The Application Of Carbon Nanotubes In The Design Of Biosensors And Supercapacitors

Carbon nanotubes (CNTs) are a new kind of one-dimension quanta material who has unique structures. The discovery of CNTs revolutionizes the area of structural materials or even the whole science. At present three mature methods to synthesize CNTs: arc discharge, laser blaze and chemical vapor deposition have been widely used.Many of CNTs' properties have been theoretically calculated and experimentally verified: high mechanical strength, high flexibility, low mass density, chemical inertness, large specific surface area, etc. These amazing properties make this material a promising candidate for various applications, such as the most tenuous wire in nanoelectronic devices, field-effect transistors, tips for atomic force microscope, etc. CNTs are considered as "super fiber" used in reinforced materials due to there high flexibility.The application of CNTs most widely employed so far has been the construction of various detection devices, especially biosensors with immobilized biomolecules. As electrodes or modifiers of conventional working electrodes, CNTs have many advantages in electrochemical measurements, such as the large active surface at electrodes of small dimensions, the enhanced electron transfer or the oftenindicated electrocatalytic properties which highly enhanced the sensibility and stability of biosensors.Lots of studies about the applications of CNTs in supercapacitor were carried out for the CNTs' novel hollow-tube structure, nanometer dimensions, high spscific surface area, conductivity, low resistivity, chemical stability, etc. CNTs have higher valid specific surface area for their more aggregated pores within from 2nm to 50 nm. The electrochemical capacitance of CNTs can be further increased by activating CNTs.The new applications of CNTs in the construction of biosensor and supercapacitor were presented in this paper: Chapter 1 the reviewThe discovery, the synthesis methods, the structure, and the category, especially the marvelous properties of CNTs were presented. On the bases of the principles of biosensors (including DNA biosensors and glucose biosensors) and supercapacitors, the applications of CNTs in above areas were reviewed.Chapter 2 Impedance DNA biosensor using electropolymerized polypyrrole/multiwalled carbon nanotubes modified electrodeAn electrochemical impedance-based DNA biosensor by using a composite material of polypyrrole (PPy) and multiwalled carbon nanotubes (MWNTs) to modify glassy carbon electrode (GCE) was presented. The polymer film was electropolymerized onto GCE by cyclic voltammetry (CV) in the presence of carboxylic groups ended MWNTs (MWNTs-COOH). Such electrode modification method is new for DNA hybridization sensor. Aminogroup ended single-stranded DNA (NH2-ssDNA) probe was linked onto the PPy/MWNTs-COOH/GCE by using EDAC, a widely used water-soluble carbodiimide for crosslinking amine and carboxylic acid group. The hybridization reaction of this ssDNA/PPy/MWNTs-COOH/GCE resulted in a decreased impedance, which was attributed to the lower electronic transfer resistance of double-stranded DNA than single-stranded DNA. As the result of the PPy/MWNTs modification, the electrode obtained a good electronic transfer property and a large specific surface area. Consequently, the sensitivity and selectivity of this sensor for biosensing DNA hybridization were improved. Complementary DNA sequence as low as 5.0×10^-12 mol/L can be detected without using hybridization marker or intercalator. Additionally, it was found that the electropolymerization scan rate was an important factor for DNA biosensor fabrication. It has been optimized at 20mV/s.Chapter 3 chemical deposition of Pt nanoparticles and its application on glucose biosensor designA new glucose biosensor design based on glucose oxidase (GOD) immobilized by polypyrrole has been described. The polymerization of pyrrole was initiated by a hexachloroplatinate which itself was reduced into Pt nanoparticles and thus served as a catalyst for the H2O2 oxidation. Properties of the produced GOD modified electrode were examined and the activity of the entrapped enzyme was determined by basic application on the amperometric detection of glucose. Much better results were found comparing with the enzyme electrode for which the enzyme was entrapped by the electrochemically polymerized polypyrrole. This kind of technique for Pt nanoparticles deposition can be applied in many cases where polypyrrole is used.Chapter 4 the supercapacitor based on well-alined carbon nanotubes(ACNTs) Large scale vertically aligned carbon nanotubes(ACNTs) with uniform length and diameter were prepared by the pyrolysis of iron(II) phthalocyanine at low pressure. The ACNTs can be activated by electrolyte-activation, acid-activation and electro-activation. The performance of the capacitor based on activated ACNTs was characterized by Cyclic Voltammograms (CVs) which was of rectangular shape, Impedence spectroscopy in which the phase is above 80° and the result specific capacitance was 16 — 32F/g. The tightly-aligned CNTs and loosely-aligned CNTs were compared when they were used as the electrodes of capacitor. In this way, the tightly-aligned CNTs are the most promising material for the supercapacitor.