BIOLOGICAL AND ECOLOGICAL RESPONSES TO CARBON-BASED NANOMATERIALS

Nanotechnology has been undergoing tremendous development in recent decades, driven by realized perceived applications of nanomaterials in electronics, therapeutics, imaging, sensing, environmental remediation, and consumer products. Along with these developments there have been increased evidences that engineered nanomaterials are often associated with hazardous effects they invoke in biological and ecosystems through intentional designs or unintentional discharge. Consequently there is a crucial need for documenting and understanding the interactions between nanoparticles and biological and ecosystems. This dissertation is aimed at bridging such a knowledge gap by examining the biological and ecological responses to carbon nanoparticles, a major class of nanomaterials which have been mass produced and extensively studied for their rich physical properties and commercial values. Chapter I of this dissertation offers a comprehensive review on the structures, properties, applications, and implications of carbon nanomaterials, especially related to the perspectives of biological and ecosystems. Given that there are many types of carbon nanomaterials available, this chapter is focused on three major types of carbon-based nanomaterials only, namely, fullerenes, single walled and multi-walled carbon nanotubes. Based on the literature review in Chapter I, Chapters II-VI present step-by-step my Doctor of Philosophy (PhD) research on elucidating the biological and ecological responses to carbon nanoparticle exposure, from the whole organism level down to the cellular and molecular level. On the whole organism level, specifically, Chapter II presents a first study on the fate of fullerenes and multiwalled carbon nanotubes in rice plants, which was facilitated by the self assembly of these nanomaterials with NOM. The aspects of fullerene uptake, translocation, biodistribution, and generational transfer in the plants were examined and quantified using bright field and electron microscopy, FT-Raman, and FTIR spectroscopy. The uptake and transport of fullerene in the plant vascular system were attributed to water transpiration, convection, capillary force, and the fullerene concentration gradient from the roots to the leaves of the plants. On the cellular level, Chapter III documents the differential uptake of hydrophilic C60(OH)20 vs. amphiphilic C70-NOM complex in Allium cepa plant cells and HT-29 colon carcinoma cells. This study was conducted using a plant cell viability assay, and complemented by bright field, fluorescence and electron microscopy imaging. In particular, C60(OH)20 and C70-NOM showed contrasting uptake in both the plant and mammalian cells, due to their significant differences in physicochemistry and the presence of an extra hydrophobic plant cell wall in the plant cells. Consequently, C60(OH)20 was found to induce toxicity in Allium cepa cells but not in HT-29 cells, while C70-NOM was toxic to HT-29 cells but not to the plant cells. Along with the biophysical study presented in Chapter III, Chapter IV further delineates the toxicological consequences of cell exposure to C60(OH)20. The cytoprotective properties of C60(OH)20 against copper were demonstrated using a double-exposure system: HT-29 cells were first exposed to C60(OH)20 and then to copper, a physicologically essential element and a major toxin. Using cell viability, proliferation, and intracellular reactive oxygen species (ROS) production assays, I demonstrated the inhibition of copper-induced cell damage and ROS production by C60(OH)20. Neutralization of copper ions by C60(OH)20 in the extracellular space, as well as adsorption and uptake of the nanoparticles surface-modified by the cell medium were identified as plausible mechanisms for the cytoprotective activities of C60(OH)20 against copper. Extended from the cellular studies in Chapters III and IV, Chapter V and VI show molecular-level inhibitions of two major cellular processes -- DNA amplification and MT polymerization -- by C60(OH)20. Such inhibitions were mainly attributed to the formation of hydrogen bonding between the nanoparticles and the hydrogens of the triphosphate tail of the nucleotide/DNA or the tubulin heterodimers, the building blocks of microtubules. Specifically, in Chapter V, the effect of C60(OH)20 on the amplification of an HSTF gene was examined using PCR and real-time PCR, whereas in Chapter VI circular dichroism spectroscopy, GTP hydrolysis assay, and ITC measurements were utilized to examine the effect of C60(OH)20 on MT polymerization. In both cases, the experimental results were confirmed and substantiated by molecular dynamics simulations. Based on the studies documented in Chapters II-VI, Chapter VII summarizes and rationalizes the results obtained from the dissertation research and projects future work which may be beneficial to our understanding of nanoparticles at large. In short, this dissertation is composed of the following chapters: o Chapter I: Literature review o Chapter II: Uptake, translocation and transmission of carbon-based nanomaterials in rice plants o Chapter III: Differential uptake of carbon nanomaterials by plant and mammalian cells o Chapter IV: Cytoprotective properties of a fullerene derivative against copper o Chapter V: Experimental and simulations studies of a real-time PCR in the presence of a fullerene derivative o Chapter VI: In vitro polymerization of microtubules with a fullerene derivative o Chapter VII: Conclusions and future wor