Surface chemical activation of quartz crystal microbalance gold electrodes - analysis by frequency changes, contact angle measurements and grazing angle FTIR

Abstract

A hydroxyalkanethiol, HS(CH2)12OH was deposited onto the gold electrodes of quartz crystal microbalances and gold-coated quartz microscope slides in order to aid in subsequent immobilization of antibodies. FTIR and contact angle measurements confirm the presence of thiol on the fresh gold substrates. In contrast, the change in frequency of the quartz crystal during thiol adsorption indicates an apparent decrease in mass rather than the expected increase due to thiol coverage of the surface. This anomalous behavior appears to be partly due to the removal of organic contaminants from the "aged" gold surface by solvent action. In addition, there may be some dissolution of gold by the thiol solution. QCM frequency changes and FTIR have also been used to monitor subsequent carbodiimide activation of the thiol, as well as antibody binding to the activated surface. The thiolated gold surface was used to fabricate an ordered layer of IgG molecules for probing various immuno-reactions. This was demonstrated by the binding of anti-IgG to IgG in the ratio of ca. 1:1. © 1995.