With a little help from a fluorescent protein, mammalian cells have been transformed into living lasers. This discovery could help improve imaging of living cells, enabling researchers to explore what's going on inside.

Laser stands for light amplification by stimulated emission of radiation, where amplification is usually achieved using dyes or crystals sat between two mirrors. Light is amplified by bouncing it between the two mirrors through a gain medium, which increases its power.

There was already some evidence that green fluorescent protein (GFP) could support lasing, but no-one had tried using the protein while it was still inside the cell. Seok Hyun Yun and his post-doc Malte Gather, both at Harvard Medical School, US, decided to try using it as a way to mark the 50th birthday of the laser. 

Normally, GFP just fluoresces when light is shone on it, but Gather and Yun discovered that when they fired very short pulses (~5ns) of blue light at a single cell expressing GFP, the protein amplified the light and the cell emitted a green laser. GFP is able to act as a gain medium for the blue light because the protein has an energy level system that is equivalent to that found in normal dye lasers. 

The cell survives the process, although Gather says he killed many cells by mistake while he was still learning the biological techniques to make GFP containing cells. Being a physicist he had to learn a lot of new techniques to insert the GFP gene into HEK cells and then grow them up. 'We both knew in theory how the protein should work, but neither of us had a good idea how to do the hands on work,' says Gather. 'It was quite an experience.' 

Having made their laser, Gather and Yun are now trying to integrate the optical cavity - the two mirrors - into cells, rather than using external mirrors. More immediately though, they think their cells could be used for biological assays. 

Clive Bagshaw, a visiting researcher at University of California, Santa Cruz, US, who is interested in GFP as a biological probe, says: 'The immediate application I can see is for multi colour imaging and separation.' Because the cell has sharp emission peaks, Bagshaw says it would be a great improvement on the fluorophores currently used, which have much broader emission spectra. 'I guess in principle the other GFP variants would lase at different wavelengths and that would really help and I think that's doable in the next year or so.' 

Laura Howes 

 

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