While laser beam-shooting plants or animals might seem like something straight out of Star Trek, two researchers from the Wellman Center for Photomedicine at Massachusetts General Hospital recently wondered whether such organisms could theoretically exist. In order to satisfy their curiosity, Dr. Malte Gather and Dr. Seok Hyun Yun successfully created a laser that uses a living cell as its light source. The device, which utilizes a protein found in jellyfish, could have applications in the fields of biomedicine and optical computing.
Traditionally, lasers have used synthetic materials such as crystals, dyes and purified gases to amplify photon pulses as they bounce back and forth between two mirrors. Gather and Yun instead used a single, living cell as the optical gain media.
The cell was genetically engineered to express green fluorescent protein (GFP), which a species of jellyfish uses to create bioluminescent light. GFP was chosen because the application of additional enzymes isn't required in order to induce it to emit light, it has well-understood properties, and techniques were already in place for genetically programming organisms to express it.
One of the first steps of the experiment involved building an inch-long cylinder with mirrors at each end. This was then filled with a solution of GFP in water. After some trial and error, the scientists determined the concentration of GFP required to amplify short pulses of energy into laser light.
Next, a line of mammalian cells were produced, that expressed GFP at the required level. One of those cells, with a diameter of 15 to 20 micrometers, was then placed in a microcavity, between two highly-reflective mirrors placed 20 micrometers apart from one another. As was the case with the solution-filled chamber, the cell-based device was able to produce short pulses of laser light. The spherical shape of the cell was even found to help focus the light, resulting in lower input energy levels than were required for the solution.
The cells survived the process, with each one being able to generate hundreds of pulses.
"While the individual laser pulses last for only a few nanoseconds, they are bright enough to be readily detected and appear to carry very useful information that may give us new ways to analyze the properties of large numbers of cells almost instantaneously," said Yun. "And the ability to generate laser light from a biocompatible source placed inside a patient could be useful for photodynamic therapies, in which drugs are activated by the application of light, or novel forms of imaging."
"One of our long-term goals will be finding ways to bring optical communications and computing, currently done with inanimate electronic devices, into the realm of biotechnology," added Gather. "That could be particularly useful in projects requiring the interfacing of electronics with biological organisms. We also hope to be able to implant a structure equivalent to the mirrored chamber right into a cell, which would the next milestone in this research."
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