A simple and label-free electrochemical sensor for recognition of the DNA sensor event was prepared by electrochemical polymerization of 4-hydroxyphenyl thiophene-3-carboxylate. Poly(4-hydroxyphenyl thiophene-3-carboxylate) (PHPT) was synthesized electrochemically onto glassy carbon electrode and characterized by cyclic voltammetry, FTIR and AFM measurements. An ODN-probe was physisorbed onto PHPT film and tested on hybridization with complementary ODN segments. A biological recognition can be monitored by comparison with electrochemical signal (cyclic voltammogram) of single and double strand state oligonucleotide. The oxidation current of double strand state oligonucleotide is lower than that of single strand, that is corresponding to the decrease of electroactivity of PHPT with the increase of stiffness of polymer structure. Physisorbed ODN-probe and its hybridization were observed morphologically onto ITO electrodes using AFM. The sensitivity of the electrochemical sensor is 0.02 mu A/nmol, detection limit is 1.49 nmol and it has good selectivity. (C) 2009 Elsevier B.V. All rights reserved.