Buckyballs at bat: toxic nanomaterials get a tune-up.

Over the past decade, the development of nanomaterials has progressed rapidly toward their eventual use in products ranging from solar cells to medicines. However, tests of possible toxic effects of these substances on human health and the environment have been slow to get under way. Recently, an experiment raised concern about the soccer-ball-shaped carbon molecules commonly known as buckyballs. Now, other chemists confirm that finding and report an innovation that might disarm potentially toxic buckyballs.

To preempt the same kind of public backlash that genetically modified crops have received, governments and industry are starting to look at nanomaterial toxicity more closely, says Kristen Kulinowski, executive director of Rice University's Center for Biological and Environmental Nanotechnology in Houston. "Over the last year and a half, there's been an enormous upswell in interest and funding for research into the environmental health and safety of nanomaterials," she says.

The subcellular size of these materials endows them with valuable properties but could also permit them to interact with living cells in unanticipated, potentially hazardous ways. For instance, this year, researchers found that buckyballs can damage fish brain cells by disrupting their membranes (SN: 4/3/04, p. 211).

To see whether the same effect occurs in human cells, a group of researchers led by Rice University chemist Vicki Colvin exposed lab-grown human liver and skin cells for 48 hours to solutions containing varying concentrations of buckyballs. The team found that a dilute solution--20 parts per billion--could kill half the cells.

"This study really validates our findings," says Eva Oberdoster at Southern Methodist University in Dallas, who conducted the buckyball-toxicity studies in fish.

The Rice researchers extended their experiment by adorning the carbon spheres with simple chemicals, for example, hydroxyl or carboxyl groups. They found that the more decorated the buckyballs, the less toxic they became. In fact, for those buckyballs with the largest number of chemical groups, the concentration needed to kill half the cells was more than 10 million times that required with naked buckyballs.

The Rice team's findings will appear in the Oct. 13 Nano Letters.

The researchers offer a possible explanation for the droll in toxicity. Naked buckyballs aggregate in solution, they note. Those clumpings generate reactive chemicals known as free radicals, which can attack cell membranes. Chemically coated buckyballs didn't clump, and the researchers detected no free radicals in solutions of those molecules.

Further analyses revealed that aggregates of naked buckyballs didn't harm DNA inside the cells, reducing the likelihood that these nanomaterials could be carcinogenic, says team member Christie Sayes.

The buckyball coatings in the Rice experiment might not decrease toxicity in all situations, Oberdorster notes. In the environment, for example, ultraviolet light from the sun might break off the hydroxyl groups, rendering the spheres toxic again. On the other hand, in the body, the coated buckyballs might remain intact and safely serve as drug-delivery vehicles.

The Rice team plans to test the potential toxicity of other nanoscale materials, such as the titanium dioxide nanoparticles that are used in cosmetics and sunscreens, and to investigate whether their toxicity is affected by size and shape.