The proposed wearable sensor for measuring chloride ion levels in sweat can be easily applied to textiles using the heat-transfer printing technique, preventing skin irritation and allergies. (Credit: Isao Shitanda/TUS, Japan)

An innovative sweat biosensor uses a technique called heat-transfer printing to fix a thin, flexible chloride ion sensor onto a textile substrate. The biosensor can be transferred to fiber substrates, and thus can be incorporated into textiles such as T-shirts, wristbands, and insoles.

The sensor is transferred outside of the piece of clothing, which prevents skin irritation. In addition, the wicking effect of the textile helps spread the sweat evenly between the electrodes of the sensor, creating a stable electrical contact. Moreover, printing the sensor on a flat surface and then transferring it prevents the formation of blurred edges that commonly occur when printing directly onto a textile.

After developing the sensor, the researchers conducted various experiments using artificial sweat to verify its accuracy in measuring chloride ion concentration. The change in the electromotive force of the sensor was −59.5 mTV/log CCl−. Additionally, it displayed a Nernst response and a linear relationship with the concentration range of chloride ions in human sweat. No other ions or substances typically present in sweat were found to interfere with the measurements.