Surface enhanced Raman scattering spectroscopy of Ag nanoparticle aggregates directly photo-reduced on pathogenic bacterium (Helicobacter pylori)

To enable us surface enhanced Raman scattering (SERS) spectroscopic detection of bacteria having low affinity for Ag colloidal nanoparticles, we examined simple experimental methodology; SERS detections using Ag nanoparticles aggregates directly synthesized by photo-reduction on the surfaces of such bacteria (Helicobacter pylori). The synthesized Ag nanoparticles aggregated on bacterial surfaces and generated temporally and spectrally fluctuated SERS spectra that are tentatively attributed to amide groups of surface proteins. The selective appearance of amide groups and fluctuation in SERS spectra indicated chemical contribution to SERS. By referring to previous reports, we estimated total SERS enhancement factors to be ∼1011. Electromagnetic (EM) enhancement factors of SERS are up to ∼108. Thus, we considered that chemical ones may be <∼103 in the present SERS active system.