A fully integrated electronic system that continuously monitors multiple biochemicals in sweat has been fitted to wearable devices that alerts users to potential health problems such as fatigue, dehydration and high body temperatures.

"Sweat is complex, and it is necessary to measure multiple targets to extract meaningful information about your state of health,” notes Ali Javey, University of California Berkeley professor of electrical engineering and computer sciences, who led research into the development of the sweat monitoring system. "In this regard, we have developed a fully integrated system that simultaneously and selectively measures multiple sweat analytes and wirelessly transmits the processed data to a smartphone."

Wearable sensors measure skin temperature as well as glucose, lactate, sodium and potassium in sweat. Image credit: Der-Hsien Lien/Hiroki Ota, UC Berkeley.The prototype developed by Javey and his research team packs five sensors onto a flexible circuit board that measure skin temperature, the metabolites glucose and lactate and the electrolytes sodium and potassium.

“The integrated system allows us to use the measured skin temperature to calibrate and adjust the readings of other sensors in real time,” says Wei Gao, a postdoctoral fellow who assisted in the research. “This is important because the response of glucose and lactate sensors can be greatly influenced by temperature.”

The researchers used more than 10 integrated circuit chips responsible for taking the measurements from the sensors, amplifying the signals, adjusting for temperature changes and wirelessly transmitting the data. They then developed an app to sync the data from the sensors to mobile phones and fitted the device onto “smart” wristbands and headbands.

The device, and dozens of volunteers, were then put through various indoor and outdoor exercises. Study subjects cycled on stationary bikes or ran outdoors on tracks and trails for periods ranging from several minutes to more than an hour.

“We can easily shrink this device by integrating all the circuit functionalities into a single chip,” says fellow researcher Sam Emaminejad. “The number of biochemicals we target can also be ramped up so we can measure a lot of things at once. That makes large-scale clinical studies possible, which will help us better understand athletic performance and physiological responses to exercise.”

In addition to measuring perspiration, the researchers believe the non-invasive wearable technology could be adapted to monitor other body fluids for those suffering from illness and injury.