Showing papers on "Fluorescence spectrometry published in 2004"

DNA-templated Ag nanocluster formation.

Abstract: The high affinity of Ag+ for DNA bases has enabled creation of short oligonucleotide-encapsulated Ag nanoclusters without formation of large nanoparticles. Time-dependent formation of cluster sizes ranging from Ag1 to Ag4/oligonucleotide were observed with strong, characteristic electronic transitions between 400 and 600 nm. The slow nanocluster formation kinetics enables observation of specific aqueous nanocluster absorptions that evolve over a period of 12 h. Induced circular dichroism bands confirm that the nanoclusters are associated with the chiral ss-DNA template. Fluorescence, absorption, mass, and NMR spectra all indicate that multiple species are present, but that their creation is both nucleotide- and time-dependent.

Digital photoswitching of fluorescence based on the photochromism of diarylethene derivatives at a single-molecule level.

Abstract: Photochromic reactions of diarylethene derivatives were detected at a single-molecule level by using a fluorescence technique. Fluorescent photoswitching molecules in which photochromic diarylethene and fluorescent bis(phenylethynyl)anthracene units are linked through an adamantyl spacer were synthesized, and switching of fluorescence upon irradiation with UV and visible light was followed in solution as well as on polymer films at the single-molecule level. Although in solution the fluorescence intensity gradually changed upon irradiation with UV and visible light, digital on/off switching between two discrete states was observed at the single-molecule level. The “on”- and “off”-times were dependent on the power of UV and visible light. When the power of UV and visible light was increased, the average on- and off-times became short in proportion to the reciprocal power of the light. The response-times were found to show distribution. The distribution of the on- and off-times is considered to reflect the ...

Lanthanide coordination polymers and their Ag+-modulated fluorescence.

Abstract: Four 3-D coordination polymers of lanthanide with a tetra(amino acid) ligand, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrapropionic acid (H4L, 1), were synthesized. The structure of the Gd(III) complex was characterized. The fluorescence of the Eu(III) complex can be modulated by Ag+.

A Fluorogenic Probe for the Copper(I)-Catalyzed Azide−Alkyne Ligation Reaction: Modulation of the Fluorescence Emission via 3(n,π*)−1(π,π*) Inversion

Abstract: Chemoselective ligation reactions represent a powerful approach for labeling of proteins or small molecules in a biological environment. We report here a fluorogenic probe that is activated by click chemistry, a highly versatile bio-orthogonal and chemoselective ligation reaction which is based on the azide moiety as the functional group. The electron-donating properties of the triazole ring that is formed in the course of the coupling reaction was effectively utilized to modulate the fluorescence output of an electronically coupled coumarin fluorophore. Under physiological conditions the probe is essentially nonfluorescent and undergoes a bright emission enhancement upon ligation with an azide. Time-resolved emission spectroscopy and semiempirical quantum-mechanical calculations suggest that the fluorescence switching is due to an inversion of the energy ordering of the emissive 1(pi,pi*) and nonemissive 3(n,pi*) excited states. The rapid kinetics of the ligation reaction render the probe attractive for a wide range of applications in biology, analytical chemistry, or material science.

Fluorescent polymeric AND logic gate with temperature and pH as inputs.

Abstract: We illustrate a general polymeric design of fluorescent logic gates, for example, AND, using temperature and pH as inputs.

Real-Time Measurements of Dissolved Oxygen Inside Live Cells by Organically Modified Silicate Fluorescent Nanosensors

Abstract: Optical PEBBLE (probes encapsulated by biologically localized embedding) nanosensors have been developed for dissolved oxygen using organically modified silicate (ormosil) nanoparticles as a matrix. The ormosil nanoparticles are prepared via a sol−gel-based process, which includes the formation of core particles with phenyltrimethoxysilane as a precursor followed by the formation of a coating layer with methyltrimethoxysilane as a precursor. The average diameter of the resultant particles is 120 nm. These sensors incorporate the oxygen-sensitive platinum porphyrin dye as an indicator and an oxygen-insensitive dye as a reference for ratiometric intensity measurement. Two pairs of indicator dye and reference dye, respectively, platinum(II) octaethylporphine and 3,3‘-dioctadecyloxacarbocyanine perchlorate, and platinum(II) octaethylporphine ketone and octaethylporphine, were used. The sensors have excellent sensitivity with an overall quenching response of 97%, as well as excellent linearity of the Stern−Vol...

