Quantifying fluorescence enhancement for slowly diffusing single molecules in plasmonic near fields

Abstract

Gold nanorods are extensively used for single-molecule fluorescence enhancement as they are easy to synthesize, bio-compatible, and provide high light confinement at their nanometer-sized tips. The current way to estimate fluorescence enhancement relies on binned time traces or on fluorescence correlation spectroscopy. We report on novel ways to extract the enhancement factor in a single-molecule enhancement experiment, avoiding the arbitrary selection of one or a few high-intensity burst(s). These new estimates for the enhancement factor make use of the whole distribution of intensity bursts or of the interphoton delay distribution, which avoids the arbitrary binning of the fluorescence intensity time traces. We present experimental results on the bi-dimensional case, experimentally achieved using a lipid bilayer to support the diffusion of fluorophores. We support our findings with histograms of fluorescence bursts and with an analytical derivation of the interphoton delay distribution of (nearly) immobilized emitters from the fluorescence intensity profile.

Quantum Yield Limits for the Detection of Single-Molecule Fluorescence Enhancement by a Gold Nanorod

“…The intensities of the bursts in the time traces depend on the orientation and spatial position of the molecules with respect to the gold nanorods during their residence within the hot spot. As an approximation, we represented the maximum enhanced fluorescence as the largest intensity of the bursts in the time trace, subtracting the background . Those maximum bursts are around 55 counts/ms, whereas the background is 16 counts/ms.…”

“…As an approximation, we represented the maximum enhanced fluorescence as the largest intensity of the bursts in the time trace, subtracting the background. 45 Those maximum bursts are around 55 counts/ ms, whereas the background is 16 counts/ms. To get the enhancement factor, we evaluated the fluorescence signal of one NDI-2TEG-3T molecule from a high-concentration solution (50 μM) by recording the fluorescence signal under the same experimental conditions but on an area without a nanorod.…”

Plasmonic Enhancement of Two-Photon-Excited Luminescence of Single Quantum Dots by Individual Gold Nanorods

“…However, there are other alternative methods to obtain the enhancement factor from the same type of experimental data, leading to similar results. 41 …”

Label-Free Plasmonic Detection of Untethered Nanometer-Sized Brownian Particles

“…We think this reflects the variation in near-field distributions of individual gold nanorods and shows the promise of our method for their characterization. Despite these differences, individual nanorods, once calibrated with a standard or an appropriate optical technique, such as enhanced fluorescence, 36 may be used for the accurate sizing of analytes. Furthermore, we have demonstrated that our system is capable of recognizing single analyte particles with 5 nm diameter at lower concentration levels of ∼10 nM.…”