Development Of Gold Nanoelectrode Ensembles And Their Modified Electrodes And Their Applications In Bioelectrochemistry

As an assembled nanostructure, nanoelectrode ensembles (NEEs) present many advantages such as enhanced responding signal, good maneuverability, higher sensitivity, besides the strongpoint of the single nanoelectrode. The present difficult and effort in the field of NEEs have been concentrated on fabricating controllable NEEs both in figures and dimensions, objectively evaluating their morphology and electrochemical properties, in order to realize the effective control of their performance. On this basis, the development methods and techniques of gold two dimensional disk NEEs(2DNEEs), three dimensionnal brush NEEs(3DBNEEs) and the chemical modified NEEs of L-cysteine (L-Cys/NEEs) were studied. In addition, the above developed electrodes were objectively evaluated.The 3DBNEEs and their modified electrodes were applied in the field of bioelectroanalysis.The development methods and techniques of continuous and strong gold nano fiber ensembles with high ratio of length to diameter 200 were investigated. The gold nano fiber ensembles with 6μm in length were prepared by electroless template synthesis in polycarbonate filter membranes with (1~5)×108 pore/cm2 in pore density. The stablization method designed in this thesis overcame the shortcomings such as deformation and sink in deposition process, which is the basis for developing nanoelectrode ensembles with reliable performance. The deposition mechanism and process were discussed. Gold deposition in the pore of polycarbonate belongs to reducing process, in which pH value and temperature play key important roles in the deposition speed and quality of nanofibers. The deposition is started by the formation of gold nuclei and then the nuclei grow, until they are bound together to produce the final nanofiber with polycrystalline structure. This deposition and structure characteristics are the basis for the development of NEEs with high electrochemical activity. This structure characteristic of the nanofibers can greatly improve the active area and electrochemical activity of 3DBNEEs.The 2DNEEs were developed by effectively removing the deposited gold layer on the surface of polycarbonate filter membrane using the combination technology of mechanical method and cyanide chemical etching. The 3DBNEEs which are better in length controlling and orientation than that reported in literatures were made by chemical etching using methanol and dichloromethane mixtures. The quantity of the etching solution and etching time were carefully controlled during the process. The development method and technique of L-Cys chemical modified nanoelectrode ensembles (L-Cys/NEEs) by self-assembly were investigated.The scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) were employed to evaluate the characters of nano-fiber ensembles including figures, morphologies and compositions. The elechemical characteristics of 2DNEEs and 3DBNEEs such as the diffusion styles, charge transfer and warburg resistance were investigated by using Fe(CN)63-/4- as electrochemical probe. The diffusion styles of Fe(CN)63-/4- are related to the radius, the distance between adjacent electrodes and the scanning rate. The active area of 3DBNEEs was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy by using Fe(CN)63-/4-, daunorubicin (DNR) and gold as redox probe, respectively. The smaller area got from Fe(CN)63-/4- indicates that the probe cannot reflect the real micro structure of 3DBNEEs because of the thickness of the diffusion layer. However, DNR and gold atom at gold electrode surface can denote the micro roughness and larger active area of 3DBNEEs, because their electrochemical processes depend on surface properties. This result is significant for the objective evaluation and application of 3DBNEEs in theoretical and applications aspect.The eletrochemical processes of daunorubicin (DNR) at 3DBNEEs and L-Cys/3DBNEEs were studied. The electrochemical parameters of DNR such as rate constant, transfer coefficient and adsorption quantity were determined. The SWV was used to determine the quantity detection of DNR at 3DBNEEs andL-Cys/3DBNEEs. The results show that both 3DBNEEs and L-Cys/3DBNEEs exhibited electrocatalyzing ability. The rate constants are 0.76 s-1 and 4.6 s-1, respectively, which are 2 and 12 times larger than the results reported in literature. Particularly, the redox rate and peak current values were both enhanced more by L-Cys/3DBNEEs. Besides, lower detection limit was gotten at L-Cys/3DBNEEs. The detection limit reaches 1.0×10-8 mol/L.The eletrochemical characteristic of enzymatic reaction system was studied, in which horseradish peroxide acts as a catalyst for the reaction of H2O2 oxidize o-phenylene- diamine. The electroreduction behavior of enzymatic reaction product, 2,3-diamino- phenazine is quasi-reversible diffusion-controlled process. The detection limit at 3DBNEEs reaches 1×10-11 mol/L (S/N =3), one order magnitude lower than that gotten from macro gold electrode and literature reported glass carbonate electrode.The unique special three dimentional ensemble and micro roughness of 3DBNEEs are especially beneficial for the performances improvement and design of electrode. This is of great significance for miniaturizing and exploiting novel electrochemical sensors.