Raman spectroscopy is a rapid, nondestructive analytical method that measures vibrational transitions resulting in Raman scattering of electrons. Surface-enhanced Raman spectroscopy (SERS) is a variation that enhances the Raman scattering utilizing a metal substrate. For the purpose of bacteria analysis, SERS can be applied because the bacteria have extremely weak Raman scattering due to their chemical makeup. The signal can be increased using a metal substrate to interact with the bacterial cell wall. Previous studies have shown that bacteria can be identified by SERS, but many projects couple it with the use of expensive nanoparticles, specific microscope slides, and Raman microscopy. In this study, a low-cost commercial gold colloid acted as the SERS substrate component that was added to the bacteria samples suspended in water. The use of SERS for bacterial identification can save money and time as compared to traditional techniques of bacterial identification, like plating, polymerase chain reaction, and genetic sequencing. This less expensive approach has the capability to be used in both academic and clinical settings. In medical laboratories with few resources and many backlogs, this quick analytical method to identify bacterial infections could save time and money. In this work, the bacterial species analyzed were Escherichia coli, Staphylococcus aureus, and Bacillus cereus. The sample preparation included adding the bacteria suspended in water (OD of 0.8-1.2) into glass vials, along with the gold colloid and 0.1M NaCl. Each sample was incubated at room temperature for twenty minutes. After the incubation period, the samples were analyzed using a portable Raman instrument with measurements completed in triplicate over the range of 1100-2100cm^-1. Preliminary data using principal component analysis (PCA) showed a clear isolated grouping for E.coli and overlapping groupings for S.aureus and B.cereus. This rapid process using SERS with PCA has strong potential for fast, inexpensive determination of bacterial species.

Thomas Spudich

Maryville University

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