Detection of stress biomarkers cortisol and creatinine with a grating-coupled surface plasmon resonance sensor

Stress is a widely spread phenomenon in the modern society. Only work-related stress was estimated to cost US companies more than $300 billion a year in healthcare costs, absences and decreased performance. Early diagnosis of stress conditions and therefore improved recovery and reduced costs could potentially be achieved with continuous monitoring of stress biomarkers using wearable devices. Compared to the conventional electrochemical and optical sensing methods used in current wearable devices, plasmonic sensing could offer higher sensitivity, better stability and faster data collection. Our developed plasmonic sensor chip represents a nanograting structured polymer on a silicon substrate, covered with gold. The sensing method is based on detecting a surface plasmon resonance wavelength shift due to refractive index change caused by presence of analytes in the vicinity of the plasmonic grating. The sensitivity of the chip was tested with two different stress-related biomarkers: cortisol and creatinine. With the tested range from 0 to 265 mM, in the current version of the system, without a receptor layer, the detection limits for cortisol and creatinine were 10.65 and 7.09 mM, respectively, which are close to the physiological ranges of these analytes in body fluids. When integrated into a wearable device, this approach has a potential in future healthcare applications paving the way to continuous stress monitoring.