Carbon Nanotubes for Medical Applications

INTRODUCTION: Recent discoveries of various forms of carbon nanostructures have stimulated research on their applications in diverse fields. They hold promise for applications in medicine, drug and gene delivery areas [1]. For instance, carbon nanotubes have the potential to carry drugs in the organism as they are hollow and much smaller than the blood cells. The methods were developed for attaching DNA and protein molecules to the inside and outside of the nanotubes. This gives one the ability to target and destroy individual cells that may be cancerous or infected by a virus. Nanotubes with attached enzymes might, in the long term, be used as enzymatic biosensors that could simultaneously detect and measure a variety of biological molecules [2]. Carbon nanotubes arrays can play a key role in the artificial cochlea development (JPL in Pasadena, CA). It has been established that growing of the carbon nanotubes requires use of small metal catalyst particles (~5100 nm). Usually 3d metals (Fe, Co, Ni) or their combinations with other metals are very effective as catalysts. Carbon nanofibers/nanotubes grow through or from the surface of such metal catalyst particles. A combination of carbon nanotubes and the magnetic, metal catalyst particles may allow one using carbon nanofibers/nanotubes for the magnetically guided drug delivery purposes. A successful application of such a nanotubemagnetic particle combination depends significantly on the physical, chemical and biological properties of the material. The particles must be biologically inert and biodegradable, they must have high sorption capacity, the sorption selectivity must be adjustable, convenient binding with antibodies must be possible, and high magnetization and magnetic susceptibility in the relatively weak magnetic fields should also be achievable (particularly if such particles are designed for the guided drug delivery). Iron particles with combination of different carbon nanostructures meet all these requirements. Therefore, they are likely candidates for medical applications. Proposed medical applications of the carbon nanotubes require pure nanotube material. However, it has been established that beside nanotubes, the reaction product contains a mixture of different carbon forms, such as amorphous carbon (which covers the nanotubes), multi-shell carbon, as well as metal catalyst residues. The impurities affect the properties of the carbon nanotube reaction product and make its application problematic. Therefore, a controlled synthesis of different kinds of carbon nanofibers/nanotubes, their purification and the property modification became a very important object of materials research investigations. The growing interest in basic research on carbon nanotubes and in their applications require new, flexible approaches to their synthesis. Many researchers consider chemical vapor decomposition (CVD) method as the only viable approach to a controlled, large-scale production of carbon nanotubes, and in particular, the single wall nanotubes. In this work we present CVD synthesis of different forms of carbon nanofibers and nanotubes, their purification and modification by filling the nanotubes with different metals and large molecules like the fullerene (a “peapod” structure). Also we discuss problems that can become a serious barrier to the nanotubes applications.