Spectroscopic and fluorescence properties of silver-dye composite nanoparticles

The aim of this work was to investigate the formation of J-aggregates of thiacyanine dye (TC, 5,5'-disulfopropyl-3,3'-dichlorothiacyanine sodium salt) in the presence of 6 nm spherical silver nanoparticles (Ag NPs) using spectrophotometric and fluorescence methods. The formation of J-aggregates was concentration dependent and characterized by the appearance of the new absorption band with the maximum at 481 nm. Spectrophotometric study of J-aggregate formation and time stability suggested that they were formed on the account of monomer form of TC. Moreover, the stability of J-aggregates increased with the lowering AgNPs concentration. The measurements of fluorescence of the NPs-dye assembly clearly indicated that the fluorescence of TC was quenched by Ag NPs on the concentration dependent manner. The spectrophotometric and fluorescence properties of NPs-dye assembly were found to be quantitatively related to the surface coverage of the dye on the Ag NPs.