Fluorescence Of Dye Molecules Research Articles

Plasmon-enhanced two photon excited emission from edges of one-dimensional plasmonic hotspots with continuous-wave laser excitation.

One-dimensional junctions between parallelly and closely arranged multiple silver nanowires (NWs) exhibit a large electromagnetic (EM) enhancement factor (FR) owing to both localized and surface plasmon resonances. Such junctions are referred to as one-dimensional (1D) hotspots (HSs). This study found that two-photon excited emissions, such as hyper-Rayleigh, hyper-Raman, and two-photon fluorescence of dye molecules, are generated at the edge of 1D HSs of NW dimers with continuous-wave near-infrared (NIR) laser excitation and propagated through 1D HSs; however, they were not generated from the centers of 1D HSs. Numerical EM calculations showed that FR of the NIR region for the edges of 1D HSs was larger than that for the centers by ∼102 times, resulting in the observation of two-photon excited emissions only from the edge of 1D HSs. The analysis of the NW dimer gap distance dependence of FR revealed that the lowest surface plasmon (SP) mode, compressed and localized at the edges of 1D HSs, was the origin of the large FR in the NIR region. The propagation of two-photon-excited emissions was supported by the higher-order coupled SP mode.

Effect of Spheroidal Nanoparticles on the Fluorescence of Dye Molecules and Adsorbed MEH-PPV Macrochains in Solutions

Effect of Spheroidal Nanoparticles on the Fluorescence of Dye Molecules and Adsorbed MEH-PPV Macrochains in Solutions

Effect of Spheroidal Nanoparticles on the Fluorescence of Dye Molecules and Adsorbed MEH–PPV Macrochains in Solutions

Effect of Spheroidal Nanoparticles on the Fluorescence of Dye Molecules and Adsorbed MEH–PPV Macrochains in Solutions

Distance dependence of plasmon-enhanced fluorescence and delayed luminescence of molecular planar nanostructures

The distance dependence of the plasmon-accelerated decay of excited singlet and triplet states of Eosin molecules was studied. Layered films of dye were prepared using the Langmuir-Blodgett technology on the surface of silver island films. The plasmon effect manifests itself in an increase in the intensity and a decrease in the lifetimes of fluorescence, delayed fluorescence and phosphorescence of the dye films with metal nanoparticles. It is shown that the optimal distance at which the maximum enhancement of all luminescence types was achieved is equal to 6–8 nm and approximately coincides with the Förster radius of the nonradiative inductive-resonance process. A proposed mathematical model is in agreement with the experimental data. From the model it is follows that the distance dependences of the long-lived luminescence intensity are qualitatively similar to the distance dependence of the fluorescence of dye molecules on the metal island films.

Amyloidophilic Molecule Interactions on the Surface of Insulin Fibrils: Cooperative Binding and Fluorescence Quenching

Protein aggregation into insoluble fibrillar aggregates is linked to several neurodegenerative disorders, such as Alzheimer’s or Parkinson’s disease. Commonly used methods to study aggregation inhibition or fibril destabilization by potential drugs include spectroscopic measurements of amyloidophilic dye molecule fluorescence or absorbance changes. In this work we show the cross-interactions of five different dye molecules on the surface of insulin amyloid fibrils, resulting in cooperative binding and fluorescence quenching.

A Study of Plasmon-Coupled Fluorescence of Rhodamine 6G on Thin Nickel Films

Plasmon-coupled luminescence of rhodamine 6G dye molecules on a thin nickel film has been studied experimentally and theoretically. The spatial distribution of fluorescence of dye molecules, which is calculated using the transfer matrix method for describing flat-layered media, is in good agreement with the experimental diagrams obtained for the spatial distribution of radiation with different polarization. The coupling efficiency between the luminophore and nickel film plasmons is experimentally determined.

Исследование плазмонно-связанной флуоресценции родамина 6Ж на тонких никелевых пленках

The plasmon-coupled luminescence of rhodamine 6G dye molecules on a thin nickel film was experimentally and theoretically studied. The spatial distribution of the fluorescence of dye molecules, calculated using the transfer matrix method for the description of plane-layered media, agrees well with the experimental diagrams obtained for the spatial distribution of radiation of different polarization. The efficiency of the coupling of the fluorophor with the plasmons of a nickel film has been experimentally established.