Fluorescein provides a resonance gate for FRET from conjugated polymers to DNA intercalated dyes.

Abstract: Fluorescence spectra show that excitation of the cationic water-soluble conjugated polymer poly[(1,4-phenylene)-2,7-[9,9-bis(6'-N,N,N-trimethylammonium)-hexyl]fluorene diiodide] (1) results in inefficient fluorescence resonance energy transfer (FRET) to ethidium bromide (EB) intercalated within double-stranded DNA (dsDNA). When fluorescein (Fl) is attached to one terminus of the dsDNA, there is efficient FRET from 1 through Fl to EB. The cascading energy-transfer process was examined mechanistically via fluorescence decay kinetics and fluorescence anisotropy measurements. These experiments show that the proximity and conformational freedom of Fl provide a FRET gate to dyes intercalated within DNA which are optically amplified by the properties of the conjugated polymer. The overall process provides a substantial improvement over previous homogeneous conjugated polymer based DNA sensors, namely, in the form of improved selectivity.

DNA sequence detection using selective fluorescence quenching of tagged oligonucleotide probes by gold nanoparticles.

Abstract: Simple, fast, economical, and sensitive detection of specific DNA sequences is crucial to pathogen detection and biomedical research. We have designed a novel fluorescent assay for DNA hybridization based on the electrostatic properties of DNA. We exploit the ability to create conditions where single-stranded DNA adsorbs on negatively charged gold nanoparticles while double-stranded DNA does not. Dye-tagged probe sequences have their fluorescence efficiently quenched when they are mixed with gold nanoparticles unless they hybridize with components of the analyte. Subfemtomole amounts of untagged target are detected in minutes using commercially available materials. Target sequences in complex mixtures of DNA and single-base mismatches in DNA sequences are easily detected.

Pyrene-Labeled Base-Discriminating Fluorescent DNA Probes for Homogeneous SNP Typing

Abstract: This paper describes the design of novel base-discriminating fluorescent (BDF) nucleobases and their application to single nucleotide polymorphism (SNP) typing. We devised novel BDF nucleosides, (Py)U and (Py)C, which contain a pyrenecarboxamide chromophore connected by a propargyl linker. The fluorescence spectrum of the duplex containing a (Py)U/A base pair showed a strong emission at 397 nm on 327 nm excitation. In contrast, the fluorescence of duplexes containing (Py)U/N base pairs (N = C, G, or T) was considerably weaker. The proposed structure of the duplex containing a matched (Py)U/A base pair suggests that the high polarity near the pyrenecarboxamide group is responsible for the strong A-selective fluorescence emission. Moreover, the fluorescence of the duplex containing a (Py)U/A base pair was not quenched by a flanking C/G base pair. The fluorescence properties are quite different from previous BDF nucleobases, where fluorescence is quenchable by flanking C/G base pairs. The duplex containing the C derivative, (Py)C, selectively emitted fluorescence when the base opposite (Py)C was G. The drastic change of fluorescence intensity by the nature of the complementary base is extremely useful for SNP typing. (Py)U- and (Py)C-containing oligodeoxynucleotides acted as effective reporter probes for homogeneous SNP typing of DNA samples containing c-Ha-ras and BRCA2 SNP sites.

