Electrochemical Sensor For Sensitive Determination Of Alkaloid Using Metal-Graphene Nanocomposite

Alkaloids are one of the main active ingredients of Chinese herbal medicines.They are widely used in food and medicine as the cornerstone of the pharmaceutical industry.However,some alkaloids are highly biotoxic and human poisoning events occur from time to time.Therefore,good methods are needed to determine trace amounts of alkaloids in food testing,toxicology research,clinical research,and forensic analysis.In this thesis,the electrochemical method is simple,rapid and sensitive.The electrochemical sensor for detection of capsaicin and strychnine is constructed by using metal-graphene nanocomposites.The main research contents are as follows:(1)Sensitive detection of capsaicin by an electrochemical sensor based on polydiallyldimethylammonium chloride(PDDA)-graphene/Pd nanocomposite.PDDA functionalized graphene was synthesized using a one-step in-situ reduction method and loaded with palladium nanoparticles.The prepared PDDA-Gr/Pd nanocomposite is used for electrochemical detection of capsaicin.The morphology and composition of the synthesized materials were analyzed by UV-vis absorption spectroscopy(UV-vis)and transmission electron microscopy(TEM).The TEM images showed that the palladium nanoparticles were uniformly distributed on the graphene surface.The electrochemical performance of the prepared sensor was investigated by cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).The results show that PDDA-Gr/Pd nanocomposites have good electrocatalytic activity for capsaicin redox.This is attributed to the synergistic effect of the excellent properties of palladium nanoparticles and graphene nanosheets.Under optimal conditions,the capsaicin electrochemical sensor has a broad linear range of 0.32 ?M to 64 ?M with a detection limit(LOD)of 0.10 ?M(s/n=3).In addition,the method has the advantages of low cost,simple preparation process,good reproducibility,good stability,and good accuracy in the detection of actual samples,and is expected to play an important role in the detection of other amide alkaloids.(2)Electrochemical sensor for sensitive detection of strychnine based on sulfhydryl-?-cyclodextrin(SH-?-CD)-graphene/Pd Ag nanocompositesThe SH-?-CD/Gr/Pd Ag nanocomposites were successfully synthesized.The preparation method of Pd Ag nano-alloy colloids was simple and rapid.This is the first time that graphene-based nanomaterials have been used for the electrochemical detection of strychnine.Due to the synergistic effect of Pd,Ag,and Gr,the synthesized materials have excellent electrocatalytic ability.The morphology and composition of the prepared materials were analyzed by TEM and XPS.The results show that the materials are successfully synthesized and the Pd Ag nano-alloy particles are uniformly dispersed on the graphene.The electrochemical properties of CV and other electrochemical methods were investigated and found the nanocomposite exhibits good conductivity and catalytic properties.The effects of several operating parameters on the sensor were investigated.Under the optimal conditions,the linear range of the sensor was 0.63?M to 1.89 m M,and the detection limit was 0.10?M.It was found to be satisfactory in the detection of fresh human urine samples,and the prepared electrochemical sensor has great potential for quantitative analysis of strychnine in clinical human urine samples.