Stretchable and Superwettable Colorimetric Sensing Patch for Epidermal Collection and Analysis of Sweat

Stretchable and wearable sensors allow intimate integration with the human body for health and fitness monitoring. In addition to the acquisition of various physical parameters, quantitative analysis of chemical biomarkers present in sweat may provide vital insights into the physiological state of an individual. A widely investigated system utilizes electrochemical techniques for continuous monitoring of these biomarkers. The required supporting electronics and batteries are often challenging to form a deformable system. In this study, an intrinsically stretchable sensing patch is developed with compliant mechanical properties for conformal attachment to the skin and reliable collection of sweat. In these patches, superhydrophilic colorimetric assays consisting of thermoplastic polyurethane nanofiber textiles decorated with silica nanoparticles are assembled over a styrene-ethylene-butylene-styrene-based superhydrophobic substrate, thereby generating a large wettability contrast to efficiently concentrate the sweat. The system supports multiplexed colorimetric analysis of sweat to quantify pH and ion concentrations with images acquired using smartphones, in which the influence of ambient lighting conditions is largely compensated with a set of reference color markers. Successful demonstrations of insitu analysis of sweat after physical exercises effectively illustrate the practical suitability of the sensing patch, which is attractive for advanced health monitoring, clinical diagnostics, and competitive sports.