Blood is king in the world of Point of Care Testing. But the process of drawing blood is invasive, and it represents a challenge for continuous monitoring over hours or days. Sweat, a rich source of electrolytes, is often undervalued for its role in assessing one’s health. Numerous diseases are associated with abnormal sweat or sweating behavior. When sweat glands become exhausted and unable to secrete sweat, a person can suffer heat stroke. Cystic fibrosis patients can be diagnosed with a sweat test because their sweat gland ducts tend to reabsorb less chloride, resulting in an extra high concentration of chloride in their sweat. Even though sweat is an attractive alternative to blood, not all people can benefit from sweat-base biometric analysis. To generate sweat, one has to perform exercises and be subject to a warm environment. For some this is simply impossible. For instance, any stress on the cardiovascular system can be a life-endangering threat to cardiac patients.
The Band-Aid size biosensor that can stimulate and analyze sweat. Credit: University of Cincinnati
A research team from the University of Cincinnati lead by Professor Jason Heikenfeld has developed a wearable sweat sensor that can chemically stimulate sweat for hours, as well as detect and analyze the chemical analytes without cross-contamination.
Their band-aid size device combines a sensor, electricity-conducting gel, and memory foam padding with stimulant delivery mechanism: it uses a 0.22 milliamps of electrical current to drive carbachol (a cholinomimetic drug and sweat stimulant) into the upper layer of the skin. The amount of carbachol is so small that it does not irritate or harm the skin other than inducing sweat locally. The group recorded 30-minutes worth of data on sweat electrolytes from study subjects. Carbachol was capable of inducing sweating under the sensor for as long as five hours. According to the unpublished results of a follow-up study, their sensor was able to record results for several days under the same sweat stimulation mechanism.
With this innovative technology, doctors can monitor the chemical profile of patients’ sweat over an hour-long time frame while the patients can be resting and remain in a thermally comfortable environment. "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 Dr. Heikenfeld.
The researchers described their achievement as “a significant leap forward” in terms of sweat sensing technology. They hope that their design could attract broader interest so that it can gain widespread application. “The end goal is to take the idea from a bench-top test to a portable device—perhaps for people in high-stress jobs like airline pilots—and analyze them for stress," Sonner said. "If you're a pilot, you can't do blood draws while you're flying the plane. But a sensor could analyze sweat so we can begin to understand how their body responds to stressful situations," explained Zachary Sonner, the lead author of the paper.
Dr. Jason Heikenfeld explained his research and development of fluidics at the University of Cincinnati. Credit: EnterchangeCincinnati