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.