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Sweat stimulating biosensor could rival blood tests
August 20, 2017, 11:50 am

One downside to medical sensors that test human sweat is that you have to sweat. But sweating from exertion on a treadmill or a stifling room temperature can be impractical for some patients and unsafe for others. Also, it is unlikely patients will want to sweat all day for the benefit of a sensor reading.

But researchers at the University of Cincinnati have come up with a novel way to stimulate sweat glands on a small, isolated patch of skin so subjects can stay cool and comfortable and go about their daily routine without spending hours on a treadmill.

The device, about the size of a Band-Aid, uses carbachol, a chemical stimulant, to produce sweat, even when the patient is relaxed and cool. The sensors also can predict how much a patient sweats, which is an important factor in understanding the hormones or chemicals the biosensors measure.

Blood analysis is considered the gold standard for biometric analysis. But biometric testing with blood is invasive and often requires the use of a lab. And, 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, say researchers behind the new device.

Scientists say sweat provides much of the same useful information about patients as blood. The problem has always been getting the same consistent sample as is possible with a standard blood draw. “Though sweat is better quality biomarker for many tests, it was previously neglected as you could not rely on accessing it when needed. Our research aimed to stimulate sweat whenever needed -- or for days,” said the researchers.

Testing sweat has other possible benefits over blood said the team behind the device. “If you do a blood draw, you get one data point. But in many cases, doctors would love to know if concentrations are increasing or decreasing over time. And this is possible with our device,” they added.

For the study, the researchers applied sensors and a gel containing carbachol to their subject's forearm for 2.5 minutes. They then used iontophoresis, an electrical current at 0.2 milliamps that drives a tiny amount of carbachol into the upper layer of the skin and locally stimulates sweat glands but causes no physical sensation or discomfort.

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

The study concluded that the work represented a significant leap forward in sweat-sensing technology. "Imagine being able to monitor cardiac patients after they have been released from the hospital, or preventing dehydration in athletes or even helping ensure that your body is getting the exact right concentrations of a prescription drug,” said the team.

Possible uses for the device include testing airline and air-force pilots by measuring their cortisol, which is produced in response to stress, to assess their mental and physical condition in stressful situations. Likewise, it could be useful for patients who might want to perform regular health monitoring at home after a surgery or for follow-up visits to doctors where instead of a blood test, they could wear a disposable sweat patch for 20 minutes.

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