Japanese researchers develop new sweat-sensing smartwatch capable of real-time monitoring of sodium and potassium changes in sweat

Japanese researchers have developed a wristband-type sensor that successfully tracked sweat-related sodium and potassium signals for 2 hours and 45 minutes during testing at a real construction site. The wearable device, developed by the Tokyo Institute of Technology, combines printed electrodes, a sweat collection layer, and wireless electronics to monitor changes in the chemical composition of sweat during work. Unlike conventional printed sensors, the system uses a liquid-junction reference electrode designed to stabilize quickly, producing stable readings without lengthy preparation.

The prototype was tested during a construction worker's routine activities, including movement, rest, drinking water, and eating. Researchers said the results demonstrate the system can collect and transmit sweat-related signals outside laboratory conditions. The sensor operates by measuring voltage changes associated with sodium and potassium ions in sweat; these minerals participate in various physiological processes, making them useful targets for wearable monitoring research. Such sensors rely on a reference electrode to provide a stable electrical baseline; without one, voltage changes cannot be reliably linked to ion concentration changes.

System testing and operating principle

Conventional printed reference electrodes require a considerable time to stabilize, limiting their practicality in wearable systems designed for continuous measurement. To address this, the researchers integrated a screen-printed liquid-junction reference electrode containing silica. The material allows water to enter the electrolyte layer, helping the electrode reach a stable measurement potential without lengthy pre-conditioning. The device also includes separate sodium-selective and potassium-selective electrodes, enabling simultaneous response to both ions. A layer of fabric and super-absorbent fiber sits above the electrodes to help collect sweat, keep the sensing area moist, and transport the sample to the sensors.

These components connect to a custom wristband-type electronic unit that processes signals, transmits them wirelessly to a computer, and stores the measurements on a microSD card. The researchers noted that the combination of these components, rather than the development of new electrode materials, constitutes the main engineering advance.

Field testing and future applications

The team tested the complete system at an active construction site, with a participant wearing the device for approximately 165 minutes while performing normal daily activities. During the test, the sensor continuously acquired signals responsive to sodium and potassium, and these readings were transmitted to a nearby computer and saved locally. Isamu Shida, an associate professor at the Tokyo Institute of Technology, said: "The main achievement of this work lies not in proposing a new electrode material, but in the integration of printed electrodes, a sample transport mechanism, and wireless measurement circuitry, demonstrating feasibility in a real-world environment."

The field test involved only one participant. The researchers emphasized that these signals have not yet been validated to accurately quantify sweat electrolyte concentrations; further testing under controlled sweating conditions is needed before they can reliably support hydration assessment or health monitoring. The research team believes that printed electrode manufacturing could eventually enable mass production of similar wearable systems at low cost. Potential applications include monitoring workers at construction sites and factories, as well as athletes and outdoor exercisers active in hot conditions. The study was published in ACS Omega.

Potential of wearable technology in health monitoring

The development of this new sweat-sensing smartwatch demonstrates the potential of wearable technology in health monitoring. By monitoring electrolyte changes in sweat in real time, such devices can provide workers and athletes with important physiological data, helping them better manage hydration and health status. Although current testing still requires further validation, the successful integration of this technology is expected to drive future applications across various industries, particularly in high-intensity work and exercise environments.