Smart Wearable Sensor Takes Sweat-Monitoring To Next Level

Plastic sensor array combined with flexible silicon IC accurately measures several biomarkers in sweat

2 min read
Smart Wearable Sensor Takes Sweat-Monitoring To Next Level
Illustration: Der-Hsien Lien and Hiroki Ota

Sweat might not be pleasant but it contains dozens of chemical compounds whose concentrations change in real time, compounds that could reveal your body’s response to disease, drugs, diet, injury, and stress, among other things. To tap into that treasure-trove of information, researchers have built a wearable sensor that measures levels of specific molecules in sweat and then wirelessly relays the data to a smartphone via a Bluetooth module.

The smart device, fashioned as a wristband or headband, combines a panel of plastic chemical sensors with silicon integrated circuits made on a flexible circuit board. It continuously measures levels of four different components of sweat: two electrolytes, potassium and sodium ions, and two metabolites, glucose and lactate. Ali Javey, electrical engineering and computer sciences professor at the University of California, Berkeley and his colleagues reported the sensor in Nature.

Other research groups have demonstrated wearable sweat sensors before. But those measure one analyte at a time or don’t have the signal processing circuitry and calibration mechanism to accurately monitor analyte levels.

Javey and his colleagues built an array of chemical sensors, each 3-mm wide, on a flexible plastic substrate. The sensors are similar to ones reported before. They are based on enzymes or special chemical cocktails that react with the metabolite or ion to be measured and generate an electrical signal. But the researchers built on previous sensors by treating electrodes with specific added chemicals that reduce potential drift and make the new sensors more stable and reliable.

The team also added a temperature sensor made of a winding metal microwire across which resistance changes in response to temperature. The temperature sensor is a critical component for accurate monitoring, Javey says. Many sensors developed so far have had a strong temperature dependency. “As temperature changes, output of the sensor changes,” he says. “Of course when you sweat, there are big changes in skin temperatures. So you need to constantly measure temperature and correct the sensor’s output as a function of temperature.”

Electrical signals from the sensor array, which comes in contact with the skin, go to a silicon IC made on a flexible circuit board. The IC filters, processes and calibrates the data and converts it to an output denoting concentration of the analyte, which is sent to the phone.

To test the sensor, a human subject wore the smart wristband and headband while exercising on a stationary cycle. The researchers found that measurements from the sensor matched the metabolite and electrolyte numbers measured in sweat samples taken every few minutes.

Finally, the researchers demonstrated the sensor array’s use to monitor dehydration in people running outdoors by measuring sodium and potassium ions, whose concentration increases with dehydration. “We’re now extending our work to look at a broader spectrum of molecules in sweat for a broader application domain,” Javey says. “Our design is very generic. Should be easy to extend sensors to other chemicals.”

“They’re the first academic group to combine sweat sensors into a complete wearable system with Bluetooth,” says Jason Heikenfeld, a professor of electrical engineering at the University of Cincinnati, who has co-founded the startup Eccrine Systems to commercialize his own lab’s sweat-sensing technology. “This system can sync up to a phone and give continuous data that’s certainly exciting. It’s all engineering but it’s very hard to bring everything together. This takes us a step closer to what people would primarily want to use.”

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Restoring Hearing With Beams of Light

Gene therapy and optoelectronics could radically upgrade hearing for millions of people

13 min read
A computer graphic shows a gray structure that’s curled like a snail’s shell. A big purple line runs through it. Many clusters of smaller red lines are scattered throughout the curled structure.

Human hearing depends on the cochlea, a snail-shaped structure in the inner ear. A new kind of cochlear implant for people with disabling hearing loss would use beams of light to stimulate the cochlear nerve.

Lakshay Khurana and Daniel Keppeler
Blue

There’s a popular misconception that cochlear implants restore natural hearing. In fact, these marvels of engineering give people a new kind of “electric hearing” that they must learn how to use.

Natural hearing results from vibrations hitting tiny structures called hair cells within the cochlea in the inner ear. A cochlear implant bypasses the damaged or dysfunctional parts of the ear and uses electrodes to directly stimulate the cochlear nerve, which sends signals to the brain. When my hearing-impaired patients have their cochlear implants turned on for the first time, they often report that voices sound flat and robotic and that background noises blur together and drown out voices. Although users can have many sessions with technicians to “tune” and adjust their implants’ settings to make sounds more pleasant and helpful, there’s a limit to what can be achieved with today’s technology.

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