Nanomaterial-based enzyme-linked immunosorbent assay (ELISA) with sufficient sensing specificity is a useful analytical tool for the detection of toxicologically important substances in complicated biological systems. Increasing worldwide demand for nanomaterials and increasing concern on their safe development and use, require a simple, stable, and sensitive detection assay for pathogen evaluation and environmental monitoring. However, this goal is not yet achieved. A design for a hybrid MnO 2 nanowire-ELISA using the sandwich assay format, which provides quantitative binding information for both a specific antibody and the pathogen, sulfate-reducing bacteria, and detects pathogen concentration, is presented. 3,3′,5,5′-Tetramethylbenzidine was used as the substrate and was allowed to react with the MnO 2 nanowires without H 2 O 2 in the reaction system. The kinetic parameters were measured with the system acting as a catalytic biosensor. The effectiveness of the MnO 2 nanowire-based biosensor was demonstrated by its sensitive detection of the pathogen.