Dielectric-loading approach for extra electric field enhancement and spatially transferring plasmonic hot-spots

Spectral and photophysical modifications of porphyrins attached to core-shell nanoparticles. Theory and experiment

Plasmonic nanostructures, of which gold nanoparticles are the most elementary example, owe their unique properties to localized surface plasmons (LSP), the modes of free electron oscillation. LSP alter significantly electromagnetic field in the nanostructure neighborhood (i.e., near-field), which can modify the electric dipole transition rates in organic emitters. This study aims at investigating the influence of Au@SiO₂core-shell nanoparticles on the photophysics of porphyrins covalently attached to the nanoparticles surface. Guided by theoretical predictions, three sets of gold nanoparticles of different sizes were coated with a silica layer of similar thickness. The outer silica surface was functionalized with either free-basemeso-tetraphenylporphyrin or its zinc complex. Absorption and emission bands of porphyrin overlap in energy with a gold nanoparticle LSP resonance that provides the field enhancement. Silica separates the emitters from the gold surface, while the gold core size tunes the energy of the LSP resonance. The signatures of weak-coupling regime have been observed. Apart from modified emission profiles and shortened S₁lifetimes, Q band part intensity of the excitation spectra significantly increased with respect to the Soret band. The results were explained using classical transfer matrix simulations and electronic states kinetics, taking into account the photophysical properties of each chromophore. The calculations could reasonably well predict and explain the experimental outcomes. The discrepancies between the two were discussed.

Extraordinary Fluorescence Enhancement in Metal-Dielectric Core-Shell Nanoparticles

We show that in metal-dielectric core-shell nanoparticles, unusually thick dielectric coatings can produce extreme fluorescence enhancement with an enhancement factor F̅ ≳ 3000 for emitters located on the surface or in the interior of the shell of Au@dielectric spherical particles under realistic conditions, even for the emitters with 100% intrinsic quantum yield. Thick dielectric coatings facilitate high-quality transverse electric (TE) multipole (l = 7) resonances which are shown as the major cause for the reported extraordinary values of F̅.

Widely tunable surface plasmon resonance and uniquely superior SERS performance of Au nanotube network films

Three-dimensional Au network films with flexibility and transferability were fabricated based on sputtering deposition onto electrospun nanofibers as a template. The films are constructed using long Au nanotubes that are cross-linked with each other and that have dense nanoparticles on the tube wall surface. The surface plasmon resonance (SPR) peaks for the films are tunable in a wide range, from visible light to the near-infrared region, by tuning the inner diameter and/or wall thickness of the nanotubes. Such structured film exhibits significant surface-enhanced Raman scattering (SERS) activity with good signal uniformity and stability, and possesses great potential in thein situdetection of trace organic pollutants on a solid surface by simple transferring. This study provides a Au film with a unique structure and widely tunable SPR forin situSERS sensing and other needs.