Preparation and properties of enzyme sensors for l-lactic and d-lactic acids in optical isomers Original Research Article

Enzyme sensors using l-lactate dehydrogenase (EC 1.1.1.27) and d-lactate dehydrogenase (EC 1.1.1.28) with osmium complex were developed for measuring l-lactic and d-lactic acids, respectively. Cyclic voltammograms of the lactic acids isomers on the porous carbon electrodes were recorded. In addition, the effects of pH and temperature, calibration curves for l-lactic and d-lactic acids, the effects of the other optical isomer on measurements, and the lifetime of the sensors were investigated. Under optimal conditions, the responses of the sensors were linear in the concentration range 0.1–10 mM l-lactic acid and 1–20 mM d-lactic acid. l-Lactic acid and d-lactic acid could each be measured in the presence of the other isomer, with maximum relative errors of ±5.4%. The sensitivities of the sensors were constant for more than one month.