Purification And Modification Of Single-walled Carbon Nanotubes And The Prelimilary Application In Field-effect Biosensor

Since the first finding by Iijima in 1991, the carbon nanotubes (CNTs) have received considerable attention by many researchers because of their unique mechanical, chemical and electrical properties. Their remarkable properties offer the possibilities of wide promising applications, such as field emission plane display, high strength fiber and strengthen composite materials, gas adsorption and energy storage materials and so on, especially in nano-electronic device and biological detection. The electrical properties of single-walled carbon nanotubes (SWNTs), which range from semiconducting to metallic depending on their chirality, should make them to be regarded as ideal materials for nano electronic devices and circuits in future such as nanowires, diodes, triodes, rectifying heterojunctions, field effect transistors (FETs) and sensors. Nanoelectronics using SWNTs as components to make nano devices and circuits break the shrink limitation of traditional silicon integrated circuit, hence promote the development of integrated circuit research.These potential applications are, however, often limited because of their insolubility in many solvents and a high amount of impurities in SWNTs produced. Therefore, strategic approaches toward the high-quality SWNTs by purification and solubilized SWNTs by modification are important for their applications. Purification, modification and applications research of SWNTs have been developed in recent years. However, there is big room for improvement and research in purification, modification and pretreatment of the nanotubes as well as their applications in nano-electronic device and biological detection. So we are interested in developing an efficient high-quality purification, a rapid and facile noncovalent glycosylated functionalization and controlled ring formation method for SWNTs synthesized by chemical vapor deposition (CVD). Moreover, we have further done some researches on field effect transistor (FET) based on a single SWNTs bundle and its preliminary application in detection of sugar-lectin recognition.High-quality SWNTs were obtained from CVD-produced commercial materials using a three-step purification process consisting of hydrochloric acid treatment, air oxidation, and a high-temperature annealing in N2 atmosphere. After the final step, about 17~19% of the weight of the initial raw materials remained and the final product contained less than 2% metal, with a Raman peak intensity ratio, the IG/ID value, of 38.6. High-temperature treatment at 1600℃in N2 atmosphere for 3 h was found effective to remove residual metal catalyst in the nanotubes and reduce the wall defects. After the high temperature annealing purification, the purified SWNTs have an increased degree of graphitization. The three-step purification process presents a low-cost, efficient method of purifying and ordering single-walled carbon nanotubes.Nanotube rings were fabricated with a certain yield by heating the hydrochloric acid treatmented SWNTs under ambient conditions, which offers a controlled ring formation process to a certain extent. We explored several factors in the ring formation process with air oxidation and the possible mechanism of the ring-closure, and we first described the rolled-up rings mechanism in air oxidation, which would have active influence upon the application of the CNTs ring fabrication method with air oxidation.A sugar-based surfactant N-n-octadecyl-D-maltonamide (NOMA) was synthesized via the reaction of n-octadecylamine with D-maltonolactone in the absence of catalyst. The results of surface tension and fluorescence measurements show that the prepared NOMA is a sugar-based surfactant with good surface activity and fluorescence. We reported for the first time that SWNTs were functionalized with NOMA, a simple sugar-containing amphipathic molecule, by a method of noncovalent adsorption to form a NOMA-SWNTs nanocomposite. The experiment results showed that NOMA can be rapidly and effectively adsorbed on the surface of SWNTs without changing the native structure of NOMA and the structure properties of SWNTs. Moreover, it was shown that the dispersion ability of SWNTs in aqueous solution had a significant improvement after coating with NOMA. The presented method for functionalization of SWNTs had several advantages, such as rapid and facile CNTs functionalization, good hydrophilicity and biocompatibility, and uniform functionalization of CNTs with various carbohydrate molecules. Hence it could be used as a versatile and efficient noncovalent glycosylated method for CNTs and would have promising application in bio-functionalized materials, detection of glycoligand-receptor interactions and diagnose processes of deleterious disease.FET devices with a single SWNTs bundle as the conducting channel have been developed by a drop method and the device characteristic is p-type in an ambient environment. The SWNT-FETs were submerged in a NOMA solution and then a Concanavalin A (Con A)/PBS solution to be tried to detect maltose-Con A interaction. An n-type characteristic after NOMA coating and significant changes of characteristics after exposure to Con A were detected. Obvious changes in the CNTFET electronic characteristics at each attachment stage demenstrate the possobility of noncovalent glycosylated functionalization of SWNTs with simple molecue NOMA and sugar-lectin recognition detection by CNTFET. This noncovalent glycosylated CNTFET can be used as versatile, sensitive and effective biosensor based on SWNTs.