Direct Electrochemical DNA Detection Originated from the Self-Redox Signal of Sulfonated Polyaniline Enhanced by Graphene Oxide in Neutral Solution

In this paper, a type of direct DNA impedance detection using the self-redox signal change of sulfonated polyaniline (SPAN) enhanced by graphene oxide (GNO) was reported, here SPAN is a copolymer obtained from aniline and m-aminobenzenesulfonic acid. The resulting nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The π-π planar structure of GNO and the carboxyl groups on the surface of GNO ensured it could act as an excellent substrate for adsorption and polymerization of aniline monomer. Because of the existence of GNO, the electrochemical activities of SPAN were enhanced obviously. Because of abundant sulfonic acid groups, the resulting nanocomposite showed obvious self-redox signal even at physiological pH, which is beneficial for biosensing field. DNA probes with amine groups could be covalently attached to the modified electrode surface through the acyl chloride cross-linking reaction of sulfonic groups and amines. When the flexible probe DNA was successfully grafted, the electrode was coated and electron transfer between electrode and buffer was restrained. Thus, the inner impedance value of SPAN (rather than using outer classic EIS probe, [Fe(CN)6](3-/4-)) increased significantly. After hybridization, the rigid helix opened the electron channel, which induced impedance value decreased dramatically. As an initial application of this system, the PML/RARA fusion gene sequence formed from promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARA) was successfully detected.