The researchers are also experimenting with other, more specific mechanisms for triggering a drug's release. For example, diseased cells might express a particular enzyme not present in their healthy counterparts. "If we can play to the presence of an enzyme--specifically in a diseased cell--to break a particular chemical bond, then we can introduce that chemical bond into the machinery," says Stoddart.

Stoddart hopes that the new nanovalve system will eventually be employed for cancer treatment, where it could deliver drugs directly to tumor cells. Existing chemotherapy drugs come with nasty side effects, such as nausea and hair loss, precisely because they can't distinguish different targets. "The drugs are as much bad news to healthy cells as they are to the diseased cells," says Stoddart.

The nanovalve system might also be adapted to treat degenerative diseases where a particular cell type is affected, or for the controlled release of insulin to treat diabetes. Other, nonmedical applications--in food and cosmetics, or for environmental remediation--are also possible.

All these applications will require substantial modification and refinement of the nanovalve machinery. Ideally, the cucurbituril molecules would fall off their stems at a very specific pH, which could be tailored to specific applications. At the moment, that level of control remains elusive.

And while the valves have proven highly effective at controlling the release of dye in a test tube, their safety and efficacy in living systems have yet to be demonstrated. Tests on cells, animals, and eventually humans will be necessary before any potential medical applications can be realized.