Reusable and Wireless Sensor for On-Demand Molecular Stress Biomarker Assessment

The profound effects of stress on health demand precise and objective measurement techniques, as traditional self-report questionnaires often fall short. Molecular biosensors, particularly those detecting cortisol-a key stress hormone-offer a compelling alternative. Yet, traditional cortisol assays, which rely on saliva, urine, or blood samples, are cumbersome, costly, and unsuitable for continuous monitoring. Our research introduces an innovative wearable sensing system that employs a molecularly imprinted polymer-radiofrequency (MIP-RF) mechanism for non-invasive, real-time cortisol detection in sweat. This advanced system is wireless, flexible, battery-free, reusable, and environmentally stable, optimized for long-term use with an inductance-capacitance transducer. This transducer accurately translates cortisol levels into resonant frequency shifts, demonstrating high sensitivity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\sim 160\text{kHz}/\log[\mu \mathrm{M}])$</tex> within a physiological range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0-1_{1}\mathrm{M}$</tex>. Enhanced with Near-Field Communication (NFC) for seamless, battery-free operation and a 3D-printed microfluidic channel for direct sweat collection, the device allows continuous cortisol monitoring throughout daily activities. Validation through circadian rhythm tracking-comparing morning and evening cortisol levels-confirms its efficacy. This breakthrough signifies a transformative advancement in on-demand, non-laboratory health monitoring, harnessing wearable technology for precise molecular stress biomarker detection.