Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods

Abstract

Enhancing the fluorescence of a weak emitter is important to further extend the reach of single-molecule fluorescence imaging to many unexplored systems. Here we study fluorescence enhancement by isolated gold nanorods and explore the role of the surface plasmon resonance (SPR) on the observed enhancements. Gold nanorods can be cheaply synthesized in large volumes, yet we find similar fluorescence enhancements as literature reports on lithographically fabricated nanoparticle assemblies. The fluorescence of a weak emitter, crystal violet, can be enhanced more than 1000-fold by a single nanorod with its SPR at 629 nm excited at 633 nm. This strong enhancement results from both an excitation rate enhancement of ∼130 and an effective emission enhancement of ∼9. The fluorescence enhancement, however, decreases sharply when the SPR wavelength moves away from the excitation laser wavelength or when the SPR has only a partial overlap with the emission spectrum of the fluorophore. The reported measurements of fluorescence enhancement by 11 nanorods with varying SPR wavelengths are consistent with numerical simulations.

Simple model for plasmon enhanced fluorescence correlation spectroscopy

“…This improvement is mostly due to geometric confinement of the detection volume. Nano-antennas [16,17] also localize fields in deep-sub-wavelength volumes but do not provide an effective suppression of the excitation focus in the solute, which reduces the benefits of the strong field confinement around the antenna in fluorescence fluctuation measurements unless the intensity enhancement at the antenna is very large. Several reports have recently claimed FCS enhancement in plasmon antennas, notably including the bow tie antenna [18] famous for its large field enhancement, as well as simple colloidal metal nanoparticles [19][20][21][22] or self assembled silver nano-islands [23].…”

In-Plane Plasmonic Antenna Arrays with Surface Nanogaps for Giant Fluorescence Enhancement

“…13 For crystal violet and Alexa Fluor 647, the fluorescence enhancement figures of merit amount to 300 and 420, respectively, and are the highest reported values to date. [8][9][10][11][12][13]16 The measured fluorescence enhancement factors come very close to the values predicted theoretically using the formula 41 This equation states that the fluorescence enhancement η F is the product of the excitation intensity enhancement in the nanogap I exc * /I exc , times the enhancement of the radiative decay rates Γ rad * /Γ rad , and a third term that depends on the initial quantum yield ϕ 0 of the fluorescent molecule and an additional decay rate Γ loss * describing the nonradiative energy transfer to the antenna's material induced by ohmic losses. Here we neglect the collection efficiency improvement brought by the antenna (back focal plane imaging confirms this assumption 10,42 ).…”

Reshaping anisotropic gold nanoparticles through oxidative etching: the role of the surfactant and nanoparticle surface curvature

“…20 Particularly, the longitudinal SPRs (LSPRs), which strongly depend on the aspect ratio of GNPs [1][2][3] , are promising for sensing and optical applications because of their sensitivity to the surrounding medium 4 and strong plasmon-related enhancements of optical signals 5,6 . 25 Many applications such as plasmon-enhanced spectroscopy, however, require precisely defined LSPR wavelength to achieve optimal performance [7][8][9] . Therefore, it is important to control the dimensions and shape anisotropy of GNPs to obtain well-defined LSPRs, tailored for specific applications.…”