In this short letter, we describe the effects of low temperature on the Metal-Enhanced Fluorescence (MEF) phenomenon. Fluorophores
close to Silver Island Films (SiFs) show on average two- to ten-fold enhancements in their fluorescence signatures at room
temperature. However, at 77 K, we have observed that MEF is even more pronounced as compared to an identical glass control
sample. We also demonstrate that the further enhancements in MEF occur at low temperature over a range of visible wavelengths
for different fluorophores, for both SiFs and 20 nm surface deposited gold colloids. 相似文献
In this letter we report further findings on the ability of an applied direct current to modulate Metal-Enhanced Fluorescence
(MEF). Fluorophores in close-proximity to just-continuous silver films (JCS) show significantly enhanced fluorescence intensities. However, when a current is applied to the films,
the enhanced fluorescence can be gated in a manner that depends on both the fluorophore concentration, the magnitude of the
applied current and the extent of the protein mono to multi-layer surface coverage. Our results are consistent and indeed
further support our previous hypothesis and model that fluorophore-metal near-field interactions can be influenced by an applied
direct current. 相似文献
In this Rapid Communication, we report the first observation of Metal-Enhanced singlet oxygen generation (ME1O2). Rose Bengal in close proximity to Silver Island Films (SiFs) can generate more singlet oxygen, a three-fold increase observed,
as compared to an identical glass control sample but containing no silver. The enhanced absorption of the photo-sensitizer,
due to coupling to silver surface plasmons, facilitates enhanced singlet oxygen generation. The singlet oxygen yield can potentially
be adjusted by modifying the choice of MEF (Metal-Enhanced Fluorescence) & MEP (Metal Enhance Phosphorescence) parameters,
such as distance dependence for plasmon coupling and wavelength emission of the coupling fluorophore. This is a most helpful
observation in understanding the interactions between plasmons and lumophores, and this approach may well be of significance
for singlet oxygen based clinical therapy. 相似文献
We report the first findings of Metal-Enhanced Fluorescence (MEF) from modified plastic substrates. In the past several years our laboratories have reported the favorable effects of fluorophores in close proximity to silver nanoparticles. These effects include, enhanced fluorescence intensities, (increased detectability), and reduced lifetimes, (enhanced fluorophore photostability). All of these reports have featured silver nanostructures and fluorophores which have been immobilized onto clean glass or quartz surfaces. In this report we show how plastic surfaces can be modified to obtain surface functionality, which in turn allows for silver deposition and therefore metal-enhanced fluorescence of fluorophores positioned above the silver using a protein spacer. Our findings show that plastic substrates are ideal surfaces for metal-enhanced phenomena, producing similar enhancements as compared to clean glass surfaces. Subsequently, we speculate that plastic substrates for MEF will find common place, as compared to the more expensive and less versatile traditional silica based supports. 相似文献
Gold decorated NaYF4:Yb,Er/NaYF4/silica (core/shell/shell) upconversion (UC) nanoparticles (~70–80 nm) were synthesized using tetraethyl orthosilicate and
chloroauric acid in a one-step reverse microemulsion method. Gold nanoparticles (~6 nm) were deposited on the surface of silica
shell of these core/shell/shell nanoparticles. The total upconversion emission intensity (green, red, and blue) of the core/shell/shell
nanoparticles decreased by ~31% after Au was deposited on the surface of silica shell. The upconverted green light was coupled
with the surface plasmon of Au leading to rapid heat conversion. These UC/silica/Au nanoparticles were very efficient to destroy
BE(2)-C cancer cells and showed strong potential in photothermal therapy. 相似文献
The first observation of Metal-Enhanced Fluorescence (MEF) from large gold colloids is presented. Gold colloids, 40 and 200 nm
diameter, were deposited onto glass substrates in a homogeneous fashion. The angular-dependent fluorescence emission of FITC-HSA,
adsorbed onto gold colloids, was measured on a rotating stage which was used to evaluate MEF at all spatial angles. The emission
intensity of FITC-HSA was found to be up to 2.5-fold brighter than the emission on bare glass substrates at an angle of 270
degrees. This is explained by the Radiating Plasmon Model, whereby the combined system, composed of the fluorophore and the
metal colloids, emits with the photophysical characteristics of the fluorophore, after the excitation and the partial radiationless
energy transfer between the excited states of the fluorophore and the surface plasmons of the gold colloids. The fluorescence
enhancement was found to be higher with 200 nm gold colloids as compared to 40 nm colloids due to the increased contribution
of the scattering portion of the 200 nm gold colloid extinction spectrum. These observations suggest that gold colloids could
be used in MEF applications, offering more stable surfaces than the commonly used silvered surfaces, for applications requiring
longer term storage and use. 相似文献
We describe a fundamental observation in Metal-Enhanced Fluorescence (MEF), which has become a leading technology in the life sciences today, namely, how the lifetime of fluorophores near-to metallic plasmon-supporting silver islands/nanoparticles, modulates as a function of excitation power irradiance. This finding is in stark contrast to that observed in classical far-field fluorescence spectroscopy, where excitation power does not influence fluorophore radiative decay/lifetime. 相似文献
Water dispersible boron nanoparticles have great potential as materials for boron neutron capture therapy of cancer and magnetic resonance imaging, if they are prepared on a large scale with uniform size and shape and hydrophilic modifiable surface. We report the first method to prepare spherical, monodisperse, water dispersible boron core silica shell nanoparticles (B@SiO2 NPs) suitable for aforementioned biomedical applications. In this method, 40 nm elemental boron nanoparticles, easily prepared by mechanical milling and carrying 10-undecenoic acid surface ligands, are hydrosilylated using triethoxysilane, followed by base-catalyzed hydrolysis of tetraethoxysilane, which forms a 10-nm silica shell around the boron core. This simple two-step process converts irregularly shaped hydrophobic boron particles into the spherically shaped uniform nanoparticles. The B@SiO2 NPs are dispersible in water and the silica shell surface can be modified with primary amines that allow for the attachment of a fluorophore and, potentially, of targeting moieties.
