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Efficient Separation and Sensitive Detection of Listeria monocytogenes Using an Impedance Immunosensor Based on Magnetic Nanoparticles, a Microfluidic Chip, and an Interdigitated Microelectrode

Kanayeva, Damira A., Wang, Ronghui, Rhoads, Douglas, Erf, Gisela F., Slavik, Michael F., Tung, Steve, Li, Yanbin
Journal of food protection 2012 v.75 no.11 pp. 1951-1959
Escherichia coli K12, death, Staphylococcus aureus, magnetism, immunosensors, antibodies, ground beef, Salmonella Typhimurium, pregnant women, lettuce, washing, food pathogens, foodborne illness, mannitol, milk, Listeria monocytogenes, Escherichia coli O157, nanoparticles, sodium chloride, bacteria
Listeria monocytogenes continues to be a major foodborne pathogen that causes food poisoning, and sometimes death, among immunosuppressed people and abortion among pregnant women. In this study, magnetic nanoparticles with a diameter of 30 nm were functionalized with anti–L. monocytogenes antibodies via biotin-streptavidin bonds to become immunomagnetic nanoparticles (IMNPs) to capture L. monocytogenes in a sample during a 2-h immunoreaction. A magnetic separator was used to collect and hold the IMNPs–L. monocytogenes complex while the supernatants were removed. After the washing step, the nanoparticle–L. monocytogenes complex was separated from the sample and injected into a microfluidic chip. The impedance change caused by L. monocytogenes was measured by an impedance analyzer through the interdigitated microelectrode in the microfluidic chip. For L. monocytogenes in phosphate-buffered saline solution, up to 75% of the cells in the sample could be separated, and as few as three to five cells in the microfluidic chip could be detected, which is equivalent to 103 CFU/ml of cells in the original sample. The detection of L. monocytogenes was not interfered with by other major foodborne bacteria, including E. coli O157:H7, E. coli K-12, L. innocua, Salmonella Typhimurium, and Staphylococcus aureus. A linear correlation (R2 = 0.86) was found between the impedance change and the number of L. monocytogenes in a range of 10(3) to 10(7) CFU/ml. Equivalent circuit analysis indicated that the impedance change was mainly due to the decrease in medium resistance when the IMNPs–L. monocytogenes complexes existed in mannitol solution. Finally, the immunosensor was evaluated with food sample tests; the results showed that, without preenrichment and labeling, 10(4) and 10(5) CFU/ml L. monocytogenes in lettuce, milk, and ground beef samples could be detected in 3 h.