Wireless Wearable Electrochemical Sensing Platform with Zero-Power Osmotic Sweat Extraction for Continuous Lactate Monitoring

Abstract

Wearable and wireless monitoring of biomarkers such as lactate in sweat can provide a deeper understanding of a subject's metabolic stressors, cardiovascular health, and physiological response to exercise. However, the state-of-the-art wearable and wireless electrochemical systems rely on active sweat released either via high-exertion exercise, electrical stimulation (such as iontophoresis requiring electrical power), or chemical stimulation (such as by delivering pilocarpine or carbachol inside skin), to extract sweat under lowperspiring conditions such as at rest. Here, we present a continuous sweat lactate monitoring platform combining a hydrogel for osmotic sweat extraction, with a paper microfluidic channel for facilitating sweat transport and management, a screen-printed electrochemical lactate sensor, and a custom-built wireless wearable potentiostat system. Osmosis enables zeroelectrical power sweat extraction at rest, while continuous evaporation at the end of a paper channel allows long-term sensing from fresh sweat. The positioning of the lactate sensors provides near-instantaneous sensing at low sweat volume, and the custom-designed potentiostat supports continuous monitoring with ultra-low power consumption. For a proof of concept, the prototype system was evaluated for continuous measurement of sweat lactate across a range of physiological activities with changing lactate concentrations and sweat rates: for 2 h at the resting state, 1 h during mediumintensity exercise, and 30 min during high-intensity exercise. Overall, this wearable system holds the potential of providing comprehensive and long-term continuous analysis of sweat lactate trends in the human body during rest and under exercising conditions.

Electrochemical Nanosensors for Sensitization of Sweat Metabolites: From Concept Mapping to Personalized Health Monitoring

“…Herein, an electrochemical screen printed lactate sensor coupled with a potentiostat system has been attached to the microfluidic device, which provides prompt recognition responses at trace levels of sweat lactate with low power consumption and is monitored by the potentiostat. This osmotic wearable sensor for lactate recognition from sweat, entitled OWLSS, was further used for continuous measurement of sweat lactate transversely over workout activities with altering lactate concentrations [ 42 ]. Yang et al have reported another sweat sensor for one-to-one health care through combining Ni-MOF (Ni 3 HHTP 2 )-based electrodes on the surface of a flexible nanocellulose substrate ( Figure 5 b).…”

“… ( a )OWLSS for continuous biochemical monitoring, adopted with permission from Ref. [ 42 ]; ( b ) Ni-MOF-based wearable sweat sensor, adopted with permission from Ref. [ 43 ]; ( c ) selective detection of lactic acid by MWCNT-polypyrrole nanowire; and ( d ) the fabricated flexible printed electrode, on which MWCNT-polypyrrole nanowires were impregnated.…”

A Soft Wearable Microfluidic Patch with Finger-Actuated Pumps and Valves for On-Demand, Longitudinal, and Multianalyte Sweat Sensing

“…Figure F exhibits a photo of the soft microfluidic device intimately mounted onto the forearm. The described design can be tailored to include more sensing chambers for high-frequency analysis and other forms of transducers, for example electrochemical ,− and fluorometric, − to further expand its capabilities in sweat analysis. The following sections describe the systematic characterization of the key components of the device followed by a validation of the system through human trials.…”

Self-Testing of Ketone Bodies, along with Glucose, Using Touch-Based Sweat Analysis

“…Here, we report a simple and rapid touch-based device capable of simultaneously detecting HB, along with glucose, from sweat generated at the fingertip. Among the different biofluids, sweat is an attractive, easily collected noninvasive biofluid that contains rich chemical information. , Sweat can be generated in connection to different sweat collection mechanisms involving exercise, heat, stress, or chemical stimulation. , Recent reports have shown the human fingertip to be an attractive site for rapid noninvasive sweat sampling due to its extremely high density of sweat glands . Such natural fingertip sweat secretion facilitates convenient sweat assays under resting conditions, without the necessity of active perspiration or vigorous sweat stimulation protocols before the testing. − Sweat represents and remains a good candidate for testing for HB and glucose, having the potential to generate useful information regarding the health status of an individual, since both HB and glucose levels are linked with long-lasting implications on the physical and mental health and the functioning of the human immune system. , The only reported wearable sweat HB sensor requires active perspiration during physical exercise activity, which hinders practical HB self-testing applications.…”

“…5,6 Sweat can be generated in connection to different sweat collection mechanisms involving exercise, heat, stress, or chemical stimulation. 7,8 Recent reports have shown the human fingertip to be an attractive site for rapid noninvasive sweat sampling due to its extremely high density of sweat glands. 9 Such natural fingertip sweat secretion facilitates convenient sweat assays under resting conditions, without the necessity of active perspiration or vigorous sweat stimulation protocols before the testing.…”