An improved terthiophene conducting polymer for DNA-sensing

The synthesis of an improved terthiophene monomer functionalized with acrylic acid and a methylhydroxy group, 3-[3′,3‴-bis(hydroxymethyl) -2′:2″,5″:2‴-terthiophene)-3″-yl](E)acrylic acid, (HTAA), and its electropolymerization into a conducting polymer is described and evaluated as a label-free DNA sensor. The aim was to construct an improved thiophene-based conducting polymer whose microstructure could mitigate the collapse in aqueous solution seen in similar previously made thiophene-based conducting polymers. The effects of immersion in aqueous solution assessed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were complex. The microstructure collapse was significantly mitigated compared to previously made terthiophene polymers but the observed behaviour was dependent on the dopant anion. With a hydrophobic, non-exchangeable anionic dopant, bis-trifluoromethanesulfonimidate, (CF₃)₂(SO ₂)₂^-, the polymer film developed a multilayer structure. Electrochemical activity towards the solution redox couple Fe(CN)₆^3-/4- was sustained but with a significant anodic shift of redox potential. A DNA hybridisation response was observed with the hydrophobic dopant but not with the hydrophilic dopant. We have demonstrated that, by attention to both the nature of the polymer and to the choice of dopant anion, the effects of solvent-induced microstructure collapse in aqueous solution on the DNA sensor performance can be mitigated.