Switching Off Buckyball Toxicity

Since their discovery at Rice in 1985, buckyballs—soccer-ball-shaped carbon molecules just one nanometer in diameter—have shown great promise in applications as diverse as fuel cells, batteries, pharmaceuticals, and coatings.

Recently, however, some scientists and activists have raised concerns about their potential toxicity to humans and animals. But there may be a solution to the problem, say researchers at Rice’s Center for Biological and Environmental Nanotechnology (CBEN), who have demonstrated a simple way to reduce the toxicity of water-soluble buckyballs by a factor of more than 10 million.

“There are many cases where toxicity is desirable,” says Vicki Colvin, CBEN director, professor of chemistry and chemical engineering, and the principal investigator for the research. “For example, we might want particles that kill cancer cells or harmful bacteria. In other cases—like applications where particles may make their way into the environment—toxicity is undesirable.”

CBEN’s study is the first cytotoxicity study of human cells exposed to buckyballs. Cytotoxicity refers to toxic effects on individual cells. The study found that even minor alterations to the surface of buckyballs can dramatically affect how toxic they are to individual cells, and the researchers identified specific alterations that render them much less toxic. In general, the greater the degree of surface modification, the lower the toxicity.

“We’re encouraged to see that controlling the surface properties of buckyballs allows us to dial the level of toxicity up or down, because making those kinds of modifications is something that chemists do every day in university research labs and in industry,” Colvin says.

“Moreover, we believe the technique can prove useful in tuning the toxicity of other nanoparticles.”

Colvin and her colleagues emphasize that the study only fills in part of the puzzle regarding fullerene toxicity. For example, because cytotoxic studies look only at cells in culture, they don’t tell scientists what happens inside the body, where cellular repair mechanisms and whole-organ and whole-body processes come into play.

“Cytotoxicity should not be confused with a full-fledged toxicological risk assessment,” says Kevin Ausman, CBEN executive director and a co-author of the paper. “Risk assessments take into account exposure rates, uptake mechanisms, transport within the body, and much more. Most often, cytotoxicity studies are used as indicators of whether more extensive toxicological study is needed. Based on our results, we think buckyballs should be studied in more detail, and we’re already working to arrange additional studies.”

CBEN’s research is funded by the National Science Foundation. The research appeared in the journal Nano Letters (2004, vol. 4, no. 10), published by the American Chemical Society.

—Jade Boyd