Showing papers on "Fluorescence spectrometry published in 2007"
TL;DR: A series of fluorophores with single-exponential fluorescence decays in liquid solution at 20 degrees C were measured independently by nine laboratories using single-photon timing and multifrequency phase and modulation fluorometry instruments with lasers as excitation source.
Abstract: A series of fluorophores with single-exponential fluorescence decays in liquid solution at 20 °C were measured independently by nine laboratories using single-photon timing and multifrequency phase and modulation fluorometry instruments with lasers as excitation source. The dyes that can serve as fluorescence lifetime standards for time-domain and frequency-domain measurements are all commercially available, are photostable under the conditions of the measurements, and are soluble in solvents of spectroscopic quality (methanol, cyclohexane, water). These lifetime standards are anthracene, 9-cyanoanthracene, 9,10-diphenylanthracene, N-methylcarbazole, coumarin 153, erythrosin B, N-acetyl-l-tryptophanamide, 1,4-bis(5-phenyloxazol-2-yl)benzene, 2,5-diphenyloxazole, rhodamine B, rubrene, N-(3-sulfopropyl)acridinium, and 1,4-diphenylbenzene. At 20 °C, the fluorescence lifetimes vary from 89 ps to 31.2 ns, depending on fluorescent dye and solvent, which is a useful range for modern pico- and nanosecond time-dom...
406 citations
TL;DR: It is concluded that the new measurement scheme is robust against optical and photophysical artefacts which are inherent to standard FCS.
Abstract: We present a new method to measure absolute diffusion coefficients at nanomolar concentrations with high precision. Based on a modified fluorescence correlation spectroscopy (FCS)-setup, this method is improved by introducing an external ruler for measuring the diffusion time by generating two laterally shifted and overlapping laser foci at a fixed and known distance. Data fitting is facilitated by a new two-parameter model to describe the molecule detection function (MDF). We present a recorded MDF and show the excellent agreement with the fitting model. We measure the diffusion coefficient of the red fluorescent dye Atto655 under various conditions and compare these values with a value achieved by gradient pulsed field NMR (GPF NMR). From these measurements we conclude, that the new measurement scheme is robust against optical and photophysical artefacts which are inherent to standard FCS. With two-focus-FCS, the diffusion coefficient of 4.26 x 10(-6) cm2s(-1) for Atto655 in water at 25 degrees C compares well with the GPF NMR value of 4.28 x 10(-6) cm2s(-1).
335 citations
TL;DR: A number of applications are presented, selected from recent second- and third-order experimental works based on data obtained through excitation-emission fluorescence spectroscopy, spectral-kinetic and spectral-pH measurements, and hyphenated techniques.
Abstract: We review second- and third-order multivariate calibration, based on the growing literature in this field, the variety of data being produced by modern instruments, and the proliferation of algorithms capable of dealing with higher-order data. We primarily emphasize the relevance of the subject to analytical chemistry. We intend, in the terminology section, to clarify some confusing features relating to the definition of sample constituents in second-order calibration. We then classify and compare instrumental data and available algorithms. We provide insight into the relative advantages and disadvantages of the existing algorithms (e.g., in terms of: achieving second-order advantage (the ability to cope with varying amounts of potential interferents in test samples), presence of linear dependency in the data, handling trilinear deviations, using incomplete calibration data, extension to higher-order information, handling missing values; and, providing physico-chemical information. Finally, we present a number of applications, selected from recent second- and third-order experimental works based on data obtained through excitation-emission fluorescence spectroscopy, spectral-kinetic and spectral-pH measurements, and hyphenated techniques.
301 citations
TL;DR: Coupling the GSH-capped QDs with a high-throughput detection system, a simple scheme for quick and ultrasensitive Pb(2+) detection without the need for additional electronic devices is developed.
