Mechanism and Kinetics of J-Aggregation of Thiacyanine Dye in the Presence of Silver Nanoparticles

Abstract

The aim of the present work was to elucidate the binding mechanism and kinetics of anionic cyanine dye 3,3′-disulfopropyl-5,5′-dichlorothiacyanine sodium salt (TC) J-aggregation on the surface of silver nanoparticles (AgNPs, particle size ∼6 nm). The hybrid J-aggregate–AgNPs assembly was characterized by TEM analysis, UV–vis spectrophotometry, and fluorescence measurements. In the elucidation of TC binding on the surface of AgNPs, they were considered as macromolecules with several binding sites and TC dye was considered as a ligand. Scatchard and Hill analysis revealed that TC binding was a random process rather than cooperative, with ∼200 bonded TC molecules per AgNP and a binding constant Ka = 4.8 × 107 M. The TC–AgNP assembly exerted concentration-dependent fluorescence quenching properties. The linearity of the Stern–Volmer relation, accounting for both static and dynamic quenching, indicated that only one type of quenching occurred, suggesting that AgNPs quenched the fluorescence of TC with an extraordinarily high Stern–Volmer constant (KSV) in the range of 108 M–1. Additionally, the kinetics of J-aggregation of TC in the presence of AgNPs was studied using a stopped–flow technique. Kinetic measurements were performed as a function of the TC and AgNP concentration, yielding sigmoidal kinetic curves. The concentration dependence of the parameters of the kinetic curves indicated that J-aggregate formation on the AgNP surface occurred via a two-step process; the first was adsorption of the initial dye layer, followed by the growth of consecutive layers.