Quantum dot biolabeling coupled with immunomagnetic separation for detection of Escherichia coli O157:H7

Abstract: A sensitive, specific, and rapid method for the detection of E. coli O157:H7 was demonstrated using quantum dots (QDs) as a fluorescence marker coupled with immunomagnetic separation. Magnetic beads coated with anti-E. coli O157 antibodies were employed to selectively capture the target bacteria, and biotin-conjugated anti-E. coli antibodies were added to form sandwich immuno complexes. After magnetic separation, the immuno complexes were labeled with QDs via biotin−streptavidin conjugation. This was followed by a fluorescence measurement using a laptop-controlled portable device, which consisted of a blue LED and a CCD-array spectrometer. The peak intensity of the fluorescence emission was proportional to the initial cell concentration of E. coli O157:H7 in the range of 103−107 CFU/mL with a detection limit at least 100 times lower than that of the FITC-based method. The total detection time was less than 2 h. Neither E. coli K12 nor Salmonella typhimurium interfered with the detection of E. coli O157:H7.

Coordination-driven self-assembly directs a single-crystal-to-single-crystal transformation that exhibits photocontrolled fluorescence.

Abstract: Coordination-driven self-assembly is employed to direct a single-crystal-to-single-crystal [2 + 2] photodimerization that exhibits tunable fluorescence.

Surface-enhanced Raman spectroscopy for bacterial discrimination utilizing a scanning electron microscope with a Raman spectroscopy interface.

Abstract: Surface-enhanced Raman scattering (SERS) utilizing colloidal silver has already been shown to provide a rapid means of generating “whole-organism fingerprints” for use in bacterial identification and discrimination. However, one of the main drawbacks of the technique for the analysis of microbiological samples with optical Raman microspectroscopy has been the inability to acquire pre-emptively a region of the sample matrix where both the SERS substrate and biomass are both present. In this study, we introduce a Raman interface for scanning electron microscopy (SEM) and demonstrate the application of this technology to the reproducible and targeted collection of bacterial SERS spectra. In secondary electron mode, the SEM images clearly reveal regions of the sample matrix where the sodium borohydride-reduced silver colloidal particles are present, Stokes spectra collected from these regions are rich in vibrational bands, whereas spectra taken from other areas of the sample elicit a strong fluorescence respo...

Preparation, characterization, and time-resolved fluorometric application of silica-coated terbium(III) fluorescent nanoparticles.

Abstract: Novel silica-coated terbium(III) chelate fluorescent nanoparticles have been prepared and characterized as a new type of fluorescence probe for highly sensitive time-resolved fluorescence bioassay. The preparation was carried out in a water-in-oil microemulsion containing a strongly fluorescent Tb(3+) chelate, N,N,N(1),N(1)-[2,6-bis(3'-aminomethyl-1'-pyrazolyl)-phenylpyridine]tetrakis(acetate)-Tb(3+), Triton X-100, hexanol, and cyclohexane by controlling hydrolysis of tetraethyl orthosilicate. The nanoparticles are spherical and uniform in size, 42 +/- 3 nm in diameter, strongly fluorescent, and highly photostable and have enough of a long fluorescence lifetime (1.52 ms) for time-resolved fluorescence measurement. A stable and nontoxic method was developed for the surface modification and protein immobilization of the nanoparticles. As a model of application, the nanoparticle-labeled streptavidin was prepared and used in a sandwich-type time-resolved fluoroimmunoassay of human prostate-specific antigen (PSA) by using a 96-well microtiter plate as the solid-phase carrier. The method gives a detection limit of 7.0 pg/mL for the PSA assay.

