Surface enhanced Raman scattering (SERS) with biopolymer encapsulated silver nanosubstrates for rapid detection of foodborne pathogens

A biopolymer encapsulated with silver nanoparticles was prepared using silver nitrate, polyvinyl alcohol (PVA) solution, and trisodium citrate. It was deposited on a mica sheet to use as SERS substrate. Fresh cultures of Salmonella Typhimurium, Escherichia coli, Staphylococcus aureus and Listeria innocua were washed from chicken rinse and suspended in 10ml of sterile deionized water. Approximately 5μl of the bacterial suspensions was placed on the substrate individually and exposed to 785nm HeNe laser excitation. SERS spectral data were recorded over the Raman shift between 400 and 1800cm−1 from 15 different spots on the substrate for each sample; and three replicates were done on each bacteria type. Principal component analysis (PCA) model was developed to classify foodborne bacteria types. PC1 identified 96% of the variation among the given bacteria specimen, and PC2 identified 3%, resulted in a total of 99% classification accuracy. Soft Independent Modeling of Class Analogies (SIMCA) of validation set gave an overall correct classification of 97%. Comparison of the SERS spectra of different types of gram-negative and gram-positive bacteria indicated that all of them have similar cell walls and cell membrane structures. Conversely, major differences were noted around the nucleic acid and amino acid structure information between 1200cm−1 and 1700cm−1 and at the finger print region between 400cm−1 and 700cm−1. Silver biopolymer nanoparticle substrate could be a promising SERS tool for pathogen detection. Also this study indicates that SERS technology could be used for reliable and rapid detection and classification of food borne pathogens. •SERS technique is widely applied in identification of foodborne pathogens.•SERS scattering gives molecular characteristics to identify bacterial species.•Aggregation of silver colloids produces wide variation in SERS.•Biopolymer-based nanosubstrates showed promising for bacteria detection