Metal-Enhanced Fluorescence: Wavelength-Dependent Ultrafast Energy Transfer

The fluorescence of dye molecules often shows a strong increase in intensity near metal surfaces or nanoparticles. The excited-state dynamics of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) in the presence of a silver island film (SIF) were explored by femtosecond transient absorption spectroscopy. Under 403 nm excitation, we found clear differences in the excited-state spectra and kinetics of DCM with the SIF. From the analysis of the emission kinetics of DCM, an additional process with a 40–60 ps time constant was distinguished, which was hypothesized to be surface plasmon-coupled fluorescence. This ultrafast process for 403 nm excitation was confirmed as ultrafast energy transfer directly from the surface plasmon of the SIF to DCM. Under 480 nm excitation, no such ultrafast process was observed, but a constant increase in the emission intensity by ∼10% due to the increased electric field of the silver nanoparticles occurred.

CuII-selective bispidine–dye conjugates

The substitution of tetradentate bispidine ligands with rhodamine and cyanine dye molecules, coupled to an amine donor, forming an amide as potential fifth donor, is described. Bispidines are known to lead to very stable CuII complexes, and the coordination to CuII was expected to efficiently quench the fluorescence of dye molecules. However, at physiological pH the amide is not coordinated, as shown by titration experiments and crystallographic structural data of three possible isomers of these complexes. This may be due to the specific cavity shape of bispidines and the Jahn–Teller lability of the CuII center. While CuII coordination in aqueous solution leads to efficient fluorescence quenching, experiments show that the complex stabilities are not large enough for CuII sensing in biological media, and possibilities are discussed, how this may be achieved by optimized bispidine–dye conjugates.

The mutual influence of two different dyes on their sensitized fluorescence (cofluorescence) in nanoparticles from complexes

We have studied the fluorescence sensitization and quenching for pairs of different dyes simultaneously incorporated into nanoparticles from complexes M(diketone)3phen, where M(III) is La(III), Lu(III), or Sc(III); diketone is p-phenylbenzoyltrifluoroacetone (PhBTA) or naphthoyltrifluoroacetone (NTA); and phen is 1,10-phenanthroline. We have shown that, upon formation of nanoparticles in the solution in the presence of two dyes the concentrations of which are either comparable with or lower than the concentration of nanoparticles (<20 nM), the intensities of the sensitized fluorescence of dyes in nanoparticles in binary solutions and in solutions of either of the dyes coincide. We have found that the intensity of sensitized fluorescence of small (<20 nM) concentrations of rhodamine 6G (R6G) or Nile blue (NB) increases by an order of magnitude upon simultaneous introduction into nanoparticles of 1 μM of coumarin 30 (C30), while the intensity of fluorescence of C30 sensitized by complexes decreases by an order of magnitude. The same effect is observed as 1 μM of R6G are introduced into nanoparticles with NB ([NB] ≤ 20 nM). The increase in the fluorescence of dye molecules upon their incorporation from the solution into nanoparticles from complexes is noticeably lower than that expected from the proposed ratio of concentrations of complexes and dyes in nanoparticles. Analysis of the obtained data indicates that the introduction of large concentrations of C30 or R6G dyes into nanoparticles makes it possible to prevent large energy losses due to impurities or upon transition to a triplet state that arises during the migration of the excitation energy over S1 levels of complexes. Energy accumulated by these dyes is efficiently transferred to another dye that is present in the solution at lower concentrations and that has a lower-lying S1 level, which makes it possible to increase its fluorescence by an order of magnitude upon its incorporation into nanoparticles.

Surface plasmon-enhanced lasing in dye-doped cholesteric liquid crystals

This study shows the results of a photonic band-edge laser using dye-doped cholesteric liquid crystals (CLCs) combined with silver (Ag) nanoparticles. When the Ag nanoparticle surface plasmon resonance wavelength matched the excitation source wavelength, the large optical fields provided by surface plasmons increased the fluorescence of dye molecules by enhancing the molecular excitation rate, achieving a low lasing threshold and high pumping efficiency.

