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

Abstract

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.

FRET Enhancement in Aluminum Zero‐Mode Waveguides

“…1c). These results stand in good agreement with numerical simulations [37,38] and the behavior expected from previous measurements on red fluorescent dyes [40,51]. The difference between the fluorescence enhancement factors for aluminum and gold ZMWs stems mainly from the 550 nm laser excitation intensity which is lower in gold ZMW due to the increased losses for gold permittivity at 550 nm [37,38,41,42] (the phenomena leading to the observation of enhanced fluorescence are discussed with more details below).…”

“…The time interval for fit is set to ensure that more than 85% of the detected count events are taken into account in the region of interest. As shown already in some of our earlier work [40,45,48] and by the results in Fig. 2a, a single exponential fit is a satisfactory approximation to the fluorescence decay traces in nanoapertures (Fig.…”

“…The shape parameter κ is fixed to κ = 5 for the confocal microscope from the PSF calibration, and kept as a free parameter for the fits in the ZMWs. As already noted in our previous works [40,51], this parameter converges towards values close to 1 in ZMWs.…”

“…The fluorescence enhancement η F for the isolated donor is quantified by burst intensity analysis or alternatively FCS (Fig. 1c) [40,51]. Below the fluorescence saturation regime, three phenomena contribute to the fluorescence enhancement η F : the gains in collection efficiency η κ , quantum yield η φ , and excitation intensity η exc , so that η F = η κ η φ η exc .…”

Fluorescence fluctuations analysis in nanoapertures: physical concepts and biological applications

“…Two recent studies have focused on the case of Alexa Fluor 647 dye (quantum yield in water solution 30%) and nanoapertures milled in gold Wlms Wenger et al 2008). Nanometric apertures milled in gold exhibit signiWcantly higher (50%) Xuorescence enhancement factors than apertures in aluminum, with a maximum enhancement of 12 for a 120-nm diameter aperture in gold, as shown in Fig.…”