A One-Step Homogeneous Sandwich Immunosensor for Salmonella Detection Based on Magnetic Nanoparticles (MNPs) and Quantum Dots (QDs)

Simple immuno-magnetic separation tandem fluorescent probes based on quantum dots-antibody (QDs-Ab) were developed to detectSalmonellawith sensitivity of 500 cfu mL−1. With two monoclonal antibodies, which recognize different antigenic determinant on the surface ofSalmonella, we prepared antibody-coated magnetic nanoparticles (MNPs) and conjugates of QDs-Ab. The immune-magnetic beads were verified with high enrichment efficiency forSalmonella(90%). A sandwich structure formed if theSalmonellasolution was mixed together with immune-beads and QDs-Ab, and the fluorescent single from QDs was related to the amount ofSalmonella. A linear response between fluorescence intensity and various concentrations ofSalmonella(2.5 × 103to 1.95 × 108cfu mL−1) were observed with this proposed method. The total assay time forSalmonellawas 30 min, and no cross-reaction to other microbial strains, such asStaphylococcus aureus,Escherichia coli(E. coli) andEscherichia coli O157:H7(E. coli O157:H7), were found using this detection system. All our results showed that the simple homogeneous immunoassay could be applied inSalmonellascreening without time-consuming extra-enrichment of bacteria.Keywords:Salmonella;fluorescent immunoassay;magnetic separation;quantum dots