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Wearable sensors reveal much from perspiration

30 January 2016

Flexible sensors measure metabolites and electrolytes in sweat, calibrate the data based on skin temperature and send the results to a smartphone.

UC Berkeley's wearable sensors measure skin temperature in addition to glucose, lactate, sodium and potassium in sweat (image: Der-Hsien Lien and Hiroki Ota, UC Berkeley)

While health monitors have exploded onto the consumer electronics scene over the past decade, University of California Berkeley researchers say this device is the first fully integrated electronic system that can provide continuous, non-invasive monitoring of multiple biochemicals in sweat.

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,” says principal investigator, UC Berkeley's Professor Ali Javey. “However, sweat is complex and it is necessary to measure multiple targets to extract meaningful information about your state of health. 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. Our work presents a technology platform for sweat-based health monitors.”

The prototype developed by Javey and his research team 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,” says co-researcher, Wei Gao. “This is important because the response of glucose and lactate sensors can be greatly influenced by temperature.”

Adjacent to the sensor array is the wireless printed circuit board with off-the-shelf silicon components. The researchers used more than ten chips responsible for taking the measurements from the sensors, amplifying the signals, adjusting for temperature changes and wirelessly transmitting the data. The researchers also developed an app to sync the data from the sensors to mobile phones in real time, and fitted the device on 'smart' wristbands and headbands.

“We can easily shrink this device by integrating all the circuit functionalities into a single chip,” says co-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.”

Javey notes that a long-term goal would be to use this device for population-level studies for medical applications. Other applications of the technology could include measuring vital metabolite and electrolyte levels of healthy persons in daily life. It can also be adapted to monitor other body fluids for those suffering from illness and injury.

An article describing this work is published in the journal, Nature.

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