Nano Bowties Pump Up Fluorescence

Bow-tie-shaped nanoantennae can boost the signal from individual fluorescent dye molecules, according to a new report. W. E. Moerner of Stanford University and coworkers achieve large enhancements in fluorescence from individual dye molecules embedded in a thin polymer film coated on gold bow-tie nanoantennae (Nature Photon., DOI: 10.1038/nphoton.2009.187). The bow-tie structures consist of a pair of triangles with a small gap between them. The dye molecules with the highest enhancement are optimally coupled to the bow ties; they have their dipole moment oriented along the nanoantenna’s long axis and are located in the middle of the bow tie’s gap. The largest enhancements—as much as a factor of 1,340—came from the antennae with the smallest gaps. Calculations show that although both high- and low-quantum-efficiency molecules benefit from the enhanced fields of the nanoantennae through increases in their absorption of light, low-quantum-efficiency molecules also benefit from an increase in their emission. Such antennae will allow scientists to focus on individual dye molecules in a microscopy sample or might function as single photon sources in optical communication devices.