Toxicity of Single-Walled Carbon Nanotubes (SWCNTs): Effect of Lengths, Functional Groups and Electronic Structures Revealed by a Quantitative Toxicogenomics Assay.

Single-walled carbon nanotubes (SWCNTs) are a group of widely used carbon-based nanomaterials (CNMs) with various applications, which raise increasing public concerns associated with their potential toxicological effect and risks on human and ecosystems. In this report, we comprehensively evaluated the nanotoxicity of SWCNTs with their relationship to varying lengths, functional groups and electronic structures, by employing both newly established quantitative toxicogenomics test, as well as conventional phenotypic bioassays. The objective is to reveal potential cellular toxicity and mechanisms of SWCNTs at the molecular level, and to probe their potential relationships with their morphological, surface, and electronic properties. The results indicated that DNA damage and oxidative stress were the dominant mechanisms of action for all SWCNTs and, the toxicity level and characteristics varied with length, surface functionalization and electronic structure. Distinguishable molecular toxicity fingerprints were revealed for the two SWCNTs with varying length, with short SWCNT exhibiting higher toxicity level than the long one. In terms of surface properties, SWCNT functionalization, namely carboxylation and hydroxylation, led to elevated overall toxicity, especially genotoxicity, as compared to unmodified SWCNT. Carboxylated SWCNT induced a greater toxicity than the hydroxylated SWCNT. The nucleus is likely the primary target site for long, short, and carboxylated SWCNTs and mechanical perturbation is likely responsible for the DNA damage, specifically related to degradation of the DNA double helix structure. Finally, dramatically different electronic structure-dependent toxicity was observed with metallic SWCNT exerting much higher toxicity than the semiconducting one that exhibited minimal toxicity among all SWCNTs.