advance with overtones of Star Trek phasers and other sci-fi ray guns,
scientists in Canada are reporting development of an internal on-off “switch”
that paralyzes animals when exposed to a beam of ultraviolet light. The animals
stay paralyzed even when the light is turned off. When exposed to ordinary
light, the animals become unparalyzed and wake up. Their study appears in the Journal of the American Chemical
It reports the first demonstration of such a light-activated switch in animals.
Neil Branda and colleagues point out that such “photoswitches” --
light-sensitive materials that undergo photoreactions -- have been available
for years. Scientists use them in research. Doctors use light-sensitive
materials and photoreactions in medicine in photodynamic therapy to treat
certain forms of cancer. Those light-sensitive materials, however, do not have
the reversibility that exists in photoswitching.
The JACS report
describes development and successful testing of a photoswitch composed of the
light-sensitive material, dithienylethene. The scientists grew transparent,
pinhead-sized worms (C.
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 were not sure how the switch causes paralysis. The study
demonstrates that photoswitches may have great potential in turning
photodynamic therapy on and off, and for other applications in medicine and
research, they indicate.
-- News release courtesy of the