Silver nanoparticles were synthesized by chemical reduction of silver ions by sodium borohydride in the presence of poly-(N)-vinyl-2-pyrrolidone in solution of short chain alcohols. The nanoparticles are stable in 2-propanol, and the average diameter
of the Ag colloid obtained in this solvent is about 6 nm. The photophysical properties of acridinium and coumarin dyes in
2-propanol are affected by the presence of silver nanoparticles. The interaction of silver nanoparticles with acridinium derivative
leads to a spectral change of its intramolecular charge transfer (ICT) absorption band. The dye emission increases suddenly
with the initial addition of the Ag metal nanoparticles, but at a high concentration of the colloid, static fluorescence quenching
occurs with a progressive decrease of the fluorescence efficiency. Amino coumarin fluorescence is only quenched by the silver
nanoparticles in solution. 相似文献
Using T-matrix method, plasmon resonance properties of metal core–shell nanoparticles are systematically investigated. It is shown that dielectric/metal core–shell structure may be excited stronger at resonance than metal/dielectric and hetero-metal ones, but the resonance states are extremely sensible to the layers thickness. For three-layer nanospheres, resonance properties will be dominated by a sub-10 nm silver outermost shell, while only weakened by a silica one. Finally, tiny eccentric distance between the centers of core and shell in eccentric two-layer nanoparticles may fundamentally change the resonance mode of nanoparticles, and results in higher local electrical field enhancement than concentric nanospheres. 相似文献
La0.45Ce0.45F3:Tb (10 mol% Tb) nanoparticles was synthesized via sonochemical method and then coated with silica (SiO2) shells through a microemulsion process, resulting in the formation of core/shell structured LaCeF3:Tb/SiO2 nanoparticles. The obtained core/shell LaCeF3:Tb/SiO2 nanoparticles are spherical and uniform in size (average size about 60 nm), strongly fluorescent, and long fluorescence lifetime
(1.87 ms). This kind of nanoparticles was water-soluble, which could be applied in biological labeling and other fields. 相似文献
Magnetic core/shell (CS) nanocomposites (MNCs) are synthesized using a simple method, in which a magnesium ferrite nanoparticle (MgFe2O4) is a core, and an amorphous silicon dioxide (silica SiO2) layer is a shell. The composition, morphology, and structure of synthesized particles are studied using X-ray diffraction, field emission electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), scattering electrophoretic photometer, thermogravimetric analysis (TGA), and Mössbauer spectroscopy. It is found that the MgFe2O4/SiO2 MNC has the core/shell structure formed by the Fe?O–Si chemical bond. After coating with silica, the MgFe2O4/SiO2 MNC saturation magnetization significantly decreases in comparison with MgFe2O4 particles without a SiO2 shell. Spherical particles agglomerated from MgFe2O4 nanocrystallites ~9.6 and ~11.5 nm in size function as cores coated with SiO2 shells ~30 and ~50 nm thick, respectively. The total size of obtained CS MNCs is ~200 and 300 nm, respectively. Synthesized CS MgFe2O4/SiO2 MNCs are very promising for biomedical applications, due to the biological compatibility of silicon dioxide, its sizes, and the fact that the Curie temperature is in the region required for hyperthermal therapy, 320 K. 相似文献
Obtaining small (<50 nm), monodispersed, well-separated, single iron oxide core–silica (SiO2) shell nanoparticles for biomedical applications is still a challenge. Preferably, they are synthesised by inverse microemulsion
method. However, substantial amount of aggregated and multicore core–shell nanoparticles is the undesired outcome of the method.
