Last year Roger Tsien of the University of California in San Diego shared the Nobel Prize in Chemistry with Osamu Shimomura and Martin Chalfie for their discovery of the famous green fluorescent protein, now widely used as a biological marker. A little lateral thinking suggests that infrared would offer much better penetration in living things owing to the reduced scattering compared with visible light. This is precisely what lies behind the latest discovery by Tsien and his team, who have engineered the first fluorescent protein to absorb and emit in the infrared.
Xiaokun Shu was able to coerce infrared fluorescence in a phytochrome – a receptor sensitive to light at the red end of the spectrum – from the bacterium Deinococcus radiodurans, which is best known for its extremely high tolerance to radiation. The work holds promise for imaging of small animals, but for humans, who are larger and more opaque, Tsien's team is working on different techniques.