Dual-color upconversion fluorescence and aptamer-functionalized magnetic nanoparticles-based bioassay for the simultaneous detection of Salmonella Typhimurium and Staphylococcus aureus

A sensitive luminescent bioassay for the simultaneous detection of Salmonella Typhimurium and Staphylococcus aureus was developed using aptamer-conjugated magnetic nanoparticles (MNPs) for both recognition and concentration elements and using upconversion nanoparticles (UCNPs) as highly sensitive dual-color labels. The bioassay system was fabricated by immobilizing aptamer 1 and aptamer 2 onto the surface of MNPs, which were employed to capture and concentrate S. Typhimurium and S. aureus. NaY0.78F4:Yb0.2,Tm0.02 UCNPs modified aptamer 1 and NaY0.28F4:Yb0.70,Er0.02 UCNPs modified aptamer 2 further were bond onto the captured bacteria surface to form sandwich-type complexes. Under optimal conditions, the correlation between the concentration of S. Typhimurium and the luminescent signal was found to be linear within the range of 101–105 cfu mL−1 (R2 = 0.9964), and the signal was in the range of 101–105 cfu mL−1 (R2 = 0.9936) for S. aureus. The limits of detection of the developed method were found to be 5 and 8 cfu mL−1 for S. Typhimurium and S. aureus, respectively. The ability of the bioassay to detect S. Typhimurium and S. aureus in real water samples was also investigated, and the results were compared to the experimental results from the plate-counting methods. Improved by the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, and the different emission lines of Yb/Er- and Yb/Tm-doped NaYF4 UCNPs excited by a 980 nm laser, the present method performs with both high sensitivity and selectivity for the two different types of bacteria.

Fabrication process of biofunctionalized nanoparticles and principle of the performed bioassay. First, aptamer 1 and aptamer 2 were immobilized onto the surface of MNPs and the surface of NaY0.78F4:Yb0.2, Tm0.02 UCNPs, and NaY0.28F4:Yb0.70, Er0.02 UCNPs. Next, S. Typhimurium and S. aureus were added and, due to the highly affinity of aptamer to corresponding bacteria, the aptamer 1-MNPs-S. Typhimurium complex bind NaY0.78F4:Yb0.2, Tm0.02 UCNPs modified aptamer 1, and the aptamer 2-MNPs-S. aureus bind NaY0.28F4:Yb0.70, Er0.02 UCNPs modified aptamer 2. Finally, the luminescent signal was effectively amplified with the help of a magnetic field.Figure optionsDownload as PowerPoint slideHighlights
► Simultaneous detection of two kind of bacteria.
► Bacteria-specific aptamer recognition.
► Dual-color upconversion luminescent nanoparticles labeling.
► Aptamer conjugated-magnetic nanoparticles-based separation and concentration.