Cortisol is a steroid hormone that can spike in response to stress, however current methods for measuring it typically require an invasive blood test and waiting several days for results from a lab. The new stretchy patch developed by the Stanford researchers, when applied directly to the skin, uses sweat to assess and monitor how much cortisol a person is producing.
“We are particularly interested in sweat sensing, because it offers noninvasive and continuous monitoring of various biomarkers for a range of physiological conditions,” says Onur Parlak, a post-doctoral scholar in the Salleo lab and lead author of a paper on the research. “This offers a novel approach for the early detection of various diseases and evaluation of sports performance.”
Clinical tests that measure cortisol can help doctors tell if a patient’s adrenal or pituitary gland is working properly. The researchers’ prototype wearable device promises to allow people with an imbalance to monitor their own levels at home.
Measuring cortisol has presented a challenge for biosensors, say the researchers, as these sensors work by detecting a molecule’s positive or negative charge, and cortisol has no charge. To address this, the researchers created their sensor around a membrane that specifically binds only to cortisol.
When stuck to the skin, the sensor “sucks in” sweat passively through holes in the bottom of the patch, collecting the sweat in a reservoir that is topped by the cortisol-sensitive membrane. Charged ions like sodium or potassium – also found in sweat – pass through the membrane unless they are blocked by cortisol.
The sensor detects those backed up charged ions – not the cortisol itself. A top waterproof layer protects the patch from contamination.
All a user needs to measure cortisol levels is to sweat enough to glisten, apply the patch, and then connect it to a device for analysis, which gives results in seconds. In the future, the researchers hope the sensor could be part of a fully integrated system.
In both lab and real world testing of the sensor, results were similar to clinical tests in the lab. As long as it is not saturated with sweat, the prototype was found to be usable multiple times.
Looking ahead, the researchers hope to make the sensor both more reliable and accurate, and also make sure it is reusable. In addition, they say they may try the cortisol sensor on saliva, which would avoid patients needing to sweat.