Characterization, Nanosafety, and Cellular Imaging of Carbon Nanotubes
This dissertation presents three important contributions to the field of carbon nanotube (CNT) environmental health and safety (EH&S). The first concerns aqueous CNT samples purified by centrifugation, the importance of thorough CNT sample characterizations, and improving the comparability of CNT toxicity assessments. Herein, using carboxylated multi-walled CNTs (cMWCNTs) suspended in water without a surfactant, a Boehm titrimetric method was developed and used to show for the first time that the surface acidity of oxidized carbon materials in aqueous cMWCNT suspensions was enriched by ~40% by a single low-speed centrifugation step. This significant difference in surface acidity between un-centrifuged and centrifuged cMWCNT suspensions has not been previously appreciated and is important because the degree of surface acidity is known to affect the interactions of cMWCNTs with biological systems. The second concerns the lack of CNT exposure data from laboratories where dry CNT powders are handled, the need to fully understand CNT release scenarios to make accurate EH&S risk assessments and to implement effective control measures, and the lack of chemical specificity with the current suite of instrumentation used to monitor the release of CNTs in workplaces. Herein, the first demonstration of Raman spectroscopy to unequivocally identify whether particulate matter collected from a multi-user analytical balance workstation comprised CNTs is presented. The approach revealed CNT contamination at this workstation, led to the identification of the exact CNT products, the users who handled these CNTs, and an improved protocol for safely weighing CNTs. The third concerns the need to more thoroughly understand how macrophage cells, the primary responders to foreign particles, process the CNTs that they accumulate. Herein, the distribution of poloxamer-coated, pristine and carboxylated MWCNTs within murine RAW 264.7 macrophage cells is assessed using Raman microscopy to image MWCNTs and immunofluorescence microscopy to image phagolysosomes. In both cases, MWCNTs were observed to co-localize in phagolysosomes, which supports the hypothesis that these cells can accumulate MWCNTs by phagocytosis. This evidence has implications with respect to the proper functioning of phagolysosomes in maintaining cellular health, as well as, being able to rationally design novel approaches to remediate potential chronic toxicity by accumulated MWCNTs.