A sticker-like wearable sensor measures glucose, chloride, and other biomarkers in sweat—without the need for a battery (Sci. Adv. 2019, DOI: 10.1126/sciadv.aav3294). With further clinical testing, the sweat sensor may find applications in sports medicine or as a glucose monitor for people with diabetes.
Researchers have been developing implantable or wearable skin-like electronics for about 15 years and have made many demonstrations of potential clinical applications. These technologies are beginning to mature, says John Rogers, a materials scientist at Northwestern University. But powering them in a user-friendly way remains challenging. Most demonstrations of wearable devices—especially those that collect biochemical data—require bulky batteries or tether the user to an external power source.
The Northwestern team tackled this by developing self-powered sensing elements and a set of compact electronics to transmit data and receive power. They added these components to a disposable microfluidic sticker that passively sops up sweat on a person’s skin and routes it to teardrop-shaped chambers. Some of the chambers measure the volume of sweat; others contain dyes that change color in response to pH or chloride levels.
In the new device, some chambers contain electrochemical reagents that react with glucose or lactate, generating a tiny local voltage that can be read out by electronics on the sticker. When the wearer stands near an antenna or swipes a phone over the sensor, flexible circuits within the sensor pick up a small amount of power from emitted radio waves and use the resulting electrical pulses to read out the electrochemical sensors and transmit the data.
Levels of chloride or lactate in sweat could tell people working out that they are dehydrated or that their cells have stopped burning calories aerobically. Rogers’s start-up Epicore Biosystems has partnered with L’Oréal and Gatorade to develop consumer versions of the pH and electrolyte sensors.
Whether there are broader medical implications isn’t yet clear. “Sweat is understudied in general,” says Wei Gao, a medical engineer who’s developing wearable sweat sensors at the California Institute of Technology. He hopes wearable technologies will help fill in the gaps. Sweat chloride levels are used to diagnose cystic fibrosis in newborns, and there is a strong correlation between sweat alcohol and blood alcohol levels. But without an easy way to take real-time readings, it’s been unclear whether or how levels of other biomarkers in sweat correlate with blood levels.
Rogers’s team used the new sensors to measure glucose levels in sweat from people wearing the devices for two days. The data correlated with blood glucose levels, but there was a time delay between when the blood levels changed and when the sweat levels did. Rogers says further study is needed to determine whether sweat glucose can be used to inform insulin dosing for people with diabetes.