Detection of escherichia coli O157:H7 using interdigitated array microelectrode-based immunosensor

In this study, a label-free interdigitated array (IDA) microelectrode-based immunosensor was designed and tested for rapid and sensitive detection of E. coli O157:H7. The surface of gold IDA microelectrodes (25 pairs of fingers with 700 μm length and 10 μm width and space) was modified with protein A and further immobilized with polyclonal antibodies against E. coli O157:H7. A 20 μL sample containing E. coli O157:H7 in 0.01 M phosphate buffered saline (PBS) at pH 7.4 was dropped on the surface of the modified microelectrodes and incubated for 2 h at room temperature. After the target bacteria were captured by the antibodies immobilized on the microelectrode, a wash with PBS was applied to rinse off all unbound parts of the sample. Finally, the impedance, both magnitude and phase angle, was measured over a broad frequency range from 1 Hz to 1 MHz. The results showed that the impedance in a frequency range of 1 Hz to 1 kHz increased with the increasing number of E. coli O157:H7 in a range from 80 to 2 × 105 cells per 20 μL. A linear relationship between the magnitude of measured impedance and the log number of cells was determined at the frequency of 1 kHz. This biosensing method was able to detect as few as 80 cells of E. coli O157:H7 within 2 h. The specificity of the immunosensor was validated using five non-target bacteria, and none of them generated detectable signals. The application of the immunosensor for food safety was demonstrated with food samples including chicken carcasses, ground beef, and fresh cut broccoli inoculated with E. coli O157:H7. At the same time, the capture of E. coli O157:H7 cells on the microelectrode surface was confirmed using atomic force microscopy. © 2010 ASABE ISSN 1934-2799.