Bioreceptor-free electrochemical cortisol sensing on Ti3C2Tx MXene/ AuNPs/G flexible electrode: A diffusion-controlled proton-coupled electron transfer mechanism

Abstract

Flexible electrochemical sensors are of critical importance for non-invasive biomonitoring in wearable health applications. Cortisol (COR), a primary stress biomarker, is typically detected using antibody- or aptamer-based receptors. However, these methods often face challenges regarding long-term stability and cost. To overcome these limitations, in this study we developed a flexible screen-printed electrode (SPE) without a bioreceptor, utilizing a Ti3C2Tx MXene/gold nanoparticles (AuNPs)/graphite (G) composite conductive ink. The flexible screen-printed electrode was optimized at a physiological pH of 7.4 to ensure compatibility with human biofluids. Following a - 1.0 V preconditioning step, the SPE achieved a detection limit (LOD) of 2.59 ng/mL and a wide linear range of 0.02 to 40 mu M using linear sweep voltammetry (LSV). The SPE demonstrated robust longterm stability, providing consistent responses for up to 14 days. Selectivity studies against common interfering substances showed a signal deviation of less than 5%, confirming high sensitivity in complex matrices. Analytical performance was also validated in artificial sweat and saliva samples, yielding recovery rates ranging from 103.0% to 109.4%. This study presents a practical and scalable sensing strategy that holds strong promise for integration into personalized, on-skin diagnostics for real-time stress and health monitoring.