Study On Synergistic Electrocatalysis And Biosensing Of Carbon Nanotube Nanocomposites

Since their discovery in 1991, carbon nanotubes (CNTs) have been found great applications in many fields including nanoelectronics and biosensors, due to their special electrical, chemical, and mechanical properties. Many efforts have been focused on the design and preparation of CNTs composites because those composites possess the properties of individual components with a synergistic effect, which was strongly depended on their structure and greatly influenced by the method and conditions used to obtain them. Compared with the individual components, CNTs composites with synergistic effect could further improve the electrocatalytic characteristics of electrochemical sensors and biosensors. In this thesis, a series of studies on the development of carbon nanotube nanocomposites and their application for electrocatalysis and biosensing were carried out, and some valuble results were obtained. The main points of this thesis are summarized as follows:1. A novel method was proposed for fabrication of a carbon nanotubes/poly(1,2-diaminobenzene) nanoporous composite based electrode. The poly(1,2-diaminobenzene) was deposited onto the surface of a glassy carbon electrode (GCE) modified with multi-wall carbon nanotubes (MWNTs) via multipulse chronoamperometric electropolymerization (MCE) process. Compared with the composite prepared by conventional electropolymerization (CE), the electronic and ionic transport capacities of the MCE-based composite were significantly improved due to its unique nanoporous structure. The surface of the composite-modified GCE was characterized with scanning electron microscopy (SEM) and cyclic voltammetry (CV). The nanoporous MCE-based electrode was applied to determination of NADH at a much low potential of 70 mV, and a linear range from 2.0μM to 4.0 mM was observed with fast response (within 5 s) and a lower detection limit of 0.5μM (based on S/N = 3). In comparison, a narrow linear range from 5.0μM to 2.0 mM, slower response (up to 15 s) and a higher detection limit of 3.0μM (based on S/N = 3) was obtained with the electrode prepared by CE.2. A new and simple method for construction of NADH electrochemical sensor was proposed. The electrochemical sensor was constructed by assembling toluidine blue O (TBO) onto the surface of MWNTs modified glassy carbon electrode throughπ～πelectronic and hydrophobic interactions between TBO and MWNTs. Also TBO-MWNTs modified GC electrodes exhibiting a strong and stable electrocatalytic response toward NADH were described. Compared with a bare GC electrode, the TBO-MWNTs modified GC electrodes could decrease the oxidization overpotential of NADH by 730 mV, with a peak current at 0.0 V, since there was a positively synergistic electrocatalytic effect between the MWNTs and TBO toward NADH. Furthermore, the TBO-MWNTs modified GC electrodes had perfect performances, such as a low detection limit (down to 0.5μΜ), being very stable (the current diminutions is lower than 6% in a period over 35 min), a fast response (within 3s), and a wide linear range (from 2.0μΜto 3.5 mM).3. A new type of poly(toluidine blue O)/multiwall carbon nanotube (PTBO/MWNTs) composite nanowires was fabricated and characterized with scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The PTBO/MWNTs composite nanowires modified electrode was applied to determinate NADH. Compared with bare GCE and MWNTs modified GCE, the PTBO/MWNTs composite nanowires modified GCE decreased the NADH oxidization overpotential by about 650 mV and 260 mV, respectively, with a much low peak potential at about 0.0 V. The peak current response at PTBO/MWNTs composite nanowires modified GCE was about 4.5 times higher than that of ultrathin PTBO modified GCE, at the same peak potential. A linear range from 2.0μM to 4.5 mM was observed with fast response (within 5 s) and a low detection limit of 0.5μM (based on S/N=3). The current diminution to 1.0 mM NADH is lower than 10% in a period over 70 min shows that the PTBO/MWNTs composite nanowires modified GCE is quite stable4. A new type of carbon nanotubes/conducting polymer nanocomposites of carbon nanotubes and poly(azure A) with high catalytic surface area was proposed. And the electrocatalytic activity of the nanocomposites was tested using sodium nitrite. The results showed thus prepared electrode exhibited excellent electrocatalytic behavior to the reduction of nitrite and facilitates the detection of nitrite at an applied reduction peak potential of 0.1 V. A linear range from 3.0μΜto 4.5 mM for the detection of sodium nitrite has been observed with fast response (within 3s) and a detection limit of 1.0μM based on a signal-to-noise ratio of 3.5. A novel direct, fast and facile electrodeposition method for fabrication of carbon nanotubes/Prussian blue nanoparticles/poly(1,2-aminobenzene) nanocomposite based glucose biosensor was proposed. The Prussian blue (PB) nanoparticles were direct electrodeposited onto the surface of a glassy carbon electrode modified with MWNTs. The experiments results showed that the MWNTs/PB nanocomposite exhibited excellent synergistic electrocatalytic effect toward reduction of hydrogen peroxide. An ultrthin conducting poly(1,2-diaminobenzene) film was electrodeposited onto the surface of MWNTs/PB nanocomposites to immobilize the glucose oxidase via glutaraldehyde cross-linking for fabrication of a glucose biosensor. The resulting biosensor showed excellent electrocatalytic characteristics toward determination of glucose. The linear range of the glucose biosensor is from 10μM to 2.5 mM with a detection limit of about 5μΜ. Furthermore, the response is very fast, which is less than 5 s.6. A novel glucose biosensor based on carbon nanotube nanocomposite of copper nanoparticles/chitosan/ carbon nanotube-modified glassy carbon electrode was proposed. The copper nanoparticles and carbon nanotubes exhibits a synergistic electrocatalytic effect toward the reduction of hydrogen peroxide in the matrix of biopolymer chitosan, which obtained abundant amino-groups facilitating for immobilize glucose oxidase via glutaraldehyde cross-linking for fabrication of a new glucose biosensor. The biosensor exhibited excellent sensitivity (the detection limit is down to 0.02 mM), fast response time (less than 4 s), wide linear range (from 0.05 mM to 12 mM), and perfect selection.7. A novel layer-by-layer assembled carbon nanotubes (CNTs) multilayer film with molecule recognition function and lower capacitive background current was presented. Theβ-CD absorbed and attached at the side wall of CNTs could be assembled successfully on the electrode using chitosan. Theβ-CD located at the side wall of CNTs changed the CNTs surface from hydrophobic to hydrophilic, which facilitate theβ-CD-CNTs to form a relatively compact structure with a relatively smaller specific surface area. The assembledβ-CD-CNTs offered a lower capacitive background current and higher current response toward oxidation of dopamine. This type of the assembled CNTs combined the advantages of the layer-by-layer self-assembly method, the excellent electrocatalytic activity of MWNTs, the molecule recognition ofβ-cyclodextrin and decreased capacitive background current.