A newly developed internal “on-off” photoswitch paralyzes animals exposed to a beam of UV light – and keeps them paralyzed even after the light is extinguished. When the animals are exposed to ordinary visible light, the paralysis is reversed. Neil Branda and colleagues at Simon Fraser University published their findings, the first demonstration of such a light-activated switch in animals, in the Nov. 11, 2009, issue of the Journal of the American Chemical Society. This tiny worm became temporarily paralyzed when scientists fed it a light-sensitive material, or a photoswitch, and then exposed it to ultraviolet light. Courtesy of the American Chemical Society. The report describes the development and successful testing of a photoswitch composed of the light-sensitive material dithienylethene. The scientists grew transparent, pinhead-size worms (Caenorhabditis elegans) and fed them a dithienylethene. When exposed to ultraviolet light, the worms turned blue and became paralyzed. When exposed to visible light, the dithienylethene became colorless again and the worms’ paralysis ended. Many of the worms lived through the paralyze/unparalyze cycle. Scientists are not sure how the switch causes paralysis.