In this work, the development of an impedimetric label-free immunosensor for the detection of Escherichia coli O157:H7 is reported. Different immobilization techniques of monoclonal anti-E. coli were tested, in order to reach the very low limit of detections. The comparison between the immobilization procedures underlined the advantages of the oriented procedure and the use of a dendrimer, which allowed for immobilizing a higher number of antibody units, reaching a very high sensitivity. However, the use of activated ferrocene as electron-transferring mediator, which improved the electrical properties of the system, resulted in a very low limit of detection equal to 3 cfu/mL. This immunosensor was used to analyze milk and meat samples obtaining a good agreement with the results of the ELISA methods.
Keywords: Escherichia coli 0157:H7; electrochemical impedance spectroscopy; label-free immunosensor.