Immunopotentiometric electrodes based on bioelectrocatalysis in the absence of mediators

A new method of immunoelectrochemical analysis employing laccase as the enzyme label is described. The ability of the enzyme to catalyze electroreduction of oxygen via a direct mechanism allows the detection of the biospecific interaction of a laccase-labeled receptor, or antibody, with a ligand-modified electrode. Formation of a complex between the laccase-labeled antibody and the antigen on the electrode surface resulted in a considerable (greater than 300 mV) change in the electrode potential. Analysis was performed in a competitive scheme, and a single measurement could be made within 20 min in the absence of an electrochemically active mediator. The reaction substrates were atmospheric oxygen and electrons that were transferred directly from the electrode to the active site of the enzyme label. The use of a composite carbon material containing a polyethyleneimine-based polymer eliminated nonspecific interactions between the reaction components and the electrode surface. Insulin and mouse immunoglobulin were used as a model analytes.