A wearable electrochemical sensor for the real-time measurement of sweat sodium concentration

Abstract

We report a new easier method for the quantitative analysis of sodium in human sweat. To the best of our knowledge this is the first time this has been done successfully in a real-time manner. We consolidate sweat stimulation, collection and analysis functions into a single method. This temporal data opens up new possibilities in the study of human physiology, broadly applicable from assessing athletic performance and hydration levels to monitoring Cystic Fibrosis (CF) sufferers. Our compact Sodium Sensor Belt (SSB) consists of a sodium selective Ion Selective Electrode (ISE) integrated into a platform that can be interfaced with the human body during exercise. No skin cleaning regime or sweat storage technology is required as samples is continually wicked from skin to a sensing surface and on to a waste terminal via a fabric pump. After an initial equilibration period, a sodium plateau concentration was reached and monitored continuously. Atomic Absorption Spectroscopy (AAS) was used as a refe rence method, confirming accuracy. The plateau concentrations observed fell within expected literature ranges, further confirming accuracy. Daily calibration 2 repeatability (n=4) was ±3.0% RSD and over a three month period reproducibility was ±12.1% RSD (n=56). As a further application, we attempted to monitor the sweat of Cystic Fibrosis (CF) sufferers using the same device. We observed high sodium concentrations symptomatic of CF (~60mM Na + ) for 2 CF patients, with no conclusive results for the remaining patients due to their limited exercising capability. The real-time monitoring of hydration levels during physical exercise for health and performance purposes is a particularly promising application for the SSB at present.

Autonomous sweat extraction and analysis applied to cystic fibrosis and glucose monitoring using a fully integrated wearable platform

“…S5). Ag/AgCl electrodes were chosen for chloride ion detection (23) whereas the measurement of sodium ions was achieved by using previously reported sodium ionophore X selectophore-based ion-selective electrodes (15). A polyvinyl butyral (PVB)-coated electrode containing saturated chloride ions was chosen as the reference electrode due to its stable potentials in different analyte solutions (16).…”

“…Despite significant progress made in printed and flexible biosensors in the field, a majority of wearable devices focus on monitoring of physical activity or selected electrophysiological parameters, providing only limited information regarding physiological changes of complex homeostatic responses (4)(5)(6)(7)(8)(9)(10). Wearable chemical sensors offer great opportunities for collecting physiological information at the molecular level (3,(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Recently research advances have resulted in a variety of wearable sweat sensors that can be used for real-time analysis of sweat biomarkers including electrolytes, metabolites, and heavy metals (11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”

Wearable Bio and Chemical Sensors

“…In recent years, significant effort has been focused on sampling and analysis of alternative body fluids, such as interstitial fluid [5], tears [6], saliva [7], and sweat [8]. The transition from blood to other body fluids provides a less invasive means of sampling, which in turn may provide a route to facilitate longer-term continuous monitoring.…”

“…The integration of the sensor into a band-aid for real-time detection of potassium on a manikin was demonstrated, although, as the authors well highlighted, the incorporation of the sensor into a truly wearable platform would require further investigation. Also using a potentiometric sensor, Schazmann et al [8] developed a wearable platform to perform realtime measurements of sodium concentration in sweat. A liquid contact ion selective electrode (ISE) was integrated within a sodium sensor belt (SSB), which was then applied to the comparison of sodium concentration in sweat emitted by healthy and cystic fibrosis-positive people during exercise.…”

Gold Nanoparticle Treated Textile-Based Materials for Potential use as Wearable Sensors

“…Modern high performance textile fabrics have been developed for a variety of sportswear that promote moisture repelling and temperature regulating properties [15]. And recent studies have also shown that wearable sweat-based electrochemical biosensors can monitor sodium, chloride and lactate levels [16,17]. Accordingly, developing electrically enhanced textile fabrics will be at the forefront of smart clothing with the ability to sense and communicate information to remote data collection centres via the internet [18].…”