The hormone cortisol rises and falls naturally throughout the day and can spike in response to stress, but current methods for measuring cortisol levels require waiting several days for results from a lab. By the time a person learns the results of a cortisol test — which may inform treatment for certain medical conditions — it is likely different from when the test was taken.
A stretchy patch was created that, applied directly to the skin, wicks up sweat and assesses how much cortisol a person is producing. It offers noninvasive and continuous monitoring of various biomarkers for a range of physiological conditions and helps in early detection of various diseases and evaluation of sports performance.
Clinical tests that measure cortisol provide an objective gauge of emotional or physical stress in research subjects and can help doctors tell if a patient’s adrenal or pituitary gland is working properly. The new device could allow people with an imbalance to monitor their own levels at home. It could also reveal the emotional state of young — even non-verbal — children, who might not otherwise be able to communicate that they feel stress.
The stretchy, rectangular sensor was built around a membrane that specifically binds only to cortisol. Stuck to the skin, it sucks in sweat passively through holes in the bottom of the patch. The sweat pools in a reservoir, which 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. It’s those backed-up charged ions the sensor detects, not the cortisol itself. On top of all this is a waterproof layer that protects the patch from contamination.
All a user needs in order to see cortisol levels is to sweat (enough to glisten), apply the patch, and connect it to a device for analysis, which gives results in seconds. In the future, the sensor could be part of a fully integrated system.
Researchers want to make the patch more reliable and accurate, and also make sure it is reusable. The prototype works multiple times as long as it is not saturated with sweat. In the future, the cortisol sensor could be used on saliva, which would avoid the need for patients to sweat.