First 'living' laser made from kidney cell

A human cell, alive and lasing (Image: Malte Gather)

Typically, a laser consists of two mirrors on either side of a gain medium – 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 gain medium, releasing photons. Normally, these would shoot out in random directions, as in the broad beam of a flashlight, but a laser uses mirrors on either end of the gain medium to create a directed beam.

As photons bounce back and forth between the mirrors, repeatedly passing through the gain medium, they stimulate other atoms to release photons of exactly the same wavelength, phase and direction. Eventually, a concentrated single-frequency beam of light erupts through one of the mirrors as laser light.
Hundreds of different gain media have been used, including various dyes and gases. But no one has used living tissue. Mostly out of curiosity, Malte Gather and Seok-Hyun Yun of Harvard University decided to investigate with a single mammalian cell.

They injected 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 researchers 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. Even after a few minutes of lasing, the cell was still alive and well.

Christopher Fang-Yen of the University of Pennsylvania, who has worked on single-atom lasers but was not involved in the recent study, says he finds the new research fascinating. "GFP is similar to dyes used to make commercial dye lasers, so it's not surprising that if you put it in a little bag like a cell and pump it optically you should be able to get a laser," he says. "But the fact that they show it really works is very cool."
via New Scientist/read more