Scientists have created a stretchy patch that, applied directly to the skin, can monitor a person's stress levels by measuring the hormones in their sweat.
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.
"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, a post-doctoral scholar at Stanford University in the US.
"This offers a novel approach for the early detection of various diseases and evaluation of sports performance," said Parlak.
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.
If the prototype version of the wearable device becomes a reality, it could allow people with an imbalance to monitor their own levels at home.
A fast-working test like this 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 around a membrane 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 is 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 to see cortisol levels is to sweat, apply the patch and 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.