Credit: © 2009 ACS

Molecular photoswitches use light to swap between states that can have different colours or absorption/emission properties. Diarylethylene switches have been used to control chemical and biochemical reactivity, but have not previously been used in vivo.

Now, Neil Branda and colleagues have shown (J. Am. Chem. Soc. 131, 15966–15967; 2009) that a molecular photoswitch can reversibly control paralysis in Caenorhabditis elegans nematode worms. The transparent worms were incubated in a mixture of the bipyridinium dithienylethene switch and a 10% dimethylsulfoxide buffer. One group of worms was exposed to the ring-open form and another to the ring-closed.

The 'ring-closed' group showed the characteristic blue/green photoswitch colour demonstrating its absorption into the worms (pictured). Although the 'ring-open' group did not, a 2-minute exposure to UV light flipped the photoswitch and the worms changed colour. Worms fed the ring-closed form for 60 minutes appeared immobile, and this paralysis could be turned on and off by alternating their exposure to UV and visible light.