| Scanning electrochemical microscopy(SECM) introduced by Bard in 1986 has been found many appli-cations in characterizing many different kinds of systems(e.g.electrode surfaces,liquid/liquid interfaces and biologicalsamples), including surface structures in liquid environments with micrometer and nanometer resolution.SECM is a noncontact scanning probe technique that uses a microelectrode for the imaging of surfaces and surface reactions,in which the surface can be a solid surface or a liquid surface.The phenomenon exploited to obtain topographic images of the target surface is that in close proximity of the microelectrode to the target surface the steady state current of the microelectrode(the tip,which is the central piece of the microscope) in the solution of a redox species(mediator) changes in a distinctive way. SECM has been widely used for the electrochemical imaging,ET transportation of liquid/liquid interfaces,and so on.Scanning electrochemical microscopy is however more than just a tool for the imaging the target surface.One of the main advantages of using SECM is the possibility to map the surface reactivity allowing the assessment of surface reaction kinetics as well as identifying the bioactive sites.The application of SECM to monitor targets of biological origin started in the early 1990s involving topographic imaging of leaf surfaces as well as the determination of local oxygen concentration changes due to photosynthesis.Since then a variety of targets(species) of biologicalorigin including enzymes,antibodies,cells,etc.,have been the subject of SECM studies.In recent years SECM has been further used for the imaging of confined DNA molecules and protein in a highly localized surface area.The interaction between DNA and drugs is a hot subject of research in the field of biology,medical science,chemical analysis,and so on.Application of SECM to the interaction between DNA and drugs is a very interesting work.This thesis includes a review and a research section.In the review,the basic apparatus,operation modes and theory of SECM were introduced briefly.First,the tips in SECM and the technique for obtaining SECM imaging were discussed.Then,the applications of SECM in the investigation for enzyme,antigen/antibody complex,DNA and cells were reviewed.Finally,the purpose and content of this thesis are presented.The research section contains two subunits.In the first subunit,the interaction between thrombin-binding aptamer self-assembled on the gold surface and the target analyte thrombin was investigated by SECM.The "feedback mode" was used and ferricyanide was primarily used as the redox probe.The different surfaces including bare gold,aptamer self-assembled monolayer,aptamer/HT self-assembled mixture monolayer(called biosensor) and biosensor interacted with thrombin were characterized with SECM and cyclic votalmmetry.It was found that the current of the biosensor decreased greatly in presence of thrombin.Based on this finding,a novel SECM method for the detection ofthrombin with a high selectivity has been developed.Additionally,it was found that hexammineruthenium(Ⅲ)chloride was a promising redox probe compared with ferrocenemonocarboxylic acid and ferrocene,attributed to its positive charge.This work demonstrates that SECM is a promising technique for investigating the interaction between aptamer and proteins.In the second subunit,the electrochemical behaviors of curcumin at glass carbon electrode were studied by cyclic voltammetry and a novel electrochemical method for the determination of curcumin was developed.The oxidation peak current was linear with the concentration of curcumin in the range from 4.9×10-7 to 1.4×10-3 mol/L.The detection limit is 1×10-7 mol/L.The interaction of ds-DNA with curcumin in homogenous solution and on ds-DNA modified electrode was studied by absorption spectroscopy and surface electrochemical methods.The results suggested that curcumin can bind ds-DNA with electrostatic interaction at lower ionic strength and intercalate at high ionic strength. |
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