The copper complex of 4,5-diazafluorene-9-one (dafone) and bromine ligands ([Cu(dafone)(2)]Br-2) was prepared and its interaction with double-stranded salmon sperm DNA (dsDNA) in pH 8.0 Britton-Robinson (B-R) buffer solution was studied by electrochemical experiments at the glassy carbon electrode (GCE). It was revealed that Cu(dafone)(2)Br-2 could bind with salmon sperm DNA strands mainly by intercalation mode. The binding number of [Cu(dafone)(2)]Br-2 for each salmon sperm dsDNA chain and equilibrium constant of the binding reaction were calculated to be 3 and 2.8 x 10(12) L-3 mol(-3), respectively. The Cu(dafone)(2)Br-2 was further utilized as a new electrochemical DNA indicator for the detection of human hepatitis B virus (HBV) DNA fragment by differential pulse voltammetry (DPV). The difference of its electrochemical responses occurred between hybridized dsDNA duplex and probe DNA was explored to assess the selectivity of the developed electrochemical DNA biosensor. The constructed electrochemical DNA biosensor achieved a detection limit of 3.18 x 10(-9) mol L-(1) for complementary target DNA and also realized a robust stability and good reusability. (C) 2007 Elsevier Ltd. All rights reserved.