Emission and excitation contributions to enhanced single molecule fluorescence by gold nanometric apertures

We detail the role of single nanometric apertures milled in a gold film to enhance the fluorescence emission of Alexa Fluor 647 molecules. Combining fluorescence correlation spectroscopy and lifetime measurements, we determine the respective contributions of excitation and emission in the observed enhanced fluorescence. We characterize a broad range of nanoaperture diameters from 80 to 310 nm, and highlight the link between the fluorescence enhancement and the local photonic density of states. These results are of great interest to increase the effectiveness of fluorescence-based single molecule detection and to understand the interaction between a quantum emitter and a nanometric metal structure. (C) 2008 Optical Society of America.