Fast Amperometric Assay for E. coli O157:H7 Using Partially Immersed Immunoelectrodes

A novel amperometric immunoelectrode for fast and sensitive assay of E. coli O157:H7 is presented. Antibodies against E. coli O157:H7 were immobilized on the surface of carbon rods, which acted as both working electrode and sorbent surface. A sandwich scheme of immunoassay was used and 5-aminosalicylic acid was employed as a redox mediator for the amperometric detection of the enzyme-label (horseradish peroxidase). The immunoelectrodes were operated while being partly immersed in the detection cell which resulted in the acceleration of the diffusion-controlled rates of immunological, enzymatic and electrochemical reactions. The amperometric immunoelectrode allows the achievement of significantly lower detection limits (40 times lower) than that achievable with standard spectrophotometric detection ELISA method using the same immunochemicals. The immunoelectrode allows determination of E. coli cell concentrations in the range from 200 to 7000 cells/mL with an overall analysis time of 40 min. This immunoelectrode can be easily adapted for assay of other microorganisms and may be a basis for creating a new class of highly sensitive and rapid immunosensors.

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