sensor exhibited a shortest preconcentration time,a best stability,a lowest LOD and a most excellent interference property.In a word,the dimethoate electrochemical sensors have been successfully constructed to realize the trace detection of dimethoate,which are greatly worth of application and promotion.