Studies On The Recognition Of Chiral Acids By Electrochemical Sensors Based On Graphene-based Composites

Chirality is an universality phenomenon to nature and organisms,which plays an indispensable role in the metabolism of life.Most of the molecules in the organism are chiral molecules,which plays different roles in life sciences and pharmacological due to different configurations.It is particularly important that the identification and detection of enantiomers in a large number of chiral drugs,new methods for chiral recognition is needed to developing.The emergence of a large number of chiral drugs makes the recognition and detection of enantiomers in chiral drugs particularly important,which poses a new challenge to the method of chiral recognition.Chirality recognition by electrochemistry is a new method developed in recent years.It is widely used because of its high recognition efficiency and low detection cost.Graphene is the fastest conductive material in the existing materials,and has excellent physical and chemical properties such as large specific surface area.It can be used to prepare sensitive molecular sensors to improve their sensitivity.Graphene-based chiral composites have attracted more and more researchers' attention.In this paper,chiral polysaccharides and graphene were covalently grafted to improve the stability of chiral composites.Chiral sensors were prepared by dropping coating,and successfully applied to the recognition and detection of chiral molecules.The main content of the study consists of three parts.1.Hydroxypropyl ?-cyclodextrin(HP-?-CD)functionalized graphene oxide chiral composites were prepared by in-situ reduction.The hydrophilicity of cyclodextrin was enhanced by modification on the basis of beta-cyclodextrin.Chiral composite rGO/HP-?-CD was successfully prepared by in-situ reduction of HP-beta-CD and GO using hydrazine hydrate as reducing agent.The rGO/HP-?-CD composite material was coated on the surface of glassy carbon electrode to prepare rGO/HP-?-CD/GCE chiral electrochemical sensor.Differential pulse voltammetry(DPV)was used for chiral recognition of Trp enantiomers.It was found that the chiral electrochemical sensor had a strong affinity for D-tryptophan.2.In order to improve the efficiency of chiral recognition,graphene is used as the substrate material.Chitosan(CS)was selected as chiral recognition reagent.CS reacted with glutaraldehyde to form CCS.GO and CCS were covalently grafted byamidation,and ascorbic acid(VC)was added as reducing agent to reduce them.Porous rGO-CCS composites were successfully prepared.The functional groups(FT-IR and XPS),morphology(SEM and TEM)and electrochemical behavior(CV and EIS)all confirmed the success of porous rGO-CCS composites with chiral microenvironment.Finally,rGO-CCS was modified on glassy carbon electrode to form an electrochemical chiral sensing interface rGO-CCS/GCE.The electrochemical recognition of chiral molecules by this chiral sensing interface was studied by cyclic voltammetry(CV).It was found that rGO-CCS/GCE could realize chiral recognition of mandelic acid(MA)isomers quickly and sensitively.Due to the difference of steric hindrance between R-and S-MA and rGO-CCS/GCE,rGO-CCS/GCE showed excellent selectivity for S-MA% in MA racemic solution.3.In order to further study the role of polysaccharides and graphene-based composites in chiral recognition,a highly ordered chiral composite rGO-EDA-CMC was prepared by covalent grafting of sodium carboxymethyl cellulose(CMC)with graphene oxide and adding ethylenediamine(EDA)as reductant,which successfully solved the aggregation effect of CMC.In addition,the effect of preparation temperature on the ordered structure of rGO-EDA-CMC and the degree of amide formation in GO,CMC and EDA were studied.The chiral sensing interface of rGO-EDA-CMC composite was prepared by dropping coating on the surface of glassy carbon electrode(GCE).The chiral recognition of chiral molecules was carried out by differential pulse voltammetry(DPV).It was found that the electrochemical sensor could efficiently recognize tryptophan(Trp)enantiomers.By optimizing the interaction temperature,contact time and pH between Trp enantiomer and chiral interface,it was found that the enantiomer exhibited excellent affinity for D-Trp.Therefore,the chiral electrochemical sensor can quickly and sensitively identify Trp enantiomers.