New biosensor monitors sweat electrolytes in healthcare and sports

Newswise — The impressive extent of miniaturization achievable in contemporary electronics has cleared the path for achieving healthcare gadgets formerly limited to the domain of speculative literature. Wearable detectors exemplify this phenomenon. Just as the term implies, these gadgets are affixed to the physique, typically in direct contact with the dermis. They possess the capability to oversee vital physical indicators such as pulse rate, arterial tension, and muscular function.

Certain wearable sensors are also capable of detecting chemical substances in bodily fluids. For instance, perspiration biosensors have the ability to gauge the concentration of ions present in sweat, thus offering insights into their levels in the bloodstream. However, the process of designing such chemical sensors is more intricate compared to physical sensors. Establishing direct contact between a wearable chemical sensor and the skin can induce irritation and allergies. Conversely, if the sensor is directly integrated into a wearable fabric, its precision diminishes due to surface irregularities.

In a recent study, a team of researchers, headed by Associate Professor Isao Shitanda from the Tokyo University of Science (TUS) in Japan, has introduced an innovative sweat biosensor that tackles the aforementioned challenges. Their findings were published online on June 15, 2023, in ACS Sensors. The study outlines the utilization of a technique known as “heat-transfer printing” to affix a slim, flexible chloride ion sensor onto a textile substrate. Co-authored by Dr. Masahiro Motosuke, Dr. Tatsunori Suzuki, Dr. Shinya Yanagita, and Dr. Takahiro Mukaimoto from TUS, the research sheds light on this significant development.

Dr. Shitanda elucidates, “The sensor we have developed can be seamlessly transferred onto fiber substrates, allowing its integration into various textile-based articles like T-shirts, wristbands, and insoles.” He further highlights, “Moreover, by wearing these textiles, individuals can effortlessly measure health indicators, including the concentration of chloride ions in their sweat.”

The utilization of heat-transfer printing presents numerous advantages. Firstly, this approach enables the sensor to be applied externally to the garment, thereby avoiding any potential skin irritation. Furthermore, the textile’s wicking effect facilitates the uniform distribution of sweat across the sensor’s electrodes, ensuring a stable electrical connection. Additionally, by printing the sensor on a flat surface and subsequently transferring it, the issue of blurred edges, often encountered when directly printing onto textiles, is effectively circumvented.

The researchers took meticulous care in choosing materials and electrochemical mechanisms for the sensor to mitigate the risk of allergic reactions in wearers. Following the sensor’s development, they carried out a series of experiments utilizing artificial sweat to validate its precision in measuring chloride ion concentration. The sensor demonstrated a change in electromotive force of -59.5 mTV/log CCl^-, exhibiting both a Nernst response and a linear correlation within the concentration range of chloride ions found in human sweat. Furthermore, no interference from other ions or substances commonly present in sweat was observed during the measurements.

Finally, the research team conducted a test using the sensor on a volunteer who engaged in a 30-minute session of exercise on a stationary bicycle. They measured the individual’s perspiration rate, chloride ion levels in blood, and saliva osmolality at five-minute intervals, comparing the results with the data collected by the sensor earlier. Through this comparative analysis, it was established that the proposed wearable sensor consistently and accurately measured the concentration of chloride ions in sweat.

In addition to its accurate measurements, the sensor also possesses the capability to wirelessly transmit data, enabling real-time health monitoring. Dr. Shitanda emphasizes the significance of this feature, stating, “As chloride is the predominant electrolyte in human sweat, measuring its concentration serves as an excellent indicator of the body’s electrolyte balance and proves to be a valuable tool for diagnosing and preventing heat stroke.” The wireless data transmission functionality further enhances the sensor’s utility in monitoring and maintaining optimal health.

This research thus demonstrates the potential of using wearable ion sensors for the real-time monitoring of sweat biomarkers, facilitating personalized healthcare development and athlete training management



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