Directional control of molecular fluorescence with bull's eye apertures

The authors report that gold nanoapertures surrounded by periodic corrugations transform standard molecules into bright unidirectional fluorescence sources. The authors obtain enhancement factors of the fluorescence rate per molecule up to 75 fold simultaneously with a directional emission of the fluorescence into a narrow angular cone into a cone of ±15° in the direction normal to the sample plane. The bright emission and narrow directionality enable the detection of single molecules with a low numerical aperture objective, and improve the effectiveness of fluorescence-based applications.