Carbohydrate-coated nanoparticles for PCR-less genomic detection of Salmonella from fresh produce

Foodborne outbreaks related to Salmonella are a growing concern as it is commonly associated with raw and uncooked food. Traditional methods for extracting and detecting this pathogen from complex food matrices can be time-consuming and expensive. This study used carbohydrate-coated magnetic and gold nanoparticles to successfully extract and detect Salmonella Enteritidis from artificially contaminated cucumbers and melons. Rapid separation of bacterial cells from buffer solution and food matrices using glycan-coated magnetic nanoparticles (gMNP) was confirmed using Transmission Electron Microscopy (TEM). Quantitative PCR verified the successful magnetic extraction of S. Enteritidis from artificially contaminated foods. Genomic detection was achieved using dextrin-capped gold nanoparticles (dGNP) synthesized using alkaline synthesis route. The synthesized dGNP were wine-red in color, and dynamic light scattering confirmed their size to be <50 nm. A colorimetric biosensor utilizing the stability of dGNP was developed with Salmonella-specific probes (invA), allowing the detection of bacterial loads as low as 4 x 102 CFU/g of food matrix in <30 min. The biosensor was found to be specific when tested against E. coli, K. Pneumoniae, E. cloacae, B. cereus, and L. monocytogenes. PCR amplification of the invA gene confirmed the contribution of target DNA towards the stability of dGNP and maintenance of their red appearance. PCR-less detection was achieved in the presence of natural microbiota and food microparticles in <7 h with magnetic extraction, a short enrichment step, and visual detection.