Electrodeposition of Insulating Thin Film Polymers from Aliphatic Monomers as Transducers for Biosensor Applications

Abstract

Molecules can be oxidized anodically or reduced cathodically depending on their chemical functions but only some of them can be electropolymerized. The electropolymerization process of organic molecules leading to conductive, semiconducting or insulating polymer takes place at the surface of a biased electrode. In this case, a modification of an electrode surface, that can be a semiconductor or a conductive one, occurs in an irreversible way. Electrodes coated with conducting polymer films, have attracted considerable interest in the last two decades. A multitude of reviews and monographs have been written on the subject (Adhikari et al., 2004). Many electrochemical works were performed with aromatic or conjugated compounds yielding insulating polymer too. But few studies were made up to now with aliphatic molecules concerning their electropolymerization behavior. One of the reasons comes from the problem to study thin film which requires characterizations with expansive and not widespread spectroscopic analysis methods such as x-ray photoelectron spectroscopy and AFM imaging for instance. Furthermore, thin coatings at the electrode surface which could occur during a reaction, were neglected for a long time and regarded as a baneful interference hushing a possible insulating polymer up. Electropolymerized thin film polymers possess a wide range of applications in electroanalysis (Kalimuthu et al., 2009), energy storage (Granqvist, 2007), electrocatalysis (Xiao et al., 2009), biosensing (Merkoci, 2009), corrosion protection (Medrano-Vaca et al., 2008), sensors and electronic devices (Liu et al., 2010), electrochromic displays (Reiter et al., 2009), etc. Although polymer films on a surface can be formed in several chemical ways, electropolymerization is one of the most convenient and advantageous especially the thickness control during the film growth. On one hand, poly(thiophene), poly(pyrrole), poly(aniline) and their derivatives are amongst the most widely studied conducting polymers. This is probably due to the high conductivities of their oxidized forms and their ability to reversibly switch between conducting and insulating states by doping and undoping. On the other hand, insulating polymers have not paid so much attraction. Their electrochemical growth on an electrode surface is limited to thin film especially for aliphatic molecules due to the resulting current drop. If their thickness does not reach more than tens of nanometers, the surface electrode is