Far-Field Polarization Optics Control the Nanometer-Scale Pattern of High-Fluorescence Dissymmetry Emission from Achiral Molecules near Plasmonic Nanodimers

Abstract

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.