Wearable Microfluidic Chip Integrated with Chrono-Sampling for Cortisol Detection in Sweat

Sweat is rich in various biomarkers, including metabolites, hormones, and inorganic ions, and thus, it provides a wealth of physiological information. The real-time monitoring of these biomarkers preserves critical dynamic physiological data, enabling a more comprehensive assessment of the health status. For a sensor, it is desirable to maintain a strong affinity between the recognition probe and the targets while retaining reversible binding. However, these two properties are often mutually contradictory since strong affinity usually gives rise to slow or irreversible dissociation. To address this issue, we developed a microfluidic chip integrated with a chronosampling function. It can collect sweat at different time points, achieving the dynamic detection of cortisol levels in sweat. The chip was integrated with a series of valves prepared with filter paper containing polymers of varying concentrations. These polymers in valves were dissolved in sweat and sequentially opened, allowing the collection and detection of sweat samples from distinct periods. The sampling temporal window spans 0-90 min, generally meeting the requirements for sweat monitoring during most exercises. Additionally, the partitioned design of the main and branch channels in the microfluidic chip effectively prevents cross-contamination among the sweat samples. This wearable microfluidic chip successfully detected sweat cortisol at different time points during the volunteer exercise.