Hot under the collar? Sweat sensor could provide quantitative measure of stress

A graphene-based wireless sweat sensor could be capable of detecting and monitoring real time stress levels through quantitative cortisol analysis, say researchers from California Institute of Technology (Caltech, CA, USA).

The research, published in the journal Matter, concerns the development of a fully integrated, wireless sensing device capable of providing fast, non-invasive and quantitative cortisol analysis. Cortisol, a natural compound, is often referred to as the stress hormone. Traditionally, evaluating stress levels has required a questionnaire or a blood test. Although a blood test can provide a quantitative measure of serum cortisol levels, the necessary blood draw requires a professional and can itself skew results by inducing stress.

Scientists from Caltech developed the wearable sensor by laser etching graphene to develop a highly porous 3D structure. The large surface area granted by the pores help the sensor detect compounds present in very small concentrations in sweat. To facilitate cortisol detection, the team grafted carboxylate-rich pyrrole derivatives to the surface of the graphene with further modifications activating the surface with anti-cortisol monoclonal antibodies.

In the pilot study, Wei Gao (Caltech) and his colleagues evaluated the sensor in two ways. The first investigation analyzed a volunteer’s sweat over a period of 6 days. From the results collected by the sensor, the team we able to construct the first cortisol diurnal cycle from human sweat.The second investigation evaluated the volunteers’ cortisol levels in response to acute stressors, including aerobic exercises and the submersion of participants hands in ice cold water. From these data, the team successfully constructed the first dynamic stress-response profile from human sweat.

With the team’s results demonstrating a strong empirical correlation between serum and sweat cortisol, it is theorized that the device could find applications in other conditions associated with changes in cortisol levels – including anxiety, post-traumatic stress disorder and depression.

As well as cortisol analysis applications here on earth, the sweat sensor could find itself being used in space. Wei Gao is one of six researchers participating in studies of the health of humans on deep-space missions. Gao explained: “We aim to develop a wearable system that can collect multimodal data, including both vital sign and molecular biomarker information, to obtain the accurate classification for deep space stress and anxiety.”

Sources: Torrente-Rodríguez RM, Tu J, Gao W et al. Investigation of cortisol dynamics in human sweat using a graphene-based wireless mHealth system. Matter doi:10.1016/j.matt.2020.01.021 (2020)(Epub ahead of print); www.caltech.edu/about/news/sweat-sensor-detects-stress-levels-may-find-use-space-exploration