Electrochemical Sensing Of Exogenous Plant Hormones On Electrochemical Exfoliation Graphene-Based Nanocomposite Material Modified Electrode

Exogenous plant hormone plays an important role in regulation of yield and quality of crops.However,the use of no standard will pose threats to the environment and human health.So,the development of sensitive and reliable analytical methods for determination of exogenous plant hormone is necessary.Electroanalysis methods have been used for exogenous plant hormone quantification in that they exhibit protability and simple operation.Due to the huge specific surface area,graphene acts as an excellent 2D support material for metals,metal oxides and other materials.The combination of different materials could produce improved electrical,chemical and optical properties.In this work,three kinds convenient and simple electrochemical sensors with selectivity and good stability were constructed based on the exfoliation graphene,Ce O₂nanocubics and Ce O₂@Au nanoparticles as modified electrode materials.The electrochemical sensors achieved sensitive detection of kinetin(KT),4-bromophenoxyacetic acid(4-BPA),and 1-Naphthaleneacetic acid(NAA).The specific research content includes the following aspects:(1)Highly Sensitive Detection of Kinetin with Electrochemical Exfoliation of Graphene NanosheetsIn this work,graphene nanosheets(e Gr)were exfoliated in ammonium sulfate electrolyte with graphite sheets as anodes.Newly designed nanosheets-like e Gr electrode possessed large specific surface area,low defect and good electrical conductivity,which facilitates the preconcentration of Kinetin(KT)onto the electrode surface.The e Gr/Ce O₂/GCE sensor was successfully constructed by applying e Gr/Ce O₂suspension coated to the surface of glasssy carbon electrode(GCE).The electrochemical behavior of KT on the bare GCE,e Gr/GCE were investigated by CV.Under the optimized conditions,the signal changes were quantified using square wave voltammetry(SWV).It exhibits a linear range extending from 0.5 to 100?mol/L and the lowest detection limit at 0.15?mol/L.The results showed that after placing the electrode for 15 days,the oxidation peak current of KT did not change much,and common ions and quercetin,rutin,and luteolin did not interfere with the detection of KT.Finally,the recoveries are in the range of 89.6%-117.43%with a relative standard deviation(RSD)<4%(n=3)for KT detection in lettuce.(2)Electrochemical determination of 4-bromophenoxyacetic acid based on e Gr/Ce O₂compositeIn this work,e Gr/Ce O₂nanocomposites were prepared by the ultrasonic and stir mixing of e Gr and Ce O₂nanoparticles(1:1 wt.),and the e Gr/Ce O₂/GCE was prepared by dropping e Gr/Ce O₂suspension to the surface of GCE.The study also investigated the effects of parameters such as coating amount of the composite,p H,supporting electrolyte and the ration of e Gr and Ce O₂.Under the optimization of the parameters,the developed e Gr/Ce O₂sensor has a good linearity in the range from 0.3?mol/L to 150?mol/L and the lowest detection limit is 0.06?mol/L.The 4-BPA oxidation on e Gr/Ce O₂electrode is a diffusion-controlled process,which involves a total of 2 e^-in the transferring processes.Finally,some common substances such as fenitrothion,imidacloprid,clothianidin will not significant interfering.It was employed to detect4-BPA in apple samples,with recoveries ranging from 90%-108%.(3)Voltammetric Analysis of Naphthalene Acetic Acid by Pencil Lead-Exfoliated Graphene Supported Ce O₂@Au NanoparticlesThe e Gr_4Bwas synthesized by electrochemical exfoliation of pencil graphite in an aqueous solution of ammonium sulfate and melamine.A novel electrochemical sensor with Ce O₂@Au and e Gr_4Bnanocomposites modified glassy carbon electrode(e Gr_4B/Ce O₂@Au/GCE)was successfully fabricated by ultrasonic synthesis method for the detection of NAA.CV analysis has been performed to explore different electrodes performance and the results showed that the e Gr_4B/Ce O₂@Au can provide a sensitive interface to accelerate the electron transfer.DPV results showed that the oxidation peak current of NAA was linearly correlated with the concentration between 0.35-50mmol/L and the lowest detection limits is 0.045mmol/L.At the same time,repeated measurement of NAA after the sensor was placed for 15 days showed the peak current RSD is 4.82%.It was employed to detect NAA in strawberry samples,with recoveries ranging from 94.8%to 111.5%.