Contact lenses that change their appearance according to the wearer’s blood-sugar level could one day help people with diabetes keep track of their levels non-invasively.

Diabetes affects the body’s ability to make or use the hormone insulin, which can cause dangerously large swings in levels of blood sugar, or glucose. Currently, most people suffering diabetes monitor their blood sugar by pricking their skin and drawing blood.



But Chris Geddes, the study’s lead author and associate director of the Center for Fluorescence Spectroscopy at the University of Maryland, US, has tried to create less painful alternatives. Developing a monitoring system through contact lenses makes sense because many people with diabetes also need glasses or contact lenses due to the way diabetes affects the blood vessels in the retina, Geddes says.



To make glucose-sensing contacts, scientists added boronic acid to disposable contact lenses. Moisture from the tear ducts contains glucose that binds with the molecules of boronic acid, with the reaction causing fluorescence. A handheld device flashes a blue light into the eye and measures the intensity of the resulting glow, letting the user know their blood glucose level.



When they were working on the contact lens, Geddes and his group hit a snag early in the development phase. Most boronic acid molecules prefer a slightly alkaline environment. But the inside of a contact lens is slightly acidic.



“We had to go back to the drawing board and design molecules that used boronic acid yet survived in a mildly acidic environment,” Geddes says. “They also had to be sensitive to ultra-low concentrations of glucose.”



Geddes’ team is looking at several options for users. Rather than having the entire contact lens glow, tiny sensor spots could be placed around the contact lens. Those spots could monitor glucose, as well as sodium, cholesterol and potassium.



Another sugar – fructose – is present in tears, but it exists in much lower concentrations so Geddes says it should not interfere with the glucose readings.



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