Distance and Plasmon Wavelength Dependent Fluorescence of Molecules Bound to Silica-Coated Gold Nanorods

Abstract

Plasmonic nanoparticles can strongly interact with adjacent fluorophores, resulting in plasmon-enhanced fluorescence or fluorescence quenching. This dipolar coupling is dependent upon nanoparticle composition, distance between the fluorophore and the plasmonic surface, the transition dipole orientation, and the degree of spectral overlap between the fluorophore's absorbance/emission and the surface plasmon band of the nanoparticles. In this work, we examine the distance and plasmon wavelength dependent fluorescence of an infrared dye ("IRDye") bound to silica-coated gold nanorods. Nanorods with plasmon band maxima ranging from 530 to 850 nm are synthesized and then coated with mesoporous silica shells 11-26 nm thick. IRDye is covalently attached to the nanoparticle surface via a click reaction. Steady-state fluorescence measurements demonstrate plasmon wavelength and silica shell thickness dependent fluorescence emission. Maximum fluorescence intensity, with approximately 10-fold enhancement, is observed with 17 nm shells when the nanorod plasmon maximum is resonant with IRDye absorption. Time-resolved photoluminescence reveals multiexponential decay and a sharp reduction in fluorescence lifetime with decreasing silica shell thickness and when the plasmon maximum is closer to IRDye absorption/emission. Control experiments are carried out to confirm that the observed changes in fluorescence are due to plasmonic interactions, is simply surface attachment. There is no change in fluorescence intensity or lifetime when IRDye is bound to mesoporous silica nanoparticles. In addition, IRDye loading is limited to maintain a distance between dye molecules on the surface to more than 9 nm, well above the Förster radius. This assures minimal dye-dye interactions on the surface of the nanoparticles.

Recent Progress on Plasmon-Enhanced Fluorescence

“…Recently, several works have reported that the result of investigations of the distance and plasmon wavelength dependent fluorescence of fluorophore via nanorod or nanoparticle substrate [85,86]. In particular, core-shell configuration, precisely controlling the distance between fluorophore and plasmonic nanostructure, have been widely used in the investigation of PEF effect recently [87][88][89][90]. It is found that by introduction of silica shell with various thicknesses to isolated fluorophore Au nanoparticles (AuNPs) and four different target molecules with different absorbance properties, the investigation of fluorescence quenching effect from complete quenching to no coupling was comprehensively carried out.…”

“…It is found that by introduction of silica shell with various thicknesses to isolated fluorophore Au nanoparticles (AuNPs) and four different target molecules with different absorbance properties, the investigation of fluorescence quenching effect from complete quenching to no coupling was comprehensively carried out. It is found that the energy transfer from the fluorophore to the metal substrate plays a critical role in fluorescence quenching phenomenon, as shown in Figure 11 [89].…”

Review—Organic-Inorganic Hybrid Functional Materials: An Integrated Platform for Applied Technologies

“…181 Among the most investigated strategies is the use of core shell nanostructures with metal core and silica based shell, which provides also a good possibility of spacing control between the dyes and the metallic surface. [183][184][185][186][187][188][189][190][191][192] The dye can be either directly incorporated in the silica shell during the synthesis of post-grafted at the surface of the silica. M. A. Noginov used this configuration to generate coreshell structure functionalized at the surface by Oregon green 488 fluorophore encapsulated in the outer silica shell.…”

Controlled Crystallization of Gold Nanocrystals

“…The adjustment of plasmon resonance peaks has been extensively reported [41,41,43], as well as highly sensitive SPR detection methods using functionalized anisotropic Au NPs [42,43]. The SPR peaks can be altered by variation of the Au NR aspect ratios, for example changing the CTAB concentration [44].…”