Transparent sensor on contact lens developed to help monitor glucose

Researchers have developed a transparent sensor on a contact lens that may one day help type 1 diabetes patients monitor their blood glucose levels and control their insulin infusions.

With a nanostructured transistor, specifically an amorphous indium gallium oxide field effect transistor, or IGZO FET, the sensor can detect subtle glucose changes in physiological buffer solutions, such as the tear fluid in eyes.

The sensor, according to researchers at the Oregon State University College (OSU) of Engineering, will be able to transmit real-time glucose information to a wearable pump that delivers the hormones needed to regulate blood sugar: insulin and glucagon.

The sensor and pump would act as an artificial pancreas for people with type 1 diabetes, which can lead to serious health complications unless glucose levels are carefully controlled. Problems can include retinopathy, blindness, neuropathy, kidney and cardiac disease.

"We have fully transparent sensors that are working," said Greg Herman, an OSU professor of chemical engineering and corresponding author of a study published online in the journal Nanoscale. "What we want to do next is fully develop the communication aspect, and we want to use the entire contact lens as real estate for sensing and communications electronics."

The FET's closely packed, hexagonal, nanostructured network resulted from complimentary patterning techniques that have the potential for low-cost fabrication. Those techniques include colloidal nanolithography and electrohydrodynamic printing, or e-jet, which is somewhat like an inkjet printer that creates much finer drop sizes and works with biological materials instead of ink.

"It's an amperometric sensor and you can see the chips -- that means it has to be off to the side of the contact lens," Herman was quoted as saying in a news release from OSU. "Another issue is the signal is dependent on the size of the sensor and you can only make it so small or you won't be able to get a usable signal. With an FET sensor, you can actually make it smaller and enhance the output signal by doing this."

The research builds on earlier work by Herman and other OSU engineers that developed a glucose sensor that could be wrapped around a catheter, such as one used to administer insulin from a pump. "We can integrate an array of sensors into the lens and also test for other things: stress hormones, uric acid, pressure sensing for glaucoma, and things like that. We can monitor many compounds in tears - and since the sensor is transparent, it doesn't obstruct vision; more real estate is available for sensing on the contact lens," Herman said.

"A lot of type 1 diabetics don't wear a pump," Herman noted. "Many are still managing with blood droplets on glucose strips, then using self-injection. Even with the contact lens, someone could still manage their diabetes with self-injection. The sensor could communicate with your phone to warn you if your glucose was high or low." The transparent FET sensors, he said, might ultimately be used for cancer detection, by sensing characteristic biomarkers of cancer risk. Their high sensitivity could also measure things such as pulse rate, oxygen levels, and other aspects of health monitoring that require precise control. Endit