Thin films of conducting polymers (CP) due to coupled electronic and ionic conductivity as well as capability of reversible oxidation / reduction and membrane properties seem to be optimal materials for electrochemical sensors construction with facile chemical to electrical signal transduction.
Electrodes modified with stable CP films, as e.g. polypyrrole, polianiline and poly(3,4-ethylenedioxythiophene) are characterized by either anion- or cation-exchange properties and can be utilized to construct potentiometric ion-sensors . The accessible concentration range from 10-5 M to 1 M is similar to that of classical ion-selective electrodes, the properties can be easy tailored by the choice of dopant ion and low-cost sensors can be obtained by a simple electropolymerization.
However, these simple sensors suffer from low selectivity and high susceptibility toward pH and redox interferences. Therefore, the most promising application of CP in potentiometric ion sensors is to use them as ion to electron transducer for ion-selective plastic membrane electrodes [1,2], where the above mentioned disadvantages are eliminated. All-solid-state and single-piece constructions of these electrodes will be characterized.
The capability of reversible oxidation / reduction of CP films, coupled with counter-ions release or incorporation can be utilized in amperometric ion-sensors . Pulse- and ac-techniques applied with polypyrrole coated electrodes enable ion concentration determination within the range comparable to that typical for potentiometric method, but with significant elimination of redox interferences. A method of sensitivity and selectivity enhancement by appropriate choice of signal recording and time-scale of the experiment will be presented.
1. J. Bobacka, A. Ivaska, A. Lewenstam, Electroanalysis, 15 (2003) 366.
2. E. Bakker, M. Telting-Diaz, Anal.Chem., 74 (2002) 2781.
3. A. Michalska, S. Walkiewicz, K. Maksymiuk, Electroanalysis, 15 (2003) 509.