Simultaneous Detection of Multifood-Borne Pathogenic Bacteria Based on Functionalized Quantum Dots Coupled with Immunomagnetic Separation in Food Samples

Abstract

This paper reports a method that simultaneously detects three food-borne pathogenic bacteria, Salmonella typhimurium, Shigella flexneri, and Escherichia coli O157:H7, via an approach that combines magnetic microparticles for the enrichment and antibody-conjugated semiconductor quantum dots (QDs) as fluorescence markers. Using the water-in-oil reverse microemulsions method, the gamma-Fe(2)O(3) magnetic nanoparticles were coated with silica to empower the particles with high dispersibility and broad compatibility to biomacromolecules. The magnetic beads were then modified with amino silane, which could immobilize antibodies by glutaraldehyde treatment. The immunized magnetic beads and pathogenic bacteria formed "bead-cell" complexes in the enrichment procedure. QDs with different emission wavelengths (620, 560, and 520 nm) were immobilized with anti-S. typhimurium antibody, anti-S. flexneri antibody, and anti-E. coli O157:H7 antibody, respectively. Fluorescence microscope images and the fluorescence intensity of QDs labeled "sandwich" complexes (conjungated with antibodies against S. typhimurium, S. flexneri, and E. coli O157:H7, respectively) demonstrated that antibody-conjugated QDs could attach to the surface of bacterial cells selectively and specifically. In our method, we could detect food-borne pathogen bacteria in a food matrix at 10(-3) cfu/mL. We determined that a high concentration of proteins in food matrix would decrease the sensitivity of this method. This method, of which the detection procedures are completed within 2 h, can be applied to the rapid and cost-effective monitoring of bacterial contamination in food samples.

Application of Nanoparticles for the Detection and Sorting of Pathogenic Bacteria by Flow-Cytometry

“…In order to overcome such problems, an IMS (ImmunoMagnetic Separation) process for pre enrichment of bacteria was used. Although the use of micro-magnetic beads for preenrichment of bacteria is well established (Fisher et al 2009 ;Jenikova et al 2000 ;Stevens and Jaykus 2004 ;Zhao et al 2009 ) in here we would show the benefi t of using nano-magnetic beads as pre enrichment of bacteria prior to the FACS sorting. In previous work (Fuchslin et al 2010 ) it was shown that the use of pre enrichment of the pathogen Legionella pneumophila improved its detection limits by fl ow cytometry.…”

Fluorescent nanoparticles for chemical and biological sensing

“…Zhao et al have reported a direct labeling method for single E. coli O157:H7 cells using dye-doped silica NPs [175]. Combining magnetic microparticles for the enrichment and antibody-conjugated QDs as fluorescence markers, Shen group described a method that simultaneously detected three food-borne pathogenic bacteria, Salmonella typhimurium, Shigella flexneri, and E. coli O157:H7 [176]. In this method, food-borne pathogen bacteria at 10 −3 cfu mL −1 could be detected in a food matrix.…”

Recent developments in rapid multiplexed bioanalytical methods for foodborne pathogenic bacteria detection

“…Various multiplex immunoassays for foodborne pathogen detection were developed following the "signal encoding" approach, employing a combination of labels (e.g., quantum dots or time resolved fluorescence labels) that can be spectrally distinguished when present in a mixture [6,[37][38][39][40][41]. More frequently, the "position encoding" approach was used, mainly exploiting electrochemical, fluorescence or chemiluminescence detection in microarray formats and/or multichannel platforms.…”

“…Different populations of nanosized labels, each targeted to a pathogen of interest, have been used for multiplexed assays based on optical detection, such as quantum dots [37][38][39], dye-doped nanoparticles [41], composite nanoparticles [40,81] or nanoparticles doped with different Raman reporters [82,83]. The recently developed biobarcode assay offers great potentialities for high detectability (nucleic acids can be detected without PCR amplification) and multiplexing.…”