Enhanced Raman imaging and optical spectra of gold nanoparticle doped microcapsules

Gold nanoparticle doped hollow polyelectrolyte microcapsules (gold-doped capsules) were prepared by the layer-by-layer self-assembly method. After sequential adsorption of oppositely charged polyelectrolytes of poly(styrenesulfonate) sodium salt (PSS), poly(allylamine hydrochloride) (PAH) or gold nanoparticles onto melamine formaldehyde particles (MF), intact gold-doped capsules were obtained by dissolving the MF templates via low pH. The maximum absorbance peaks of gold-doped capsules shifted to long wavelengths with increasing filling factor of the gold nanoparticles in accordance with Maxwell-Garnet theory. Due to protection of the nanoparticle surfaces by the polyelectrolyte multilayer surroundings, stable optical properties of gold-doped capsules were observed in low pH solution or organic solvent. Gold nanoparticles in the multilayer enhance the Raman spectra of the polyelectrolyte multilayers, in contrast with the weak Raman signal, which was observed for normal capsules. High-resolution surface Raman imaging was performed by controlling the filling factor.