COMPARISON OF ELECTROCHEMICAL WITH OPTICAL BIOSENSORS

Abstract

NAD*/NADH und NADP*/NADPH systems, which are important coenzymes, are studied with respect to their determination by electrochemical or optical methods relevant for biosensors. Concerning their sensitivity and linearity of the calibration curves, similar results were obtained, when the technique of Flow-Injection Analysis (FIA) was used in conjunction with an amperometric flow-through cell and when a fiberoptic device measuring the fluorescence of NAD(P)H was employed. In both cases the limit of detection was around 1 nmol/l and the calibration curves showed two linear ranges. As a consequence an optical glucosesensor based on this technique resulted in a correspondingly high sensitivity compared to a classical needle type amperometric device based on the glucose-oxidase (GOD) method. Otherwise, the superb sensitivity achievable by the amperometric NADH oxidation could by used for a sensitive formaldehyde FIA method yielding a limit of detection in the sub-nmol/l range. In addition, a reagentless fiber optic lactate sensor based on lactate-dehydrogenase (LDH) and a reversible redox-dye is described and also a novel potentiometric immunosensor based on the principle of selectivity modulation of ion-selective membranes.