Particle size distributions and compositions of aerosols produced by near-IR femto- and nanosecond laser ablation of brass

Abstract: Particle size distributions and compositions of primary aerosols produced by means of near-IR femtosecond laser ablation (λ = 775 nm) of brass in He or Ar at atmospheric pressure have been measured. Aerosols were characterized using a 13-stage low-pressure impactor covering a size range from 5 nm up to 5 μm and subsequently analyzed applying total reflection X-ray fluorescence spectrometry. The results indicate, that for femtosecond laser ablation in the low-fluence regime (<5 J cm−2) ultra-fine aerosols (mean diameter dp ≈ 10 nm/peak width wp ≈ 35 nm) are produced. Furthermore, the total Cu/Zn ratio of these aerosols corresponds to the composition of the bulk material. In contrast, ablation above 10 J cm−2 results in the formation of polydisperse, bimodal aerosols, which are distributed around dp1 ≈ 20 nm (wp1 ≈ 50 nm) and dp2 ≈ 1 μm (wp2 ≈ 5 µm), respectively, and whose total Cu/Zn ratio slightly deviates from the bulk composition. In order to examine the influence of pulse duration on particle size distribution and aerosol composition, comparative measurements by means of near-IR nanosecond ablation were also performed. The data show that nanosecond ablation generally leads to an intensified formation of particles in the micrometer range. Moreover, the composition of these aerosols strongly departs from the stoichiometry of the bulk. Aspects concerning the formation of particles during ablation as well as implications for the element-selective analysis by inductively coupled plasma spectrometry are discussed.

Photocatalytic Oxygenation of Anthracenes and Olefins with Dioxygen via Selective Radical Coupling Using 9-Mesityl-10-methylacridinium Ion as an Effective Electron-Transfer Photocatalyst

Abstract: Visible light irradiation of the absorption band of 9-mesityl-10-methylacridinium ion (Acr+−Mes) in an O2-saturated acetonitrile (MeCN) solution containing 9,10-dimethylanthracene results in formation of oxygenation product, i.e., dimethylepidioxyanthracene (Me2An-O2). Anthracene and 9-methylanthracene also undergo photocatalytic oxygenation with Acr+−Mes to afford the corresponding epidioxyanthracenes under the photoirradiation. In the case of anthracene, the further photoirradiation results in formation of anthraquinone as the final six-electron oxidation product, via 10-hydroxyanthrone, accompanied by generation of H2O2. When anthracene is replaced by olefins (tetraphenylethylene and tetramethylethylene), the photocatalytic oxygenation of olefins affords the corresponding dioxetane, in which the O−O bond is cleaved to yield the corresponding ketones. The photocatalytic oxygenation of anthracenes and olefins is initiated by photoexcitation of Acr+−Mes, which results in formation of the electron-transfer...

Functionalized CdSe quantum dots as selective silver ion chemodosimeter.

Abstract: CdSe quantum dots (QDs) have been prepared and modified with mercaptoacetic acid. They are water-soluble and biocompatible. To improve their fluorescence intensity and stability in water solution, bovine serum albumin (BSA) was absorbed onto their surface. Based on the quench of fluorescence signals of the functionalized CdSe QDs in the 543 nm wavelength and enhancement of them in the 570–700 nm wavelength range by Ag(I) ions at pH 5.0, a simple, rapid and specific method for Ag(I) determination was proposed. In comparison with single organic fluorophores, these nanoparticles are brighter, more stable against photobleaching, and do not suffer from blinking. Under the optimum conditions, the response is linearly proportional to the concentration of Ag(I) between 4.0 × 10−7 and 1.5 × 10−5 mol L−1, and the limit of detection is 7.0 × 10−8 mol L−1. The mechanism of reaction is also discussed.

Metal-Ion Sensing Fluorophores with Large Two-Photon Absorption Cross Sections: Aza-Crown Ether Substituted Donor-Acceptor-Donor Distyrylbenzenes

Abstract: Chromophores based on a donor−acceptor−donor structure possessing a large two-photon absorption cross section and one or two mono-aza-15-crown-5 ether moieties, which can bind metal cations, have been synthesized. The influence of Mg2+ binding on their one- and two-photon spectroscopic properties has been investigated. Upon binding, the two-photon action cross sections at 810 nm decrease by a factor of up to 50 at high Mg2+ concentrations and this results in a large contrast in the two-photon excited fluorescence signal between the bound and unbound forms, for excitation in the range of 730 to 860 nm. Experimental and computational results indicate that there is a significant reduction of the electron donating strength of the aza-crown nitrogen atom(s) upon metal ion binding and that this leads to a blue shift in the position as well as a reduction in the strength of the lowest-energy two-photon absorption band. The molecules reported here can serve as models for the design of improved two-photon excitabl...

