Highly sensitive indicator-free impedance sensing of DNA hybridization based on poly(m-aminobenzenesulfonic acid)/TiO2 nanosheet membranes with pulse potentiostatic method preparation.

A direct electrochemical detection procedure for DNA hybridization by using the electrochemical signal changes of conductive poly(m-aminobenzenesulfonic) acid (PABSA)/TiO(2) nanosheet membranes, which were electropolymerized by using the pulse potentiostatic method, is reported. Due to the unique properties of TiO(2) nanoparticles, m-aminobenzenesulfonic acid monomers tend to be adsorbed around the particles, and the electropolymerization efficiency is greatly improved. The combination of TiO(2) nanoparticles and PABSA resulted in a nanocomposite membrane with unique and novel nanosheet morphology that provides more activation sites and enhances the surface electron-transfer rate. These characteristics were propitious for the magnification of PABSA electrochemical signals and the direct detection of DNA hybridization. Owing to the presence of abundant sulfonic acid groups, PABSA could overcome the drawbacks of polyaniline and be used to detect bioanalytes at physiological pH. DNA probes could be covalently attached to the sulfonic groups through the amines of DNA sequences by using an acyl chloride cross-linking reaction. After immobilization of probe DNA, the electrochemical impedance value increased significantly compared to that of PABSA/TiO(2) nanosheet membranes, and then decreased dramatically after the hybridization reaction of the probe DNA with the complementary DNA sequence compared to that of the probe-immobilized electrode. Electrochemical impedance spectroscopy was adopted for indicator-free DNA biosensing, which had an eminent ability for the recognition between double-base mismatched sequences or non-complementary DNA sequences and complementary DNA sequences. A gene fragment, which is related to one of the screening genes for the transgenically modified plants, the cauliflower mosaic virus 35S gene was satisfactorily detected. This is the first report for the indicator-free impedance DNA hybridization detection by using PABSA/TiO(2) membranes under neutral conditions.