We report the characterization of a new bifunctional electroactive polymer, poly(5-hydroxy-1,4-naphthoquinone (juglone)-co-5-hydroxy-3-thioacetic acid-1.4-naphthoquinone), which can be used for direct electrochemical detection of DNA hybridization. The polymer structure was characterized based on molecular orbital calculations and ex situ and in situ FT-IR spectroscopy. T he quinone group integrated in the polymer presents very stable electroactivity in neutral aqueous medium and can act as a redox marker for hybridization. The carboxylic function allows the preparation of oligonucleotides (ODN) probe-modified films by covalent binding. The mechanism of hybridization detection was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The "signal-on" upon hybridization could be attributed to a change in conformation from random ODN coils on the probe-modified film to helix double stranded ODNs upon hybridization. (c) 2004 Elsevier B.V. All rights reserved.