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On hot days, when life seems to mimic a line in the chorus of Lil Jon & the East Side Boyz’ banger “Get Low,” our sweat could actually give us important information about how our bodies are doing.
In fact, researchers have gone to the windows and walls to demonstrate the potential of sweat. Unlike wearables that can only measure electrical currents at the skin’s surface (think FitBits and Apple Watches), a sweat-based biosensor could track the concentrations of electrolytes and sugar in the bloodstream and alert the wearer when their levels drop too low.
Now, engineers at The Ohio State University and the University of Wisconsin-Madison have developed battery-free sweat sensors that can measure several chemicals and give accurate readouts at a range of concentrations. Their sensors can be worn like a necklace or even implanted into the skin, where they would work throughout a user’s lifetime.
“We hope that eventually these sensors can be seamlessly integrated into our personal belongings," Ohio State engineering researcher and senior author Jinghua Li told Ohio State News. "Some of us may wear necklaces, some may wear earrings or rings. But we believe these sensors could be placed in something we all wear and that it could help us better track our health."
Sweat biosensors are not a new idea for noninvasive monitoring, but most designs are bulky and require batteries that limit their lifespan. In the new study published on July 6 in Science Advances, the researchers combined typical biosensor design with electrical engineering principles to develop their sensors, which work in the same way as radios tuning into channels do. They then tested how well their flexible biosensors could measure dissolved potassium, calcium, sodium, and hydrogen ions at concentrations typically found in human sweat. Dropped into solutions of sodium, potassium, and hydrogen ions, a calibrated system of sensors measured the concentrations of each to between 97.5 and 98.9 percent accuracy.
When they found that the sensors performed well, they expanded the chemicals tested to include serotonin and glucose and then designed a wearable version of their sensor that looked identical to a necklace. However, the clasp, chain, and pendant each contained part of their battery-free circuit. The researchers recruited two people to work out on an exercise bike while the necklace recorded their blood sugar levels. In one experiment, they took a break to rest, then continued pedaling; in another, they drank a sugary beverage during the break. The necklace sensors accurately measured an increase in blood glucose when the participants drank the sweetened beverage, offering additional confirmation that the sensors worked.
The scientists see a clear use for their sweat sensors: Being able to measure blood sugar without finger picks, for instance, could improve patients with diabetes’ day-to-day experience.
“By wirelessly tracking biomarker concentrations associated with the response of the body to environment, stress, and disease, this innovative, versatile device concept can find broad applications in biomedical research and clinical practices,” the researchers wrote in the study.