Carbon Nanotubes Become Nontoxic

"For medical applications, it is reassuring to see that the cytotoxicity of nanotubes is low and can be further reduced with simple chemical changes”, said Rice University's Center for Biological and Environmental Nanotechnology (CBEN) Director Vicki Colvin, the lead researcher on the project. Research has been conducted on the toxicity of carbon nanotubes, but CBEN's is the first to examine the cytotoxicity of water-soluble forms of the hollow carbon molecules.

In previous studies with buckyballs, CBEN found that even minor surface modifications could dramatically reduce cytotoxicity. The nanotube study found similar results. In both cases, the researchers identified specific alterations that reduce toxicity.

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. "In both cases, it's the same answer: change the surfaces."; Source: Rice University