This is the first report demonstrating proof of concept for the passive, non-invasive extraction and in situ potentiometric detection of human sweat chloride ions (Cl− ions) using a stable printed planar liquid-junction reference electrode-integrated hydrogel-based touch-sensor pad without activities such as exercise to induce perspiration, environmental temperature control, or requiring cholinergic drug administration. The sensor pad was composed entirely of a screen-printed bare Ag/AgCl-based chloride ion-selective electrode and a planar liquid-junction Ag/AgCl reference electrode, which were fully covered by an agarose hydrogel in phosphate-buffered saline (PBS). When human skin contacted the hydrogel pad, sweat Cl− ions were continuously extracted into the gel, followed by in situ potentiometric detection. The planar liquid-junction Ag/AgCl reference electrode had a polymer-based KCl-saturated inner electrolyte layer to stabilize the potential of the Ag/AgCl electrode even with a substantial change in the chloride ion concentration in the hydrogel pad. We expect this fully screen-printed sensor to achieve the low-cost passive and non-invasive daily monitoring of human Cl− ions in sweat in the future.
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This work was partly supported by the Center of Innovation Program (COI) from the Japan Science and Technology Agency, JST (JPMJCE1312 and R02W05), and by the Leading Initiative for Excellent Young Researchers (LEADER), a Grant-in-Aid for Scientific Research C (18K04910) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan, the YU-COE (C), a research grant from Yamagata University, Japan, and the Foundation for Technology Promotion of Electronic Circuit Board.
Conflict of interest
The authors declare that they have no conflicts of interest.
All subjects gave their informed consent for inclusion before they participated in the study. The study was conducted in accordance with the Declaration of Helsinki, and the Ethics Committee approved the protocol of the Faculty of Medicine, Yamagata University (Approval No. 30–7).
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Ichimura, Y., Kuritsubo, T., Nagamine, K. et al. A fully screen-printed potentiometric chloride ion sensor employing a hydrogel-based touchpad for simple and non-invasive daily electrolyte analysis. Anal Bioanal Chem (2021). https://doi.org/10.1007/s00216-021-03156-3
- Sweat analysis
- Printed electronics