Sweet beams: Lasers to measure blood sugar

Technique shows early promise in gauging diabetics’ glucose levels

A new, gentler technique for measuring blood sugar uses a pair of laser beams instead of a needle. The device could provide a way for diabetics to monitor their glucose levels without the pain of pricked fingers.

The physicists who created the device hope it will one day be used in hospitals to monitor patients continually, or miniaturized for the home. But first, the researchers will have to prove that their approach works not just for sugar water but in actual humans, a hurdle that has tripped up many previous efforts.

“Having a noninvasive way to measure glucose has long been a holy grail for our community,” says Andreas Mandelis, an applied physicist at the University of Toronto, who with a colleague describes the technique in an upcoming issue of Physical Review E.

For at least 20 years, scientists have tried to use beams of near-infrared light to measure glucose levels in the body. This light passes through human tissue harmlessly. Chemical bonds in the sugar molecule vibrate when struck by it, absorbing energy. This absorption can be measured, providing information about the concentration of glucose in the blood.

But this fingerprint of glucose is easily smudged. Other materials floating around in the soup that is blood can also absorb near-infrared, creating a mess that’s difficult to untangle.

For a more specific signature, some researchers have turned to slightly longer wavelengths. Mid-infrared light is absorbed by glucose, but not by other molecules in the blood — with one huge exception. Water, which makes up most of blood’s volume, overwhelmingly soaks up this kind of light.

To erase this background noise, Mandelis’ team used two beams of mid-infrared light tuned to slightly different wavelengths. One is absorbed by both water and glucose, the other by only water. When both beams strike dissolved glucose in concert, the water absorptions cancel each other out, giving off measurable heat that spotlights just the sugar.

Tested on sugar dissolved in water and on human blood serum, the technique has proved to be sensitive even to small quantities of glucose. But other researchers, along with Mandelis himself, recognize that there’s a long road to travel before the technology can be commercialized.

“Performance in whole blood samples, physical tissue models and, importantly, in human subjects has still to be proven,” says Ishan Barman, an analytical chemist trying to develop noninvasive glucose testing systems at MIT. Mandelis says he is working with a Toronto hospital to set up tests in people.

Another obstacle to widespread use may be the sophisticated lasers required to produce the finely tuned twin beams of light.

“The equipment is very complex,” says Andrea Tura, a biomedical engineer at the Italian National Research Council’s Institute of Biomedical Engineering in Padua. “One can wonder whether it will ever be possible to develop a simpler system that a diabetic patient can buy and use at his home for daily monitoring.”

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