Bioluminescent flow sensor for d-(−)-lactate

Abstract

Previously, a bioluminescent flow sensor was developed for the determination of the content of l-lactate in biological fluids (serum, plasma, ventricular fluid) by monitoring the reduced form of nicotinamide adenine dinucleotide (NADH), produced by immobilized lactate dehydrogenase (LDH), with bacterial bioluminescent enzymes immobilized on a separate nylon coil. Based on a similar scheme, a sensor has now been developed for d-(−)-lactate. The co-immobilization of alanine aminotransferase (ALT) with d-LDH improved the lactate transformation to 40–60%. The response was linear from 1 to 100 μmol 1 −1 at 25 °C for the LDH-ALT reactor. The intra- and inter-assay relative standard deviations were less than 75% and the recoveries ranged from 93 to 106%. The results agreed well with those obtained with a spectrophotometric method and applications to d-(−)-lactate determination in serum, milk and microorganism extracts are reported together with those for l-(+)-lactate.