Do Surface Defects and Modification Determine the Observed Toxicity of Carbon Nanotubes?

The role of charge and surface modification in the toxicity of CNT is investigated. Two-photon confocal microscopy, Raman microscopy and Lactate Dehydrogenase (LDH) assay are employed to study the effect of CNT on Rat glioma cell line (C6 cells) and rat alveolar macrophage continuous cell line (AM 11). Two-photon confocal microscopy reveals that unmodified CNT is toxic to the C6 cell line but when modified by DNA it becomes relatively non-toxic. Both LDH assay and Raman microscopy show that CNT dispersed in serum is not toxic to the AM11 and C6 cell lines. We have illustrated that the controversy in CNT toxicity will continue, even within the same laboratory, if the surface properties of nanomaterials both before and after modification are not considered and understood before these materials are tested for toxicological properties.