In this study, we report on the production of less than 50 nm overall size, monodispersed, free of necking, single core iron
oxide–SiO2 shell nanoparticles with tuneable shell thickness by a carefully optimized inverse microemulsion method. The high degree
of control over the process is achieved by understanding the mechanism of core–shell nanoparticles formation. By varying the
reaction time and precursor concentration, the thickness of silica layer on the core nanoparticles can be finely adjusted
from 5 to 13 nm. Residual reactions during the workup were inhibited by a combination of pH control with shock freezing and
ultracentrifuging. These high-quality tuneable core–shell nanocomposite particles exhibit superparamagnetic character and
sufficiently high magnetization with great potential for biomedical applications (e.g. MRI, cell separation and magnetically
driven drug delivery systems) either as-prepared or by additional surface modification for improved biocompatibility. 相似文献
Bactericidal activity of high concentration Ag nanoparticles immobilized on surface of an aqueous sol–gel silica thin film was investigated against Escherichia coli and Staphylococcus aureus bacteria. Size of the surface nanoparticles was estimated in the range of 35–80 nm by using atomic force microscopy. Due to accumulation of the silver nanoparticles at near the surface (at depth of 6 nm and about 40 times greater than the silver concentration in the sol), the synthesized Ag–SiO2 thin film (with area of 10 mm2) presented strong antibacterial activities against E. coli and S. aureus bacteria with relative rate of reduction of the viable bacteria of 1.05 and 0.73 h−1 for initial concentration of about 105 cfu/ml, respectively. In addition, the dominant mechanism of silver release in long times was determined based on water diffusion in surface pores of the silica film, unlike the usual diffusion of water on the surface of silver-based bulk materials. Therefore, the Ag nanoparticles embedded near the surface of the SiO2 thin film can be utilized in various antibacterial applications with a strong and long life activity. 相似文献
The controllable synthesis and characterization of novel thermally stable silver-based particles are described. The experimental approach involves the design of thermally stable nanostructures by the deposition of an interfacial thick, active titania layer between the primary substrate (SiO2 particles) and the metal nanoparticles (Ag NPs), as well as the doping of Ag nanoparticles with an organic molecule (Congo Red, CR). The nanostructured particles were composed of a 330-nm silica core capped by a granular titania layer (10 to 13 nm in thickness), along with monodisperse 5 to 30 nm CR-Ag NPs deposited on top. The titania-coated support (SiO2/TiO2 particles) was shown to be chemically and thermally stable and promoted the nucleation and anchoring of CR-Ag NPs, which prevented the sintering of CR-Ag NPs when the structure was exposed to high temperatures. The thermal stability of the silver composites was examined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Larger than 10 nm CR-Ag NPs were thermally stable up to 300 °C. Such temperature was high enough to destabilize the CR-Ag NPs due to the melting point of the CR. On the other hand, smaller than 10 nm Ag NPs were stable at temperatures up to 500 °C because of the strong metal-metal oxide binding energy. Energy dispersion X-ray spectroscopy (EDS) was carried out to qualitatively analyze the chemical stability of the structure at different temperatures which confirmed the stability of the structure and the existence of silver NPs at temperatures up to 500 °C. 相似文献
Luminescent core-shell europium(III)-silica nanoparticles were prepared using europium(III) chelate core structure and polyvinylpyrrolidone
synthesis strategy for silica shell. Europium(III):naphtoyltrifluoroacetone:trioctylphosphineoxide complex was spontaneously
agglomerated from organic solvent to water. Polyvinylpyrrolidone was adsorbed onto the core structure and stable silica shell
was synthesized using tetraethylorthosilicate. Nanosized particles with a diameter of 71 ± 5 nm and 11 nm shell thickness
were obtained with fluorescence decay rate of 517 μs and excitation and emission wavelengths of 334 and 614 nm, respectively. 相似文献
Ag@SnO2 core-shell nanoparticles dispersed in poly-(vinyl) alcohol films were fabricated on glass substrate by employing a dip-coating
technique. Synthesis of Ag@SnO2 nanoparticles with core-shell morphology is carried out by a soft-chemical technique in aqueous phase at 60°C. Formation
of core-shell structure is monitored by the red-shift of the surface plasmon band of Ag nanoparticles (from 390 to 410 nm)
in the UV-visible spectrum. These nanoparticles are deposited on the glass substrate. The structure and morphology of these
films were investigated by X-ray diffraction technique and field-emission transmission electron microscopy, respectively.
Optical properties of these pseudo-solids were studied by UV-visible spectroscopy. Surface plasmon spectrum of the core-shell
nanoparticles film remained unaltered with increase in the number of layers. However, silver nanoparticles films have shown
peak broadening and development of additional peaks with increase in the number of layers. Our investigations showed that
the surface plasmon band of the silver nanoparticles could be preserved by controlled deposition of the tin dioxide shell. 相似文献