Photoisomerization Dynamics of Azobenzene in Solution with S1 Excitation: A Femtosecond Fluorescence Anisotropy Study

Abstract: Measurements of anisotropy of femtosecond fluorescence after direct excitation of the S1(n,π*) state of azobenzene in hexane and ethylene glycol solutions have been carried out to address the controversy about inversion and rotation in the mechanism of photoisomerization. The observed anisotropies in hexane decay to a nonzero asymptotic level with a relaxation period the same as that for slow decay of the corresponding biexponential transient; this effect is attributed to involvement of the out-of-plane CNNC-torsional motion on approach to a twisted conical intersection along the “rotation channel” that depolarizes the original in-plane transition moment. In contrast, when the rotational channel becomes substantially hindered in ethylene glycol, the anisotropies show no discernible decay feature, but the corresponding transients show prominent decays attributed to involvement of in-plane symmetric motions; the latter approach a planar-sloped conical intersection along a “concerted inversion channel” for e...

Fate of Elemental Mercury in the Arctic during Atmospheric Mercury Depletion Episodes and the Load of Atmospheric Mercury to the Arctic

Abstract: Atmospheric mercury depletion episodes (AMDEs) were studied at Station Nord, Northeast Greenland, 81°36‘ N, 16°40‘ W, during the Arctic Spring. Gaseous elemental mercury (GEM) and ozone were measured starting from 1998 and 1999, respectively, until August 2002. GEM was measured with a TEKRAN 2735A automatic mercury analyzer based on preconcentration of mercury on a gold trap followed by detection using fluorescence spectroscopy. Ozone was measured by UV absorption. A scatter plot of GEM and ozone concentrations confirmed that also at Station Nord GEM and ozone are linearly correlated during AMDEs. The relationship between ozone and GEM is further investigated in this paper using basic reaction kinetics (i.e., Cl, ClO, Br, and BrO have been suggested as reactants for GEM). The analyses in this paper show that GEM in the Arctic troposphere most probably reacts with Br. On the basis of the experimental results of this paper and results from the literature, a simple parametrization for AMDE was included into ...

Nile red-adsorbed gold nanoparticles for selective determination of thiols based on energy transfer and aggregation.

Abstract: For the first time, an aqueous solution of 32-nm gold nanoparticles (GNPs), to which Nile red (NR) has been noncovalently adsorbed, has been used for sensing thiols. The as-prepared NRGNPs fluoresce weakly as a result of fluorescence resonance energy transfer between NR and the GNPs. The fluorescence of a solution containing NRGNPs at pH 4.0 increases upon the addition of thiols, but not when amines, acids, alcohols, bovine serum albumin, or hemoglobin are added. This phenomenon allows for the selective determination of thiols such as cysteamine and homocysteine, which have limits of detection of 10.2 and 10.9 nM, respectively, at a signal-to-noise ratio of 3. Interestingly, we have found that the excitation (lambda(ex) = 480 nm), emission (lambda(em) = 610 nm), and mass spectra (m/z 282) of the substance that desorbs from the GNPs in the presence of thiols are different from those of NR (lambda(ex) = 580 nm; lambda(em) = 652 nm; m/z 318), which indicates that a new product forms. When simultaneously conducting fluorescence and colorimetric assays, the selectivity of this approach further improves because at pH 4.0, the color of the NRGNPs does not change in the presence of negatively charged thiols, (e.g., N-(2-mercaptopropionyl)glycine), but changes from maroon to purple and lavender in the presence of neutral thiols (e.g., 3-mercapto-1,2-propanediol) and positively charged thiols (e.g., cysteamine), respectively, as a result of aggregation. This feature allows the types of thiols to be determined at concentrations >1.0 and 0.1 microM by the naked eye and by UV-vis absorption, respectively. Depending on the rate at which the NRGNP color changes, reduced glutathione (slow) is readily distinguishable from oxidized glutathione (no aggregation and no displacement) and from cysteine and homocysteine (fast).

