A team from Stanford University has developed the first wearable skin sensor that can measure a person's cortisol levels from their sweat. Cortisol, a hormone that spikes in response to stress levels, is an important biomarker for scientists that can help measure everything from emotional stress to metabolism and immune function.

Our perspiration contains a goldmine of valuable information on the well-being of our bodies. There is an exciting array of burgeoning research into sweat-sensing devices that are designed to offer new ways for diabetics to measure glucose levels, help athletes measure metabolic conditions while exercising, and even measure levels of medications in a person's system.

"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, lead author on the new study.

Parlak and his team have been developing wearable sweat-sensing technologies for several years but detecting cortisol levels from perspiration presented a particular challenge. The sweat sensors the team has previously developed worked primarily by detecting a positive or negative charge in a given molecule. Cortisol, on other other hand, has no charge, so a more creative solution was necessary.

The answer was to develop an extra membrane that binds specifically to cortisol. The traditional sweat sensor has the ability to detect charged ions such as sodium or potassium, so the new device is designed to block those detectable charged ions from moving through the membrane when in the presence of cortisol. Essentially, the trick was to use cortisol to create a roadblock in particles that the sensor can detect, so when a build-up of those charged ions is identified it indicates there is a certain volume of cortisol present.

"I always get excited about a device, but the sweat collection system that Onur devised is really clever,"says Alberto Salleo, lead materials scientists at Stanford. "Without any active microfluidics, he's able to collect enough sweat to do the measurements."

Early tests are proving incredibly promising, with the experimental device able to deliver results in seconds where previously scientists needed blood samples and hours of analysis. The next stage for the research is to improve the reliability and accuracy of the sensor while also trying to engineer it into a reusable and functional design that can be applied in real-world conditions.

The big hurdle with all these sweat-sensing devices is that they obviously require a person to perspire, which limits their applications quite significantly. A team at the University of Cincinnati is working on a biosensor that can stimulate sweat glands in a localized area of skin, allowing for perspiration without physical exertion. The Stanford team, on the other hand, is suggesting future research into adapting this kind of cortisol sensor to saliva may be a better approach for broader clinical uses.

The new study was published in the journal Science Advances.

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