A fully reversible fiber optic lactate biosensor based on the intrinsic fluorescence of lactate monooxygenase

Summary

The intrinsic fluorescence intensity of the enzyme lactate monooxygenase is used as the analytical parameter in a new type of lactate biosensor. It is found that the fluorescence quantum yield of the coenzyme changes during its interaction with lactate at the point of saturation. The changes in intensity are fully reversible in the presence of molecular oxygen and can be monitored via fiber optic light guides. Enzyme solutions were entrapped at the fiber end using a semipermeable membrane which retains the enzyme. The change in fluorescence occurs within a rather small range of lactate concentration (0.5–1 mmol/l) with an lactate-invariable signal at higher levels. Response times of 7.5 to 25 min (to reach the full steady state) and regeneration times between 1 and 8 min are observed. Measurements are performed in flowing air-saturated solutions containing 0.1 mol/l pH 7.0 citrate buffer. The effect of pH has also been investigated. In order to achieve a more expanded analytical range (e.g., 1.4–10 mmol/l) and shorter response times, kinetic measurements are performed in a fashion similar to flow-injection analysis.