Dressing a wound may stop the bleeding, but it can't tell you whether the cut has become infected. Now "smart" bandages being developed at the University of Rochester change color not only to warn patients and doctors that there is an infection, but also to specify which bacteria are present.

The smart bandage is a thin sensor made of crystalline silicon and layers of porous silicon. The porous silicon is treated with a liquid that contains probe molecules engineered to bind to fat molecules found on the surface of specific bacteria. When the bandage is placed over an infected area, bacteria from the wound move into the porous silicon and attach themselves to the probe molecules, altering the optical properties of the silicon. Doctors illuminate the bandage with light from a handheld semiconductor laser device, and the bandage luminesces in a color that indicates the kind of bacteria that are present-red for E. coli, for example, or yellow for strep. With the immediate diagnosis of the culprit germs, doctors won't have to wait for the results of laboratory cultures.

Researchers at the University of California, San Diego, are working on similar sensors. Refinements to the technology should help smart bandages make their way into hospitals within a year or two as sensors embedded in the mesh of standard dressings. But you may see them popping up elsewhere sooner. The same technology could be applied to meat wrappers and other food packaging, which would show a warning color upon detection of food-borne bacteria. Such sensors could also be affixed to drinking glasses that would check for water purity or indications of biowarfare. Bandages aren't just for skinned knees anymore.