The development of materials for the ultra sensitive detection of biological species has received great attention. Here, a new electrochemical immunosensor for sensitive detection of tumor marker was reported. Polydopamine (PDA) coating was used to modify indium tin oxide (ITO) electrode for functionalized mesoporous silica nanoparticles immobilization. The carcinoembryonic antigen (CEA) was used as a model analyte. The capture anti-CEA was immobilized on functionalized mesoporous silica nanopartides. The horseradish peroxidase (HRP)-labeled signal anti-CEA antibodies were used to conjugated with gold nanoparticles. After the sandwich immunoreaction, under optimized conditions, the proposed immunosensor showed a high sensitivity and a linear range of 0.01-40.0 ng/mL with a detection limit of 1.7 pg/mL. The assay results of clinical serum samples obtained by the immunosensor we proposed were in acceptable agreement with the reference values. The designed immunoassay system with ultrahigh sensitivity and efficient and economical, might have potentially broad applications in protein diagnostics and bioassay. (C) 2013 Elsevier Ltd. All rights reserved.