Wavelength-Dependent Super-resolution Images of Dye Molecules Coupled to Plasmonic Nanotriangles

The emission properties of fluorescent molecules are strongly affected by proximal plasmonic nanoparticles that act as optical nanoantennas. In particular, fluorescence intensity can be greatly increased by enhancing both the excitation and emission rates of a fluorophore, and the angular and spatial emission pattern from a dye coupled to a plasmonic nanoantenna will be altered. Here, we use single-molecule imaging to measure this shifted emission pattern based on the super-resolution image of cyanine dye molecules coupled to gold nanotriangles. To compare the relative effects of excitation versus emission enhancement on the emission pattern, we vary laser excitation wavelengths, dye emission and absorbance spectra, and local surface plasmon resonance frequency. We demonstrate that the emission pattern is dramatically changed when coupling occurs and that coupling between the dye and gold nanotriangle happens even in the absence of intensity enhancement.