Sensing methods for stress biomarker detection in human saliva: a new frontier for wearable electronics and biosensing

The human stress response triggers a complex array of physiological, psychological, and biochemical reactions, involving neuroendocrine pathways such as the sympathetic adrenomedullary axis and hypothalamic–pituitary–adrenal axis. Prolonged experience of stress can have adverse effects on overall cognitive and physical well-being, making the routine monitoring of everyday stress highly desired for the delivery of personalised health management solutions. Saliva, as a diagnostic fluid, has garnered considerable attention in this regard due to its non-invasiveness, ease of collection and high compliance among diverse populations. Salivary biomarkers, including cortisol, salivary a-amylase, chromogranin A, brain-derived neurotrophic factor, and immunoglobulin A, are responsive to acute and/or chronic stressors, and thus, are prerequisite biomarkers in stress-related research. A number of sensing technologies are available for stress biomarker monitoring in saliva and other fluids. Enzyme-linked immunosorbent assays, colorimetric techniques, surface plasmon resonance sensing, and molecular imprinted polymers offer sensitive and selective cortisol detection in saliva. The integration of aptamers with electrochemiluminescence biosensing provides a label-free and cost-effective approach to biomarker detection. Wearable sensors that couple on-body sampling with edge computing for real time analytics open up new avenues for ambulatory monitoring and predictive diagnostics. The development of sensitive and reliable, saliva-based biosensing technologies in form of smart dentures and braces, holds the potential to revolutionize stress research with potential to provide personalized stress management solutions for health management in the future.