Nanoplasmonic Enhancement of Molecular Fluorescence: Theory and Numerical Modeling
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Date
2014
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Abstract
Significant emission enhancement of fluorescent
molecules placed in close proximity to metallic nanoparticles
has been observed. Recent advances in nanotechnology have
enabled the introduction of plasmon-enhanced molecular
fluorescence in various applications. Comprehensive theory
of the physics behind this enhancement mechanism has also
been developed. However, most of the existing analytical
tools are applicable mainly for particular nanoparticles in
either spherical or ellipsoidal shapes. Since the plasmonic
enhancement of molecular fluorescence is dependent on various
parameters such as shape, size, and distribution of nearby
nanoparticles, it is crucial to have more powerful analysis
tools to be able to handle any arbitrary nanoparticles. For this
purpose, the 3D finite element method, which is a commonly
used technique for arbitrary structures, is implemented and
reported in this paper. The emitting molecule is assumed to be
an electric dipole point source. The fluorescence enhancement
factor is described in term of a local electric fieldenhancement
factor and the quantum yield of the system.
The model is validated by comparison to the approximate
quasistatic model and the exact Mie theory. It provides more
accurate results than those of the quasistatic model, which
makes it become the powerful numerical approach for investigation
of arbitrary nanostructure influence on molecular
fluorescence. It is then applied for investigating the emission
characteristics of the fluorescent molecule when it is placed in
the vicinity of more complicated structures including dimers
and chains of coupled nanoparticles. It is found that these
coupled nanoparticle configurations provide stronger fluorescence
enhancement than the single nanoparticle of the same
particle size when the inter-particle gap is small. It is attributed
to the higher electric-field enhancement in the inter-particle
gap region via strong surface plasmon coupling effects of two
neighboring nanoparticles.
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Keywords
Plasmon-enhanced fluorescence . Mie theory . Quasistatic model . Finite element method