Probing the electrochemical deposition and/or desorption of self-assembled and electropolymerizable organic thin films by surface plasmon spectroscopy and atomic force microscopy

Abstract

The combination of surface plasmon spectroscopy (SPS) and atomic force microscopy (AFM) with electrochemical methods (cyclic voltammetry, potential step) is used to (i) probe the film/substrate interaction in alkanethiol monolayers formed on gold surfaces and (ii) monitor the electrochemically driven deposition of organic molecules onto a metal surface. The reductive desorption of alkanethiols at single crystal and polycrystalline gold surfaces was investigated by SPS and AFM. These experiments demonstrate the possibility of desorbing a self-assembled monolayer at a well-defined potential with all the consequences for selective (re)-functionalization. The self-assembly of alkanethiols on gold under potential control was also monitored by SPS. The results show that the surface derivatization of gold electrodes can be actively controlled by the manipulation of the electrode potential. Finally, the immobilization of biotin on gold surfaces has been carried out by the electropolymerization of a water-soluble, biotinylated derivative of 3-hydroxyphenylacetic acid. The molecular recognition of the biotinylated polyphenol film by the bacterial protein streptavidin was monitored by SPS. The packing density of the biotin labels in the polymer film leads to a very fast diffusion-controlled docking of the streptavidin to the surface. These studies clearly prove the usefulness of electrochemically controlled deposition to produce ultrathin film organic surfaces with specific function.