Filtration capture and immunoelectrochemical detection for rapid assay of Escherichia coli O157:H7

A new approach for rapid assay of bacteria in liquid samples is described. Cells were labeled by incubation with an enzyme-antibody conjugate and captured by filtration of the sample/conjugate mixture through a 0.2 microm filter. The enzyme-labeled cells were detected by placing the filter on the surface of an electrode, incubating with enzyme substrate, and measuring the current produced by oxidation of the electroactive enzyme product. Assay time was 25 min and a detection limit of approximately 5000 cells/ml was obtained for E. coli O157:H7. Background current due to non-specific binding of conjugate to the filter was the primary factor controlling the detection limit, and fewer than 50 cells could be detected when very small sample volumes (10 microl) were used to minimize background current.