| The aim of chemically modified electrodes is to carry out the molecular design on the electrode surface. In other words, some molecules, ions and polymer with excellent properties are immobilized on electrode surface and the electrode with special chemical and physical properties is obtained. The application of chemically modified electrodes has involved in chemistry, life science, medicine, environment, food and militarization, and so on. On the other hand, carbon nanotubes (CNTs) have found great applications in many fields including physics, chemistry and material science, due to their unique one dimensional tubular structure, unusual mechanical, electrical and electrochemical properties. Nanocomposites based on CNTs and nanoparticles have been of great interest in chemically modified electrodes in recent years. Furthermore, doping CNTs with foreign atoms would produce large amounts of edge sites and oxygen-rich groups located on the defect sites introduced by boron doping. The electrochemical properties of the nanotubes were improved due to these active sites on the surface of nanotubes. There are potential applications in constructing electrochemical biosensors based on BCNTs. In this thesis, CNTs/metal oxide nanoparticles composite and BCNTs modified electrodes have been constructed, and applied in detecting biological active molecules. The main points of this thesis were summarized as follows:(1) The cobalt oxide nanoparticles were electrochemically deposited on the CNTs modified electrode and the nanostructured PG/CNTs/CoOx-NPs electrode can be obtained. The morphology of the nanocomposit was investigated by scanning electron microscopy (SEM). The direct electrocatalytic oxidation of glucose in alkaline medium at pyrolytic graphite/multi-walled carbon nanotubes/cobalt oxide nanoparticles (PG/CNTs/CoOx-NPs) electrode has been investigated. At an applied potential of +0.40 V, the higher current response to glucose can be obtained at PG/CNTs/CoOx-NPs electrode than that at CNTs or CoOx-NPs modified electrode. Additionally, high sensitivity (3.81μA cm-2 mM-1), low detection limit (3μM, S/N=3), wide liner range (6μM ~ 1.2 mM) and good stability can also be obtained at PG/CNTs/ CoOx-NPs electrode. This kind of modified electrode has great potential in nonenzymatic glucose detection.(2) The boron-doped carbon nanotubes (BCNTs) were used in amperometric biosensors. It has been found that the electrocatalytic activity of the BCNTs modified glassy carbon electrode toward the oxidation of hydrogen peroxide is much higher than that of the un-doped CNTs modified electrode due to the large amount of edge sites and oxygen-rich groups located at the defective sites induced by boron doping. Glucose oxidase (GOD) was selected as the model enzyme and immobilized on the BCNTs modified glassy carbon (GC) electrode by entrapping GOD into Poly(o-aminophenol) film. The performance of the sensor was investigated by electrochemical methods. At an optimum potential of +0.60 V and pH 7.0, the biosensor exhibits good characteristics, such as high sensitivity (171.2 nA mM-1), low detection limit (3.6μM), short response time (within 6 s), satisfactory anti-interference ability and good stability. The apparent Michaelis-Menten constant (Kmapp) is 15.19 mM. The applicability to the whole blood analysis of the enzyme electrode was also evaluated.(3) GC/BCNTs electrode has been constructed. The catalytic properties of the GC/BCNTs electrode towards oxidation of L-cysteine has been investigated by CV. GC/BCNTs electrode is comparably stable, and could be kept from fouling by selecting suitable potential. Compared with GC/CNTs electrode, the GC/BCNTs electrode has shown higher sensitivity (25.3 nA mM-1). There are also other good performances such as low detection limit ?(0.26μM), wide linear range (0.78μM~0.50 mM) and short response time (within 7 s). Other oxidable amino acid (tryptophan and tyrosine) would make little interference signals in the cysteine detection.
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