Stress Monitoring and Recent Advancements in Wearable Biosensors

Abstract

The stress response allows the body to overcome obstacles and prepare for threats, but sustained levels of stress can damage one's health. Stress has long been measured through physical tests and questionnaires that rely primarily on user-inputted data, which can be subjective and inaccurate. To quantify the amount of stress that the body is experiencing biologically, analytical detection of biomarkers associated with the stress response recently have been developed. Novel stress sensing devices focus on cortisol sweat sensing as a part of wearable, flexible devices. These devices promise a real-time, continuous collection of stress data that can be used in clinical diagnoses or for personal stress monitoring and mediation.

Keywords: skin-interfaced cortisol sensors; stress analysis and evaluation; stress biomarkers; stress sensors; wearable cortisol sensors.

FIGURE 1

Mechanism of release for epinephrine, norepinephrine, alpha-amylase, and cortisol. Biomarkers in the figure are controlled by the hypothalamus. The hypothalamic pituitary adrenal (HPA) axis is activated by hypothalamic release of corticotropin-releasing hormone (CRH), which stimulates the secretion of adrenocorticotropin hormone (ACH) from the anterior pituitary gland. ACH then acts on the adrenal cortex to stimulate the release of cortisol (Lanoix and Plusquellec, 2013; Antoun et al., 2017), which is regulated by negative feedback loops to both the anterior pituitary and adrenal cortex. The sympathetic adrenal medullary (SAM) axis is activated by the hypothalamus to stimulate a sympathetic nervous system response, which then stimulates the adrenal medulla to produce epinephrine and norepinephrine (Antoun et al., 2017). The release of norepinephrine is then responsible for the synthesis and release of alpha-amylase (Sawami et al., 2017).

FIGURE 2

Recent sweat stress sensor designs. (A) Wearable CortiWatch (Rice et al., 2019) reprinted via Creative Commons Attribution 4.0, (B) MIP sensor on flexible SEBS substrate (Parlak et al., 2018) reprinted via Creative Commons Attribution 4.0. (C) printed graphene-based wireless cortisol sensor, reprinted with permission from Torrente-Rodríguez et al., copyright 2020 by Elsevier (Torrente-Rodríguez et al., 2020). (D) galvanic skin response sensor SKINTRONICS (Kim et al., 2020) reprinted via Creative Commons Attribution 4.0.