Glucose meter incorporates photonic crystal to help provide continuous monitoring

University of Illinois (U. of I.; Champaign, IL) researchers have developed a continuous glucose-monitoring material that changes color as glucose levels fluctuate, with super-presise wavelength shift. Doctors and patients may be able to use it for automatic insulin dosing and it overcomes limitations with current continuous glucose monitoring technologies, as it has the ability to recalibrate frequently, according to Paul Braun, a U. of I. professor of materials science and engineering who led the work.

Related: Biosensor aims to measure glucose in saliva

The material the research team developed is made of hydrogel, a soft elastic jelly-like material, laced with boronic acid compounds. Boronic acid binds to glucose, causing the gel to swell and expand as the glucose concentration rises. Embedded within the hydrogel is a photonic crystal made of tiny, carefully arranged beads. A photonic crystal is like a mirror that only reflects one wavelength of light while the rest of the spectrum passes through. As the hydrogel expands, the reflected color shifts from blue to green to red.

Researchers have previously explored the possibility of using boronic acid hydrogels for glucose detection because they are not prone to interference from most factors in the bloodstream. However, they have been met with a specific challenge inherent to the chemistry: Boronic acid likes glucose so much that, if there isn’t enough glucose to go around, two boronic acids will bind to one glucose. This causes the hydrogel to shrink before the glucose concentration gets high enough for it to expand again.

The research team devised a solution to this problem by introducing a third chemical, called a volume resetting agent, to bind up the boronic acid before the glucose is added, pre-shrinking the gel and giving a baseline for measurements. This development enabled the researchers to capitalize on the advantages of a boronic acid system without the limitation of shrinking at lower concentrations.

The color-changing material is simple and low-cost to manufacture, and, according to Braun, a square inch of hydrogel could be enough for up to 25 patients.

The researchers envision the hydrogel as part of a subcutaneous system or a sophisticated device that taps into the bloodstream—an insulin pump, for example. However, the application they are most excited about is in short-term continuous monitoring of patients hospitalized or in intensive care units, when patients are most critically in need of continuous monitoring—diabetic or not.

"The sensor would be put on the end of a fiber-optic cable, for example, and threaded into the bloodstream along with IVs or other monitors," says Braun. "You could just slide it into an open port. Then you can monitor the patient for several days or longer."

Full details of the work appear in the journal Advanced Materials; for more information, please visit http://dx.doi.org/10.1002/adma.201401710.

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