Metal-Enhanced Fluorescence Platforms Based on Plasmonic Ordered Copper Arrays: Wavelength Dependence of Quenching and Enhancement Effects

Abstract

Ordered arrays of copper nanostructures were fabricated and modified with porphyrin molecules in order to evaluate fluorescence enhancement due to the localized surface plasmon resonance. The nanostructures were prepared by thermally depositing copper on the upper hemispheres of two-dimensional silica colloidal crystals. The wavelength at which the surface plasmon resonance of the nanostructures was generated was tuned to a longer wavelength than the interband transition region of copper (>590 nm) by controlling the diameter of the underlying silica particles. Immobilization of porphyrin monolayers onto the nanostructures was achieved via self-assembly of 16-mercaptohexadecanoic acid, which also suppressed the oxidation of the copper surface. The maximum fluorescence enhancement of porphyrin by a factor of 89.2 was achieved as compared with that on a planar Cu plate (CuP) due to the generation of the surface plasmon resonance. Furthermore, it was found that while the fluorescence from the porphyrin was quenched within the interband transition region, it was efficiently enhanced at longer wavelengths. It was demonstrated that the enhancement induced by the proximity of the fluorophore to the nanostructures was enough to overcome the highly efficient quenching effects of the metal. From these results, it is speculated that the surface plasmon resonance of copper has tremendous potential for practical use as high functional plasmonic sensor and devices.

Gold nanodisc arrays as near infrared metal-enhanced fluorescence platforms with tuneable enhancement factors

“…Most previous work on MEF, however, has focused on fluorophores emitting in the visible region, with only a limited number of studies investigating the NIR. 18,20,[25][26][27] Recently, gold (Au) nanocages microprinted into a defined structure with spatial control, allowed fluorescence enhancement in the NIR, but only by a factor of ~2-7. 26 Indeed, most of the recent work for the fluorescent enhancement of NIR dyes has been based on Au or silver (Ag) nanostructures, including nanorods, nanoshells and porous films obtained by dealloying.…”

Plasmon-induced charge separation at two-dimensional gold semishell arrays on SiO2@TiO2 colloidal crystals

“…[11][12][13][14][15][16][17][18][19][20][21] Transmission and absorption spectra of the 2D arrays can be easily tailored in the visible range and near infrared range by varying thickness and roughness of the semishells as well as dielectric properties and size of the spheres constituting the colloidal crystal. 12,15,16,20,21 Consequently, the metal semishell arrays have been applied to surface-enhanced Raman scattering (SERS), 11,17,[19][20][21] surface-enhanced fluorescence (SEF), 14,16,20 plasmonic refractometry, 15 and plasmonic enhancement of photocurrents. 18 Nevertheless, to the best of our knowledge, PICS behavior of metal semishell arrays has not yet been reported.…”

“…The difference in the coverage between the sputtered and evaporated semishells may be explained in terms of directionality of sputtered metal ions and evaporated metal atoms. Actually, the most of metal halfshell structures have been fabricated by evaporation, [14][15][16][17][18][19][20] while sputtering gives structures more like core-shell particles. 21 The optical absorption spectra of SiO 2 @TiO 2 colloidal crystals with and without Au semishells were collected by a spectrophotometer (V-670, JASCO) equipped with an integrating sphere.…”

“…Semishell arrays are known to be so stable that even copper can be used. 20 The stability would allow further improvement and functionalization by changing the metal species used for the semishell array.…”

High-throughput patterning of photonic structures with tunable periodicity

“…Periodic circular or linear patterns of nonmetallic and metallic submicrometer structures are of interest as waveguides and plasmonic cavities for sensing and integrated optical applications (20,21). The features patterned by RIPPLE are characterized by low surface roughness, high patterning selectivity, and small dispersion for periods <1 μm, characteristics that are relevant to the design of high-quality optical gratings.…”