Magnetic beads modified with Pt/Pd nanoparticle and aptamer as a catalytic nano-bioprobe in combination with loop mediated isothermal amplification for the on-site detection of Salmonella Typhimurium in food and fecal samples

Concentration of pathogens directly from food samples by using magnetic beads is a potential strategy in the on site food sample analysis. In this study, magnetic beads, double modified with platinum/palladium nanoparticle (Pt/Pd NP) and DNA aptamer, is presented as catalytic nano-bioprobes for the on-site detection of Salmonella enterica serovar Typhimurium in food and fecal samples. Combination of the developed catalytic nano-bioprobes with loop mediated isothermal amplification (LAMP) enabled rapid detection of low levels of S. Typhimurium in food and chicken fecal samples without culture enrichment. S. Typhimurium-specific DNA aptamer immobilized on the magnetic bead could efficiently concentrate S. Typhimurium with a capturing efficiency higher than 76% in phosphate-buffered saline (PBS). Further, DNA-mediated inhibition of peroxidase-mimic activity of Pt/Pd NP in combination with LAMP was used as a unique approach to detect S. Typhimurium. With this unique approach, it was possible to capture and detect S. Typhimurium as low as 10-15 CFU/mL in chicken meat sample and 3-10 CFU/mL in both whole egg and chicken fecal samples within less than 3 h. Analysis of S. Typhimurium-spiked chicken meat, whole egg and chicken fecal materials have confirmed the precision of the method. A relative accuracy of 90% with an intra and inter assay precision of 8.36% and 9.92% respectively was achieved in the S. Typhimurium-spiked food samples. This unique approach has the potential for the integration in to Lab-on-a-chip based biosensors for on-site monitoring of foodborne pathogens in future.