Effect of surfactant assemblies on the resonance energy transfer from 4′,6-diamidino-2-phenylindole to silver nanoclusters

Abstract

In the present work, we have demonstrated the effect of sodium dodecyl sulfate (SDS) assemblies on the Förster resonance energy transfer (FRET) between 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) and silver nanocluster (Ag NC) in phosphate buffer by using fluorescence spectroscopy. While DAPI interacts specifically with SDS surfactants in a concentration-dependent manner, Ag NC shows no specific interaction with surfactant assemblies. At very low concentrations of SDS (<0.6mM), DAPI forms surfactant-induced aggregates at the interface. In the case of intermediate concentrations (0.6mM≤SDS<4mM), DAPI associates with the negatively charged SDS pre-micelles via electrostatic interaction. Beyond 4mM SDS, the FL intensity of DAPI saturates due to complete incorporation of DAPI into the micellar Stern layer. Notably, the interaction between DAPI and Ag NC significantly perturbs in the presence of SDS. In phosphate buffer, FRET efficiency (ϕEff) of 78% has been estimated for DAPI-Ag NC pair. Interestingly, the ϕEff decreases to 23% in the presence of 1mM SDS. However, in the presence of 16mM SDS, complete suppression of this nonradiative FRET has been observed due to incorporation of DAPI into the micellar Stern layer. This efficient modulation of FRET due to the association of the donor molecule with surfactant assemblies, may find promising applications in various photophysical and biological phenomena.