A team from the Pennsylvania State University constructed the device first with laser-induced graphene (LIG) -- a material consisting of atom-thick carbon layers in various shapes. While LIG appeared to be an ideal framework for the sensing device -- it was "not sensitive to glucose at all".
The team then chose nickel because of its robust glucose sensitivity, and combined it with gold to lower potential risks of an allergic reaction.
While the concentration of glucose in sweat is about 100 times less than the concentration in blood, the team's new device is sensitive enough to accurately measure the glucose in sweat and reflect the concentration in blood, revealed the paper published online in Biosensors and Bioelectronics.
The nickel-gold alloy's sensitivity allowed the team to exclude enzymes, which are often used to measure glucose in more invasive, commercially available devices, said Huanyu "Larry" Cheng, Professor in Penn State's Department of Engineering Science and Mechanics.
However, nonenzymatic sensors require alkaline solution, which can damage the skin and typically limits device wearability. To curb this, the teama-attached a microfluidic chamber to the LIG alloy, which is connected to a collection inlet that passes sweat into the solution without allowing the solution to touch the skin.
The basic solution interacts with the glucose molecules to produce a compound that reacts with the alloy. This reaction triggers an electrical signal, indicating the concentration of glucose in the sweat, Cheng said.
In a proof-of-concept test, the researchers used a skin-safe adhesive to attach the reusable device to a person's arm one hour and three hours after a meal. The subject performed a brief workout -- just enough to produce sweat -- right before each measurement time.
A few minutes after collecting the sweat, the researchers found that the detected glucose concentration dropped from the first measurement to the next. The glucose measurements from the device were verified by measurements made with 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," Cheng said. "This glucose sensor serves as a foundational example to show that we can improve the detection of biomarkers in sweat at extremely low concentrations."