Indicator free DNA hybridization detection by impedance measurement based on the DNA-doped conducting polymer film formed on the carbon nanotube modified electrode

A new biosensing strategy for direct electrochemical detection of DNA hybridization by AC impedance measurement is described. The indicator or label free approach was developed on the basis of the carbon nanotubes coupled with a conductive polymer polypyrrole (PPy). Multi-walled carbon nanotubes functionalized with carboxylic group (MWNTs-COOH) were modified on the glassy carbon electrode (GCE) and the oligonucleotide probes were doped within the electro-polymerized PPy films by serving as the sole counter anion during the growth of the conducting films. Before and after hybridization reaction with the complementary DNA sequences, a decrease of impedance values was observed as a result of the reduction of the electrode resistance: Hybridization amounts of the one-base, two-base and three-base mismatched sequences were obtained only in a 51%, 18% and 8.2% response when compared to that for the complementary matched sequence. Such unique response is attributed to the concomitant conductivity changes of the PPy-polymerized carbon nanotubes, and offers great promise for reagentless DNA hybridization analysis.