Cryogenic laser induced fluorescence characterization of U(VI) in Hanford Vadose Zone pore waters.

Abstract: Ambient and liquid helium temperature laser-induced time-resolved uranyl fluorescence spectroscopy was applied to study the speciation of aqueous uranyl solutions containing carbonate and phosphate and two porewater samples obtained by ultracentrifugation of U(VI)-contaminated sediments. The significantly enhanced fluorescence signal intensity and spectral resolution found at liquid helium temperature allowed, for the first time, direct fluorescence spectroscopic observation of the higher aqueous uranyl complexes with carbonate: UO2(CO3)2(2-), UO2(CO3)3(4-), and (UO2)2(OH)3CO3-. The porewater samples were nonfluorescent at room temperature. However, at liquid helium temperature, both porewater samples displayed strong, well-resolved fluorescence spectra. Comparisons of the spectroscopic characteristics of the porewaters with those of the standard uranyl-carbonate complexes confirmed that U(VI) in the porewaters existed primarily as UO2(CO3)3(4-) along with a small amount of other minor components, such as dicalcium-urano-tricarbonate complex, Ca2UO2(CO3)3, consistent with thermodynamic calculation. The U(VI)-carbonate complex is apparently the mobile species responsible for the subsurface migration of U(VI), even though the majority of the in-ground U(VI) inventory at the site from which the samples were obtained exists as intragrain U(VI)-silicate precipitates.

A laser induced fluorescence instrument for detecting tropospheric OH and HO2: Characteristics and calibration

Abstract: Measurement capability for the detection of atmospheric OH and HO2 has been developed at the Pennsylvania State Universityover the last decade. The instrument is used in two forms: an aircraft configuration, Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS), and the configuration used on towers, Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS). The instrument uses ultraviolet laser induced fluorescence (LIF) to detect OH in air that is pulled by a vacuum pump through a small inlet into a low-pressure detection chamber; HO2 is detected by reacting it with NO to form OH, which is detected by LIF in a second detection chamber. In the calibration, equal amounts of OH and HO2 ranging from 0.15 pptv to 100 pptv are produced via photolysis of water vapor by the 185 nm emission from a low-pressure Hg lamp. Estimated absolute uncertainty at the 2σ confidence level is ± 32% for bothOH and HO2. The dependence of the instrument detection sensitivity hasbeen quantified for changes in ambient water vapor, pressure, laser power, and the flow velocity of ambient air past the inlet. During the last 7 years, the instrument has been deployed in multi-investigator intensive field studies 5 times on the NASA DC-8 aircraft and 8 times on ground-based towers. The descriptions in this manuscript detail our cumulative wisdom of the instrumental response and calibration techniques developed over this time.

Highly effective fluorescent sensor for H2PO4(

Abstract: A new anthracene dimer connected by two imidazolium moieties has been systematically designed and synthesized as a fluorescent chemosensor for selective binding of H2PO4- over other anions, which have been examined using fluorescence and 1H NMR and rationalized with ab initio study.

A highly discriminating quencher-free molecular beacon for probing DNA.

Abstract: We inserted a fluorene-labeled deoxyuridine derivative, synthesized using Sonogashira coupling, efficiently into the loop region of a DNA hairpin using phosphoramidite chemistry. This molecular beacon, which features no additional fluorescence quencher, discriminates between perfect and one-base-mismatched base pairing by changes in its fluorescence intensity. The discrimination factor is 14.7 for the recognition of a single (A/C) base mismatch.