( ld dramatically reduce cytotoxicity. Th...)Modifications render carbon nanotubes nontoxic

Cytotoxicity refers to toxic effects on individual cells. In cytotoxicological studies, identical cell cultures are exposed to various forms and concentrations of toxins. In order to compare the toxicity of different compounds, scientists look for the concentration -- typically measured in parts per million or parts per billion -- of materials that lead to the death of 50 percent of the cells in a culture within 48 hours.

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."

Co-authors on the paper include graduate students Christie Sayes, Feng Liang, Jared Hudson, Jonathan Beach and Condell Doyle; undergraduate
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Source:Rice University