Core-shell red silica nanoparticles based immunochromatographic assay for detection of Escherichia coli O157:H7

In this paper, a new type immunochromatographic assay (ICA) based on core-shell red silica nanoparticles (core-shell red SiO₂NPs) was proposed and used to detect Escherichia coli O157:H7 (E. coli O157:H7). This is the first report of qualitative ICA for detecting E. coli O157:H7 in phosphate buffer saline (PBS) and food sample using core-shell red SiO₂NPs. Monodispersed red SiO₂NPs were synthesized in the aqueous solution by modifying amino silane and C.I Reactive Red 136 on unmodified silica nanoparticles. The limit of detection (LOD) of this core-shell red SiO₂NPs based ICA for E. coli O157:H7 was 4.5 × 10⁵ CFU/mL in sterile PBS within 20 min. The LOD of this ICA strip for E. coli O157:H7 in milk and pork samples both were 4.5 × 10⁶ CFU/mL. The core-shell red SiO₂NPs based ICA for detection of E. coli O157:H7 has no cross activity with other bacteria. All these results show that this new kind of core-shell colored SiO₂NPs is promising for the practical applications in ICA and other rapid detection fields.