Lasers are behind so much of our cutting-edge technology. Now scientists at the University of Michigan have successfully shown that is possible to build a working laser with blood, the better to spot tumours in the human body.
A laser is technically defined as any device that creates and amplifies a narrow, focused beam of light whose photos are all travelling in the same direction, rather than in every direction at once, like the light emitted by, say, a torch. There are many different types of lasers, from the semiconductor lasers found in laser pointers and DVD players, to CO2 lasers capable of melting through objects. (These were no doubt the type coveted by Dr. Evil when he demanded “sharks with frickin’ laser beams” on their heads in the first Austin Powers movie.)
Image: Austin Powers n Goldmember (2002)
All you need to build a laser is an empty cavity holding two mirrors on either end — one of which should be half-silvered, so that it reflects some light but lets other light through — and a lasing medium. The latter medium can be a crystal, like ruby or garnet, or some kind of gas or liquid. Really, almost anything that can be made to emit light will do. Pioneering laser scientists Theodor Hänsch and Arthur Schawlow even created the first edible laser out of jelly around 1970, trying out 12 different flavours before finding just the right one.
Zap the medium with light or electricity boosts the atoms to higher energy levels — an “excited” state. Then photons are pumped into the cavity. If one strikes an excited atom, that atom will drop back down to its ground state, releasing a second photon of the same frequency and direction. These in turn strike other energised atoms, releasing even more photons. The end result is a sudden burst of coherent light — the laser beam — as all the atoms discharge in a rapid chain reaction. It’s called stimulated emission, and yes, we’ve heard all the dirty jokes before.
In recent years, scientists have figured out how to turn individual cells into functioning lasers, injecting fatty cells in pig skin with fluorescent dye and zapping them with lasers to get them to emit light. In 2011, Harvard scientists built a laser out of a human kidney cell injected with DNA coding for a green fluorescent protein typically found in jellyfish. And the same team of Michigan scientists figured out how to turn the light-sensitive chlorophyll in plants into laser beams earlier this year.
Now Xudong Fan and his Ann Arbor colleagues are back with a new study using a fluorescent dye commonly injected into the bloodstream for medical imaging: indocyanine green (ICG). It’s the combination of the dye binding with proteins in blood plasma that results in the blood emitting light — essentially amplifying the emission and turning your blood into a lasing medium.
Because the dye accumulates in blood vessels, and tumours usually have lots of them, the technique should make it easier to spot tumours in the body. Just inject a bit of ICG and shine a laser onto the skin, using an infrared camera to capture any resulting glow. Fan and his colleagues still need to test the concept in animal tissue. But so far, the blood laser seems promising. [New Scientist]