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)₆^3-/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.