We demonstrated the new antibody/gold nanoparticle/magnetic nanoparticle nanocomposites (antibody/AuNP/MNPs)
and their application in the detection of the foodborne pathogen, Staphylococcus
aureus (S. aureus), in milk. The nanocomposites were synthesized by coating the MNPs with bovine
serum albumin (BSA) then adsorbing the AuNPs and anti-S. aureus antibodies on their surface. Using the
completed immunomagnetic nanostructures, S. aureus inoculated in the milk sample was captured and
isolated from the medium using the permanent magnet. The nanoparticle-bound cells as well as the
unbound cells in the supernatant were enumerated via surface plating to evaluate the target binding
capacity of the nanocomposites. The capture efficiencies of the antibody/AuNP/MNPs were 96% and 78%
for S. aureus in PBS and the milk sample respectively, which were significantly higher than those of the
antibody-coupled MNPs without any AuNP. The captured cells were also applied to the selective
filtration system to produce color signals that were used for the detection of the target pathogen.
During the filtration, the cells bound to the antibody/AuNP/MNPs remained on the surface of the
membrane filter while unbound nanoparticles passed through the uniform pores of the membrane.
After the gold enhancement, the cells-particles complex resting on the membrane surface rendered a
visible color, and the signal intensity became higher as the target cell concentration increased. The
detection limits of this colorimetric sensor were 1.5 103 and 1.5 105 CFU for S. aureus in PBS and
the milk sample respectively. This sensing mechanism also had the high specificity for S. aureus over the
other pathogens such as Escherichia coli, Listeria monocytogenes, and Salmonella enterica. The assay
required only 40 min to obtain the results. With the use of the appropriate antibodies, our
immunomagnetic nanocomposites-based detection strategy can provide an easy, convenient, and rapid
sensing method for a wide range of pathogens.
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