Vitamin B 12 (B 12) - possessing a redox active cobalt centre - is a candidate to be used as a mediator in bioelectrochemical processes. In order to exploit the possible redox activity of 1312, Pt has been modified by a bio-conform conducting layer polypyrrole/piperazine-1,4-bis(2-ethane sulfonate) PPy/PIPES. The electrochemical and spectral behaviour of this film proved to be similar to PPy/dodecyl-sulfate (DS), widely considered and accepted as one of the best combinations of conducting polymer films. The capability of the PPy/PIPES film for acting as adsorbant in the accumulation of B 12 has been evidenced by the electrochemical quartz crystal microbalance (EQCM) technique. B 12 could also be incorporated into the polymer layer during its electrochemical deposition. The results proving the preserved redox activity of B 12 within the film open new perspectives towards redox mediated bioelectrochernical applications based on the immobilization of this biomolecule. (c) 2007 Elsevier Ltd. All rights reserved.