New York: Researchers have developed a wearable device that can be placed directly on a patient's skin and can continually measure the concentration of cortisol, the main stress biomarker, in the patient's sweat.
While cortisol helps our bodies respond to stressful situations, it is actually a double-edged sword.
It is usually secreted throughout the day according to a circadian rhythm, peaking between 6am and 8am and then gradually decreasing into the afternoon and evening.
"But in people who suffer from stress-related diseases, this circadian rhythm is completely thrown off," said one of the researchers Adrian Ionescu, head of Nanoelectronic Devices Laboratory (Nanolab) at Ecole polytechnique federale de Lausanne (EPFL) in Switzerland.
"And if the body makes too much or not enough cortisol, that can seriously damage an individual's health, potentially leading to obesity, cardiovascular disease, depression or burnout."
Blood tests can be used to take snapshot measurements of patients' cortisol levels. However, detectable amounts of cortisol can also be found in saliva, urine and sweat. Ionescu's team at Nanolab decided to focus on sweat as the detection fluid and developed a wearable smart patch with a miniaturised sensor.
The patch contains a transistor and an electrode made from graphene which, due to its unique proprieties, offers high sensitivity and very low detection limits.
The graphene is functionalised through aptamers, which are short fragments of single-stranded DNA or RNA that can bind to specific compounds.
The aptamer in the EPFL patch carries a negative charge; when it comes into contact with cortisol, it immediately captures the hormone, causing the strands to fold onto themselves and bringing the charge closer to the electrode surface.
The device then detects the charge, and is consequently able to measure the cortisol concentration in the wearer's sweat.
"Because it can be worn, scientists can collect quantitative, objective data on certain stress-related diseases. And they can do so in a non-invasive, precise and instantaneous manner over the full range of cortisol concentrations in human sweat," said Ionescu. The findings were published in the journal Communications Materials.