Pseudomonas putida DSM 50026 cells were used as the biological component and the measurement was based on the respiratory activity of the cells estimated from electrochemical measurements. The cells were immobilised on carbon nanotube (CNT) modified carbon paste electrodes (CPE) by means of a redox osmium polymer, viz. poly(1-vinylimidazole)(12)-[Os-(4,4'-dimethyl-2,2'-dipyridyl)(2)Cl(2)](2+/+). The osmium polymer efficiently shuttles electrons between redox enzymes located in the cell wall of the cells and promotes a stable binding to the electrode surface. The effect of varying the amounts of CNT and osmium polymer on the response to glucose was investigated to find the optimum composition of the sensor. The effects of pH and temperature were also examined. After the optimisation studies, the system was characterised by using glucose as substrate. Moreover, the microbial biosensor was also prepared by using phenol adapted bacteria and then, calibrated to phenol. After that, it was applied for phenol detection in an artificial waste water sample. (C) 2007 Published by Elsevier B.V.