A sandwich-type amperometric immunosensor for carcinoembryonic antigen was fabricated by using functionalized carbon nanotubes decorated with concanavalin A along with horseradish peroxidase-labeled carcinoembryonic secondary antibodies. The HRP-Ab(2) was assembled onto carbon nanotubes templates based on the biospecific affinity between concanavalin A and HRP. The carcinoembryonic antibody was immobilized on the gold electrode modified by monolayer cysteine. The response is linear in the range of 0.05-5 ng mL(-1) and 5-200 ng mL(-1), with a detection limit of 0.018 ng mL(-1). The biosensor can be used in serum directly. (C) 2014 Elsevier B.V. All rights reserved.