Piezoelectric Electrochemistry And Electrochemical Surface Plasmon Resonance Studies On Several Charge-Transfer Complexes And Their Analytical Applications For Polysaccharides And H₂O₂

The electrochemical quartz crystal microbalance(EQCM)is based on the reverse piezoelectric effect of a piezoelectric quartz crystal and can be used to study the chemical/physical parameters and materials characteristics during an electrochemical process/reaction in a real-time manner via measurements of the information on the piezoelectric quartz crystal resonance.Surface plasmon resonance(SPR),which is based on the surface electromagnetic waves that propagate parallel along a metal/dielectric(or metal/vacuum)interface,is very sensitive to any change of this boundary,such as the adsorption of molecules to the metal surface.In addition,the dynamic refreshment of the sensor surface(like the dropping mercury electrode)is always a hot but difficult problem in electroanalysis,here on the basis of the electrochemical modulation of the CTC,the electrochemical analyses of several anionic polysaccharides featured by dynamically renewed surfaces are made.The studies in this thesis are summarized as follows:1.The electrochemical quartz crystal microbalance(EQCM) technique was used to investigate the electrodeposition of the charge-transfer complex(CTC)generated during electrooxidation of o-tolidine(o-TD)in B-R buffers and effects of coexisting chondroitin sulfate(CS).A V-shaped frequency response to the cyclic voltammetric switching of o-TD indicated the precipitation and dissolution of the poorly soluble CTC,an oxidation intermediate,formed at the Au electrode during the redox switching of o-TD in a neutral or weakly acidic medium(pH=4.07～6.5).The effects of potential scan rate,solution pH and several supporting electrolytes were examined.The depth of the V-shaped frequency curves(-Δf_0V)was related to the supporting electrolyte employed,with a sequence for -Δf_0Vas 0.20 mol·L^-1NaNO₃> 0.20 mol·L^-1NaClO₄ > 0.10 mol·L^-1Na₂SO₄.The -Δf_0Vresponse to the redox switching of the CTC/o-TD "couple" was notably enhanced by the introduction of CS,due to the formation of the CTC-CS adduct,as also characterized and supported by UV-Vis and FT-IR spectrophotometry. The molar ratio(x)of the CTC to CS in the adduct was estimated via EQCM.The values of-Δf_0Vincreased with CS concentration,with a linear range from 0.75 to 15.2μmol·L^-1and a detection limit down to 50 nmol·L^-1.The new method proposed for CS assay is featured by a dynamically renewed surface of the detection electrode.2.The electrochemical quartz crystal microbalance(EQCM) technique was used to investigate the electrochemistry of three benzidine derivatives,o-tolidine(o-TD),3,3',5,5'-tetramethyl-benzidine(TMB) and o-dianisidine(o-DA),in Britton-Robinson(B-R)buffer solutions with and without coexisting dextran sodium sulphate(DSS),respectively. The mechanism for the CTC-DSS interaction is briefly discussed from EQCM,FT-IR and UV-Vis data.The CTC-based EQCM determination of DSS,which is featured by a dynamically renewed surface of the detection electrode,was thus proposed,with a linear range from 0.002 to 1.6μmol L^-1and a detection limit down to 0.7 nmol L^-1(o-TD system).3.An ESPR sensor for dermatan sulfate(DS)was developed based on the interaction of DS and the CTC generated from the electrooxidation of o-TD.The response of SPR increased with the increase of DS concentration,with a linear range from 0.164 to 10.6μmol·L^-1and a detection limit of 8 nmol·L^-1,which is superior to than that from a comparative EQCM study4.A new third-generation biosensor for H₂O₂ assay was developed based on the immobilization of horseradish peroxidase(HRP)in a nanocomposite film of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ)/multiwalled carbon nanotubes(MWCNTs)modified gold electrode.The prepared HRP/TTF-TCNQ/MWCNTs/Au electrode was used for the bioelectrocatalytic reduction of H₂O₂,with a linear range from 0.005 to 1.05 mmol·L^-1and a detection limit of 0.5μmol·L^-1for amperometric sensing of H₂O₂.In addition,a novel method on the basis of EQCM measurements was proposed to determine the effective enzymatic specific activity(ESA)of the immobilized HRP for the first time,and the ESA was found to be greater at the TTF-TCNQ/MWCNTs/Au electrode than that at the MWCNTs/Au or TTF-TCNQ/Au electrode,indicating that the TTF-TCNQ/MWCNTs film is a good HRP-immobilization matrix to achieve the direct electron transfer between the enzyme and the electrode.