Autonomous wearable sweat rate monitoring based on digitized microbubble detection

• Published in: Lab on a chip Vol. 22; no. 22; pp. 4267 - 4275
• Main Authors: Lin, Haisong, Yu, Wenzhuo, Suarez, Jorge Emiliano De Dios, Athavan, Harish, Wang, Yibo, Yeung, Christopher, Lin, Shuyu, Sankararaman, Sriram, Milla, Carlos, Emaminejad, Sam
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 08.11.2022
• Subjects: Biomarkers; Biosensing Techniques; Digitization; Electrolysis; Electronic systems; Homeostasis; Humans; Hybrid systems; Microbubbles; Microfluidics; Monitoring; Signal to noise ratio; Sweat; Wearable Electronic Devices; Wearable technology
• ISSN: 1473-0197; 1473-0189; 1473-0189
• DOI: 10.1039/d2lc00670g

Advancements in wearable bioanalytical microsystems have enabled diurnal and (semi)continuous monitoring of physiologically-relevant indices that are accessible through probing sweat. To deliver an undistorted and physiologically-meaningful interpretation of these readings, tracking the sweat secretion rate is essential, because it allows for calibrating the biomarker readings against variations in sweat secretion and inferring the body's hydration/electrolyte homeostasis status. To realize an autonomous wearable solution with intrinsically high signal-to-noise ratio sweat rate sensing capabilities, here, we devise a digitized microbubble detection mechanism-delivered by a hybrid microfluidic/electronic system with a compact footprint. This mechanism is based on the intermittent generation of microliter-scale bubbles via electrolysis and the instantaneous measurement of their time-of-flight (and thus, velocity) via impedimetric sensing. In this way, we overcome the limitations of previously proposed sweat rate sensing modalities that are inherently susceptible to non-targeted secretion characteristics (pH, conductivity, and temperature), constrained by volume, or lack system integration for autonomous on-body operation. By deploying our solution in human subject trials, we validate the utility of our solution for seamless monitoring of exercise- and iontophoretically-induced sweat secretion profiles. A digitized microbubble detection mechanism delivered by a hybrid microfluidic/electronic system is devised for autonomous wearable high signal-to-noise ratio sweat rate monitoring.