Finger bandage uses sweat to provide health monitoring at fingertips

A sweat-powered wearable could make it possible to continuously and individually monitor health as easy as wearing a Band-Aid. Engineers at the University of California, San Diego, have developed an electronic device that monitors levels of vital chemicals (such as glucose, vitamins, and even medications) in the sweat on your fingertips, from which it draws its energy.

The advance was published on September 3 in Natural electronics by the research group of Joseph Wang, Aiiso Yufeng Li Family Professor in the Department of Chemical and Nano Engineering at UC San Diego.

The device, which wraps around the finger, draws its power from an unexpected source: sweat from the fingertips. Despite their small size, fingers are among the largest producers of sweat in the body, with more than a thousand sweat glands each. These glands can produce 100 to 1,000 times more sweat than most other parts of the body, even at rest.

This constant trickle of natural perspiration, without any stimulus or physical activity, provides a reliable source of energy, powering the device even during periods of inactivity or sleep.

The device consists of several electronic components printed on a thin, flexible and stretchable polymer material. Its design allows it to conform to the finger while being robust enough to withstand repeated bending, stretching and movements.

“It relies on a remarkable integration of energy harvesting and storage components, with multiple biosensors in a fluidic microchannel, as well as the corresponding electronic controller, all within reach,” Wang said.

At the heart of its operation are biofuel cells placed where the device contacts the fingertip. These cells have been specially designed to efficiently collect and convert chemicals in sweat into electricity. This electricity is stored in a pair of expandable silver-zinc chloride batteries, which power a series of sensors (four in total), each tasked with monitoring a specific biomarker: glucose, vitamin C, lactate and levodopa, a drug used to treat Parkinson’s disease.

Sweat is channeled to these sensors through tiny paper microfluidic channels. The device analyzes biomarker levels, while drawing the energy it needs from the sweat it collects. A small chip processes the signals from the sensors and wirelessly transmits the data via Bluetooth Low Energy to a custom-designed smartphone or laptop app.

“This is an automatic health monitoring system at your fingertips,” said Shichao Ding, co-senior author of the study and a postdoctoral researcher in Wang’s research group at the Jacobs School of Engineering at the University of California, San Diego. “The wearer can be resting or asleep, and the device can still harvest energy and track biomarker levels.”

In testing, a subject wore the device throughout the day to track glucose levels during meals, lactate levels during desk work and exercise, vitamin C levels while drinking orange juice, and levodopa levels after eating fava beans, a natural source of the compound.

Ding and co-first author Tamoghna Saha say the device can be customized to meet individual health needs by detecting different sets of biomarkers.

Researchers are working on developing a closed-loop system that not only monitors biomarkers but also administers treatments based on the data collected. For example, in the case of diabetes, such a device could continuously monitor glucose levels and automatically administer insulin if needed, and then assess the effectiveness of the treatment by further monitoring biomarker levels.

“Autonomous power, sensing and processing all in one device: that’s the ultimate goal,” Ding said.