Fibre-optic sensor with co-immobilised bacterial bioluminescence enzymes

A fibre-optic bioluminescent sensor for the microdetermination of NADH is described. Measurements can be performed in the linear range 1 x 10(-9) M-3 x 10(-6) M with a detection limit of 3 x 10(-10) M using the bacterial luciferase and NAD(P)H:FMN oxidoreductase co-immobilised on a preactivated polyamide membrane. The relative standard deviation was 4.8-5.5% at 4 x 10(-8) M NADH and the steady-state response time was 2 min. When stored at -20 degrees C with 20% glycerol, the activity of the bioactive membranes was higher than that measured prior to freezing and then remained stable for more than four months.