The electrochemical investigations of fungal (Aspergillus terreus MTCC 6324) cytochrome P450 monooxygenase (CYP) (EC 1.14.14.1) immobilized on multi-walled carbon nanotubes-Nafion (R)-polyethyleneimine (MWCNT-NF/PEI) modified glassy carbon electrode (GCE) were carried out to understand the electrochemistry of the CYP and its application potential in electrochemical-based devices. In deoxygenated condition, the formal potential for Fe((III))/Fe((II)) redox couple of CYP was about -0.53 V (vs. Ag/AgCl reference electrode, pH 8). A positive shift in the redox potential of the bioelectrode to -0.475 V was observed in the presence of oxygen and substrate. The electrocatalytic activity towards n-hexadecane and inhibition with piperonyl butoxide (PBO) confirmed the involvement of Fe((III/II)) system of CYP in the redox process. The current response increased linearly from 1 mu M to 100 mu M of n-hexadecane with detection limit 0.1 mu M. The IC(50) for PBO was 2.7 mu M. The surface coverage of CYP immobilized on MWCNT-NF/PEI modified GCE was approximately 3.45 x 10(-10) mol cm(-2). The electron transfer rate constant (k(s)) was 1.0 +/- 0.2 s(-1), indicating facilitation of the electron transfer between CYP and GCE. (C) 2011 Elsevier B.V. All rights reserved.