Coupling Single\nMolecules to DNA-Based Optical Antennas\nwith Position and Orientation Control

Optical\nantennas have been extensively employed to manipulate the\nphotophysical properties of single-photon emitters. Coupling between\nan emitter and a given resonant mode of an optical antenna depends\nmainly on three parameters: spectral overlap, relative distance, and\nrelative orientation between the emitter’s transition dipole\nmoment and the antenna. While the first two have already been extensively\ndemonstrated, achieving full coupling control remains unexplored due\nto the challenges in manipulating at the same time both the position\nand orientation of single molecules. Here, we use the DNA origami\ntechnique to assemble a dimer optical antenna and position a single\nfluorescent molecule at the antenna gap with controlled orientation,\npredominately parallel or perpendicular to the antenna’s main\naxis. We study the coupling for both conditions through fluorescence\nmeasurements correlated with scanning electron microscopy images,\nrevealing a 5-fold higher average fluorescence intensity when the\nemitter is aligned with the antenna’s main axis and a maximum\nfluorescence enhancement of ∼1400-fold. A comparison to realistic\nnumerical simulations suggests that the observed distribution of fluorescence\nenhancement arises from small variations in the emitter orientation\nand gap size. This work establishes DNA origami as a versatile platform\nto fully control the coupling between emitters and optical antennas,\ntrailblazing the way for self-assembled nanophotonic devices with\noptimized and more homogeneous performance.