Flexible SERS sensor with piezoelectric enrichment based on PVDF/AgNWs for cortisol detection in sweat

A flexible piezoelectrically enhanced SERS sensor based on PVDF/AgNWs is developed for cortisol detection. • Mechanical bending of the PVDF membrane generates a non-uniform piezoelectric field that drives dielectrophoretic enrichment of cortisol. • The sensor achieves a low detection limit of 1.3 × 10 −10  M for cortisol in artificial sweat. • Preliminary human sweat tests show differences in SERS signals among sleep, normal activity, and exercise states. Wearable sensing platforms for non-invasive monitoring of stress biomarkers in sweat are highly desirable for personalized health management. This work presents a flexible surface-enhanced Raman scattering (SERS) sensor with piezoelectric enrichment based on a PVDF/AgNWs composite membrane for sensitive detection of cortisol. The PVDF fibrous membrane is prepared by electrospinning, which endows it with a high β-phase content and good piezoelectric response. Under mechanical bending, the piezoelectric PVDF membrane generates a non-uniform electric field that polarizes the neutral cortisol molecules, driving them toward the AgNW-decorated SERS hotspots via dielectrophoretic forces, thereby achieving active analyte enrichment without an external power source. In artificial sweat, it shows a wide linear range of 1.0 × 10 −9 to 1.0 × 10 −5  M and a low detection limit of 1.3 × 10 −10  M, along with acceptable uniformity and mechanical robustness. The sensor was further assembled into a wearable patch and preliminarily evaluated using human sweat samples collected during sleep, normal activity, and exercise. Differences in SERS intensity were observed among these states. This flexible SERS sensor shows promise for non-invasive detection of cortisol in sweat and offers a potential strategy for wearable hormone monitoring. A flexible self-powered SERS sensor based on a PVDF/AgNWs composite membrane enables electrostatic enrichment of cortisol under mechanical folding, allowing sensitive and non-invasive detection of stress biomarkers in human sweat. Download: Download high-res image (146KB) Download: Download full-size image