Electroanalysis Based On Neutral Red And Thionine Nanocomposites

The study of conjugated dye molecules and their electron-transfer properties is one of the important projects for electrochemical and electroanalytical researchers,which is also of obvious significance in biolabeling and dye-sensitized solar cells.Nanocompsite materials, composed of two or more solids of nanoscale size(1～100 nm) in at least one dimension,are very promising for diversified applications due to their special structure and thus unique physical and chemical properties.In the present thesis,a brief review on some literatures in the relevant fields is given,a new electroanalysis method for anionic polysaccharides featured by a dynamically renewed surface of the detection electrode is proposed based on the electrochemical property of neutral red(NR),and a novel platinum nanoparticles(PtNPs)-thionine (TH)-multiwalled carbon nanotubes(MWCNTs) nanocomposites material is prepared and used for chemo/biosensing of H₂O₂,glucose, methanol and nitrite.The main work herein is summarized as follows:1.On the basis of the controllable electrodeposition of NR,we put forward a novel and surface-regenerable electrochemical quartz crystal microbalance(EQCM) assay protocol to the analyses of heparin(Hep) and chondroitin sulfate(CS).The EQCM technique was used to investigate the electrochemistry redox process of NR in phosphate buffer solution(PBS) and the effects of coexisting Hep or CS for the first time. The pH dependence of the electrochemistry of NR was examined,and a V-shaped frequency response(versus time) was observed during the cyclic voltammetric experiment of NR in a nearly neutral medium(pH = ca.6.10～7.00),being due to the electrodeposition and stripping of the poorly soluble reduced product of NR(NR_Red) at these pH values.The effects of potential scan rate,the concentration of NR,and several supporting electrolytes were examined at pH 6.80.The V-shaped response to the redox switching of NR was weakened by the introduction of Hep or CS,being due to the increased inhibition of the NR_Red electrodeposition probably via the electrostatic interaction of the NR and especially the NR_Red with Hep or CS.The height of the V-shaped response decreased with the increase of Hep or CS concentration,with limits of detection down to 3 nmol L^-1 for Hep and 2 nmol L^-1 for CS,respectively.2.A novel PtNPs-TH-MWCNTs nanocomposites material prepared through the reduction by sodium borohydride(NaBH₄) in the presence of TH-MWCNTs was synthesized.The transmission electron microscope (TEM) experience showed that PtNPs dispersed well on the surface of TH-MWCNTs and the loading density was higher than that on MWCNTs without TH.The resulting PtNPs-TH-MWCNTs nanocomposites modified gold electrode(PtNPs-TH-MWCNTs/Au) exhibited good electrocatalysis toward hydrogen peroxide reduction and oxidation with the sensitivities are 2.76(reduction) and 2.26(oxidation) A M^-1 cm^-2, respectively,under the optimum conditions.The GOx/PtNPs-TH-MWCNTs /Au enzyme electrode was prepared by immersing the dried PtNPs-TH-MWCNTs/Au electrode in GOx solution for ca.24 h at 4℃. The current response of the biosensor at 0.5 V was linear with glucose concentration from 1.65μmol L^-1 to 11.1 mmol L^-1,with sensitivity as high as 0.14 A M^-1 cm^-2,detection limit down to 0.05μmol·L^-1 and response time within 5 s.At the same time,the electrocatalytic activities of PtNPs-TH-MWCNTs/Au and PtNPs-MWCNTs/Au electrodes toward methanol electrooxidation were also studied by cyclic voltammetry and chronoamperometry.3.The PtNPs-TH-MWCNTs/Au electrode was used for highly sensitive determination of nitrite in neutral solution.In comparison with MWCNTs/Au and TH-MWCNTs/Au electrodes,the PtNPs-TH-MWCNTs /Au electrode exhibited higher catalytic activity toward the reduction of nitrite.The catalytic peak current was found to be linear with the nitrite concentration in the range of 0.5～150μmol L^-1(r = 0.9964), with sensitivity as high as 5.52 A M^-1 cm^-2 and detection limit(S/N = 3) down to 0.2μmol L^-1.