Carbon Nanotube Bacterial Cytotoxicity: Does the Type of Carbon Nanotubes Matter?

We investigate the bacterial toxicity of well-characterized carbon nanotubes (CNTs) by several independent techniques. Results demonstrate that single-walled carbon nanotubes (SWNTs) are much more toxic to bacteria (E. coli) than multi-walled carbon nanotubes (MWNTs). The likely main CNT-cytotoxicity mechanism is cell membrane damage by direct contact with CNTs. Gene expression data shows that in the presence of both MWNTs and SWNTs, E. coli express high levels of stress-related gene products, with the quantity and magnitude of expression being much higher in the presence of SWNTs. The enhanced bacterial toxicity of SWNTs may be attributed to: (1) a smaller nanotube diameter that facilitates partitioning and partial penetration of nanotubes into the cell wall, (2) a larger surface area for contact and interaction with the cell surface, and/or (3) unique chemical and electronic properties conveying greater chemical reactivity.