Characterization of the HS-C6-Aptamer/Mercaptohexanol Monolayer on Gold Electrodes

Abstract

The purpose of this study was to determine characteristic parameters of aptamer-modified electrodes. These parameters are substantial for the development of an impedance model, based on equivalent circuits. This study contributes to the understanding of electron transfer kinetics for the detection of aptamer binding events. The Protein A-binding aptamer (PAA) was co-immobilized to form an aptamer/mercaptohexanol(MCH)-mixed monolayer on gold electrodes. Functionalization and binding of recombinant Protein A were verified by the use of quartz crystal microbalance (QCM) and chronocoulometry (CC). A significant mass increase of 255±108 ng/cm2 after aptamer immobilization was measured with QCM while with CC we quantified immobilized aptamers as 1.85±0.34.1012 molecules/cm2. The modified electrodes were further characterized by cyclic voltammetry (CV) and chrono-coulometry (CC), obtaining characteristic values as the diffusion coefficients Dred and Dox and the electron transfer rate k0. Herein, blank electrodes and those covered with a MCH monolayer were compared to aptamer functionalized electrodes. The electron transfer rate k0 of the aptamer electrode tends to range between the blank and the MCH electrodes indicating that the immobilization of aptamers introduces defects into the MCH monolayer.