Time-Resolved Sweat Collection for Off-Body SERS Analysis: Bridging Wearability and Sensitivity

Sweat carries a wealth of physiological information and is ideal for noninvasive health monitoring. Surface-enhanced Raman scattering (SERS) enables highly sensitive, multiplexed detection of sweat biomarkers, but its integration into wearable systems remains impractical due to the bulky nature of Raman spectrometers and laser sources. To address this limitation, we developed a wearable platform that focuses on in situ sweat collection and time-sequenced storage, enabling delayed, off-body high-sensitivity SERS detection. The system integrates a Janus microporous membrane with a wettability gradient, fabricated via femtosecond laser ablation and oxygen plasma etching, to achieve directional and continuous sweat collection from the skin. This is combined with a microfluidic chip containing burst valves that enable passive, time-sequenced sampling and storage of sweat over the course of exercise. For detection, a capillary-based SERS substrate was fabricated using a silver mirror reaction, achieving detection limits down to 1 mM for sodium lactate and urea. Characteristic peaks were clearly identified from human sweat samples. This work presents a feasible path for combining wearable sweat sensing with high-performance spectroscopic analysis, offering promising applications in personalized health monitoring and dynamic physiological assessment.