Graphene has long been heralded as a miracle material. A layer of carbon just one atom thick, it has the potential for wide-ranging applications. One of these could be helping people monitor their blood sugar without using needles to collect blood samples or having a sensor embedded under their skin.
A team of researchers at Penn State have developed a wearable, non-invasive, low-cost device that can measure glucose levels in sweat on the skin's surface in a much less intrusive way, detailed in the journal Biosensors and Bioelectronics. The main component of the device is laser-induced graphene (LIG). These are layers of graphene in various shapes that can be made in seconds. Thanks to the material's ability to conduct electricity, LIG is an excellent sensing device, though only up to a point.
Graphene is not sensitive to glucose, so the scientists had to look for something that was. They settled on nickel due to its high sensitivity and mixed it with gold, which is unreactive, to reduce the possibility of an allergic reaction.
“The challenge here is that LIG is not sensitive to glucose at all,” senior author Professor Huanyu “Larry” Cheng said in a statement. “So, we needed to deposit a glucose-sensitive material onto the LIG.”
The amount of sugar in sweat is 100 times lower than what is found in blood, but the nickel gold alloy is sensitive enough to measure this correlation between blood sugar concentration and what is excreted in sweat, according to Cheng. The device requires an alkaline solution to work but to keep the risk of damage to the skin to zero, they have a way for sweat to enter the device without the skin having to deal with the solution.
The team demonstrated the device by attaching it to a person’s arms one hour and three hours after a meal. The subject performed a brief workout, and the sugar level detected from the device was compared to a commercially available glucose monitor, that confirmed the change in glucose levels.
This new approach is simpler than sensors that use enzymes, which are also non-invasive but require more fine-tuned conditions to work and to continue working, something the graphene-nickel device doesn’t require.
“An enzymatic sensor has to be kept at a certain temperature and pH, and the enzyme can’t be stored in the long term,” Cheng explained. “A nonenzymatic glucose sensor, on the other hand, is advantageous in terms of stable performance and glucose sensitivity regardless of these changes.”
The team plans to improve the device and better understand how patients and clinicians might want to use it. Using sweat to measure more than glucose levels is also a possibility.
“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.”