A multimodal wearable microfluidic platform for in situ sweat cortisol monitoring with a NiHCF-enabled molecularly...

Cortisol is a key biomarker of stress, circadian regulation and exercise-related physiological responses. However, conventional assays based on blood, saliva, or urine are poorly suited to non-invasive and field-deployable physiological assessment. Here we report a skin-interfaced wearable microfluidic platform for in situ sweat cortisol analysis using a nickel hexacyanoferrate (NiHCF)-enabled molecularly imprinted electrochemical sensor. The NiHCF redox transducer enhances electrochemical stability in physiologically relevant media, while the polypyrrole (PPy)-based molecularly imprinted polymer (MIP) interface provides selective cortisol recognition and square-wave voltammetry (SWV)-based signal readout. The sensor array integrates iontophoretic sweat induction, microfluidic sweat sampling, Na⁺/pH-assisted sweat-matrix correction, miniaturized electronics and wireless data transmission and visualization. The cortisol sensor exhibited a broad calibration range from 0.1 fM to 100 μM, with a sensitivity of 1.62 μA(lg[nM])^-1cm^-2 and a detection limit of 0.043 fM. Human participant studies showed diurnal cortisol variation, cold-pressor-test-induced cortisol elevation and exercise-associated cortisol changes, with measurements benchmarked against enzyme-linked immunosorbent assay (ELISA). By incorporating surface electromyography (sEMG), the platform further enabled multimodal profiling of exercise-induced fatigue-related states by pairing local neuromuscular features with sweat-derived endocrine responses associated with fatigue-inducing exercise stress. This wearable strategy may support non-invasive, state-resolved assessment of stress- and fatigue-related physiology for personalized health monitoring.