We fabricated carbon nanotube (CNT)-based biosensor with field effect transistor structure for detection of matrix metallopeptidase-9 (MMP-9) and S-100B. To minimize contact effects, the metal electrodes were passivated with SiO(x) film, and anti-MMP-9 and S-100B antibody were immobilized on the CNT surface using a chemical linker. When MMP-9 or S-100B antigen was added to bind anti-MMP-9 or S-100B antibody, the decrease in electrical conductance was observed. We have also investigated the dependence of MMP-9 and S-100B concentration on the conductance change. A linear relationship was found between the conductance and the concentration in semi-logarithm scale. (C) 2009 Elsevier B.V. All rights reserved.