If researchers the world over have their way, cellphones will one day be used to detect and track everything from nuclear radiation to pollution to cancer, and it looks like you can now add one more to the group -- some researchers from the University of California, San Diego have developed a tiny sensor that could eventually let cellphones track airborne toxins in real time. To do that, the researchers have proposed a rather novel system that would consist of a tiny silicon sensor that changes color when it interacts with various chemicals, and a equally tiny camera with a macro lens that would actually capture an image of the sensor and display it on the phone's screen. As you might have guessed, however, while the researchers are now showing off the sensor itself, they still have a ways to go on the cellphone part of the equation -- although they have apparently started work on a prototype.