Conjugated, electrically conducting, polymers are multifunctional materials that are of great interest in the area of chemical sensors [1], including potentiometric ion sensors [2,3]. For many years, one of the main challenges has been to obtain functionalized conjugated polymers showing high selectivity towards specific ions. We have found that conjugated polymers, including polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3-octylthiophene) (POT), show a selective potentiometric response to silver(I) ions in aqueous solution [4-6]. The selectivity to Ag⁺ seems to be a common feature of several conjugated polymers and the doping ions do not play a crucial role. Oxidation of conjugated polymers such as PPy and PEDOT by Ag⁺ causing electroless deposition of metallic Ag onto the conjugated polymers is well described in the literature [7]. However, we have found that chemically synthesized POT shows a selective response to Ag⁺ although POT remains in the undoped form, as shown by UV-vis spectroscopy [5]. This indicates that the presence of metallic Ag in the conducting polymer is not a prerequisite for the potentiometric response to Ag⁺. In the case of POT, the potentiometric response to Ag⁺ is therefore related mainly to interactions between Ag⁺ ions and sulfur atoms of the conjugated polymer backbone. Additionally, Ag⁺ ions may interact via π-coordination with double bonds present in conjugated polymers. Conjugated polymers represent a new class of Ag⁺-selective membranes.

References:

1. J. Bobacka,”Conjugated Polymer Chemical sensors” in. C.A. Grimes, E.C. Dickey and M.V. Pishko (eds.), Encyclopedia of Sensors, American Scientific Publishers, California, USA, 2006, Vol. 2, pp. 279-294.
2. A. Michalska, Anal. Bioanal. Chem., 384 (2006) 391-406.
3. J. Bobacka, Electroanalysis, 18 (2006) 7-18.
4. Z. Mousavi, J. Bobacka and A. Ivaska, Electroanalysis, 17 (2005) 1609-1615.
5. M. Vázquez, J. Bobacka and A. Ivaska, J. Solid State Electrochem., 9 (2005) 865-873. [Erratum: J. Solid State Electrochem., 10 (2006) 1012.]
6. Z. Mousavi, J. Bobacka, A. Lewenstam and A. Ivaska, J. Electroanal. Chem., 593 (2006) 219-226.
7. M. Ocypa, M. Ptasinska, A. Michalska, K. Maksymiuk and E.A.H. Hall, J. Electroanal. Chem., 596 (2006) 157-168.

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