Fluorescence correlation spectroscopy at high concentrations using gold bowtie nanoantennas

Fluorescence correlation spectroscopy (FCS) measures the fluorescence fluctuations of fluorophores in solution, but is restricted to extremely low concentrations. Plasmonic gold bowtie nanoantennas enhance a single molecule’s fluorescence relative to a large background of unenhanced molecules, and here we show that bowties can extend FCS measurements to much higher concentrations. In this demonstration, the bowtie-FCS signal is dominated by molecules that transiently stick to the substrate near the bowtie gap, and photobleaching/photoblinking dynamics for two fluorophores are measured on the 10–100 ms