New biosensor stimulates sweat to take medical readings

Scientists have developed a new sensor that stimulates sweat glands in a small patch of skin, allowing it to take medical readings even when the user is not sweating.
Medical sensors that test human sweat need users to be sweating all day to take consistent health readings.
Researchers at the University of Cincinnati (UC) in the US developed a device the size of a Band-Aid that uses a chemical stimulant to produce sweat, even when the patient is not physically active.
The sensors can also predict how much patients sweat, an important factor in understanding the hormones or chemicals the biosensors measure.

"The challenge is not only coming up with new technological breakthroughs like this, but also bringing all these technology solutions together in a reliable and manufacturable device," said Jason Heikenfeld, professor at UC.
Blood analysis is considered the gold standard for biometric analysis. However, biometric testing with blood is invasive and often requires the use of a lab.

It is far more difficult for doctors to perform continuous monitoring of blood over hours or days.
Sweat provides a noninvasive alternative, with chemical markers that are more useful in monitoring health than saliva or tears, Heikenfeld said.
"People for a long time ignored sweat because, although it can be a higher-quality fluid for biomarkers, you can't rely on having access to it," Heikenfeld said.

"Our goal was to achieve methods to stimulate sweat whenever needed - or for days," he said.
Researchers applied sensors and a gel containing carbachol, a chemical used in eyedrops, to their subject's forearm for 2.5 minutes.
They used three methods to obtain sensor data - the gel and sensors, alone and in combination with memory foam padding and iontophoresis, an electrical current that drives a tiny amount of carbachol into the upper layer of the skin and locally stimulates sweat glands.
Then they recorded data obtained from the subject's sweat for 30 minutes using sensors that measured concentrations of sweat electrolytes. Carbachol was effective at inducing sweating under the sensor for as long as five hours.

Heikenfeld said a subsequent study successful generated sensor results for several days using this process to stimulate sweat.