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<p>We have employed DNA-directed assembly to
prepare dimers of gold nanoparticles and used their longitudinally coupled plasmon mode to
enhance the fluorescence emission of an organic red-emitting dye, Atto-655. The plasmon-
enhanced fluorescence of this dye using dimers of 80 nm particles was measured at single
molecule detection level. The top enhancement factors were above 1000-fold in 71% of the
dimers within a total of 32 dimers measured, and, in some cases, they reached almost 4000-fold,
in good agreement with model simulations. Additionally, fluorescence lifetime correlation
analysis enabled the separation of enhanced from non-enhanced emission simultaneously
collected in our confocal detection volume. This approach allowed us to recover a short
relaxation component exclusive to enhanced emission that is attributed to the interaction of the
dye with DNA in the interparticle gaps. </p>
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