Frontiers of quantum physics

Single-molecule fluorescence techniques are essential for investigating the molecular mechanisms in biological processes. However, achieving sub-millisecond temporal resolution to monitor fast molecular dynamics remains a significant challenge. The fluorescence brightness is the key parameter that generally defines the temporal resolution for these techniques. Conventional microscopes and standard fluorescent emitters fall short in achieving the high brightness required for sub-millisecond monitoring. Plasmonic nanoantennas are proposed as a solution, but despite huge fluorescence enhancement having been obtained with these structures, the brightness generally remains below 1 million photons/s/molecule. Therefore, the improvement of temporal resolution is overlooked. This article presents a method for achieving high temporal resolution in single-molecule fluorescence techniques using plasmonic nanoantennas, specifically optical horn antennas. This work demonstrates about 90% collection efficiency of the total emitted light, reaching a high fluorescence brightness of 2 million photons/s/molecule in the saturation regime. This enables observations of single molecules with microsecond binning time and fast fluorescence correlation spectroscopy measurements. This work expands the applications of plasmonic antennas and zero-mode waveguides in the fluorescence saturation regime toward brighter single-molecule signal, faster temporal resolutions, and improved detection rates to advance fluorescence sensing, DNA sequencing, and dynamic studies of molecular interactions.