‘Check-up’ at your fingertips, here’s a hi-tech patch powered by finger sweat

You wouldn’t think so, given their small size, but fingertips are by far one of the most prolific parts of the body in producing sweat. Each one, experts explain, is home to over a thousand sweat glands, and this ‘factory’ can produce 100 to 1,000 times more sweat than most other areas of the body, even at rest. This constant flow of natural sweat, which continues even without stimulation or physical activity, offers a reliable source to power a wearable device, a high-tech patch, capable of ensuring continuous and personalized health monitoring. A ‘check-up’ at your fingertips, which works 24 hours a day, even during sleep or periods of inactivity. Engineers at the University of California San Diego developed it.

It’s a tiny electronic finger band, a wearable device powered by sweat that monitors vital chemical parameters, such as glucose levels, but also vitamins and even medications, all by analyzing the sweat of the fingertips themselves, from which it draws its energy. The patch and this new health-analysis strategy were described in a study published in ‘Nature Electronics’ by the research group of Joseph Wang, a professor at UC San Diego. The device, which wraps around the finger, and draws energy from this ‘unlikely’ source, is made up of several electronic components printed on a thin, flexible and stretchable polymer material. Its design allows it to conform to the finger while being strong enough to withstand repeated bending, stretching and movement. “It is based on a unique integration of energy harvesting and storage components, with multiple biosensors in a fluidic microchannel, along with the corresponding electronic controller, all on the fingertip,” Wang describes.

At the heart of how it works are biofuel cells that sit where the device makes contact with your fingertip, and they’re specially designed to efficiently collect and convert chemicals in sweat into electricity. That electricity is stored in a pair of 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. As sweat is transported through tiny paper microfluidic channels to these sensors, the device analyzes biomarker levels, all while drawing the energy it needs from the sweat it’s sampling. A small chip processes signals from the sensors and wirelessly transmits the data via Bluetooth low energy to a custom-designed smartphone or laptop app.

It sounds like science fiction, but this system is shaping up to be “automatic health monitoring at your fingertips,” says the study’s first co-author, Shichao Ding, a postdoctoral researcher in Wang’s research group at UC San Diego Jacobs School of Engineering. “The wearer can rest or sleep, and the device can still harvest energy and track biomarker levels.” In tests conducted by the experts, a person wore the device throughout the day to monitor glucose levels during meals, lactate levels during office 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 tracking different sets of biomarkers. The researchers are working to develop a closed-loop system that not only monitors these biomarkers but also delivers treatments based on the data it collects. For example, in the case of diabetes, such a device could continuously monitor glucose levels and automatically deliver insulin as needed, then assess the effectiveness of the treatment by further monitoring the levels. “Autonomous power, sensing, and treatment all in one device—that’s the ultimate goal,” Ding says.