Human sweat is a rich source of health information, offering insights into a person’s hydration levels, electrolyte balance, and overall physiological state. For example, sweat lactate levels are a useful biomarker of exercise intensity. Its measurement helps estimate the amount of lactic acid in the blood and, in turn, predicts muscle fatigue.
Today, wearable sensors make it possible to continuously monitor biomarkers such as sweat lactate. Using the latest microfluidics technology, scientists have developed devices that deliver small amounts of sweat to tiny chemical sensors, which can transmit their measurements in real time wirelessly.
However, a common problem with such devices is that their microfluidic channels tend to trap air bubbles present in sweat. If these bubbles cover the sensor electrodes, the measurements are interrupted, which interferes with the continuous monitoring of the target biomarker.
To address this issue, a research group, led by Associate Professor Isao Shitanda from Tokyo University of Science (TUS) in Japan, has developed a novel microfluidic sweat lactate sensor whose measurements remain unaffected by the air bubbles. Their study, published in ACS sensorsco-authored by Dr. Masahiro Motosuke, Dr. Tatsunori Suzuki, Dr. Shinya Yanagita, and Dr. Takahiro Mukaimoto from TUS.
The proposed wearable device consists of a relatively simple layered structure—a conventional lactate oxidase sensor attached via double-sided tape to a microfluidic system made of silicone polymer. When the person wearing the device starts sweating, the sweat enters the microfluidic channels through four inlets and flows to a reservoir near the electrodes located. Old sweat leaves the system through an outlet while new sweat enters, and a small wireless transmitter reports the measured lactate level.
The key innovation in the proposed design is the use of a larger-than-usual sweat reservoir. “By increasing the height of the reservoir in the microfluidic channel, a space of approximately four microliters is created for trapping any air bubbles that enter the device, thus preventing them from contacting of the sensor electrodes,” explained Dr. Shitanda.
The researchers tested their sensor in a series of laboratory experiments. They verified that the bubble-trapping region worked as intended by injecting bubbles into the device while measuring lactate levels in artificial sweat. In addition, the measurements are not affected by the sweat flow rate, and the response of the sensor remains stable for approximately two hours.
Finally, the researchers tested the device on a male volunteer who exercised on a stationary bicycle for about an hour. The sensor shows a lactate concentration correlation from 1 to 50 mM as well as a correlation between sweat and blood lactate levels.
Overall, the results of this study demonstrate the potential of wearable microfluidic sensors for monitoring sweat biomarkers during exercise. “Because the microfluidic system of the proposed lactate sensor is made from a soft, flexible, and non-irritating material, it can be used to continuously monitor the level of lactate in sweat, especially in sports and medicine, said Dr. Shitanda.
“Wearable lactate sensors can be useful condition management tools in sports like soccer and basketball, allowing team managers to know when it’s best to replace a player. ”
Only time will tell what training management and health monitoring will look like in the future as wearable sensors become more capable and reliable.
Isao Shitanda et al, Air-Bubble-Insensitive Microfluidic Lactate Biosensor for Continuous Monitoring of Sweat Lactate, ACS sensors (2023). DOI: 10.1021/acssensors.3c00490
Provided by Tokyo University of Science
Citation: Scientists develop new wearable sensor for measuring sweat lactate levels during exercise (2023, July 18) retrieved July 18, 2023 from https://phys.org/news /2023-07-scientists-wearable-sensor-lactate.html
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