Ionophore/Lipid Bilayer Assembly on Soft Organic Electrodes for Potentiometric Detection of K+ Ions

Abstract

The major goal on intrinsically conducting polymers (ICP) technology development has been to combine the electrical and optical properties of these new materials with the mechanical and processibility properties of commodity bulk polymers. New conductive materials that offer significant application potential as substitutes, and new products having properties difficult or impossible to achieve by existing materials, can now be produced. The most common synthetic methods are the oxidative chemical polymerization of aniline using ammonium persulfate, electrochemical polymerization; and most recently enzyme catalyzed polymerization of aniline has also been reported (Jin 2001).The reactions of aniline with oxidants proceed in two fundamentally different ways. The oxidant can either donate oxygen to the aniline molecule or it can remove a hydrogen atom from its amino group, the latter is the prevalent method that leads to polyaniline (PANI) (Ciric-Marjanovic 2008). It was shown by Wan and co-workers that during oxidative chemical polymerization, the molar ratio of acid to aniline affected the probability of formation of fibrous nanostructures dictating the final product morphology (Zhang 2002). In the oxidative chemical polymerization method aniline and ammonium persulfate are mixed at a predetermined stoichiometric ratio and reacted in acidic medium producing a green precipitate of PANI salt. For the electrochemical method an applied potential in lieu of an oxidant is used to oxidize and polymerize the aniline on the anodic electrode surface. In 2002 the International Union of Pure and Applied Chemistry (IUPAC) in an effort to standardize the process of oxidative polymerization of aniline using ammonium persulfate, issued a Technical Report with the goal of obtaining PANI with a defined conductivity (Stejskal 2002). This report constituted the first organized robustness study of the oxidative chemical polymerization of aniline, and it included eight chemists from five different institutions executing the same IUPAC preparation protocol. The electrochemical method was excluded from this report since its efficiency has been proved to be a function of the electrode area and therefore not suitable for large-scale production. An efficient polymerization of aniline is achieved only in an acidic medium where aniline exists as the anilinium cation. The reaction is exothermic with a defined and reproducible temperature profile that can be used to monitor the progress of the reaction (Beadle 1998). Generally