In situ biofilm formation and bacterial death monitoring using surface-enhanced raman scattering

Surface-enhanced Raman scattering (SERS) is a powerful technique for characterization of biological molecules and molecular structures due to the fingerprinting property, very narrow spectral bandwidth, and easy sample preparation. In SERS, Raman scattering can be enhanced up to 10 14 times by bringing the molecule or molecular structure of interest close to or in contact with nanostructured noble metals such as gold and silver. SERS can be used for the characterization and identification of components of complex biochemical systems such as bacteria and biofilm. In this thesis, characterization and identification of biofilm components were investigated using SERS. The core AgNP- shell chitosan layer type structure was prepared by coating the AgNPs with a layer of chitosan (c-AgNPs) and they were used as a SERS substrate for biofilm formation and bacterial death monitoring. Due to absorptive property of chitosan, biomaterials that were produced by bacteria can penetrate into shell without saturating the metal surface due to the selective interaction of biofilm components with the AgNPs. The feasibility of in situ monitoring of molecular changes during the bacterial death was also demonstrated. It was found that SERS spectra could provide significant information about the morphologic changes on the bacterial cell wall and released molecular structures such as DNA/RNA bases during the decompositionof bacteria. It was also found that the band at 678 cm -1 could be used for monitoring bacterial death.