Tunable chemistry and morphology of multi-wall carbon nanotubes as a route to non-toxic, theranostic systems

Nanomedicine is one of the most promising areas of exploitation for multi-walled carbon nanotubes (MWNTs). These 'needle-like' nanovehicles are capable of carrying drug molecules via exo- and endohedral functionalisation and are steerable by an external magnetic field due to the presence of ferromagnetic nanoparticles in the nanotube core (up to 7.3 wt.%). These properties make them promising candidates for drug targeting or MRI contrast agents. Particularly, oxidised and nitrogen-doped MWNTs exhibiting enhanced chemical reactivity compared to their unmodified precursors/analogues could be exploited in this field. Here, we assessed the toxicity and intracellular localisation of two different, chemically modified and unmodified nanotubes towards human macrophage cells using a range of toxicity and imaging techniques. Oxidised and N-doped MWNTs were not significantly toxic to HMMs in contrast to unmodified MWNTs. All types of MWNTs entered the cell via active phagocytosis/endocytosis, but also passively by 'self-injection' through the plasma membrane, and were ultimately found in the cytoplasm and possibly also the nucleus. The attained results carry hope to utilise functionalised nanotube vectors as non-cytotoxic controllable drug delivery systems.