Recent anthrax scares in New York and Florida underscore the need for rapid detection of biological weapons. As this ScienCentral News video explains, scientists have developed a new laser technique that could detect anthrax in real-time.
Scanning Anthrax
In the middle of a flight to Chicago, American Airlines pilot Jim Scully received a disturbing call from the flight crew. "I'm prepared for anything. Sometimes it's a passenger illness, that's pretty common, someone having a heart attack ... I figured it was something like that," he says. But the call from the flight attendant on that November 2001 flight was much more unusual. "She said, 'There's a passenger in the back of the airplane, opening up her mail,' happened to be a doctor from Hartford, 'and she came across white powder that's in this envelope.'"
Jim Scully
It caused panic on the "fairly full" flight, he says, in a time when there were other anthrax attacks on major media organizations and legislators throughout the country. Passengers on the flight were relocated to other parts of the plane and wet towels were placed on the envelope. When they landed, Scully was frustrated that he couldn't give passengers more information. "The unfortunate thing about this whole incident was that there was no way to tell whether this substance was anthrax," he says. "So many of the passengers deplaned very concerned, in tears, and the best we could tell them was that 'We'll get back to you if it turns out to anthrax.'"
It took days for lab tests to determine that it was just a hoax. Jim Scully challenged his father, Marlan Scully, a laser physicist at Texas A&M and Princeton University, to come up with something faster. "I started looking at the problem," Marlan Scully says, "and I found that, yes, indeed, we can come up with techniques which are quicker, and those are based on light scattering." Marlan Scully's team reported in the April 2007 issue of the journal Science that they developed a new technique that's able to detect anthrax in real-time.
Their research is based on a type of light scattering called Raman scattering, which was developed by Indian physicist Chandrasekhara Venkata Raman in 1922. When light is aimed at an object, packets of light, called photons, bounce back. While most of these photons come back with the same amount of energy, Raman noticed that some of them were different. In a technique called Raman spectroscopy, these unique photons bounce back after exciting the material with a laser. As molecular bonds are disturbed, this creates a unique signature specific to that material. Marlan Scully compares the technique to making a guitar string vibrate, producing music. "It has atoms in a configuration that can be plucked. And so like a guitar, you pluck a guitar string, you hear the signal. You pluck an atom in a molecule, and you get molecular music," he says.
The source laser in Marlan Scully's lab at Princeton University.
But traditional Raman scattering produces a very weak signal for anthrax, Scully says. So his team developed a new technique, called FAST CARS, that makes the signal much stronger. They first shoot two lasers at the object, which causes its atoms to start vibrating or oscillating, and then send the third laser on a time-delay. "We start off [hitting] the molecules ... the ones we are particularly interested in go into very large oscillation, all the other bad guys just barely jiggle, and we wait a little while, not very long, we call it a picosecond, he explains. "A very tiny fraction of time, a millionth of a millionth of a second, and that’s enough for these [other] molecules, to quit vibrating." The third laser then focuses on the target molecules that are still vibrating, amplifying the signature.
In the lab, Scully adjusts the target object at the convergence of the three lasers. A bright, blue light radiates from the object. They use tanks of water in the demonstration to make the laser beams visible with the naked eye. The researchers capture the blue light and run it through a computer, which produces a line graph that identifies the substance. This all takes a fraction of a second, which could mean that the technique offers advantages over current anthrax detection methods that take minutes or even days.
"We plan on working with people who use anthrax mailroom sorter technology to use these light scattering ideas to see if there’s anthrax in the mail," Marlan Scully says. "And we’ll be able to do this, we think, by spotting each individual letter ... So we’d like to push this to where you look in a tiny fraction of a second and sample each of the pieces that is going by." Current technology sniffs samples of air, which can take a minimum of 15 minutes to process, making it harder to identify the source of anthrax.
Marlan Scully
Marlan Scully also says that the technology can be pointed up into the sky to search for airborne anthrax. "The next step is to engineer such a device so that it fits in the back of a pick-up truck. And we can take it off to various places where we’d like to be able to see [whether] we have this terrible substance in the air." Scully says that as technology progresses, they hope to scale down from van-sized equipment to a detector that could fit inside a suitcase.
He also says that the implications of this research aren't simply limited to detecting pathogens or bioweapons, it can also be used to analyze other materials, like blood chemistry. "We can have a system whereby we use scattering of light to measure glucose in the blood," he says. While the research is still in progress, Scully says that these lasers could one day be a painless way for diabetics to measure blood glucose.
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