The synthesis of a novel terthiophene monomer functionalized with pentadienoic acid, 5-(2':2 '', 5 '':2'''-terthiophene)-3 ''-yl)] (2E, 4E)penta-2,4-dienoic acid (TPDA), and its electropolymerization into a conducting polymer is described. The polymer electrochemical stability in aqueous solution was examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV revealed PTPDA film displayed good redox activity in an organic solvent (CH(2)Cl(2)) and poor electrochemical activity in aqueous PBS buffer. Both techniques revealed that the microstructure of the outer part of PTPDA film collapsed in aqueous solution. The instability is problematic for conducting polymers designed as DNA sensors and affects their DNA-sensing ability. A hybridization response occurred when the PTPDA film was doped with a large hydrophobic dopant but did not occur when the film was doped with a smaller hydrophilic dopant. By attention to both the nature of the polymer and to the choice of dopant anion, the effects on the DNA sensor performance of solvent-induced microstructure collapse in aqueous solution can be mitigated. (C) 2011 Published by Elsevier B.V.