Enhanced downconversion of UV light by resonant scattering of aluminum nanoparticles

Metallic nanoparticles are known to enhance nonlinear optical processes due to a local enhancement of the optical field. This strategy has been proposed to enhance downconversion in thin film solar cells, but has various disadvantages, among which is the fact that the enhancement occurs only in a tiny volume close to the particles. We report on a very different physical mechanism that can lead to significant downconversion enhancement, namely, that of resonant light scattering, and which is a large volume effect. We show that only a tiny amount of resonantly scattering metallic (aluminum) nanoparticles is enough to create a significant enhancement of the fluorescence of dye molecules in the visible wavelength range. The strategy can be applied in general to increase the emission of UV-absorbing constituents, and is of particular use for solar energy.

Surface Plasmon Enhanced Fluorescence of Dye Molecules on Metal Grating Films

Fluorescence enhancement of Rhodamine 6G (R 6G) molecules with a maximal enhancement factor of more than 30-fold was observed on Ag grating films. The enhancement mechanisms arise from both the surface plasmon polariton (SPP) enhanced absorption and surface plasmon coupled emission (SPCE). Time-resolved transient absorption spectroscopy was carried out to first experimentally confirm the SPP-enhanced absorption spectra of R 6G and its angle dependence on metal gratings, which cannot be directly obtained from conventional steady-state measurements. Combined with photoluminescence measurements, we observed how the contributions from two enhancement mechanisms to fluorescence emission varied with excitation incident angle and grating period. For larger grating period, the SPP-enhanced absorption becomes weaker and SPCE turns to the dominant mechanism for fluorescence enhancement. The wavelength resolution ability of SPCE makes it useful for potential applications such as wavelength-ratiometric measurements a...

Sensitization of fluorescence of dye molecules in nanoparticles of metal complexes

We studied the dependence of absorption and fluorescence spectra of complexes of Al, In, Sc, Y, and La with dibenzoylmethane and naphthoyltrifluoroacetone, as well as the dependence of sensitized fluorescence of dyes in nanoparticles of these complexes, in relation to the water pH, the ratio between ions and diketones, and the ion selection. We showed that the ability of complexes of ions to form nanoparticles that efficiently sensitize dye molecules incorporated into them is determined by stability constants of these ions with organic ligands and by their ability to compete with the formation of hydroxy complexes of these ions. We found that nanoparticles consist of diketonates of different compositions and that Nile red incorporated into nanoparticles is an indicator of the dependence of the composition of nanoparticles on the selection of the central ion of complexes and conditions of their formation. We revealed that complexes M(diketone)(OH)2 self-assemble into nanoparticles with an admixture of dye molecules and efficiently sensitize dyes upon excitation into absorption bands of complexes. We showed that, at concentrations of rhodamine 6G in water smaller than 50 nM, the use of a solution that contains 50 μM of Al(III), In(III), or Sc(III) + 50 μM of naphthoyltrifluoroacetone makes it possible to increase the sensitivity of the luminescence analysis by 20-fold for the presence of rhodamine 6G in an aqueous solution.

Surface plasmon resonance of gold nanoparticles assemblies at liquid | liquid interfaces

Surface plasmon resonance (SPR) was observed when a planar close-packed assembly of gold nanoparticles (Au NPs) is adsorbed at the water|1,2-dichloroethane interface. Aqueous gold nanoparticles, 13 or 16 nm in diameter, are deposited at the interface by adding methanol to form a close-packed film with a visible gold mirror reflectance. By total internal reflection of a light beam on the interface, the angular dependence of the interfacial reflectivity was measured in a pseudo-Kretschmann configuration and compared to Fresnel simulations for a homogeneous gold film. The experimental angles for minimum reflectivity were found to match the simulated values. Then, the fluorescence of dye molecules co-adsorbed within 13 and 16 nm gold nanoparticles assemblies at the liquid|liquid interface was measured. The fluorescence intensity under SPR is revealed to be much greater than under total internal reflection conditions, yielding an enhancement factor of approximately 30 and 50 for 13 and 16 nm Au NPs assemblies, respectively. Also, the fluorescence lifetime was found to decrease under SPR conditions.

