Sweet frequency: implantable glucose sensor transmits data wirelessly.
The sensor consists of a 4-centimeter-long strip of the magnetoelastic alloy used in antitheft markers. In a magnetic field, the alloy vibrates at a specific frequency. To adapt the material for glucose sensing, the researchers first coated the magnetic strip with a thin polymer layer and then applied a layer of the enzyme called glucose oxidase.
In a solution containing glucose, the enzyme converts that sugar to gluconic acid, increasing the acidity of the polymer. As a result, the polymer expels water, reducing its mass. This alters the frequency at which the strip vibrates in a magnetic field. The higher the concentration of glucose, the higher the frequency at which the sensor vibrates.
The researchers tested their sensor in glucose solutions representing the range of concentrations typical of the blood of diabetes patients. They describe their findings in the July 15 Analytical Chemistry.
Lead investigator Craig Grimes says that the device's sensitivity compares well with that of other glucose sensors being developed. But the real advantage is that this device is wireless and doesn't require a battery, he says. Doctors could implant the sensor under a patient's skin, say at the wrist. A small reader that both generates a magnetic field and detects changes in the sensor's frequency could then be worn like a wristwatch. "Or, if you were at home and you didn't want to wear a watch all the time, you could periodically wave your hand in front of the reader," says Grimes.
Each implantable sensor would cost less than a penny, while the cost of the reader would be about $50, the researchers estimate.
"The concept is interesting, and it's very innovative work," says Francis Moussy, a biomedical engineer at the University of South Florida in Tampa. However, modifying the device to make it work in animals is going to be a challenge, he adds.
Over the years, researchers have tried numerous schemes for implantable sensors but have had difficulty keeping them functional inside the body, says Moussy. The body forms scar tissue around foreign material, preventing a sensor from providing accurate readings. The one commercially available glucose sensor that's implanted under the skin has to be replaced every 3 days.
Grimes is also working on chemical and biowarfare sensing. Arrays of magnetic strips, each strip designed to respond to a different toxin, could simultaneously sniff out dozens of harmful agents. His group recently devised strips that sense the poison ricin and a bacterial toxin called staphylococcal enterotoxin B.
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|Title Annotation:||This Week|
|Date:||Jul 3, 2004|
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