A Cell Becomes a Laser

Lasers, the key to optical communications, data storage, and a host of other modern technology, are usually made from inanimate solids, liquids, or gases. Now, a pair of scientists have developed what could be the world's first biological laser. Built into a single cell, the laser might one day be used for light-based therapeutics, perhaps killing cancer cells deep inside the body.

Invented just over 50 years ago, the laser is essentially a light amplifier. It works by "pumping" atoms or molecules in a gas, liquid, or solid into a more energetic state, usually electrically, chemically, or with another laser. Once pumped, one of the "excited" atoms will eventually decay and emit a photon, and this photon will begin tipping the other atoms from their excited states, releasing a torrent of new photons in the process. These photons amplify their numbers further by bouncing back and forth between two mirrors, one of which is only partially silvered, which lets some of the light out in a characteristically focused beam.


   The light of life. This microscope image shows  
                green laser light shining from a single biological cell.

Physicists Malte Gather and Seok-Hyun Yun of Harvard Medical School in Boston have now figured out how to replicate this process in a living cell. "At the beginning of our work, the motivation to look at biolasers was mostly scientific curiosity," Gather says. "It was the time [last year] when the laser celebrated its 50th anniversary. We realized that although people had looked at many different types of materials for lasers, biological substances had not played a major role."

The key to Gather and Yun's biolaser is green fluorescent protein (GFP), a molecule that has proved endlessly useful to biologists since its discovery in the jellyfish Aequorea victoria in the early 1960s, partly because living cells can be so easily programmed to produce it. Gather and Yun did this with cells derived from a human kidney, adding the DNA that codes for GFP. The researchers then placed some of the cells producing GFP between two mirrors just one cell's width apart.

To lase, the GFP in the cells needed to be pumped with another laser, one that sends pulses of blue light at a low energy of about 1 nanojoule. Normally, blue light would simply make the GFP in the cells fluoresce—that is, emit light randomly in all directions. But inside the tight cavity, the light bounced back and forth, amplifying the emission from the GFP to a coherent green beam, the researchers report online today in Nature Photonics.

Qingdong Zheng, a materials scientist at John Hopkins University in Baltimore, Maryland, suggests that such biolasers could find uses in new types of sensors or in light-based therapeutics, in which light is used, for example, to kill cancer cells by triggering drugs into action that have already been administered. "It's a nice piece of work," he says.

Gather and Yun are also interested in the therapeutic possibilities of their device. And although the biolaser is still in its earliest stages of development, they speculate that in the long term it might also help the backbone of optical communications shift from inanimate electronic devices to biotechnology. This, Gather says, would make it easier to develop direct human-to-machine interfaces, in which a brain's neurons signal their operation with flashes of laser light, to be captured by an exterior device. Such an advance might enable disabled people to use computers without a mouse or keyboard, for example.

But perhaps the most intriguing aspect of the biolaser comes from its intrinsically living nature. In some types of conventional laser, the lasing medium degrades over time until it stops working properly. With biolasers, however, cells can continually make new GFP. "We might be able to make self-healing lasers," Gather says.


From   Science   |  12 June 2011