A team of engineers at the University of Illinois, Champaign, have developed a new continuous glucose monitoring material that changes color as glucose levels fluctuate. They say that the wavelength shift is so precise that doctors and patients may be able to use it for automatic insulin dosing, which is not currently possible using point measurements like test strips.

The systems available today all have some combination of limited sensitivity, limited precision, and frequent recalibration. So, without frequent recalibration, it’s not possible to make insulin dosing decisions or to drive autonomous dosing, they report.

The new sensor material is made of hydrogel laced with boronic acid compounds, which bind to glucose, causing the gel to expand as the glucose concentration rises. A photonic crystal made of tiny beads is embedded within the hydrogel and reflects only 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.

Previous research explored using boronic acid hydrogels for glucose detection, since they are not prone to interference from most factors in the bloodstream. But, if there isn’t enough glucose to go around, two boronic acids will bind to one glucose making the hydrogel shrink before the glucose concentration rises enough for it to expand again.

The researchers got around 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.