"We're trying to get a sense of what these materials do in a broader variety of contexts," says Shaw. "It makes you less dependent on the idiosyncrasies of a particular cell type." By using multiple cell types in different contexts, the researchers were able to identify classes of particles that have similar effects on cells. The group then tested three of the nanoparticles in mice and showed that the effects that the particles produced in the animals matched the effects observed in the cells.

The new screening tool, described in the Proceedings of the National Academy of Sciences, could help narrow the list of nanomaterials that need to undergo animal testing. It could also help researchers who are developing different applications focus their efforts on nanomaterials that are less risky, says Shaw.

Although the researchers tested a small range of materials, there's no reason why this method could not be applied to other types of materials, says Maynard. "The real power of this technique will be shown if it can work for really diverse nanomaterials, including different types of carbon nanotubes and different structures of materials." Recent studies suggest that certain types of carbon nanotubes behave like asbestos. Therefore, it would be interesting to see whether other types of nanotubes are less hazardous, adds Shaw. And although his team used cells that imaging nanoparticles are likely to encounter when injected intravenously, other cell types could be used as well, he says. For instance, if the particle is something that is inhaled, then researchers could use different types of lung cells.

However, Maynard cautions that testing particles for their effect on lung cells could be tricky with this system. The imaging particles used in the study mix well with water and are designed to circulate in the body. Figuring out how to expose the cells to airborne particles might be difficult. Still, he says, the study offers a new paradigm for assessing the toxicity of nanomaterials.

"We need a lot more of these kinds of well-designed and carefully thought-through studies," says John Balbus, chief health scientist at the Environmental Defense Fund, based in New York. "I'm optimistic that once these [high-throughput] studies start accumulating, we will gain a real understanding of the biological effects of nanomaterials."