Rapid colorimetric detection of Salmonella typhimuriumusing a selective filtration technique combined with antibody-magnetic nanoparticle nanocomposites

Detection of pathogenic bacteria that pose a great risk to human health requires a rapid, convenient, reliable, and sensitive detection method. In this study, we developed a selective filtration method using monoclonal antibody (MAb)-magnetic nanoparticle (MNP) nanocomposites for the rapid and sensitive colorimetric detection of Salmonella typhimurium. The method contains two key steps: the immunomagnetic separation of the bacteria using MAb-MNP nanocomposites and the filtration of the nanocomposite-bound bacteria. Color signals from the nanocomposites remaining on the membrane were measured, which reflected the amount of bacteria in test samples. Immunomagnetic capture efficiencies of 8 to 90 % for various concentrations of the pathogen (2 x 10(4)-2 x 10(1) cells) were obtained. After optimization of the method, 2 x 10(1) cells of S. typhimurium in pure culture solution was detectable as well as in artificially inoculated vegetables (100 cells/g). The method was confirmed to be highly specific to S. typhimurium without cross-reaction to other pathogenic bacteria and could be concluded within 45 min, yielding results in a shorter or similar time period as compared with recently reported antibody immobilized on magnetic-particle-based methods. This study also demonstrated direct application of MAb-MNP nanocomposites without a dissociation step of bacteria from magnetic beads in colorimetric assays in practice.