EPFL engineers working with a startup company called Xsensio have developed a new wearable sensing chip that can measure the concentration of a stress hormone called cortisol in human sweat. The wearable sensor allows for quasi-continuous monitoring and can help doctors understand and treat stress-related conditions such as burnout and obesity. The sensor could potentially be placed on the patient’s skin in the form of a wearable patch and allow near-continuous monitoring of cortisol concentrations, which is the main stress biomarker in the wearer’s sweat.
Cortisol is a steroid hormone made by the adrenal glands out of cholesterol. Secretion of the hormone is controlled by the adrenocorticotropic hormone (ACTH) produced by the pituitary gland. Cortisol does have essential bodily functions, such as regulating metabolism, blood sugar levels, and blood pressure. The hormone also has impacts on the immune system and cardiovascular functions.
Cortisol can be secreted on impulse when something happens that puts the body under stress. While cortisol has useful functions, in people who suffer from stress-related diseases, the circadian rhythm is thrown off if the body makes too much or not enough and can damage health with the potential to cause obesity, cardiovascular disease, depression, or burnout. The patch the researchers have developed has a transistor and an electrode made from graphene.
The unique properties of graphene give it high sensitivity and very low detection limits. Graphene is functionalized in the sensor using aptamers, short fragments of single-stranded DNA or RNA able to bind to specific compounds. In the wearable sensor, the aptamer patch has a negative charge. When it comes in contact with cortisol, it captures the hormone causing the strands to fold onto themselves, bringing the charge closer to the electrode surface.
The device can detect the charge and is consequently able to measure the cortisol concentration in the wearer’s sweat. The sensor is the first system developed for monitoring cortisol concentrations continuously throughout the circadian cycle.