Elucidation of Potential\nGenotoxicity of MXenes Using\na DNA Comet Assay

MXenes are among the most diverse and prominent 2D materials.\nThey\nare being explored in almost every field of science and technology,\nincluding biomedicine. In particular, they are being investigated\nfor photothermal therapy, drug delivery, medical imaging, biosensing,\ntissue engineering, blood dialysis, and antibacterial coatings. Despite\ntheir proven biocompatibility and low cytotoxicity, their genotoxicity\nhas not been addressed. To investigate whether MXenes interfere with\nDNA integrity in cultured cells, we loaded the cells with MXenes and\nexamined the fragmentation of their chromosomal DNA by a DNA comet\nassay. The presence of both Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> and Nb<sub>4</sub>C<sub>3</sub>T<sub><i>x</i></sub> MXenes generated DNA comets, suggesting a strong genotoxic\neffect in murine melanoma and human fibroblast cells. However, no\ncorresponding cytotoxicity was observed, confirming that MXenes were\nwell tolerated by the cells. The lateral size of the MXene flakes\nwas critical for developing the DNA comets; submicrometer flakes induced\nthe DNA comets, while larger flakes did not. MXenes did not induce\nDNA comets in dead cells. Moreover, the extraction of the chromosomal\nDNA from the MXene-loaded cells or mixing the purified DNA with MXenes\nshowed no signs of DNA fragmentation. Unconstrained living MXene-loaded\ncells did not show cleavage of the DNA with MXenes under electrophoresis\nconditions. Thus, the DNA comet assay showed the ability of submicrometer\nMXene particles to penetrate living cells and induce DNA fragmentation\nunder the applied field. The most probable mechanism of DNA comet\nformation is the rotation and movement of submicrometer MXene flakes\ninside cells in an electric field, leading to cleavage and DNA shredding\nby MXene’s razor-sharp edges. Under all other conditions of\ninterest, titanium- and niobium-carbide-based MXenes showed excellent\nbiocompatibility and no signs of cytotoxicity or genotoxicity. These\nfindings may contribute to the development of strategies for cancer\ntherapy.