Silver Nanorod Arrays as a Surface-Enhanced Raman Scattering Substrate for Foodborne Pathogenic Bacteria Detection

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Abstract
Surface-enhanced Raman scattering (SERS) using novel silver nanorod array substrates has been used for the detection of pathogenic bacteria. The substrate consists of a base layer of 500 nm silver film on a glass slide and a layer of silver nanorod array with a length of ∼1 μm produced by the oblique angle deposition method at a vapor incident angle of 86°. Spectra from whole cell bacteria, Generic Escherichia coli, E. coli O157:H7, E. coli DH 5α, Staphylococcus aureus, S. epidermidis, and Salmonella typhimurium, and bacteria mixtures have been obtained. This SERS active substrate can detect spectral differences between Gram types, different species, their mixture, and strains. Principal component analysis (PCA) has been applied to classify the spectra. Viable and nonviable cells have also been examined, and significantly reduced SERS responses were observed for nonviable cells. SERS detection of bacteria at the single cell level, excited at low incident laser power (12 μW) and short collection time (10 s), has also been demonstrated. These results indicate that the SERS-active silver nanorod array substrate is a potential analytical sensor for rapid identification of microorganisms with a minimum of sample preparation.