Simultaneous Detection of Lactate Enantiomers Based on Diffusion-controlled Bioelectrocatalysis.

Amperometric biosensors were constructed for the simultaneous detection of lactate enantiomers. The enantioselectivity of the sensor is based on NAD-dependent l- and d-lactate dehydrogenases that, respectively, oxidize l- and d-lactates into pyruvate. The NADH formed during the enzymatic reduction was catalytically oxidized at Meldola's blue-adsorbed mesoporous electrodes. Stable amperometric measurements were performed in a two-electrode system using Ag|AgCl|sat. KCl as a counter electrode via a salt bridge. The response of the sensor reached a pseudo-steady state within 60 s. The agreement of the sensitivities for l- and d-lactates and the pseudo-steady-state characteristics of the sensors demonstrate that the current is strongly influenced by the diffusion of lactates at the edge of the electrode, enabling reproducible measurements. The pseudo steady-state characteristics are also realized at the chip-type electrode. The sensor was successfully applied for the detection of d- and l-lactates in horse serum.