An integrated amperometric d-lactic acid biosensor involving a gold film deposited by sputtering on a stainless steel disk electrode where the enzymes d-lactic acid dehydrogenase (DLDH) and diaphorase (DP) as well as the redox mediator tetrathiafulvalene (TTF) are coimmobilized by using a dialysis membrane, is reported in this work. Amperometry in stirred solutions at a detection potential of +0.15 V (vs Ag/AgCl reference electrode) provided a linear calibration plot for d-lactic acid over the 1.0×10-4 to 3.8×10-3 g L-1 concentration range, with a limit of detection of 3.1×10-5 g L-1. The usefulness of the biosensor was demonstrated by determining d-lactic acid in beer samples with good results. Additionally, the biosensor was implemented together with a commercial l-lactic amperometric biosensor in a semiautomatic flow-injection analysis (FIA) system able to perform a rapid and simple stereo-specific determination of d- and d-lactic without a previous separation step. The operational characteristics of the biosensors under flow conditions were evaluated and its applicability was demonstrated through the simultaneous determination of both enantiomers in beer samples.

An integrated amperometric d-lactic acid biosensor involving a gold film deposited by sputtering on a stainless steel disk electrode where the enzymes d-lactic acid dehydrogenase (DLDH) and diaphorase (DP) as well as the redox mediator tetrathiafulvalene (TTF) are coimmobilized by using a dialysis membrane, is reported in this work. Amperometry in stirred solutions at a detection potential of +0.15 V (vs Ag/AgCl reference electrode) provided a linear calibration plot for d-lactic acid over the 1.0×10-4 to 3.8×10-3 g L-1 concentration range, with a limit of detection of 3.1×10-5 g L-1. The usefulness of the biosensor was demonstrated by determining d-lactic acid in beer samples with good results. Additionally, the biosensor was implemented together with a commercial l-lactic amperometric biosensor in a semiautomatic flow-injection analysis (FIA) system able to perform a rapid and simple stereo-specific determination of d- and d-lactic without a previous separation step. The operational characteristics of the biosensors under flow conditions were evaluated and its applicability was demonstrated through the simultaneous determination of both enantiomers in beer samples.