Immobilization-free direct electrochemical detection for DNA specific sequences based on electrochemically converted gold nanoparticles/graphene composite film

A direct electrochemical DNA sensor was constructed based on gold nanoparticles/graphene film. A precursor graphene film was fabricated on glassy carbon electrode (GCE) using both electrochemically reduced graphene oxide (ERGNO) and chemically reduced graphene oxide (CRGNO). The electrochemical approach was green and fast, and unlike chemical reduction, does not result in contamination of the reduced material, and at highly negative potential could reduce the oxygen functionalities (-OH, C-O-C and -COOH) of the graphene oxide more efficiently. ERGNO exhibited better electrochemical and electrocatalytic performances than CRGNO. Gold nanoparticles (AuNPs) were electrodeposited on the ERGNO/GCE to amplify the electrochemical signals. The resulting AuNPs/ERGNO composite film was characterized by scanning electron microscopy, energy dispersive spectroscopy and Raman spectroscopy. The electrochemical responses of guanine (G), adenine (A), thymine (T) and cytosine (C) were investigated at AuNPs/ERGNO/GCE, which showed more favorable electron transfer kinetics than at ERGNO/GCE, demonstrating the significantly synergistic electrocatalytic effect of ERGNO and AuNPs. Synthetic sequence-specific DNA oligonucleotides was successfully detected and the established immobilization-free biosensor had the ability to discriminate single- or double-base mismatched DNA.