Our group has introduced a simple and efficient platform for sweat sampling and handling based on osmotic-capillary principles and paper microfluidics. It can harvest sweat noninvasively without the necessity of active perspiration.Here, we will discuss how these principles were applied in the development of a class of simple and inexpensive wearable skin patches for analysis of potassium, lactate and cortisol, based on lateral flow assays (LFAs). Potassium is a key intracellular electrolyte in the body. Small variations in the range of K⁺ could affect the cardiovascular or neuromuscular functions of the body and could cause cardiac arrest. Our LFA platform is composed of silicone, a paper microfluidic conduit attached to a commercial K⁺ strip, and a polyacrylamide hydrogel with a higher osmotic strength than sweat. In-vitro testing on gelatin-based model skin (pre-infused with a known quantity of K⁺ ions) allowed calibrating the platform with model sweat. Human trials revealed that it can function with very low sweat volumes (~8-10 µL) and can detect K⁺ levels from human skin under moderate-intensity exercise. We also observed that sweat potassium levels are independent of the sweat rate. The patch could also efficiently sample sweat lactate directly from the surface of the skin. On-skin testing of the platform on both resting and exercising human subjects confirms that the patch can extract sweat and analyze the changing lactate levels. The results show that lactate in sweat increases with exercise and as a direct result of muscle activity. Our present focus is developing wearable skin LFAs for the detection of cortisol (in sweat) as a key stress biomarker in individuals, soldiers in combat, athletes and emergency personnel. We are designing and developing patches with competitive format LFA strips for cortisol. We expect that these simple and inexpensive patches could open numerous opportunities for at-home or in-field POC diagnostics.

Sneha Mukherjee

Graduate Research Assistant, North Carolina State University

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