A Portable Microfluidic Paper-Based Analytical Device for Sensing of Cortisol in Artificial Saliva

Cortisol is a key stress hormone that regulates metabolism, immune response and various physiological functions including cardiovascular, respiratory, reproductive and musculoskeletal systems. Imbalances in cortisol levels can lead to severe health complications, emphasizing the need for continuous monitoring. This paper presents a novel, portable sensing platform for affordable and selective cortisol detection in artificial saliva. The system utilizes cost-effective, wax-printed micro-pads on paper-based substrates, forming a compact colorimetric sensor. By leveraging the blue tetrazolium (BT) reagent, it detects cortisol through a distinct and quantifiable color change. A 3D-printed black box serves as a controlled detection chamber, eliminating the need for bulky traditional devices. An ESP32 microcontroller processes data from an RGB sensor, precisely analyzing color changes on reagent-coated micropads for accurate cortisol quantification. A deep learning regression model deployed directly on the microcontroller, enhances detection accuracy by correlating color intensity with cortisol concentration. The detected cortisol levels are displayed on an OLED screen and sent to a smartphone via bluetooth for seamless storage, stress monitoring, and advanced analysis. Additionally, the system securely stores recorded data for long-term reference. Offering rapid detection within 10 minutes, the system achieves a detection limit (LOD) of 1 ng/mL, a wide detection range of 1– 800 ng/mL, and an R² value of 0.96, ensuring high precision. This innovative, non-invasive, and user-friendly platform provides a reliable solution for stress monitoring and serves as a Point of Care (PoC) compatible sensing platform.