Surface enhanced Raman scattering of bacteria using capped and uncapped silver nanoparticles

Surface enhanced Raman scattering (SERS) spectra of bacteria were obtained using citrate (capped) and borohydride (uncapped) generated silver nanoparticles (Ag NPs).The observed differences in SERS spectra are attributed to the manner in which these Ag NPs interact with bacteria. Capped Ag NPs are able to partition through the surface polysaccharides of the bacterial cell to bind to the inner and outer cell membranes, as well as the periplasmic space between them. The resultant spectra show contributions due to the components of the cell envelope and cellular secretions. Uncapped Ag NPs are unable to partition through the polysaccharide outer structures of the cells. Spectral features observed for these uncapped Ag NPs are secretions primarily due to the metabolites of purine degradation.