Kinetics of J-aggregation of Tc-coated au colloidal nanoparticles in aqueous solution

The kinetics of J-aggregation of thiacyanine dye (TC, 5,5’–disulfopropyl 3,3’– dichlorothiacyanine sodium salt) was studied in the presence of gold colloid. The synthesized Au colloidal dispersions were characterized by UV-Vis spectrophotometry. Kinetic measurements were carried out using a stopped-flow method to study the mechanism of J-aggregation, capturing both the slow and the fast phases of J-aggregate formation

Adsorption and fluorescence quenching of 5,5 -disulfopropyl-3,3 -dichlorothiacyanine dye on gold nanoparticles

The aim of the work was to investigate the adsorption of negatively charged cyanine dye 5,5-disulfopropyl-3,3-dichlorothiacyanine (TC) on the surface of borate capped gold nanoparticles (AuNPs) with average core sizes of 6 and 10 nm. The characterization of AuNPs in the presence and absence of TC was performed by measurements of the absorption, fluorescence and Raman spectra, TEM, DLS and zeta potential. The measurements of fluorescence of the NPs-TC assembly in the presence of low TC concentration clearly indicated that the fluorescence of TC was quenched by AuNPs in the concentration dependent manner. This process was found to be quantitatively related to the surface coverage of AuNPs by TC molecules. NPs surface coverage by TC was obtained from the dependence of TC fluorescence on NPs or TC concentration, keeping the concentration of one of the components of the NPs-TC assembly constant. The calculated values were obtained under the assumption that the monolayer of TC molecules, which were in direct contact with the NPs surface, was adsorbed. The experimentally obtained values were in accordance with the calculated ones for TC orientation along the vertical short side. The formation of TC J-aggregates was evident only in the presence of 6 nm NPs, when TC concentration was high. In this case the experimentally obtained value for C6 concentration needed to completely quench TC dyes fluorescence was much lower than the calculated, indicating that the dye was accommodated on the surface of these NPs in more than one layer, and most probably in the slanted configuration

Fluorescence Quenching of 5,5 -Disulfopropyl-3,3 -dichlorothiacyanine Dye Adsorbed on Gold Nanoparticles

Nanoparticles (NPs) modified with fluorescent cyanine dyes can exhibit fluorescent quenching properties due to energy and/or electron transfer, and these systems have many applications in catalysis, drug delivery, nanoelectronics, medical diagnostics, and chemical sensing. The aim of this work was to investigate the adsorption of cyanine dye 5,5-disulfopropyl-3,3-dichlorothiacyanine (TC) on the surface of citrate capped gold nanoparticles (AuNPs) with the average core sizes of 9, 17, and 30 nm using various experimental techniques. The measurements of fluorescence corrected for inner filter effects (IFE) of the particle dye assembly clearly indicated that the fluorescence of TC was quenched by AuNPs on the concentration dependent 3 manner, and the equilibrium constants for the sorption of TC on the NP surface were calculated. Significant increase of fluorescence quenching was noticed when NP size increased, keeping the concentration of NPs of different size constant. By comparing experimental and calculated results for quenching of TC dye fluorescence, we assumed that the maximum quenching was restricted to full monolayer coverage of TC on the NP surface. The conclusion was drawn that the most probable orientation of TC dye molecules on the NP surface was slanted and that the dye approached NP surface with its positively charged thiazole ring