Systematic Computational Study of the Effect of Silver Nanoparticle Dimers on the Coupled Emission from Nearby Fluorophores

Abstract

We use the finite-difference time-domain method to predict how fluorescence is modified if the fluorophore is located between two silver nanoparticles of a dimer system. The fluorophore is modeled as a radiating point dipole with orientation defined by its polarization. When a fluorophore is oriented perpendicular to the metal surface, there is a large increase in total power radiated through a closed surface containing the dimer system, in comparison to the isolated fluorophore and the case of a fluorophore near a single nanoparticle. The increase in radiated power indicates increases in the relative radiative decay rates of the emission near the nanoparticles. The angle-resolved far-field distributions of the emission in a single plane are also computed. This is informative as many experimental conditions involve collection optics and detectors that collect the emission along a single plane. For fluorophores oriented perpendicular to the metal surfaces, the dimer systems lead to significant enhancements in the fluorescence emission intensity in the plane. In contrast, significant emission quenching occurs if the fluorophores are oriented parallel to the metal surfaces. We also examine the effect of the fluorophore on the near-field around the nanoparticles and correlate our results with surface plasmon excitations.

An Electromagnetic Study of Metal Enhanced Fluorescence Due to Immobilized Nanoparticle Arrays on Glass Substrates

“…This requires calculating the decay rates, m r , m abs and 0 r by considering the spontaneous emission of the fluorophore as a small electric dipole [12] [21]. These decay rates can be found in terms of the Poynting vector, as described in reference [21] such that: where s is a surface that encloses the fluorophore molecule (small dipole) and nanoparticle.…”

“…This requires calculating the decay rates, m r , m abs and 0 r by considering the spontaneous emission of the fluorophore as a small electric dipole [12] [21]. These decay rates can be found in terms of the Poynting vector, as described in reference [21] such that: where s is a surface that encloses the fluorophore molecule (small dipole) and nanoparticle. In equation (6) we consider the total electric and magnetic field crossing s, whereas in equation (7) it is the scattered fields from the nano-cylinder that are considered, hence the subscripts T and S. To find 0 r from equation (6) only the small dipole has to be considered in the calculation, whilst to find m r the metal nano-cylinder is added to the model and enclosed by the surface.…”

Enhanced Photostability of Fluoroquinolone Antibacterials Capped on Silver Nanoparticles

“…Indeed, metallic surfaces are generally known to induce strong quenching of molecular fluorescence, due to electromagnetic coupling between the metal and the fluorogenic centers. However, recent investigations have shown significant fluorescence enhancement for fluorophores located in the close proximity of AgNPs, [37,38] in opposing to the quenching effects. This is due to an intricate phenomenon arising from the resonance plasmon effect in photophysical properties of organic chromophores.…”

“…In particular, the orientation, perpendicular or parallel, of the emitting centers with respect to the metal surface has proven to be a key factor for observing either enhancement or quenching phenomena. [37,38] On these bases, the survival of fluorescence may probably reflect a balance between these two opposing effects due to the short distance S. Giuffrida and S. Sortino/Enhanced Photostability of Fluoroquinolone Antibacterials . .…”

Plasmonic Enhancement of Single Photon Emission from a Site-Controlled Quantum Dot

“…Data taken by Johnson and Christy 25 was used for the Ag 3 parameters. The LSPR is well studied [26][27][28][29] and is known to change with geometry. 28 For core-shell structures, there is hybridization 30 of the LSPR mode, causing a splitting of the single resonance into two at different resonance wavelengths as shown in Figure 1(b).…”