Exact Analysis of Nanoantenna Enhanced Fluorescence Correlation Spectroscopy at a Mie Sphere

In fluorescence correlation spectroscopy (FCS), one measures and correlates the fluctuations that occur as fluorophores diffuse into and out of the detection volume of a microscope. The resulting correlations are used to determine concentrations and diffusion rates of fluorescent species in liquid environments. The sensitivity of this technique is limited by the field intensity and the dimensions of the detection volume, both of which can be modified by nanostructures through geometric and plasmonic effects. In this paper we aim to establish how far noble metal Mie spheres, acting as plasmon antennas, can boost FCS. To that end, we model a realistic scenario that takes into account the exact solutions of the field near a plasmon antenna, the modified diffusion owing to the antenna excluding volume, as well as quantum efficiency and local density of states (LDOS) effects.