Electrochemically reduced graphene oxide-enhanced electropolymerization of poly-xanthurenic acid for direct, signal-on and high sensitive impedimetric sensing of DNA

In this paper, the poly-xanthurenic acid (PXa) was electropolymerized by cyclic voltammetry (CV) on a pre-obtained electrochemically reduced graphene oxide (ERGNO) film to construct a novel direct electrochemical DNA biosensor. Due to the unique properties of graphene, conjugated xanthurenic acid (Xa) monomers tended to be adsorbed on the graphene plane by pi-pi stacking and the electropolymerization efficiency was greatly improved, resulting in an enhanced electrochemical response of PXa. The PXa not only served as a substrate for DNA immobilization but also reflected the electrochemical transduction originating from DNA immobilization and hybridization without any outer indicators or complicated labeling. The capture probe was immobilized onto a modified electrode by covalent bonds between the amino groups of the capture probe and the carboxyl groups of the PXa/ERGNO film. The sensing platform could selectively recognize its target DNA. It is well-known that ssDNA is a flexible molecule while dsDNA acts as a rigid rod, which resulted in the change of the self-signals of the PXa after hybridization. The dynamic range of this DNA biosensor for detecting the sequence-specific DNA from promyelocytic leukemia was from 1.0 x 10(-15) mol L-1 to 1.0 x 10(-9) mol L-1 using electrochemical impedance spectroscopy, and the detection limit was 2.5 x 10(-16) mol L-1.