Interaction of gold nanoclusters with IR light emitting cyanine dyes: a systematic fluorescence quenching study

This paper describes the intermolecular interactions of gold nanoclusters (Au NCs) with cyanine dyes, namely HITC P, DTTC I, and IR 144. All the cyanine dyes quenched the fluorescence of Au NCs effectively. Steady-state and time-resolved measurements were performed to understand the competition between electron transfer and energy transfer in the Au NCs and cyanine dye system. A significant spectral overlap between the emission spectrum of the Au NCs and the absorption spectrum of cyanine dyes was observed, making both ideal for studying FRET interactions. However, after careful inspection of the steady state spectra and time resolved decays we concluded that photoinduced electron transfer (PET) could be the major pathway to quench the fluorescence intensity of Au NCs. To elucidate the interaction mechanism between Au NCs and cyanine dyes, docking studies were also performed. The docking studies reveal that the quencher molecules, i.e. cyanine dyes, come in close proximity with the 34-cysteine (Cys) in BSA where the Au clusters are located to enable the electron transfer process.