L-Lactate oxidase electrode based on methylene green and carbon paste

Abstract

An amperometric l-lactate electrode based on methylene green (MG) and carbon paste chemically modified with l-lactate oxidase is described. The electrode action is based on the effective reduction of oxidized l-lactate oxidase by reduced MG (apparent rate constant = 1.7 × 10 6 l mol −1 s −1) and rapid electrochemical mediator conversion. The enzyme electrode generates an anodic current at 0.05–0.6 V vs. SCE. The pH optimum of the electrode is 7.0. The apparent Michaelis constant depends on the amount of l-lactate, and varies in the range 4.1–9.7 mM. The maximum electrode sensitivity is 50.4 μA l mmol −1 cm −2 and does not depend on the oxygen concentration in solution. The electrode is insensitive to glucose and ethanol. At 0.15 V the response to l-ascorbic acid (40 μM) is equivalent to 9.8% of the normal physiological l-lactate level in blood. The enzyme electrodes were used for l-lactate determination in goat whole blood. They remained stable on storage in the dry state for at least 2 months.