Physiological stress monitoring using sodium ion potentiometric microsensors for sweat analysis

In the frame of sweat analysis, two technologies, based on either ISE or ISFET devices, were developed for the implementation of pNa potentiometric microsensors. Both of them demonstrated good sodium ion Na+ detection properties with a global sensitivity of around 110mV/pNa in NaCl-based solutions due to the use of an integrated “Ag/AgCl ink” pseudo-reference electrode. Then, in order to deal with in vivo analysis of sweat natremia, a physiological sweatband prototype was developed, consisting of pNa-ISE and pNa-ISFET electronic detection modules as well as a textile-based sweat pump. Finally, sweating process was studied during series of experiments on twenty-five healthy consenting subjects. The sodium ion concentration [Na+] was successfully monitored in sweat during various heat exposures, demonstrating a global increase with exercise trial duration. Furthermore, a strong correlation was found between the sweat [Na+] concentration and the subject's internal temperature θ, allowing monitoring the subject's heat stress state. All in all, the relevance of the Na+ ion analysis was demonstrated for the physiological stress monitoring and pNa potentiometric microsensors were shown to be very promising for the development of smart sweatbands.