Modulation of FRET efficiency by donor-acceptor ratio in co-condensed fluorophore-silica nanoconjugates

Abstract

Förster resonance energy transfer (FRET) in nanocomposites is an important step in many applications. In order to maximize the amount of energy transferred from donor, D, to an acceptor, A, it is essential to minimize self-quenching of the donor. In the present work, fluorescein (D) and rhodamine B (A) are covalently bound into silica nanoshells (C-dye-SNS) with varying D:A ratio where the amount of A has been held constant. The total number of dye molecules is varied from 24 to 140 per nanoshell keeping the number of A molecules at ~13 ​± ​2 molecules per particle. In these conditions, FRET is found to be governed by the D:A ratio. An energy transfer process associated with maximum efficiency of 77% with time constant of 130 ps has been observed in these nanoconjugates. Fast fluorescence decays for D and corresponding risetime for A are observed in the present systems, unlike in those with high concentration of D and A (~1000 molecules/nanoshell). Thus, the presently used dye concentrations are found to be more appropriate than the higher concentration used earlier.