Chiroptical spectroscopies like circular dichroism report
on the
handedness of molecules but are often limited to the high-concentration
regime because of the mismatch between the wavelength of propagating
visible light and the size of molecules. Recent work has demonstrated
that the electromagnetic fields generated near chiral plasmonic nanostructures
can have high optical chirality that bridges these length scales and
can induce high-fluorescence dissymmetry signals from achiral dyes
by redirecting their emission. As a step toward single-molecule chiral
sources, the induced fluorescence dissymmetry and apparent emission
pattern near chiral plasmonic nanoparticles must be quantified. Here,
we measure the induced fluorescence dissymmetry from the achiral dye
Cy5.5 near a chiral gold nanodimer structure, and we map out the apparent
emission pattern of the dyes using super-resolution single-molecule
microscopy. Our high-sensitivity approach quantifies the fluorescence
dissymmetry from sampling only ∼100 zeptomoles of Cy5.5 and
measures from Cy5.5 near gold nanodimers median fluorescence dissymmetry
factors that are 2 orders of magnitude greater than those of synthesized
chiral fluorescent molecules. We observe a spatial correlation between
the simulated optical chirality about a plasmonic gold nanodimer and
experimentally obtained super-resolution apparent emission patterns,
and we use the incident polarization to control our detection bias
for the brightest molecules to sample nanometer-scale regions of high
electric flux.
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