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 have caused increasing public concerns associated with their potential toxicological effects on and risks to humans and ecosystems. In this report, we comprehensively evaluated the nanotoxicity of SWCNTs and its relationship to varying lengths, functional groups and electronic structures, by employing both a newly established quantitative toxicogenomics test and conventional phenotypic bioassays. The objective is to reveal the potential cellular toxicity and mechanisms of SWCNTs at the molecular level, and to probe their potential relationships with the SWCNTs' morphological, surface, and electronic properties. The results indicated that DNA damage and oxidative stress were the dominant mechanisms of action for all the 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 the short SWCNT exhibiting a 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 the unmodified SWCNT. The 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, a dramatically different electronic structure-dependent toxicity was observed with the metallic SWCNT exerting a much higher toxicity than the semiconducting one which exhibited minimal toxicity among all the SWCNTs.