An optical and rapid sandwich immunoassay method for detection of Salmonella pullorum and Salmonella gallinarum based on immune blue silica nanoparticles and magnetic nanoparticles

An optical and rapid sandwich immunoassay of Salmonella pullorum and Salmonella gallinarum (S. pullorum and S. gallinarum) was designed using anti-S. pullorum and S. gallinarum antibody-functionalized blue silica nanoparticles (IgG-Blue-SiNPs) and magnetic nanoparticles (IgG-MNPs) as immunosensing probes in this article. The IgG-MNPs were used for enrichment of S. pullorum and S. gallinarum, IgG-Blue-SiNPs were used for signal amplification. The Blue-SiNPs were synthesized by doping C.I. reactive blue 14 into silica nanoparticles using an inverse microemulsion method. The morphology, surface charge and functional groups of Blue-SiNps were characterized by SEM, Zeta potential and FTIR spectroscopy. S. pullorum and S. gallinarum in sample solution was captured, enriched and separated by IgG-MNPs. Then IgG-Blue-SiNps were added into the above mixture solution, S. pullorum and S. gallinarum was sandwiched by IgG-MNPs and IgG-Blue-SiNps, forming a blue plaque. Under optimal conditions, the detection limit for pure S. pullorum and S. gallinarum was from 8.8 × 101. The detection limit for S. pullorum and S. gallinarum in milk powder was 8.8 × 102 CFU/ml. Besides, this qualitative detection method was economic, simple, rapid, specific and good stability. Such a simple optical sandwich immunoassay holds great potential as an on-site tool for clinical diagnosis of bacteria and viruses.