<p>Plasmonic
metal nanoparticles can impact the behaviour of organic molecules in a number
of ways, including enhancing or quenching fluorescence. Only through a
comprehensive understanding of the fundamental photophysical processes
regulating nano-molecular interactions can these effects be controlled, and
exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is
governed by two underlying processes,
increased rate of fluorophore excitation and increased fluorophore
emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular
systems for various applications. We report groundbreaking work on the use of
single molecule fluorescence microscopy to distinguish between the two
mechanistic components of MEF, in a model system consisting of two analogous
boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles
(AgNP). We demonstrate that the increased excitation MEF mechanism occurs to
approximately the same extent for both dyes, but that the BODIPY with the
higher quantum yield of fluorescence experiences a greater degree of MEF via
the increased fluorophore emission mechanism, and higher overall enhancement,
as a result of its superior ability to undergo near-field interactions with
AgNP. We foresee that this knowledge and methodology will be used to tailor MEF
to meet the needs of different applications, such as those requiring maximum
enhancement of fluorescence intensity or instead prioritizing excited-state
photochemistry. </p>
Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence
