Immunobiosensor Chips for Detection of Escherichia coli O157:H7 Using Electrochemical Impedance Spectroscopy

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Abstract
Impedance biosensor chips were developed for detection of Escherichia coli O157:H7 based on the surface immobilization of affinity-purified antibodies onto indium tin oxide (ITO) electrode chips. The immobilization of antibodies onto ITO chips was carried out using an epoxysilane monolayer to serve as a template for chemical anchoring of antibodies. The surface characteristics of chips before and after the binding reaction between the antibodies and antigens were characterized by atomic force microscopy (AFM). The patterns of the epoxysilanes monolayer, antibodies, and E. coli cells were clearly observed from the AFM images. Alkaline phosphatase as the labeled enzyme to anti-E. coli O157:H7 antibody was used to amplify the binding reaction of antibody−antigen on the chips. The biocatalyzed precipitation of 5-bromo-4-chloro-3-indolyl phosphate by alkaline phosphatase on the chips in pH 10 PBS buffer containing 0.1 M MgCl2 increased the electron-transfer resistance for a redox probe of Fe(CN)63-/4- at the electrode−solution interface or the electrode resistance itself. Electrochemical impedance spectroscopy and cyclic voltammetric method were employed to follow the stepwise assembly of the systems and the electronic transduction for the detection of E. coli. The biosensor could detect the target bacteria with a detection limit of 6 × 103 cells/mL. A linear response in the electron-transfer resistance for the concentration of E. coli cells was found between 6 × 104 and 6 × 107 cells/mL.