Super-absorbent polymer valves and colorimetric chemistries for time-sequenced discrete sampling and chloride analysis of sweat via skin-mounted soft microfluidics

Kim, S. B.*; Zhang, Y.*; Won, S. M.*; Bandodkar, A. J.*; Sekine, Yurina   ; Xue, Y.*; Koo, J.*; Harshman, S. W.*; Martin, J. A.*; Park, J. M.*; Ray, T. R.*; Crawford, K. E.*; Lee, K.-T.*; Choi, J.*; Pitsch, R. L.*; Grigsby, C. C.*; Strang, A. J.*; Chen, Y.-Y.*; Xu, S.*; Kim, J.*; Koh, A.*; Ha, J. S.*; Huang, Y.*; Kim, S. W.*; Rogers, J. A.*

This paper introduces super absorbent polymer valves and colorimetric sensing reagents as enabling components of soft, skin-mounted microfluidic devices designed to capture, store and chemically analyze sweat released from eccrine glands. The valving technology enables robust means for guiding the flow of sweat from an inlet location into a collection of isolated reservoirs, in a well-defined sequence. Analysis in these reservoirs involves a color responsive indicator of chloride concentration with a formulation tailored to offer stable operation with sensitivity optimized for the relevant physiological range. Evaluations on human subjects with comparisons against ex situ analysis illustrate the practical utility of these advances.