The effect of the oxidation state of a terthiophene-conducting polymer and of the presence of a redox probe on its gene-sensing properties

The gene-sensing properties of sensor films made of a terthiophene-conducting polymer, poly(3-((2′:2″, 5″:2″′-terthiophene)-3″-yl)acrylic acid) (PTAA), were evaluated using electrochemical impedance spectroscopy for films in their reduced and oxidised states with and without the Fe(CN)63−/4− redox probe (RP) in dilute tris–EDTA buffer. Porous films of PTAA were prepared and attached to an oligonucleotide sequence specific to the Salmonella virulence gene InvA. These films could be described with a dual transmission line model in which the polymer conductivity was increased as a consequence of surface binding of complementary DNA. The effect is analogous to that reported for silicon nanowires and field-effect transistors in dilute electrolyte modified by charge exchange across the polymer–electrolyte interface. As a result, gene sensing could be conveniently observed as a change in the impedance phase angle at a fixed frequency.