The wavelength shift is so precise that doctors and patients may be able to use it for automatic insulin dosing - something not possible using current measurements like test strips.

“Using today's systems, you can determine trends in glucose levels but without frequent recalibration, you do not have the accuracy or reliability to use that to make insulin dosing decisions,” explained Paul Braun, a professor of materials science and engineering at University of Illinois.

The new system 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. As the hydrogel expands, the reflected color shifts from blue to green to red.

“There was a problem. Boronic acid likes glucose so much that if there is not enough glucose to go around, two boronic acids will bind to one glucose. This causes the hydrogel to shrink,” informed Braun.

So they introduced 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 researchers to capitalize on the advantages of a boronic acid system without the limitation of shrinking at lower concentrations. The colour-changing material is simple and cheap to manufacture. A square inch of hydrogel could be enough for up to 25 patients.

The sensor would be put on the end of a fiber optic cable, for example, and threaded into the bloodstream using intravenous therapy.

“You could just slide it into an open port. Then you can monitor the patient for several days or longer,” added co-author Chunjie Zhang.

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