Bacterial cells were entrapped together with chitosan matrix onto the surface of graphite electrode to form microbial biosensors. Two types of bacterial sensors were constructed by using Pseudomonas fluorescens (Pseudomonas putida DSM 6521) and P putida DSM 50026 cells as the biological components and the measurements were based on the respiratory activity of the cells. Carbon nanotube (CNT)-modified chitosan membrane was also prepared to test nanoparticle effect on the efficiency of biosensor performances. As well as the response characteristics, stabilities and substrate specificities were investigated. Data were given as the comparison of CNT-modified and -unmodified systems. (C) 2008 Elsevier B.V. All rights reserved.