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Spectroscopic study of surface-enhanced Raman scattering of rhodamine 6G on silver colloid

The aim of this work is to determine the influence of colloidal silver on the intensity of Raman scattering observed for rhodamine 6G (Rh6G) dissolved in the water. A special emphasis is placed on the exploration of the role of chloride ions and the influence of pH on the surface-enhanced Raman scattering (SERS) efficiency and stability of colloid. Rh6G is an extremely SERS active compound so in even relatively simple experiments up to 106 108 fold increase of Raman scattering is achieved. In the colloidal systems chloride ions are mainly responsible for an aggregation of nanoparticles what is the most important factor in the SERS enhancement. Moreover, Rh6G as a cationic dye co-adsorbing with chloride ions exhibits a strong direct interactions with the metallic surface. It results in additional enhancement of the intensity of Raman scattered light and probably is responsible for observed dimerization of Rh6G molecules. The reduction of pH by addition of nitric acid also leads to a decrease of surface potential of colloid and causes in its aggregation. Simply Raman spectrometer and UV-Vis spectrophotometer are used for spectroscopic measurements. The dynamic light scattering technique is used to estimate the size of particles and the degree of their aggregation. It is observed that the magnitude of SERS enhancement strongly depends on the kind and concentration of the used aggregating agent. The differences of SERS efficiency were reflected in the absorption spectra as well as in particles/aggregates size distribution.