In-Situ Admittance Sensing of Sweat Rate and Chloride Level in Sweat Using Wearable Skin-Interfaced Microfluidic Patch

Real-time, in-situ evaluation of sweat and electrolyte loss under heat stress is critical in preventing the risks of heat-related illnesses and maintaining individual’s physical performance for athletes or individuals working in extreme environments. Simultaneous monitoring of sweat rate and sweat chloride concentration via wearable device could provide an accessible route to assess the wastage of fluid and electrolytes. In this work, we report a low-cost, easy-to-manufacture epidermal microfluidic patch via entire laser-cutting scheme and transfer-printing operation. Sandwich-structured sweat rate sensor with trigger sites can induce a high pulse of electrode admittance for quantifying sweat rate when advancing sweat arrives at trigger sites, which favors the sensor inherent higher noise tolerance and independence of sensing on the change of ionic charge. Sweat chloride concentration is also quantificationally analyzed by measuring the admittance of interdigital electrode embedded in the microchannel, representing a simple, practicable, and stable alternative to colorimetric and ion-selective sensors. In-vitro and on-body experiments demonstrate the feasibility and accuracy of continuous measurement for sweat rate and sweat chloride concentration by admittance sensing method. This intrinsically robust, reliable sensing performance of the skin-interfaced microfluidic patch contributes to potential development of such device in personalized medicine.