Fig. 3: Design and characterizations of multipurpose microfluidics for sweat sampling.

a Layer-by-layer view of microfluidic device design. b Numerical stimulation of time required to fill chamber for different numbers and shapes of inlets with embedded filter paper. c Comparison between simulated and experimental results of the sweat sampling/filling process. d Time evolution of the average Phe concentration for refreshing process in the chamber without or with embedded filter paper. e FEA of microfluidic refreshing process without or with embedded filter paper. The area marked by the dashed line is represented as an anomalous hard-to-refreshing area. f Photographs of the microfluidics during exercise on the skin (right) and optical micrograph of sweat flowing in the visualized microchannel (left, magnified view of the sweat front). Scale bar, 1 cm. g Optical reflectivity of empty channels with or without μ-dots and filled channels with μ-dots. h Measured flow rates by naked eye at different fluid filling positions under pump injection rates of 0.5, 1, or 2 μL min⁻¹. i Sweat rates measured by the algorithm form two body parts of eight healthy subjects during 10 to 20 min of exercise. j Neutral pH buffering capability of the embedded filter paper in the microfluidic chamber. Note: there were no error bars here, but the pH ranges measured by colorimetric pH test papers. k, l Sensor response changes (k) and corresponding DPV scans (l) caused by injection of different sweat sample volumes. Inset, photograph of the biochip. m DPV scans of the integrated wireless system at different flow rates (from 0.5 to 2 μL min⁻¹).