Metallic nano-antennas provide strong field confinement and intensity enhancement in hotspots and thus can ultimately enhance fluorescence detection and provide ultra small detection volumes. In solution-based fluorescence measurements, the diffraction limited focus driving the nano-antenna can outshine the fluorescence originating from the hotspot and thus render the benefits of the hotspot negligible. We introduce a model to calculate the effect of a nano-antenna, or any other object creating a nontrivial intensity distribution, for fluorescence fluctuation measurements. Approximating the local field enhancement of the nano-antenna by a 3D Gaussian profile, we show which hotspot sizes and intensities are the most beneficial for an FCS measurement and compare it to realistic antenna parameters from literature.

Opt. Express
Resonant Nanophotonics

Langguth, L., & Koenderink, F. (2014). Simple model for plasmon enhanced fluorescence correlation spectroscopy. Opt. Express, 22(13), 15397–15409. doi:10.1364/OE.22.015397