A novel electrochemical immunosensor has been fabricated for the detection of benzo[a]pyrene using dendritic SiO2 nanoparticles for biomolecule immobilization. Initially, carboxyl-terminated dendritic SiO2 nanoparticles were synthesized, characterized by TEM, contact angle and thermogravimetric analyses, and then immobilized onto an ethylenediamine-modified electrode. Aminopyrene-BSA was captured with the carboxyl groups of dendritic SiO2 nanoparticles, followed by the corresponding antibody and HRP-labeled secondary antibody. Finally, with the aid of H2O2 and hydroquinone, the changes in the cathodic current were recorded. Based on a competitive immunoassay, benzo[a]pyrene, which can compete with the immobilized aminopyrene-BSA in the association ability of the antibody, was successfully detected. The results showed that the cathodic currents were linearly dependent on the logarithm of benzo[a]pyrene concentrations between 0.01 and 10 mu M with a detection limit of 8 nM. The proposed electrochemical immunosensor provided a new alternative to the application of other antigens or other bioactive molecules. (C) 2010 Elsevier Ltd. All rights reserved.