Stanford, California, USA: Scientists are sweating over how to measure perspiration. That’s because sweat provides a lot of information about a person’s health status, since it contains important electrolytes, proteins, hormones and other factors.
Now, Stanford researchers have developed a wearable device to measure how much cortisol people produce in their sweat.
Cortisol is a hormone critical for many processes in the body, including blood pressure, metabolism, inflammation, memory formation and emotional stress. Too much cortisol over a prolonged period of time can lead to chronic diseases, such as Cushing syndrome.
“We are particularly interested in sweat sensing, because it offers noninvasive and continuous monitoring of various biomarkers for a range of physiological conditions,” said Onur Parlak, PhD, a Stanford postdoctoral research fellow in materials science and engineering, in a recent Stanford news release. “This offers a novel approach for the early detection of various diseases and evaluation of sports performance.”
Currently, cortisol levels are usually measured with a blood test that takes several days to analyze in the lab. So Stanford material scientists developed a wearable sensor — a stretchy patch placed on the skin. After the patch soaks up sweat, the user attaches it to a device for analysis and gets the cortisol level measurements in seconds.
As recently reported in Science Advances, the new wearable sensor is composed of four layers of materials. The bottom layer next to the skin passively wicks in sweat through an array of channels, and then the sweat collects in the reservoir layer. Sitting on top of the reservoir is the critical component, a specialized membrane that specifically binds to cortisol. Charged ions in the sweat, like sodium or potassium, pass through the membrane unless the bound cortisol blocks them — and those charged ions are detected by the analysis device, rather than directly measuring the cortisol. Finally, the top waterproof layer protects the sensor from contamination.
The Stanford researchers did a series of validation tests in the lab, and then they strapped the device onto the forearms of two volunteers after they went for a 20-minute outdoor run. Their device’s lab and real-world results were comparable to the corresponding cortisol measurements made with a standard analytic biochemistry assay.
Before this prototype becomes available, however, more research is needed. The research team plans to integrate the wearable patch with the analysis device, while also making it more robust when saturated with sweat so it’s reusable. They also hope to generalize the design to measure several biomarkers at once, not just cortisol.
“In summary, we have demonstrated the integration of an artificial receptor as a biomimetic polymeric membrane for stable and selective molecular recognition using OECTs to produce a wearable sweat diagnostics platform for real-time analysis of the human stress hormone cortisol,” researchers wrote.
But this team of researchers isn’t the only group looking to analyze sweat. In 2017 Eccrine Systems announced that it had developed a device that can stimulate a sweat gland on a small, isolated patch of skin. Its sensor can then make predictions on how much a given patient will sweat, allowing researchers to better understand the hormones and chemicals involved in the process.
In 2016, researchers at Stanford University and the University of California-Berkeley announced that they built a prototype for a wearable sensor that could continuously collect and monitor users’ sweat on the molecular level, then send the information via Bluetooth to a smartphone. Additionally, as early as 2014 researchers from Intermountain healthcare developed a smartphone-based test for measuring salivary cortisol.
Stanford Medicine integrates research, medical education and health care at its three institutions – Stanford University School of Medicine, Stanford Health Care (formerly Stanford Hospital & Clinics), and Lucile Packard Children’s Hospital Stanford.