Christopher Chang wants to revolutionize cellular imaging by changing the way biologists tag the molecules they want to see. Most tags fluoresce continuously, and each one binds to a target molecule of a specific shape. Chang, however, is developing probes that fluoresce only when they react chemically with their targets. This will allow scientists to observe the generation, accumulation, and release of molecules involved in passing signals within and between cells.

For example, one of Chang's tags glows green when it reacts with hydrogen peroxide--a chemical found throughout the brain, where its function is largely unknown. The brighter the color, the more hydrogen peroxide a cell is taking up. Chang has used this tag to study neurons from the hippo­campus, a brain area vital for learning and memory. His research shows that the chemical, known mostly for causing cell damage, also plays an important role in neural signaling. --Emily Singer