Highly sensitive electrochemical impedance spectroscopic detection of DNA hybridization based on Aunano-CNT/PANnano films

A polyaniline nanofibers (PAN(nano))/carbon paste electrode (CPE) was prepared via clopping PAN(nano) in the carbon paste. The nanogold (Au-nano) and carbon nanotubes (CNT) composite nanoparticles were bound on the surface of the PAN(nano)/CPE. The immobilization and hybridization of the DNA probe oil the Au-nano-CNT/PAN(nano) films were investigated with differential pulse voltammetry (DPV) and cyclic voltammetry (CV) using methylene blue (MB) as indicator, and electrochemical impedance spectroscopy (EIS) using [Fe(CN)(6)](3-/4-) as redox probe. The voltammetric peak currents of MB increased dramatically owing to the immobilization of the probe DNA on the Au-nano-CNT/PAN(nano) films. and then decreased obviously owing to the hybridization of the DNA probe with the complementary single-stranded DNA (cDNA). The electron transfer resistance (R-et) of the electrode Surface increased after the immobilization of the probe DNA on the Au-nano-CNT/PAN(nano) films and rose further after the hybridization of the probe DNA. The remarkable difference between the R,, value at the DNA-immobilized electrode and that at the hybridized electrode could be used for the label-free EIS detection of the target DNA. The loading of the DNA probe on Au-nano-CNT/PAN(nano) films was greatly enhanced and the sensitivity for the target DNA detection was markedly improved. The sequence-specific DNA of phosphinothricin acetyltransferase (PAT) gene and the polymerase chain reaction (PCR) amplification of nopaline synthase (NOS) gene from transgenically modified beans were determined with this label-free EIS DNA detection method. The dynamic range for detecting the PAT gene sequence was from 1.0 x 10(-12) mol/L to 1.0 x 10(-6) mol/L with a detection limit of 5.6. x 10(-13) mol/L. (C) 2008 Elsevier B.V. All rights reserved.