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