An ex vivo brain lactic acid (LA) monitoring system for investigating brain activity at the organ level was constructed and tested in continuous LA monitoring. Our system consists of a micro-fluidic dual-analyte (LA and glucose) biosensor and a special brain chamber that is suitable for organ level experiments. The biosensor utilizes the redox reactions of osmium-wired horseradish peroxidase (Os-HRP) to detect hydrogen peroxide produced by enzyme reactions. The sensor had sufficient sensitivity (LA: ∼ 0.01 mM, glucose: ∼ 0.01 mM) and selectivity for assessment of extracellular LA. The ex vivo monitoring of brain LA was performed using the proposed system. As a result, the change in extracellular LA was successfully monitored continuously, and the change in the LA level was considered the result of metabolic activity of the sample. Our system is expected to be useful not only for ex vivo brain monitoring, but also for monitoring other organs.
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