http://abcnews.go.com/sections/SciTe..._040727-1.html
July 27, 2004— For people with advanced cases of diabetes, monitoring the levels of glucose in their blood is a routine hassle of needles and electronic measuring devices. But soon, diabetics may be able to wave it all goodbye. Literally.
Researchers at Penn State University have been working on developing a tiny sensor that could be implanted under a patient's skin to monitor the blood's chemistry and wirelessly report back its findings.
And as reported in a recent issue of Analytical Chemistry, Craig Grimes, a professor of electrical engineering and his team took a unique approach to developing this new sensor.
Grimes says the basic research began about four years ago as he thought about how to create a sensor that would work without requiring a power source or a physical connection with monitoring equipment. And the answer, he says, was in the technology most consumers are familiar with at retail stores: those tiny anti-theft tags hidden in merchandise.
"I was thinking about how those anti-theft markers work," says Grimes. "Effectively what you have there is a passive sensor that costs about next to nothing to produce, yet can be monitored over a large area."
Securing the Sensor's Technology
Specifically, the markers — or "magnetoelastic tags" — are thin ribbons of plastic that vibrate when passed through a magnetic field. Radio scanners tuned to the correct frequencies can pick up the vibrations which occur too fast to be felt or heard.
To make their experimental glucose sensor, Grimes and his team modified these magnetoelastic tags with special chemical compositions.
The plastic threads are first coated with a material that reacts to changes in acidity. Added to that is a layer of glucose oxidase, a chemical that reacts with blood glucose.
When the sensor encounters glucose, the oxidase produces an acid which reacts with the undercoating and causes the sensor to swell. The tiny change in the sensor's shape varies the frequency of vibrations.
Cheap Decoder Ring
Grimes compares the sensor to acoustic bells.
"If you hit a bell with a hammer, it rings at a certain expected frequency," he says. "But if you coat the bell with paint, you'll get a different sound the next time you hit that bell with a hammer."
Grimes and his team have been studying the changes differing levels of blood glucose would have on the sensor. The data is then encoded into a software program which would allow an electromagnetic reader to determine how the changes in vibration frequencies correlate to changes in blood glucose levels.
In lab tests, Grimes and his team have been able to detect readings from a six millimeter long sensor using a scanner up to six inches away. And while the reader is, for now, a bulky box, Grimes expect they could shrink the electronics down to the size of a wristwatch.
What's more, the magnetoelastic material of the sensor itself is extremely inexpensive. "The ribbon is a bona fide bulk material that you can buy on a spool for about $250 per kilometer," says Grimes. And that could lead to development of a sensor that could warn of other dangers in a person's blood.
Grimes, for example, envisions a biosensor array where different lengths of the magnetoelastic material are coated with different chemical agents — say one to detect E.coli, another for ricin, and another for staph bacteria. "The sensor platform can be used for any chemical or biological analysis," says Grimes. "You're limited only by the ability of chemists to make the proper surface coating."
Working on the Nitty Gritty
Such developments, however, would be quite a few years distant, And while Grimes says he see no "roadblocks" in producing even the simple blood glucose monitor, he notes: "There's still a lot of nitty-gritty issues."
Chief among the pending research is in vitro testing. The lab has already secured several pigs which will receive implants of the prototype sensor. And as that work progresses, the team will face important challenges.
"The chemistry we use [in the detector] is pretty stable," says Grimes. "But once it goes into a [living] body you have issues like protein bio-fouling."
Grimes hopes to prevent the sensor from becoming coated with other natural blood chemicals — which would reduce the sensor's effectiveness — by "overdriving" the sensor.
"These structures actually vibrate," says Grimes. "If we periodically overdrive it — excite it to vibrate so it becomes chaotic — our initial result shows [the sensor] shakes off the crud. It would be a pretty simple solution [to bio-fouling]."
But Grimes and his team won't be sure of that solution until animal testing is complete. And the findings will have to be submitted to and approved by the Food and Drug Administration before any sensor implants become commercially available.
That means, it could be quite a few years before diabetics can dismiss the needles with a simple wave of the hand.
Wireless Implant Monitors Blood Sugar, Pathogens. 
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