Skin-Interfaced Microfluidics with capillary pressure control valves for Modification-Free Sweat Routing and Analysis

Sweat loss at microfluidic outlets often causes deviations between measured and actual biomarker concentrations. We present a skin-interfaced microfluidic platform with a capillary pressure control valve integrating a water-divider (stop valve) and water-stop dam (delay valve) to achieve efficient sweat collection while minimizing evaporation and contamination. The optimized geometry enables sequential, outlet-free routing into colorimetric chambers for time-resolved biomarker monitoring. Experiments confirm reduced evaporation, minimal cross-contamination, and accurate pH detection via integrated paper-based colorimetry. This compact, flexible PDMS patch provides a practical solution for real-time and stored sweat analysis in wearable health monitoring.