title: Efficient separation and sensitive detection of Listeria monocytogenes using an impedance immunosensor based on magnetic nanoparticles, a microfluidic chip, and an interdigitated microelectrode.
abstract: 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 10(3) 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 (R(2)  = 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.
authors.affiliation: Cell and Molecular Biology Program, University of Arkansas, Fayetteville, AR 72701, USA.
authors.forename: Damira A
authors.initials: DA
authors.lastname: Kanayeva
authors.forename: Ronghui
authors.initials: R
authors.lastname: Wang
authors.forename: Douglas
authors.initials: D
authors.lastname: Rhoads
authors.forename: Gisela F
authors.initials: GF
authors.lastname: Erf
authors.forename: Michael F
authors.initials: MF
authors.lastname: Slavik
authors.forename: Steve
authors.initials: S
authors.lastname: Tung
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Li
mesh_terms: D000907:Antibodies, Bacterial / Q000032:analysis*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D006801:Humans; D018189:Immunomagnetic Separation / Q000379:methods*; D008089:Listeria monocytogenes / Q000276:immunology / Q000302:isolation & purification; D053758:Nanoparticles; D012680:Sensitivity and Specificity
chemical_list: D000907:Antibodies, Bacterial