Wristwatch Sensor Tracks Sodium and Potassium in Sweat in Real Time

Sweat can provide real-time biochemical information about the body’s physiological state, with sodium and potassium measurements offering potential value for monitoring people working or exercising in hot environments. However, conventional printed reference electrodes may require substantial stabilization time before measurements can begin, limiting their suitability for continuous use. Addressing this limitation, researchers have developed a wristwatch-type wearable sensor for real-time monitoring of sodium and potassium in sweat.

Tokyo University of Science developed the wristwatch-type sodium- and potassium-ion sensor using a screen-printed liquid-junction reference electrode. The device integrates printed electrodes, a sample transport layer, and digital electronics into a wearable system, allowing sodium- and potassium-responsive signals to be acquired, wirelessly transmitted, and stored locally on a micro-SD card.

The sensor uses sodium- and potassium-selective electrodes with a liquid-junction reference electrode containing silica gel. This structure supports water permeation into the electrolyte layer and enables rapid initial stabilization of the reference electrode. A fabric and superabsorbent fiber sample transport layer is placed over the electrodes to wet the sensing area and move sweat through the sensing region.

The research team tested the device at an active construction site. One construction worker wore the wristwatch during a usual workday that included breaks, hydration, and meals. The device acquired sodium- and potassium-responsive signals in real time for approximately two hours and 45 minutes while the worker moved around the site.

The measurements were transmitted wirelessly to a host computer and simultaneously stored on the device. The study was published online in ACS Omega on September 21, 2026. The findings indicate field feasibility for an integrated wearable electrolyte-sensing system, while quantitative sweat analysis will require controlled sweating experiments and further validation. Because the sensor electrodes can be fabricated using printing technology, the approach could support low-cost wearable systems suitable for large-scale production.

“The central achievement of this work lies not in the proposal of a new electrode material, but in the integration of a printed electrode, sample transport mechanism, and wireless measurement circuit, demonstrating its feasibility in a real-world environment,” said Dr. Isao Shitanda, Associate Professor, Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science.

“This technology could serve as a foundation for acquiring information about ions contained in sweat without interrupting work or exercise in construction sites, manufacturing plants, sports, and outdoor activities. In the future, by combining this information with data, such as sweat volume and water intake, it could be applied to health management and hydration support in hot environments,” added Dr. Shitanda.

Related Links:
Tokyo University of Science