Wearable sensors to monitor sweat in real time

Scientists have developed a wearable sensor system that can non-invasively monitor multiple biochemicals in sweat, measure skin temperature and sync the results to a smartphone in real time.
The advance opens doors to wearable devices that alert users to health problems such as fatigue, dehydration and dangerously high body temperatures.
"Human sweat contains physiologically rich information, thus making it an attractive body fluid for non-invasive wearable sensors," said principal investigator Ali Javey, professor at University of California, Berkeley (UC Berkeley).
"However, sweat is complex and it is necessary to measure multiple targets to extract meaningful information about your state of health," Javey said.

"When studying the effects of exercise on human physiology, we typically take blood samples," said George Brooks, a UC Berkeley professor.
"With this non-invasive technology, someday it may be possible to know what's going on physiologically without needle sticks or attaching little, disposable cups on you," said Brooks.

The prototype packs five sensors onto a flexible circuit board. The sensors measure the metabolites glucose and lactate, the electrolytes sodium and potassium, and skin temperature.
"The integrated system allows us to use the measured skin temperature to calibrate and adjust the readings of other sensors in real time," said Wei Gao, a postdoctoral fellow in his Javey's lab.

"This is important because the response of glucose and lactate sensors can be greatly influenced by temperature," Gao said.
Adjacent to the sensor array is the wireless printed circuit board with off-the-shelf silicon components.
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.
The researchers developed an app to sync the data from the sensors to mobile phones, and fitted the device onto "smart" wristbands and headbands.
They put the device - and dozens of volunteers - through various indoor and outdoor exercises. Study subjects cycled on stationary bikes or ran outdoors on tracks and trails from a few minutes to more than an hour.

"We can easily shrink this device by integrating all the circuit functionalities into a single chip," said Sam Emaminejad, a postdoctoral fellows in his Javey's lab.
"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," Emaminejad said.
The study was published in the journal Nature.