Facile and Scalable Fabrication of Molecularly Imprinted Polymer (MIP) Sensors on Poriferous Laser-Engraved Graphene Electrodes for Stress Monitoring

Abstract

Monitoring cortisol levels is essential for understanding the body's response to stress. Traditional cortisol testing is confined to centralized labs, and current portable platforms are based on slow and complex assays. Here, we introduce a portable, disposable, non-invasive, and sensitive electrochemical sensor strip created using electropolymerized molecularly imprinted polymers (eMIPs) on laser engraved graphene (LEG) electrodes for rapid, simple, and reliable salivary cortisol detection. Herein, the characteristics of LEGs generated on a polyimide (PI) film with different laser processing parameters are also studied and optimized. The sensor quantifies salivary cortisol by selectively binding onto the cortisol-imprinted electropolymerized polypyrrole-Prussian blue (eMIP-PPy/PB) film on LEG electrodes. The PB redox probes embedded in the eMIP produce direct electrical signals upon cortisol binding, allowing sensitive and label-free amperometric detection. The developed cort-eMIP/LEG sensor strip displays an outstanding dynamic range (0.10 to 10,000 pg mL-1), a remarkable limit of detection (0.08 pg mL-1), and a strong correlation coefficient (R2) of 0.9983 (n=4) for cortisol detection in human saliva. A rapid 3-minute analysis can more effectively measure cortisol levels in real-time than traditional methods. This sensor's performance was evaluated in human samples and validated two-way using enzyme-linked immunosorbent assays (ELISAs) and a third-party provider, Salimetrics, on 12 student volunteers exposed to varying stress levels. Results show an excellent correlation (r = 0.9948) between the developed sensors and standardized tests. The cort-eMIP/LEG cortisol sensor strip offers a simple, accessible, sample-to-answer diagnostic platform for stress monitoring.