Point-of-Care Measurement of a Salivary Stress Biomarker

Salivary correlates of the stress response have become increasingly important in psychoneuroendocrinological research and a growing body of literature supports the utility of salivary alpha-amylase (sAA) levels as an expression of sympathetic nervous system (SNS) activity. Objective: To develop and refine a portable sAA biosensor and explore its utility for sAA qualification studies. Methods: We developed a colorimetric biosensor comprising of saliva absorbent test-strip and a handheld reader. Integrated normalizing equations adjust for any variations in ambient temperature and salivary pH. Method validation of the biosensor was performed by comparing its technical performance characteristics (precision, accuracy, reliability) with laboratory-based Olympus AU 400 clinical analyzer. Subsequently, sAA biomarker qualification was performed by comparing sAA levels measured in 54 healthy subjects to their subjective distress ratings (i.e., Brief Symptom Inventory-BSI) under low and high stress conditions. Results: The sample-analyze-report cycle for the sAA biosensor was less than 45 seconds. The biosensor accuracy and precision corresponded very closely to the clinical analyzer (R2 = 0.98; CV = 8.1%). In the biomarker qualification study, greater sAA levels were related to higher ratings of subjective distress averaged across the day (r = .28, p < .001) and at each measurement point. Individuals who reported clinical distress on the BSI above clinical cutoffs showed lower sAA levels during high stress compared to baseline. Individuals who reported baseline distress below clinical cutoffs showed greater sAA levels during high stress compared to baseline (p = .04 for the interaction). Conclusion: The biosensor provides quick and reliable measurements of sAA levels and possess a precision, accuracy and reproducibility that approaches laboratory-based analyzers. These properties along with the demonstrated covariance of sAA levels with self-reported subjective distress suggests that the sAA biosensor is a promising tool for POC measurement of exposure to stressors. Supported by NIH/NIDA grant UO1 1UO1-DAO23815.