Skin-adhered sensor tracks blood glucose levels via its wearer's sweat
Currently, most diabetics have to check their blood glucose levels by performing finger-prick blood tests, or via subdermal implanted sensors. An experimental new device, however, could someday do the job while simply adhered to the surface of the user's skin.
Presently being developed at Pennsylvania State University, the low-cost sensor is about the size of a US quarter-dollar coin, and is designed to measure glucose levels in the wearer's sweat. Although the glucose concentration in sweat is about one one-hundredth as much as that in the bloodstream, there is nonetheless a consistent correlation between the two.
The sensor incorporates a foam electrode, made up of laser-induced graphene coated with a nickel/gold alloy. Although graphene is very strong, chemically stable and electrically conductive, it isn't glucose-sensitive on its own. Nickel is very glucose-sensitive, however, which is why it's used in the electrode. The gold is added to reduce the risk of an allergic reaction to the nickel.
Via capillary action, the device draws sweat in through a small inlet, and carries it into a microfluidic chamber filled with an alkaline solution. The system keeps that solution from coming into direct contact with the wearer's body – this is an important consideration, due to the fact that alkaline solutions can damage the skin.
Glucose molecules present within the sweat react with the solution, creating a compound that is channeled into the foam electrode. That compound reacts with the nickel, producing an electrical signal. Using either an external or a built-in device to measure the strength of that signal, it's possible to ascertain the glucose level in the sweat, and thus in the bloodstream.
In a test of the technology, the sensor was placed on a volunteer's arm using a skin-safe adhesive. Readings were taken both one and three hours after they had consumed a meal – right before those readings, the person performed a brief workout to produce a small amount of sweat. The sensor indicated that their blood glucose dropped between the two readings, reporting levels in line with those obtained using a commercially available glucose monitor.
"We want to work with physicians and other health care providers to see how we can apply this technology for daily monitoring of a patient," says the lead scientist, Prof. Huanyu "Larry" Cheng. "This glucose sensor serves as a foundational example to show that we can improve the detection of biomarkers in sweat at extremely low concentrations."
The research is described in a paper that was recently published in the journal Biosensors and Bioelectronics. For examples of other wearable sensors that take different approaches to measuring glucose levels in sweat, check out the devices that are being developed at the University of Texas, the University of Cincinnati, Korea's Institute for Basic Science, and Germany's Fraunhofer Institute for Microelectronic Circuits and Systems.
Source: Penn State