October 27, 2005, Houston, TX--In follow-on work to last year's toxicological study on water-soluble buckyballs, researchers at Rice University's Center for Biological and Environmental Nanotechnology (CBEN) have found evidence that water-soluble carbon nanotubes are significantly less toxic than previously thought. Moreover, the research indicates that nanotubes, like buckyballs, can be rendered nontoxic with minor chemical modifications.
The findings come from the first toxicological studies of water-soluble carbon nanotubes. The study, which is available online, will be published in an upcoming issue of the journal Toxicology Letters.
In the current study, CBEN researchers exposed skin cell cultures to varying doses of four types of water-soluble single-walled carbon nanotubes, or SWNTs. The four included pure, undecorated SWNTs suspended in soapy solution and three forms of nanotubes that were rendered soluble via the attachment of the chemical subgroups hydrogen sulfite, sodium sulfite and carboxylic acid.
The cytotoxicity of undecorated SWNTs was 200 parts per billion, which compares to the level of 20 parts per billion identified last year for undecorated buckyballs.
The modified nanotubes were non-cytotoxic. While cell death did increase with dose concentration, cell death never exceeded 50 percent for these compounds, which were each tested to a level of 2,000 parts per million. Just as with buckyballs, CBEN found that higher degrees of surface modification led to lower toxicity for SWNTs.
"We now have two studies on carbon nanoparticles that show us how to make them dramatically less cytotoxic," said CBEN Executive Director Kevin Ausman, a co-author of the study. "In both cases, it's the same answer: change the surfaces. This is an important demonstration that there are general trends in biological responses to nanoparticles."