Sensitive DNA biosensor improved by 1,10-phenanthroline cobalt complex as indicator based on the electrode modified by gold nanoparticles and graphene

A novel and sensitive electrochemical DNA biosensor was constructed based on the gold electrode modified by graphene and gold nanoparticles (AuNPs), whose sensitivity was improved by using 1,10-phenanthroline cobalt ([Co(phen)2(Cl)(H2O)]+) as an electroactive indicator. The gold electrode was firstly modified with sulfur graphene (GR-SH), and then covalently grafted with AuNPs via sulfur–gold affinity. Finally the thiol capped probe DNA was immobilized onto the AuNPs/GR modified electrode. The target DNA could hybridize with the probe DNA to form a double-stranded DNA (ds-DNA), into which [Co(phen)2(Cl)(H2O)]+ can intercalate, which can be confirmed by cyclic voltammetry (CV). The target DNA, from Escherichia coli (E. coil), could be detected in a linear range from 2.50 × 10−11 to 1.25 × 10−9 M (R = 0.9981) with a detection limit of 8.33 × 10−12 M (3σ, n = 11). It was demonstrated that the reported electrochemical DNA biosensor offered a promising approach for the sensitive and selective detection of DNA by using [Co(phen)2(Cl)(H2O)]+ as an electroactive indicator.