Comparative cytotoxicity of kaolinite, halloysite, multiwalled carbon nanotubes and graphene oxide

This study aimed at comparative examining of the interactions between conventionally used clay and carbon nanomaterials and human lung adenocarcinoma cells (A549 cells). The following platy and tubular nanomaterials were tested: carbon nanoparticles, i.e. multi-walled carbon nanotubes (MWCNTs) and graphene oxide nanosheets (GO) as well as nanoclays, i.e. halloysite nanotubes (HNTs) and kaolinite nanosheets (Kaol). Nanoparticle physicochemical properties and their internalization into cells were examined using dynamic light scattering as well as atomic force, 3D laser scanning confocal and darkfield hyperspectral microscopies. Biological aspects of the nanomaterial-cell interaction included assessment of cellular toxicity, DNA damage, metabolic activity, and physical parameters of the cells. Regardless of a shape, carbon nanomaterials demonstrated cell surface adsorption, but negligible penetration into cells compared to nanoclays. However, carbon nanomaterials were found to be the most toxic for cells as probed by the MTS assay. They also turned out to be the most genotoxic for cells compared to nanoclays as revealed by the DNA-Comet assay. GO significantly increased the fraction of apoptotic cells and was the most cytotoxic and genotoxic nanomaterial. Comparison of flow cytometry and MTS data indicated that a cytotoxic effect of MWCNTs was not associated with increased cell death, but was rather due to a decrease in cell metabolic activity and/or proliferation. Finally, no significant effect of the shape of the tested nanomaterials on their internalization and cytotoxicity was revealed.