Biosensors have been attracting much attention as a promising tool to analyze an analyte in the field of diagnosis, environment, food, and bioprocess. However, only a limited number of biosensors has been applied to real samples, and very few are commercialized so far. A prerequisite for commercialization is that the biosensor must be fabricated at least on a medium batch scale with a reasonable cost. Thick-film technology is well known to be valuable for the production of one-shot enzyme electrode due to its high production efficiency. From an analytical point of view, $NAD^+$/NADP - dependent dehydrogenase is regarded as one of the most important enzymes. But these dehydrogenases have not been successfully used for the enzyme sensor in spite of their broad range of catalytic capabilities. Major barrier to the practical application of dehydrogenase lies in the difficulty in regeneration of the coenzyme and poor electrocatalytic behaviors of $NAD^+$/NADH couple. An amperometric biosensor for the determination of L-lactate was fabricated using L-lactate dehydrogenase by means of thick-film technology. The biosensor strip consists of three electrodes: a carbon counter electrode, a psuedo-reference electrode (Ag/AgCl), and a working electrode based on carbon / complex polymer resin / lactate dehydrogenase / $NAD^+$. Voltammetric and amperometric studies on the thick film enzyme electrodes were conducted to evaluate special electrochemical characteristics. Optimal conditions for the preparation and operation of the resulting L-lactate biosensor were evaluated in terms of the sensitivity and stability.
