Electronic Finger Wrap Uses Sweat for Automatic Monitoring of Vital Chemical Levels

Advanced wearable health monitoring platforms require sophisticated sensing capabilities and integrated electronics. Nevertheless, existing systems are hampered by issues such as limited energy supply, sensing restrictions, regulatory complexities, and bulkiness. Now, engineers have introduced a sweat-powered wearable device, energized by the sweat from a wearer's fingertip, that makes continuous, personalized health monitoring as easy as wearing a Band-Aid.

Developed by engineers at the University of California San Diego (La Jolla, CA, USA), this innovative electronic finger wrap can monitor vital chemicals like glucose, vitamins, and medications in the sweat it uses for power. The device, which fits snugly around the finger, operates by harnessing energy from the sweat produced by the fingertips—a part of the body with a high concentration of sweat glands, capable of producing sweat 100 to 1000 times more than other body areas, even at rest. This continuous production of sweat, without requiring physical activity or external stimuli, provides a dependable source of energy, allowing the device to function even during inactivity or sleep. The device, highlighted in a paper published Sept. 3 in Nature Electronics, is constructed from several electronic components printed onto a flexible, stretchable polymer, allowing it to conform to the skin and withstand repeated bending, stretching and movement.

At the core of the device's function are biofuel cells placed against the fingertip, designed to efficiently convert sweat's chemical components into electrical energy. This energy is stored in stretchable, silver chloride-zinc batteries that power the device's four sensors, each dedicated to tracking different biomarkers: glucose, vitamin C, lactate, and levodopa, a medication for Parkinson’s disease. Sweat is channeled to these sensors through microfluidic paper paths that also facilitate the biomarker analysis, simultaneously powering the device. Data from the sensors are processed by a small chip, which wirelessly transmits the information to a custom smartphone or laptop app via Bluetooth.

In trials, the device was worn by a subject for monitoring glucose during meals, lactate during desk work and physical activities, vitamin C while consuming orange juice, and levodopa levels after eating fava beans. It offers the flexibility to be tailored for monitoring different health markers based on individual needs. Researchers are now focusing on creating a closed-loop system that not only tracks but also administers treatments based on the biomarker data collected. This could be particularly transformative for conditions like diabetes, where the device could continuously adjust insulin delivery in response to real-time glucose monitoring, and then assess the efficacy of the treatment through ongoing biomarker assessment.

“This is automatic health monitoring at your fingertips,” said study co-first author Shichao Ding, a postdoctoral researcher at the UC San Diego Jacobs School of Engineering. “The wearer can be resting or asleep, and the device can still harvest energy and track biomarker levels.”

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