An impedimetric sensor based on a new semi-conducting rotaxane has been described for detection of toxic cations. The rotaxane, consists on a pi-conjugated material encapsulated into beta-cyclodextrin (beta-CD); it has been synthesized via the Williamson reaction under microwaves irradiation. The supramolecular structure of the compound was confirmed by NMR and FT-IR spectroscopies. A thin solid film of the rotaxane was deposited by spin-coating to develop a new electrochemical sensor. The morphological properties of the organic membrane were evaluated using contact angle measurements and atomic force microscopy. The gold/rotaxane/solution interfaces were investigated by electrochemical impedance spectroscopy and the obtained data were fitted using an equivalent electrical circuit. The response of the gold/rotaxane membrane towards Hg2+, Cu2+ and Pb2+ cations was studied and the results showed a good sensitivity to the mercury cations. (C) 2015 Elsevier Ltd. All rights reserved.