Nanoparticle-Mediated Nonfluorescent Bonding of Microspheres to Atomic Force Microscope Cantilevers and Imaging Fluorescence from Bonded Cantilevers with Single Molecule Sensitivity

A technique to attach silica and glass microspheres onto silicon or silicon nitride cantilevers using silica nanoparticle sol-gel chemistry is presented and a method to image the fluorescence background from the bonded cantilevers with single molecule sensitivity is described. The silica nanoparticles polymerize to form a highly branched network that covalently link the microsphere and cantilever together. The bonding is carried out at room temperature which preserves the integrity of the cantilevers and their reflective coating. Comparison of cantilever and single dye molecule fluorescence demonstrates that the cantilevers are nonfluorescent at the single molecule level.

Plasmon-enhanced fluorescence of dye molecules

Enhanced fluorescence from Rhodamine 6G (R6G) mixed with gold colloids has been observed. We used fluorescence microscopy to correlate the fluorescence intensity of the dyes with the localized surface plasmon resonance (LSPR) spectra of the gold nanoparticles to which they are attached. Spectroscopic studies show that a 2.8-fold amplification of the fluorescence signal in presence of colloidal Au nanoparticles (GNP) was observed in resonance with plasmons. Such fluorophore–metal complex presents a unique opportunity for developing a new class of contrast agents for optical imaging and fluorescence based sensing, having a great potential for applications in the fields of medical diagnostics and biotechnology.

Compound Cellular Imaging of Laser Scanning Confocal Microscopy by Using Gold Nanoparticles and Dyes.

Combining the scattered light of gold nanoparticles (GNPs) and the fluorescence of dye molecules, a compound cellular imaging of laser scanning confocal microscopy (LSCM) is obtained. The human breast cancer cell line (MDA-MB-435S, BCRC 60429) is used for experiment. These cells are incubated with a glucose medium containing GNPs for 26 hours, and then are stained by Prodium Iodide (PI) for their nuclei. By using a single laser to illuminate these cells and adjusting the ranges of two bandpass filters for the detection, the scattered light from the GNPs and the fluorescence of PI can be induced simultaneously, but be detected separately without crosstalk. Furthermore, a compound cellular image can be obtained by merging the two images of the expressions of GNP and PI together. From the TEM images of these cells, it is observed that GNPs are aggregated in the vesicles of the cytoplasm due to the cell's endocytosis. The aggregation of GNPs makes the surface plasmon resonance band of GNPs broadened, so that strong scattered light from GNPs can be generated by the illumination of different-wavelength lasers (458, 488, 514, 561, and 633 nm).

Enhanced light extraction from emitters close to clusters of resonant plasmonic nanoantennas

We perform time-resolved fluorescence spectroscopy on clusters of plasmonic nanoantennas covered with a dye–polymer mixture. Dimer antenna structures were fabricated consisting of two interacting gold nanorods with varying lengths and interparticle separation. By combining four individual antennas into a cluster within a diffraction limited spot size, we can couple out half of the dye molecule fluorescence via antenna plasmons. Two-dimensional confocal fluorescence lifetime scans visualize the spontaneous emission enhancement of the molecular fluorescence around the antenna clusters.

Controlling the Fluorescence Resonant Energy Transfer by Photonic Crystal Band Gap Engineering

The fluorescence of dye molecules embedded in a photonic crystal is known to be inhibited by the presence of a pseudo-gap acting in their emission range. Here we present the first account of the influence that an incomplete photonic band gap or pseudo-gap has on the fluorescence emission and fluorescence resonant energy transfer. By inserting synthetic, donor (D)−acceptor (A)-labeled oligonucleotide structures in self-organized colloidal photonic crystals, we were able to measure simultaneously the emission spectra and lifetimes of both donor and acceptor. Our results clearly show an inhibition of the donor emission together with an enhancement of the acceptor emission spectra, indicating improved energy transfer from donor to acceptor. These results are mainly attributed to a decrease of the number of available photonic modes for radiative decay of the donor in a photonic crystal in comparison to that of the effective homogeneous medium. The fluorescence decay parameters are also dominated by the pseudo-gap acting on the energy-transfer efficiency.