ADSORPTION OF IMMUNOGLOBULIN-G ON CARBON-PASTE ELECTRODES AS A BASIS FOR THE DEVELOPMENT OF IMMUNOELECTROCHEMICAL DEVICES

The attachment of Immunoglobulin G (IgG) to a carbon paste electrode i s investigated in this work. Studies of the immobilization of the immu noglobulin on this electrode were carried out. Alkaline phosphatase (A P) has been used as an enzyme label, linked to the antibody, for the d etermination of the adsorbed immunoglobulin. Various substrates for th is enzyme have been tested and alpha-naphthyl phosphate was found to b e the best because of the lower oxidation potential of the enzymatic p roduct, alpha-naphthol, and greater sensitivity under the same experim ental conditions. An electrodic pretreatment based on an anodic oxidat ion of the electrode surface in a phosphate media pH 9 was carried out prior to the adsorption step. This activation is also suitable for th e removal of the IgG layer and the regeneration of the electrodic surf ace after each determination, with the intention of using the same ele ctrode in the subsequent assays. A good reproducibility of the signal was achieved in this way (Relative Standard Deviation, R.S.D. = 3.7%). Using cyclic voltammetry, IgG labelled with AP has been quantified in a range from 2x10(-12) to 7x10(-11) M and a detection limit of 2.3x10 (-12) M (signal-to-noise ratio = 3) was found. Finally, human IgG was quantified under non-optimized conditions on the electrodic surface th rough the reaction with AP labelled IgG using two different immunologi cal designs. (C) 1997 Elsevier Science Limited.