Plasmon-Enhanced Resonance Energy Transfer from a Conjugated Polymer to Fluorescent Multilayer Core−Shell Nanoparticles: A Photophysical Study

Abstract

The influence of metallic silver nanoparticles on F€ orster resonance energy transfer (FRET) between a watersoluble cationic conjugated polymer and fluorescent multilayer Ag@SiO 2 @SiO 2 þFiTC core-shell nanoparticles was characterized using a combination of light scattering and luminescence techniques. Positioning the fluorescent polymer 7 nm away from the surface of a 45 nm silver nanoparticle with a silica spacing layer increases its quantum yield to 77%, as compared to 3% when measured as an isolated emitter. In the presence of the metallic core, the luminescence of the nanoparticle-bound acceptor fluorophore is increased at the expense of the polymer donor luminescence, and time-resolved fluorescence measurements indicate an enhancement of FRET efficiency from 4 to 50%, an increase in the F€ orster distance from 50 to 85 Å, and a resonant transfer rate between donors and acceptors more than 2 orders of magnitude higher than that measured in the absence of the metal core. The strong influence of plasmonic coupling in these multilayer nanocomposites offers great potential for signal amplification schemes in polymer-based and FRET-based biosensors.

Experimental and Theoretical Investigation of the Distance Dependence of Localized Surface Plasmon Coupled Förster Resonance Energy Transfer

“…6,[19][20][21][22][23][24][25][26][27][28][29] LSP coupled FRET has been observed using single metallic nanoparticles coupled to a single donor-acceptor pair 6 , core-shell structures [23][24][25] and planar structures. [26][27][28] Studying FRET from a conjugated polymer to fluorescent multilayer core-shell NP, Lessard-Viger et al observed a 70% increase in the Förster radius and an increase in the FRET-rate by two orders of magnitude.…”

“…[26][27][28] Studying FRET from a conjugated polymer to fluorescent multilayer core-shell NP, Lessard-Viger et al observed a 70% increase in the Förster radius and an increase in the FRET-rate by two orders of magnitude. 24 Also using a core-shell geometry, composed of donor and acceptor fluorophore molecules embedded in a shell coating a Au-Ag core-shell nanocrystal, Wang et al demonstrated that FRET could be switched on and off by varying the spectral position of the LSP resonance relative to the donor emission and acceptor absorption. 25 LSP coupled FRET was reported in planar structures comprised of a layer of dyes and/or QDs, acting as donors and acceptors, placed on a MNP layer.…”

Metal-Enhanced Fluorescence and FRET in Multilayer Core-Shell Nanoparticles

“…For example, we measured an average fluorescence lifetime of 0.228 ns for eosin in core-shell NPs with a 7 ± 2 nm thick spacer, which represents a distinctive reduction in lifetime over that of eosin bound to bare silica and free in solution [39]. Similarly, a reduction in excited-state lifetime from 1.72 to 0.03 ns was measured for FiTC in Ag@SiO 2 @SiO 2 + FiTC NPs of comparable core size and spacer thickness as compared with corresponding hollow silica nanoshells [41]. These observations are manifestations of the MEF phenomenon, in which metal-fluorophore interactions lead to an increase in the quantum yield of the fluorophore and a decrease in its lifetime.…”

“…When a fluorophore is perturbed by a metallic particle, the plasmonic coupling causes an increase in the molecular radiative decay rate by a factor of , and the metal-enhanced quantum yield (Φ ) and lifetime ( ) values become [30,41] …”

“…Also, this shell protects the organic dyes against collisional quenching and can be functionalized to covalently bind target biomolecules or fluorophores or form electrostatic complexes with charged molecules [19,41]. Finally, plasmonic enhancement in core-shell nanostructures improves the efficiency, range, and transfer rate of Förster resonance energy transfer (FRET) by increasing the strength of donor-acceptor interactions, which can in turn lead to the excitation by a single donor of several acceptors molecules over distances exceeding the natural range of FRET [39,41].…”