Follow the lead.

A new water-soluble, lead-sensing chemical is the first to detect the toxic metal in live cells, chemists report.

Christopher J. Chang of the University of California, Berkeley and his coworkers synthesized a molecular sensor that combines a fluorescent dye with a receptor that binds to lead. On its own, a solution of the sensing molecules weakly glows green in response to visible light. Upon binding to lead, the sensor glows 18 times as brightly.

In lab tests, the sensor detected lead in water at concentrations as low as 15 parts per billion, which is the Environmental Protection Agency's limit for the metal in drinking water. Chang and his team also demonstrated that other metal ions, such as iron and potassium, don't interfere with the selectivity of the sensor.

To test the sensor in living cells, the researchers grew two cultures of human embryonic kidney cells, added the sensor to each sample, and then exposed one of the cultures to a nontoxic amount of lead. When viewed under a confocal microscope, the metal-containing culture glowed, while the unexposed culture remained essentially dark, the team reports in the July 26 Journal of the American Chemical Society. The cells survived exposure to the sensing chemical.

Chang would like to design brighter sensors with more colors that could track lead within living cells. "What we are really interested in is, on a cellular level, the mechanism of lead toxicity," he says.