Analytical assessment of sodium ISFET based sensors for sweat analysis

Abstract

Body thermoregulation during exercise induces sweating with the consequent loss of water, electrolytes and other compounds. The use of sweat for bioanalytical purposes has recently widespread because it is an easily accessible biofluid that can be noninvasively collected and/or directly monitored using wearable devices. Different sweat biomarkers can be monitored as indicators of the physiological status of an individual. The concentration of sweat Na+ electrolyte provides information about dehydration or hyponatremia events. Among the different sensor technologies applied for Na+ ion detection in sweat, ion-sensitive field-effect transistors (ISFETs) show superior features in terms miniaturization, key for working with the low volumes of sweat available, robustness, scalability and reproducibility. They also offer fast response and low impedance output signal. This work reports an in-depth study that thoroughly assesses the potential of ISFET sensors for sweat Na+ analysis. Results show a reproducible sensitivity of 60.7 ± 0.5 mV (-Log aNa)− 1, high repeatability, and lifetime up to one month. Sensor reliability is demonstrated by analysing 20 sweat samples and results are compared with the ones provided with the standard ion chromatography technique (IC). The statistical analysis demonstrates that Na+ concentrations estimated with the ISFET sensor and IC are in good agreement showing a relative error of up to 20%. Results demonstrate that the sensor presented in this work can potentially be used for the continuous monitoring of Na+ changes in sweat during exercise.