A Biological Beacon –Laser Beam Made from a Living Cell

Dn20563-1_300 In most instances, a laser consists of two mirrors on either side of a material whose structural properties allow it to amplify light. A source of energy such as a flash tube or electrical discharge excites the atoms in the medium, releasing photons. Normally, these would shoot out in random directions, as in the broad beam of a flashlight, but a laser uses mirrors  to create a directed beam.

Malte Gather and Seok-Hyun Yun of Harvard University decided to investigate with a single mammalian cell as the gain medium structure, injecting a human kidney cell with a loop of DNA that codes for an enhanced form of green fluorescent protein. Originally isolated from jellyfish, GFP glows green when exposed to blue light and has been invaluable as a biological beacon, tracking the path of molecules inside cells and lighting up when certain genes are expressed.

After placing the cell between two mirrors, the team bombarded it with pulses of blue light until it began to glow. As the green light bounced between the mirrors, certain wavelengths were preferentially amplified until they burst through the semi-transparent mirrors as laser light. The cell was still alive and well after a few minutes of laser stress.

Yun'was simply to test whether a biological laser was even possible, but he has also been mulling over a few possible applications. "We would like to have a laser inside the body of the animal, to generate laser light directly within the animal's tissue," he says.

In a technique called laser optical tomography, laser beams are fired from outside the body at living tissues. The way the light is transmitted and scattered can reveal the tissues' size, volume and depth, and produce an image.

The ability to image from within the body might give much more detailed images. Another technique, called fluorescence microscopy, relies on the glow from living cells doped with GFP to produce images. Yun's biological laser could improve its resolution with brighter laser light.

To turn cells inside a living animal into lasers, they would have to be engineered to express GFP so that they were able to glow. The mirrors in Yun's laser would have to be replaced with nanoscale-sized bits of metal that act as antennas to collect the light.

"Previously the laser was considered an engineering material, and now we are showing the concept of the laser can be integrated into biological systems," says Yun.

The Daily Galaxy via Journal reference: Nature Photonics, DOI: 10.1038/nphoton.2011.99

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