Polypyrrole nanotubes-polyaniline composite for DNA detection using methylene blue as intercalator

Electrochemically active nanostructured polypyrrole (PPy) coated with polyaniline (PANi) was deposited on an electrode followed by gluteraldehyde (GA) attachment for grafting 5'-amine modified single strand DNA (ssDNA) to form PPy-PANi-GA-ssDNA and DNA hybridization in phosphate buffered solution. Differential pulse voltammetry (DPV) was used to monitor the hybridization events with methylene blue as the electrochemical indicator. The exhibited sensitivity and selectivity was attributed to the nanotube structure of PPy-PANi and the conductivity obtained was 472 times greater than that for the conventional PPy-PANi composite. The biosensor was characterized by cyclic voltammetry, electrochemical impedance, FT-IR, DPV and scanning electron microscopy. This sensor showed good stability, selectivity and higher sensitivity than the multi-walled carbon nanotubes (MWCNT)/Ag nanoparticles (NPs) and PPy/MWCNT/AuNPs composites reported previously. The dynamic range observed was 1 x 10(-9) to 1 x 10(-13) M, with a lower detection limit of 50 fM.