A biosensor for direct label-free DNA detection based on a polythiophene matrix is investigated by electrochemical impedance spectroscopy (EIS). Impedimetric experiments are performed with and without redox probe in solution. The non-Faradaic impedance measurements reveal two relaxation processes located at 50 Hz and 5 kHz, respectively. The first relaxation process, located at low frequencies, allows to detect biorecognition events by measuring the phase angle decrease, in accordance with a hindrance of the polaronic conduction. The second relaxation process, located at 5 kHz and originating from DNA modification, seems to increase with the length of the target sequence. These results suggest that this loaded support provides a platform for impedimetric detection of hybridization at high frequencies, leading to less time-consuming detection procedure. For a better understanding, results obtained in non-Faradaic mode are compared with Faradaic approach. (c) 2007 Published by Elsevier B.V.