Researchers reduce toxic effects of nanotechnology through chemical change.

A number of people, Prince Charles included, have raised fears about the potential dangers of nanotechnology. But while talk of nanomachines turning the world into grey goo are far fetched, US researchers are finding evidence that certain nanoparticles, poly-hedral buckminsterfullerenes (C60, also known as buckyballs), cause damage to living cells.

Research conducted by teams at Rice University, Texas, and the Georgia Institute of Technology, Atlanta, has shown that buckyballs cause damage to human skin and liver cells. Researchers also found that this cytotoxicity can be greatly reduced by chemically modifying the buckyballs' surface .

The researchers were exploring the toxicity of buckyballs dissolved in water, where the particles group together into clumps known as 'nano-C60'. A previous study had shown that such clumps could cause damage to the brains of fish, but this is the first time the effects have been studied on human cells. To assess the toxicity, the researchers determined what concentration of buckyballs in solution would cause 50 per cent of a sample of human skin and liver cells to die - the LC50 value - and discovered that it was only 20 parts per billion (ppb).

The researchers then tested the toxicity of buckyballs with slight chemical modifications to their surfaces and discovered that they were much less cytotoxic. Buckyballs with three COOH side groups had a LC50 value of 10 000 ppb, while for those with 24 hydroxyl side groups it was over 5m ppb. Indeed, the level of toxicity appears to be inversely related to the degree of surface modification.

Differences in cytotoxicity seem to be due to the relative solubility of the nanoparticles. The side groups make the buckyball derivatives more water soluble and less likely to form clumps, and it is these clumps that appear to cause cytotoxicity. The researchers also showed that the clumps generate oxygen radicals that damage cell membranes, and are now studying this process in more detail.

Jon Evans