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The purpose of this work was to fabricate an electrochemical DNA biosensor for detecting hepatitis B virus. Gold nanorods (GNRs), which are known for their conductivity, were used to increase surface area and consequently increase the immobilization of single-stranded DNA (ss-DNA) on the modified gold electrode. The GNRs were characterized via transmission electron microscopy. The morphology of the gold electrode before and after modification with GNRs was characterized by scanning electron microscopy. Atomic-force microscopy was used to evaluate the morphology of the GNR electrode surface before and after interaction with ss-DNA. Cyclic voltammetry was used to monitor DNA immobilization and hybridization, using [Co(phen)] as an electrochemical indicator. The target DNA sequences were quantified at a linear range from 1.0 × 10 to 10.0 × 10 mol L, with a detection limit of 2.0 × 10 mol L by 3 σ. The biosensor had good specificity for distinguishing complementary DNA in the presence of non-complementary and mismatched DNA sequences. [ABSTRACT FROM AUTHOR]