Large single-molecule fluorescence enhancements produced by a bowtie nanoantenna

Owing to the size mismatch between light and nanoscale objects such as single molecules, it is important to be able to control light–molecule interactions 1 , 2 , 3 , 4 . Plasmonic nanoantennas create highly enhanced local fields when pumped resonantly, leading to increased Raman scattering 5 , but whether fluorescence enhancement occurs depends upon a variety of factors. Although sharp metal tips 6 and colloids 7 , 8 can enhance fluorescence, the highly enhanced optical fields of lithographically fabricated bowtie nanoantennas 9 provide a structure that is more controllable and amenable to integration. Using gold bowties, we observe enhancements of a single molecule's fluorescence up to a factor of 1,340, ten times higher than reported previously 7 , 8 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 . Electromagnetic simulations reveal that this is a result of greatly enhanced absorption and an increased radiative emission rate, leading to enhancement of the intrinsic quantum efficiency by an estimated factor of nine, despite additional non-radiative ohmic effects. Bowtie nanoantennas thus show great potential for high-contrast selection of single nanoemitters. A 1,340-fold increase in single-molecule fluorescence has been observed from a lithographically fabricated gold bowtie nanoantenna — approximately an order of magnitude greater than that achieved in previous reports on such structures. The improvement results from an estimated ninefold increase in quantum efficiency, caused by enhanced absorption and an increased radiative emission rate.