A bio-electrochemical system consisting of Gluconobacter oxydans DSM 2343 cells as a biological material and carbon nanotube (CNT)-free and CNT-modified chitosan as immobilizing matrices has been developed. The measurement was based on the respiratory activity of the cells estimated by the oxygen consumption at -0.7 V (versus the Ag/AgCl reference electrode) due to the metabolic activity in the presence of substrates. The system was calibrated and dependence of signal amplitude on the measuring conditions and cell amount was studied as well as the substrate specificity, pH, temperature and working potential. The biosensors (CNT-modified and unmodified) were demonstrated for the quantification of glucose in the range of 0.05-1.0 mM, at 30 degrees C and pH 7.0 with the 40 s of response time. The linear relationships between sensor response (y; mu A/cm(2)) and substrate concentration (x; mM) were defined by the equations of y=1.160x+0.151 (R-2=0.990) and y = 1.261x+0.197 (R-2 = 0.982), respectively. All other data were also given as comparison of two systems one with CNT-modified and CNT-free. (c) 2009 Elsevier B.V. All rights reserved.