Low-Cost Wearable Fluidic Sweat Collection Patch for Continuous Analyte Monitoring and Offline Analysis

Abstract

Sweat sensors allow for new unobtrusive ways to continuously monitor an athlete’s performance and health status. Significant advances have been made in the optimization of sensitivity, selectivity, and durability of electrochemical sweat sensors. However, comparing the in situ performance of these sensors in detail remains challenging because standardized sweat measurement methods to validate sweat sensors in a physiological setting do not yet exist. Current collection methods, such as the absorbent patch technique, are prone to contamination and are labor-intensive, which limits the number of samples that can be collected over time for offline reference measurements. We present an easy-to-fabricate sweat collection system that allows for continuous electrochemical monitoring, as well as chronological sampling of sweat for offline analysis. The patch consists of an analysis chamber hosting a conductivity sensor and a sequence of 5 to 10 reservoirs that contain level indicators that monitor the filling speed. After testing the performance of the patch in the laboratory, elaborate physiological validation experiments (3 patch locations, 6 participants) were executed. The continuous sweat conductivity measurements were compared with laboratory [Na + ] and [Cl – ] measurements of the samples, and a strong linear relationship ( R 2 = 0.97) was found. Furthermore, sweat rate derived from ventilated capsule measurement at the three locations was compared with patch filling speed and continuous conductivity readings. As expected from the literature, sweat conductivity was linearly related to sweat rate as well. In short, a successfully validated sweat collection patch is presented that enables sensor developers to systematically validate novel sweat sensors in a physiological setting.

Soft, flexible conductivity sensors for ocean salinity monitoring

“…For instance, an Au-electrode conductivity sensor in a sweat collection patch operated at 0.2 Vpp (peak-to-peak voltage) and a frequency of 80 kHz (in the low sensitivity region of the performance diagram) exhibited a conductance sensitivity of 24 μS/mM NaCl when tested in NaCl solutions with a concentration range of 10–150 mM. 44 Another Au-electrode impedance-based sweat sensor, which was operated at 100 kHz with an AC signal amplitude of 400 mV (in the high sensitivity region of the performance diagram), possessed an improved conductance sensitivity of approximately 70 μS/mM NaCl calculated from the admittance change when the NaCl concentration varies from 15 to 60 mM. 23 The results in this study and those from previous studies effectively validate the performance diagram, which can provide significant guidance for the operation of Au-based electrochemical sensors.…”

Carbon-based electrochemical biosensors as diagnostic platforms for connected decentralized healthcare

“…systems. An example of a sweat collection patch has been reported recently, consisting of an analysis chamber for measurements of sweat conductivity and the [Na + ] and [Cl -] of samples 125 .With respect to energy harvesting, most currently developed e-tattoos rely on power sources using conventional energy devices to enable operation. A new direction to realize truly autonomous wearables is to couple the sensing system with a bioenergy microgrid such as those relying on human activity to harvest energy input, creating an autonomously integrated on-body wearable 126 .In this example, the energy requirements for the microgrid e-textile are harvested from…”

Agreement between the ventilated capsule and the KuduSmart® device for measuring sweating responses to passive heat stress and exercise

“…In brief, a highly absorbent patch is placed on the skin surface for a fixed amount of time providing an index of local sweat rate; however, this method lacks the temporal resolution offered from a ventilated capsule. Alternatively, patches have been developed that allow end-users to measure the speed of sweat accumulation within microfluidic channels (Nyein et al 2021;Ghaffari et al 2023), or assess changes in conductance as channels gradually fill (Steijlen et al 2022). However, the volume capacity of the channel limits its application for extended use or at higher sweat rates.…”

“…More recent prototypes of a portable local sweat rate monitoring device have assumed influent air in a closed loop system(Uchida et al 2022), which over time may become saturated and systematically underestimate the local sweat rate measured. While other devices and techniques have been explored to measure local sweat rate in the field(Havenith et al 2008;Nyein et al 2021;Steijlen et al 2022;Ghaffari et al 2023), to our knowledge, the KuduSmart® is the only device that operates similarly to the ventilated capsule technique without the need for an anhydrous gas supply, and communicates wirelessly over Bluetooth® to a companion application for real-time monitoring.Based on the present findings, the KuduSmart® device could serve as a portable 'drop in' replacement to the traditional ventilated capsule technique offering researchers greater accessibility and flexibility in measuring sudomotor control during passive heat stress or exercise.For example, this device could enable real-time monitoring of local sweat rate responses during occupational work in thermally stressful environments, during athletic training or competition, or over prolonged periods of exposure to extreme heat. Further, the KuduSmart® device may help clinicians and researchers characterize how various factors influence sudomotor output including, but not limited to, aging, comorbidity, medications, fitness, and heat acclimation.…”