A microfluidic system using electrochemical biosensor for continuous lactic acid (LA) monitoring at the skin's surface was fabricated and tested. The system consists of a micro flow-cell for sampling LA at the skin's surface and a microfluidic LA biosensor based on a redox reaction of osmium wired horseradish peroxidase (Os-HRP). Our system measures excreted LA by dissolving whole secretion in phosphate buffered saline (PBS), which was supplied into the micro channel as carrier flow. The measurement system was utilized in the real-time monitoring of LA secretion during stationary bike exercises. Exercise intensities were regulated by heartrates (HR) and the sampling device was attached on the right upper arm of the volunteer. During the exercise, PBS was circulated into the measurement system. As a result, change of LA levels correlated with the volunteer's physiological status was confirmed. Secretion of LA was estimated to be 4.50 µg/cm2/min when the intensity of exercise was high (HR: 160 bpm) and the signal decreased to the initial level after the exercise. This indicates that our system is suitable for not only the assessment of exercise intensity, but also useful in evaluation of metabolic activity.
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