Polypyrrole–polyaniline–Au (PPy–PANi–Au) nano composite films for label-free electrochemical DNA sensing

A bipolymer of 500 nm sized nanotubes comprising polypyrrole and polyaniline were prepared by simple chemical route onto the Au surface and gold nanoparticles were further electrodeposited to form PPy–PANi–Au composite film. DNA labeled at 5′ end using 6-mercapto-1-hexhane (HS-ssDNA) was immobilized on the PPy–PANi–Au surface to form PPy–PANi–Au–S-ssDNA and DNA hybridization sensing was made in phosphate buffer for the first time. The presence of PPy–PANi bipolymer in the PPy–PANi–Au enhances the hybridization efficiency by 2.5-fold than the transducer carrying the lone electrodeposited Au nanoparticles. Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) indicated the nanotubical nature and efficient interactions between the PPy, PANi, Au and HS-ssDNA. The sensor effectively discriminates the complementary (7742 Ω cm−2), non complementary (1216 Ω cm−2) single base mismatched target (3512 Ω cm−2) and double base mismatched target DNA hybridized surfaces (1355 Ω cm−2) and observed dynamic detection range is 1 × 10−6 and 1 × 10−13 M with the lowest detection limit of 1.0 × 10−13 M. This is one order higher sensitive than the PANi–Au composite reported previously.