Bioluminescent flow sensor for L-phenylalanine determination in serum

A highly sensitive and rapid bioluminescent flow sensor was developed for the determination of the content of L-phenylalanine (Phe) in serum by monitoring the reduced form of nicotinamide adenine dinucleotide (NADH), produced by immobilized phenylalanine dehydrogenase (PheDH), with bacterial bioluminescent enzymes immobilized on a separate nylon coil. The L-PheDHs extracted from Bacillus badius, Bacillus sphaericus and Rhodococcus sp. M 4 were investigated and the performances of the three immobilized L-PheDH's were analysed. The B. badius reactor was found to give higher transformation rate and better sensitivity; the response was linear from 1 to 100 microM at 25 degrees , with a detection limit of 10 pmoles (0.5 microM). The intra- and inter-assay coefficients of variation were less than 5% and recoveries ranged from 90 to 101%. The results agreed well with those obtained with a chromatographic method for the Phe determination in serum and with the normal reference values.