This work designed an ultrasensitive electrochemical immunosensor for Escherichia coli O157:H7 (E. coli O157:H7) detection using carbon nanohorns as immobilization scaffold and nanogold/ Bi2S3 nanorods (Au/Bi(2)S(3)NRs) as a signal tag to catalyze silver deposition for signal amplification. Au/Bi(2)S(3)NRs prepared by in situ growth of nanogold on Bi2S3 nanorods was used as a tracing tag to label signal antibody, which induced silver deposition for anodicstripping analysis. The immunosensor was constructed by immobilizing capture antibody on carbon nanohorns modified electrode with the aid of polyethylene glycol film. Through a sandwich-type immunoreaction, Au/ Bi(2)S(3)NRs tags were captured on the immunoconjugates to induce a silver deposition process. The electrochemical stripping signal of the deposited silver was used to monitor the immunoreaction. The Au/ Bi(2)S(3)NRs-mediated silver enhancement along with the carbon nanohorns-promoted electron transfer led to high detection sensitivity of E. coli O157:H7 antigen. Under the optimal conditions, the immunosensor exhibited a wide linear dependence on the logarithm of the concentration of E. coli ranging from 40 to 2.0 x 10(6) cfu mL(-1) with a detection limit of 6 cfu mL(-1). Moreover, the proposed sensor was successfully applied in the detection of E. coli O157: H7 in real samples indicating its possibility in practical application. (C) 2017 The Electrochemical Society. All rights reserved.