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

Abstract

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.