Impedance DNA biosensor using electropolymerized polypyrrole/multiwalled carbon nanotubes modified electrode

In this paper, we present an electrochemical impedance-based DNA biosensor by using a composite material of polypyrrole (PPy) and multiwalled carbon nanotubes (MWNTs) to modify glassy carbon electrode (GCE). The polymer film was electropolymerized onto GCE by cyclic voltammetry (CV) in the presence of carboxylic groups ended MWNTs (MWNTs-COOH). Such electrode modification method is new for DNA hybridization sensor. Amino group ended single-stranded DNA (NH2-ssDNA) probe was linked onto the PPy/MWNTs-COOH/GCE by using EDAC, a widely used water-soluble carbodiimide for crosslinking amine and carboxylic acid group. The hybridization reaction of this ssDNA/PPy/MWNTs-COOH/GCE resulted in a decreased impedance, which was attributed to the lower electronic transfer resistance of double-stranded DNA than single-stranded DNA. As the result of the PPy/MWNTs modification, the electrode obtained a good electronic transfer property and a large specific surface area. Consequently, the sensitivity and selectivity of this sensor for biosensing DNA hybridization were improved. Complementary DNA sequence as low as 5.0 x 10(-12) mol L-1 can be detected without using hybridization marker or intercalator. Additionally, it was found that the electropolymerization scan rate was an important factor for DNA biosensor fabrication. It has been optimized at 20 mV s(-1).