Electrochemical impedance spectroscopic technique with a functionalized microwire sensor for rapid detection of foodborne pathogens.

In this study, a label-free biosensor based on electrochemical impedance measurement followed by dielectrophoretic force and antibody-antigen interaction was developed for detection and quantification of foodborne pathogenic bacteria. In our previous work, gold-tungsten wires (25 μm in diameter) were functionalized by coating with polyethyleneimine-streptavidin-anti-Escherichia coli antibodies to improve sensing specificity, and fluorescence intensity measurement was employed to quantify bacteria captured by the sensor. The focus of this research is to evaluate the performance of the developed biosensor by monitoring the changes of electron-transfer resistance (ΔR(et)) of the microwire after the bioaffinity reaction between bacterial cells and antibodies on its surface as an alternative quantification technique to fluorescence microscopy. Electrochemical impedance spectroscopy (EIS) has been used to detect and validate the resistance changes in a conventional three-electrode system in which [Fe(CN)₆³⁻]/[Fe(CN)₆⁴⁻] served as the redox probe. The impedance data demonstrated a linear relationship between the increments of ΔR(et) and the logarithmic concentrations of E. coli suspension in the range of 10³-10⁸ CFU/mL. In addition, there were little changes of ΔR(et) when the sensor worked with Salmonella, which clearly evidenced the sensing specificity to E. coli. EIS was proven to be an ideal alternative to fluorescence microscopy for enumeration of captured cells.