Figure 1. Interaction and localization of an emitter in a plasmonic hotspot.

(a) Scheme of the emitter interacting with the plasmonic hotspot. (i) A single molecular probe diffuses to the surface of an antenna via Brownian motion where it is adsorbed. (ii) For a double-resonant dye (absorption and emission on resonance with the antenna plasmon resonance and γ/γ₀ radiative enhancement contribution, respectively), light is emitted into the far-field directly from the molecule, and indirectly via the antenna (by coupling to the available modes in the plasmonic system)—leading to a delocalized position of the emission. (iii) Emission from a molecule for which only the absorption is resonant with the plasmonic mode. (iv) Once the probe is bleached and/or desorbs from the surface, it leaves the system free for a new probe molecule to arrive. (b) FDTD simulations of a dipole placed 10 nm to the side of a plasmonic Al tri-disk antenna emitting at different wavelengths. Emission from the dipole is tuned from an on-resonance condition (400 nm) to progressively more off resonance with respect to the LDOS peak of the system (blue line shown in the spectrum in the central bottom panel). The black line in the bottom panel is the scattering spectra of the Al tri-disk structure. (c) Super-resolution localization process for an emitting single molecule. (i) The EMCCD camera image (raw data) is taken and (ii) a surface plot of the raw data is produced and (iii) fit with a Gaussian contour. The centroid position (solid contour) of the Gaussian (mesh) contour is determined. The FWHM is the precision of the localization. (v) Finally, the localized position of the emission origin is recovered—for an uncoupled probe, this corresponds to the position of the molecule.