Wearable sweat sensor could have broad range of uses

By Jonah Comstock

Researchers at Stanford University and the University of California-Berkeley have built a prototype that could lead to a slew of new features for wearable activity trackers. The group, led by principal investigator Ali Javey, a professor at UC-Berkeley, have created a wearable sensor that can continuously collect and monitor users’ sweat on the molecular level, then sends the information via Bluetooth to a smartphone. They detailed their discovery in the latest issue of Nature.

"Human sweat contains physiologically rich information, thus making it an attractive body fluid for noninvasive wearable sensors,” Javey said in a statement. "However, sweat is complex and it is necessary to measure multiple targets to extract meaningful information about your state of health. In this regard, we have developed a fully integrated system that simultaneously and selectively measures multiple sweat analytes, and wirelessly transmits the processed data to a smartphone. Our work presents a technology platform for sweat-based health monitors.”

The technology takes the form of a flexible sensor bandage that wraps around the wrist or the head (like a sweatband), which contains a set of five sensors, and a flexible circuit board that processes the signals and transmits the data. While the bandage would need to be replaced often, the flexible circuit board is reusable.

Sensors analyze the four constituent particles of sweat: sodium ions, potassium ions, glucose sugar, and lactate. In sweat studies, researchers have been able to learn a lot about athletes from their sweat, from their stress level to drug levels in their bloodstream. It could also have potential applications in diabetes management. In the past, sweat has mostly been collected in a lab setting and analyzed after the fact, so realtime monitoring could also open up new avenues of research.

In an accompanying Nature editorial, Jason Heikenfield makes the case that this could be the next big differentiator for the fitness tracking space. For athletes, sweat sensing could help alert them to dehydration, fatigue, or overheating.

“Today’s commercially available wearables largely rely on decades-old technology,” he writes. “Their market success is due to a convergence of improved affordability and ergonomics and a rapidly growing consumer awareness of health. The next watershed in wearables will probably be driven by scientific breakthroughs. Sweat biomonitoring arguably has the greatest potential among the emergent non-invasive technologies.”

Heikenfield has worked on similar technologies himself at the University of Cincinatti. In the editorial, he lays out some possible next steps to make sure the device is collecting and analyzing fresh sweat, or to create a version that induces sweating which could be used in a wider range of contexts. 

For the researchers, the aim is to use the device in population health studies when it’s ready. They hope it will open up volumes of new data that can be used in Stanford’s Precision Medicine initiative.

"Having a wearable sweat sensor is really incredible because the metabolites and electrolytes measured by the Javey device are vitally important for the health and wellbeing of an individual," George Brooks, a coauthor on the study, said in a statement. "When studying the effects of exercise on human physiology, we typically take blood samples. With this non-invasive technology, someday it may be possible to know what’s going on physiologically without needle sticks or attaching little, disposable cups on you."