Rapid Immunochromatographic Assay for Escherichia coli O157:H7 in Bovine Milk Using IgY Labeled by Fe3O4/Au Composite Nanoparticles

A rapid pretreatment-free immunochromatographic assay (ICA) was developed for the screen of Escherichia coli O157:H7 (E. coli O157:H7) in bovine milk. Anti-E. coli O157:H7 immunoglobins of yolk (IgY) was conjugated with a core/shell-structured super-paramagnetic Fe3O4/Au composite nanoparticle (GoldMag) and showed a high coupling ratio of 8 µg IgY mL−1 nanoparticles at pH 8.0. The conditions of ICA strips using this IgY conjugate were optimized and could be used to measure spiked E. coli O157:H7 samples with a detection limit of 103 CFU mL−1 obtained by visual detection. Additionally, the magnetic signal intensities of the assay can quantitatively measure E. coli O157:H7 concentration in the range of 102 – 105 CFU mL−1 both in phosphate buffer solution (pH 7.4) and pretreatment-free milk samples with a detection limit of 102 CFU mL−1.