Competitive enzyme immunosensor developed on a renewable carbon paste electrode support

A sequential competitive voltammetric immunoassay format performed on a car bon paste electrode surface for the determination of mouse immunoglobulin G (IgG) is described in this work. This device relies on the attachment of g oat anti-mouse IgG by adsorption on the electrode surface. An electrochemic al pre-treatment is performed with the aim of improving the sensitivity and reproducibility of such immobilisation. The assay comprises first an incub ation in the analyte solution and a further reaction with a tracer for the monitoring of the analyte-antibody binding. Mouse IgG labelled with alkalin e phosphatase is chosen together with 3-indoxyl phosphate as the enzymatic substrate. Its corresponding product is indigo. This molecule, generated ve ry close to the electrode surface, is insoluble in aqueous solutions and ad sorbs on the support. The electrodic oxidation is a reversible process taki ng place at around -0.4 V (versus Ag/AgCl) in Tris buffer pH 7.2. Alternati ng current (AC) voltammetry is chosen for its detection. The feasibility of reusing the same carbon paste electrode for several consecutive assays is demonstrated by performing the same electrochemical treatment as done initi ally. Thus, an effective removal of the protein layer as well as the indigo adsorbed is achieved, obtaining a regenerated surface with adsorptive prop erties similar to those of freshly prepared electrodes. (C)1999 Elsevier Sc ience B.V. All rights reserved.