Purpose: The primary objective of this study is to develop optimized vancomycin functionalized silver nanorod (AgNR) arrays substrates to detect foodborne pathogens in mung bean sprout samples based on their SERS spectra. The goal of this study is also to differentiate pathogens from different species and different serotypes of the same species.
Methods: Six different bacteria Salmonella Anatum, Salmonella Cubana, Salmonella Stanley, Salmonella Enteritidis, E. coli O157:H7, and Staphylococcus epidermidis, were inoculated in 10 g of mung bean sprout, and recovered by a two-step filtration process. The vancomycin-treated AgNR substrate was immersed in the bacteria solution for 2 hrs before the SERS spectra of the bacteria were acquired using both bench top and handheld Raman systems.
Results: We established that 1mM vancomycin-coated AgNR arrays substrate with thickness (QCM reading) of 600 nm yielded the most intense bacteria signal. The limit of detection (LOD) of the six aforementioned pathogens in mung bean sprouts samples was 102 CFU/ml or 103CFU/g of mung bean sprouts when combined with a two-step filtration process in less than 4 hrs. The SERS spectra were acquired by both a bench top and a handheld Raman system. The LOD was confirmed by principle component analysis (PCA) and partial least-squares discriminatory analysis (PLS-DA) with 100% sensitivity and specificity. These six different pathogens were also differentiated by their species and serotypes using PCA.
Significance: This label-free SERS detection technique, based on functionalized AgNR arrays substrates, is a powerful platform to detect low amounts of foodborne pathogens in a short time from real food samples. It has the potential to be used as an on-site pathogen detection method in the food industry.