On‐Demand Sweat Stimulation and Visual Quantification of Chloride via a Wearable Integrated Paperfluidic Sensor for Resource‐Limited Cystic Fibrosis Screening

Sweat‐based diagnostics offer a non‐invasive and accessible method for real‐time health monitoring, enabling direct assessment of physiological and biochemical markers from the skin without the complexity of conventional sampling. In this study, we present a wearable paper‐based sensor that enables colorimetric detection of chloride ions in sweat for cystic fibrosis (CF) screening. Unlike conventional wearable CF sensors that require complex fabrication and sophisticated instrumentation, our low‐cost, disposable device integrates a hydrophobically patterned paper substrate with an overlaid paper‐fluidic channel impregnated with a chloride‐sensitive reagent for direct visual quantification of Cl − levels. To facilitate efficient sweat stimulation, we developed an iontophoresis system that delivers controlled electrical current to stimulate localized sweat secretion, with an Arduino‐based module integrated for real‐time monitoring of output current and elapsed time. The device was validated with artificial sweat for chloride quantification and tested on human volunteers to demonstrate effectiveness in sweat stimulation and collection. The sensor exhibited a clinically relevant detection range, with strong correlation between color intensity and chloride concentration, confirming accuracy and reliability for CF diagnostics. By combining low‐cost fabrication, on‐demand sweat stimulation, and colorimetric analysis, this instrument‐free, wearable platform presents a promising alternative to traditional testing for point‐of‐care diagnostics in resource‐constrained healthcare settings.