How did the idea for this study come about?
We started more than a year ago, just before the 50th anniversary of the original demonstration of the laser. People have made many advances with lasers, but all materials they've been using were synthetic. Nobody had looked [extensively] into using natural materials for lasers laser light doesn't seem to exist in nature. We wondered whether we could actually generate laser light in a living system, and, it turns out, we can.
How did you make a laser out of a living cell?
We start out with a petri dish to which we [add] a few cells from a widely used cell line. We feed them with nutrients and add a chunk of DNA, a short program that tells the cell how to produce GFP [green fluorescent protein, which was originally derived from jellyfish and is commonly used as a biomarker in experiments]. Then we wait for two days or so for cells to take up DNA and replicate and produce GFP. We then harvest cells and put them into a cavity between a pair of two mirrors separated by a very short distance20 micrometers, which is about half the thickness of a human hair.
Then we take a blue laser and shine the light onto a single cell. That charges up the GFP, which emits green light (a process called fluorescence). In the cavity between the mirrors the green light now bounces back and forth. It'd be like standing in an elevator whose walls are mirrors. When the light passes through molecules that are charged to emit light, you can trigger the molecules to emit even more light, in a process called stimulated emission. You can think of the GFP like a photocopy machine for photons. You send in one green-light photon, and it will produce a second particle of green light that is identical. So you get two, then four, then eight, and so on. This process is repeated over and over again, and [it has] an avalanche effecta wave of photons that makes a laser.
Besides coming from a living organism, how is this laser different from others?
It can heal itself. Lasers are notorious for dying over time, because the active medium inside degrades. But with a living laser the cell can produce new GFP.
Are there any other molecules other than GFP that might work? What makes GFP special?
GFP is just one protein among a whole family of fluorescent proteins that organisms use to make light, or create bioluminescence. But GFP is much more [pervasive], and it can be inserted into just about any organism.
Why doesn't the light hurt or kill the cell?
Basically, because it's not of that high an intensity it comes from a very brief pulse of light. Between the pulses we have a long break that gives the cell time to cool down.
How strong is the light you're using?
One nanojoule, or 1 billionth of a joule.
How does this compare to a laser pointer?
During the pulse, it's actually 1000 to 10,000 times more intense than a laser pointer. But since it's in pulses, it's a lot fewer total photons.
How strong is the laser beam?
We haven't quantified it yet, but you can see it with your naked eye.
How long did it take to adjust the minute variables in this and to get everything right?
Once you know what you're doing, the experiment can be done in an afternoon (not including time to grow the cells). But to figure out how to do it, it took us more than a year.
Why did you pick this cell type, which is derived from human kidneys?
It's a widely used cell type in biologists' labs. It's relatively easy to work with and does many things that are typical for other cells.
We are working quite intensely to learn more about the inside of cells from looking at the cell's laser light. It has a relatively complex pattern [that] carries information about structures within. It could perhaps tell us, for example, if a group of cells is cancerous or benign.
We also would like to further develop the cell so that all the components could exist within the cell so that it could work as a stand-alone unit. We'd like to get rid of the blue light source that pumps that laser and try to use bioluminescence to power the laser. We don't know yet if this is possible.
It would also be interesting to use lasers to communicate with neurons in the brain. Optical communication is known to be very efficient as compared to electrical. So having the ability to generate laser light, and hopefully control when and how the laser light is generated, would possibly open a door to do optical interfacing between men and machine.