Direct electrochemical probing of DNA hybridization on oligonucleotide-functionalized polypyrrole

We here report a new approach for the direct label of a free detection of DNA hybridization using electrochemical techniques applied to a system made of a polypyrrole matrix supported at the surface of an electrode and modified with DNA probes by covalent grafting. The binding occurs at sites where the polypyrrole is functionalized with activated ester groups. The hybridization reactions with the DNA complementary target and non-complementary target were investigated by both amperometric analysis and non-faradaic electrochemical impedance spectroscopy. The results show a significant modification in the electrochemical response of the layer upon addition of the complementary target. A variation of the redox activity of polypyrrole was demonstrated and was shown to correlate with the result obtained with impedance measurement which was related to the modification of conjugation of the polypyrrole backbone.The Nyquist plots obtained upon hybridization reaction were analysed by the Randles circuit. Electrical parameters such as capacity and transfer charge resistance were analysed and it was shown that the hybridization reaction caused a decrease of charge transfer and an increase of capacity. The charge transfer resistance R2 showed a linear variation as a function of the complementary target concentration. The sensitivity and the detection limit were determined and raised 1 pmol which constituted a substantial enhancement when compared to the results obtained by other systems.