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

The combination of surface plasmon spectroscopy (SPS) and atomic force micr oscopy (AFM) with electrochemical methods (cyclic voltammetry, potential st ep) is used to (i) probe the film/substrate interaction in alkanethiol mono layers formed on gold surfaces and (ii) monitor the electrochemically drive n deposition of organic molecules onto a metal surface. The reductive desor ption of alkanethiols at single crystal and polycrystalline gold surfaces w as investigated by SPS and AFM. These experiments demonstrate the possibili ty of desorbing a self-assembled monolayer at a well-defined potential with all the consequences for selective (re)-functionalization. The self-assemb ly of alkanethiols on gold under potential control was also monitored by SP S. The results show that the surface derivatization of gold electrodes can be actively controlled by the manipulation of the electrode potential. Fina lly, 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 pol yphenol film by the bacterial protein streptavidin was monitored by SPS. Th e 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 depos ition to produce ultrathin film organic surfaces with specific function. (C ) 1999 Elsevier Science S.A. All rights reserved.