| The ultimate success of many nanotechnologies will depend on our ability to understand and manage nanomaterial health risks. Previous research suggests surface properties are very important to biological toxicity of carbon nanotubes. Carbon nantubes are now primarily fabricated by catalytic routes and typically contain significant quantities of transition metal catalyst residues, such as iron, which are hypothesized to cause reactive oxygen species. The surface properties of nanomaterials may cause interactions of nanomaterials with cells' extra celluare fluid, which induces problems to in vitro cellular assays that are currently limiting progress to understand nanomaterials' toxicity. This thesis discusses the impact of surface reactivity (iron metal effect) and properties (surface area, functionalization and hydrophobicity) of CNTs to their toxic potential from the viewpoint of material scientists. Techniques to "detoxify" CNTs by changing CNT's surface reactivity are also discussed.;Iron-catalyzed free radical generation has been proposed to contribute to oxidative stress and toxicity upon exposure to ambient particulate and amphibole asbestos fibers. Simple acellular assays were validated and used to show that toxicologically significant amounts of iron can be mobilized from a diverse set of commercial nanotube samples in the presence of ascorbate and the chelating agent ferrozine. The redox activity was examined by plasmid DNA breakage. Techniques were applied to avoid or remove this bioavailable metal. Potentially responsible mechanisms and optimized acid treatment protocols for free metal in "purified" samples are discussed.;In addition to direct interactions between cells and nanotubes (endocytosis, phagocytosis, cell attachment), the high-surface-area nanotubes may influence cell behavior indirectly by adsorbing, deactivating, or destroying biological solutes in extracellular fluid or cell culture medium. Biochemical profiling techniques and UV/visible spectroscopy were used to show that SWNTs cause dose-dependent adsorption and depletion of over 14 amino acids and vitamins from RPMI cell culture medium. The combined results suggest that the dominant mechanism is competitive multicomponent physical adsorption on hydrophobic nanotube surface patches, and the implications for biological assays and cell behavior is discussed. |
