Surface-enhanced raman scattering (SERS) of microorganisms

Normal Raman (NR) spectra and surface-enhanced Raman scattering (SERS) spectra were obtained for the bacterium Escherichia coli and were compared with those of two other microorganisms, Haloferax volcanii and Thiobacillus neapolitanus. It was found that at 514 nm the SERS of E. coli was similar to that of flavin adenine dinucleotide (FAD). Upon increasing the excitation wavelength, contributions from other cell components became evident, and they were attributed to nicotinamide adenine dinucleotide (NAD) or other adenine-containing molecules in the bacterium. A comprehensive study of FAD, riboflavin (RF), NAD, and adenine under various experimental conditions was thus performed to shed light on the features in the SERS obtained for E. coli. Comparison of NR and SERS measurements of the various samples enabled a better understanding of the SERS spectra and their sensitivity to the specific experimental conditions (excess metal ion concentration and laser excitation wavelengths and intensity). It was concluded that SERS is a highly sensitive technique and that careful examination of the spectra can provide important chemical information.