Investigating metal‐enhanced fluorescence effect on fluorescein by gold nanotriangles and nanocubes using time‐resolved fluorescence spectroscopy

Abstract

Gold nanotriangles (AuNTs) and nanocubes (NCs) coated with silica shell and fluorescein were synthesized to study the effects of metal‐enhanced fluorescence. The interaction between gold nanoparticles (GNPs) and fluorescein with silica shells of different thicknesses as spacers was investigated by using time‐resolved fluorescence spectroscopy. From the biexponential decay of fluorescence of fluorophore and the kinetic mechanism for the interaction, we obtained the rate constants of energy transfer processes. Both energy transfer rates from fluorophore to the bright and dark modes of gold nanoparticles decreased with distance d (= silica thickness) with a dependence ∝ d−n and n ≈ 2. The rate constant of nanosurface energy transfer kNEST, considering dipolar interaction between fluorophore and metal surface, has an estimated value 1.7 times slower at d = 9 nm and about four times slower at 25 nm than the obtained rate constant for energy transfer from fluorophore to GNP dipolar mode in the AuNT system. For the AuNC system, the rate constants are greater than the AuNT system because of better spectral overlap between emission of fluorescein and surface plasmon resonance.

A Review on Gold Nanotriangles: Synthesis, Self-Assembly and Their Applications

“…The LSPR modes in AuNTs were proven to locate at the corners, edges and two faces (up/down) depending on the wavelength of the incident light. As a result, the LSPR spectrum of AuNTs showed two plasmonic peaks with a typical band above 600 nm and another weak shoulder band around 530 nm [38,39]. The LSPR band of AuNTs could be well tuned by controlling their edge length, thickness and ratio.…”