Chapter 20 - Immunoelectroanalytical assay based on the electrocatalytic effect of gold labels on silver electrodeposition

Abstract

In the last decades, electrochemical immunoassays that use electroactive labels for amperometric detection have been developed in great extent. In this type of assays, the use of a reagent (antibody or antigen) coupled to a detectable species (enzyme or electroactive label) allows the detection. In this experiment, and as a model to study immunological interactions, an immunoelectroanalytical assay to determine the concentration of human serum albumin (HSA) is presented. With this aim, HSA is adsorbed directly on the electrode surface (a capture reagent is not employed) and the immunological reaction takes place following competitive or noncompetitive configurations. In this case, a nonenzymatic label, sodium aurothiomalate, is used. This is a gold (I) complex, which is conjugated to rabbit IgG anti-HSA. After interaction, gold is deposited on the electrode surface and, to magnify the signal, a silver shell is deposited over gold. This is based on the fact that gold catalyzes the electroreduction of silver, which occurs at potentials more positive than those required for its deposition on carbon electrodes. The analytical signal is then the current due to the redissolution of silver that was previously deposited on gold.