Electrochemical biosensors were developed for the determination of lactic acid in expiration. The lactic acid biosensors were fabricated using a platinum (Pt) disk electrode coupled with a thin film of immobilized enzyme (lactate oxidase, LOx). The surface of the Pt electrode was modified with LOx thin film by two different procedures;a cross-linking method and a multilayer film method. The cross-linking method employed bovine serum albumin (BSA) and glutaraldehyde together with LOx, in which BSA and LOx were chemically cross-linked with glutaraldehyde to form thin films on the surface of the Pt electrode. On the other hand, in the multilayer method, a mannose-labeled LOx and Con A were deposited alternately on the surface of the Pt electrode to form a layer-by-layer thin films. Both techniques gave useful biosensors to determine lactic acid in solution. Both sensors exhibited useful calibration graphs over the lactate concentration of 0.01-3 mM in solution. For the purpose of using the biosensors to determine lactic acid in expiration, the surface of the sensor was covered with a dialysis membrane to form an aqueous gel layer adjacent to the electrode surface. The dialysis membrane-covered sensors, unfortunately, showed very small response to expiration, probably due to the low concentration of lactic acid in the expiration. In order to improve the performance of the biosensors, lactic acid should be concentrated in the aqueous gel layer or on the surface of the electrode.

DESCENTE SPORTS SCIENCE Vol.20/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE