Silver electrodeposition catalyzed by colloidal gold on carbon paste electrode: application to biotin-streptavidin interaction monitoring

A new electrochemical method to monitor biotin-streptavidin interaction on carbon paste electrode, based on silver electrodeposition catalyzed by coll oidal gold, was investigated. Silver reduction potential changed when collo idal gold was attached to an electrode surface through the biotin-streptavi din interaction. Thus, the direct reduction of silver ions on the electrode surface could be avoided and therefore, they were only reduced to metallic silver on the colloidal gold particle surface, forming a shell around thes e particles. When an anodic scan was performed, this shell of silver was ox idized and an oxidation process at + 0.08 V was recorded in NH3 1.0 M. Biot inylated albumin was adsorbed on the pretreated electrode surface. This mod ified electrode was immersed in colloidal gold-streptavidin labeled solutio ns. The carbon paste electrode was then activated in adequate medium (NaOH 0.1 M and H2SO4 0.1 M) to remove proteins from the electrode surface while colloidal gold particles remained adsorbed on it. Then, a silver electrodep osition at -0.18 V for 2 min and anodic stripping voltammetry were carried out in NH3 1.0 M containing 2.0 x 10(-5) M of silver lactate. An electrode surface preparation was carried out to obtain a good reproducibility of the analytical signal (5.3%), using a new electrode for each experiment. In ad dition, a sequential competitive assay was carried out to determine strepta vidin. A linear relationship between peak current and logarithm of streptav idin concentration from 2.25 x 10(-15) to 2.24 x 10(-12) M and a limit of d etection of 2.0 x 10(-15) M were obtained. (C) 2000 Elsevier Science S.A. A ll rights reserved.