Shape, size and composition dependence of efficiency and dynamics of Förster resonance energy transfer in dye-silica nanoconjugates

Abstract

The role of relative concentrations of energy donors (fluorescein, D), acceptors (rhodamine, A) and silica on Förster resonance energy transfer (FRET) efficiency and dynamics in dye silica conjugates has been studied, as a part of our initial attempts to ascertain the potential of dye-silica nanoconjugates as light harvesting nanoantennae. Two types of dye-silica nanoconjugates, prepared by the co-condensation method, have been examined. The first is based on silica nanoshells (SNS-dye) while the second is based on silica nanoparticles (SNP-dye). Both these nanostructures have a diameter of approximately 25 nm. Efficient energy transfer (91% and 97%, respectively) has been observed in both, for total fluorophore concentration upto 5-6 mmol, irrespective of the D : A ratio. The lower efficiency at dye concentrations greater than these has been rationalized by the competitive self-quenching of D. A risetime of approximately 500 fs is observed in the A emission in SNS-dye, but there is no such feature in SNP-dye. The shape and size dependence of the FRET efficiency and dynamics has been rationalized as follows: the initial step of dye rich core formation in nanoparticles results in high proximity of dye molecules to each other, leading to highly efficient FRET than in nanoshells. In larger SNP-dye nanoconjugates of 65 nm in diameter, the FRET efficiency decreases to 85%, while a risetime in D emission emerges. This provides support to the proposed correlation between efficiency and packing. Hence, it is inferred that total fluorophore concentration, rather than D : A ratios, governs the FRET dynamics and efficiency in these systems.

Photochemistry and Photophysics in Silica-Based Materials: Ultrafast and Single Molecule Spectroscopy Observation

“…Here, we will focus on hetero transfer (A and D have different molecular structures). In a system containing fluorescein (D) and RhB (A) in silica materials (Scheme ), two types of dye-silica nanoconjugates have been designed and examined: one based on silica nanoshells (SNS-dye) and another on silica nanoparticles (SNP-dye). , In both nanosystems, the concentration of donor molecules affects the FRET efficiency and dynamics. While the amount of acceptors was kept constant, the D:A concentrations ratio changed from 0.5 to 3 in SNS-dye and from 0.5 to 4 in SNP-dye systems .…”

FRET on Surface of Silica Nanoparticle: Effect of Chromophore Concentration on Dynamics and Efficiency

“…Thus, it is evident that optimization of conditions for FRET can be achieved in the present experiment by modulating the D:A ratio, like in some earlier reports in different systems. This is an improvement upon our earlier experiment with co-condensed nanoconjugates …”

“…The ultrafast fluorescence transients have been recorded using the femtosecond optical gating technique (FOG) described in detail elsewhere . A brief description is as follows: λ ex = 435 nm has been generated by frequency doubling the 870 nm output of a mode-locked Ti:sapphire laser (Tsunami, pumped by a 4.6 W Millennia, both from Spectra-Physics).…”

“…Very recently, we have achieved Förster resonance energy transfer (FRET) between fluorescein (energy donor, D) and rhodamine B (energy acceptor, A, Figure S1), , co-condensed in nanoparticles and nanoshells of silica . Very high concentrations of chromophores have been used in that study, leading to competing pathways that deactivate the excited state of the donor nonradiatively.…”

Role of Solvent in Electron‐Phonon Relaxation Dynamics in Core‐Shell Au−SiO2 Nanoparticles

“…[36][37][38][39][40][41] Silica coating not only stabilizes the Au core by hindering aggregation and degradation, but also provides a functionalizable exosurface for grafting organic molecules. [42][43][44] They have been found to augment electrochemiluminescence of quantum dots grafted on them [36] and have found use in design of immunosensors for insulin, [45] in solar energy harvesting [46] and in the increase in efficiency of dye-sensitized solar cells. [47] They have also been found to enhance catalytic efficiency of palladium nanoparticles due to efficient energy transfer from Au to palladium.…”