Abstract: Water-soluble and stable quantum dots (QDs), CdTe and CdZnSe, are applied for ultrasensitive Pb(2+) detection. These QDs are capped with glutathione (GSH) shells. GSH and its polymeric form, phytochelatin, are employed by nature to detoxify heavy metal ions. As a result of specific interaction, the fluorescence intensity of GSH-capped QDs is selectively reduced in the presence of heavy metal ions such as Pb(2+). The detection limit of Pb(2+) is found to be 20 nM due to the superior fluorescence properties of QDs. Detailed studies by spectroscopy, microscopy, and dynamic light scattering show that competitive GSH binding of Pb(2+) with the QD core changed both the surface and photophysical properties of the QDs. Fluorescence of QDs is quenched, and QD aggregation occurs. Coupling the GSH-capped QDs with a high-throughput detection system, we have developed a simple scheme for quick and ultrasensitive Pb(2+) detection without the need for additional electronic devices. In the presence of ionic mixtures, our system is still capable of Pb(2+) detection with a detection limit as low as 40 nM. The system only becomes less sensitive when the ionic mixture is present at a very high concentration (i.e., > or =50 microM).
282 citations
TL;DR: The demonstrated acoustic trapping of cells and particles enables cell- or particle-based bioassays to be performed in a continuous flow format and enhances the noncontact mode of cell handling when studies on nonadherent cells are performed.
Abstract: Techniques for manipulating, separating, and trapping particles and cells are highly desired in today's bioanalytical and biomedical field. The microfluidic chip-based acoustic noncontact trapping method earlier developed within the group now provides a flexible platform for performing cell- and particle-based assays in continuous flow microsystems. An acoustic standing wave is generated in etched glass channels (600 × 61 μm2) by miniature ultrasonic transducers (550 × 550 × 200 μm3). Particles or cells passing the transducer will be retained and levitated in the center of the channel without any contact with the channel walls. The maximum trapping force was calculated to be 430 ± 135 pN by measuring the drag force exerted on a single particle levitated in the standing wave. The temperature increase in the channel was characterized by fluorescence measurements using rhodamine B, and levels of moderate temperature increase were noted. Neural stem cells were acoustically trapped and shown to be viable after...
274 citations
TL;DR: This work has developed a rational strategy for the biomimetic recognition of carbohydrates with all-equatorial stereochemistry (β-glucose, analogs, and homologs) and applied it to disaccharides such as cellobiose, showing good affinities and selectivity for the target substrates.
Abstract: Carbohydrate recognition is biologically important but intrinsically challenging, for both nature and host-guest chemists. Saccharides are complex, subtly variable, and camouflaged by hydroxyl groups that hinder discrimination between substrate and water. We have developed a rational strategy for the biomimetic recognition of carbohydrates with all-equatorial stereochemistry (β-glucose, analogs, and homologs) and have now applied it to disaccharides such as cellobiose. Our synthetic receptor showed good affinities, not unlike those of some lectins (carbohydrate-binding proteins). Binding was demonstrated by nuclear magnetic resonance, induced circular dichroism, fluorescence spectroscopy, and calorimetry, all methods giving self-consistent results. Selectivity for the target substrates was exceptional; minor changes to disaccharide structure (for instance, cellobiose to lactose) caused almost complete suppression of complex formation.
269 citations
TL;DR: In this article, a hybrid scheme combining force and fluorescence was developed to examine the effect of subpiconewton forces on the nanometer scale motion of the Holliday junction at 100-hertz bandwidth.
Abstract: Despite the recent advances in single-molecule manipulation techniques, purely mechanical approaches cannot detect subtle conformational changes in the biologically important regime of weak forces. We developed a hybrid scheme combining force and fluorescence that allowed us to examine the effect of subpiconewton forces on the nanometer scale motion of the Holliday junction (HJ) at 100-hertz bandwidth. The HJ is an exquisitely sensitive force sensor whose force response is amplified with an increase in its arm lengths, demonstrating a lever-arm effect at the nanometer-length scale. Mechanical interrogation of the HJ in three different directions helped elucidate the structures of the transient species populated during its conformational changes. This method of mapping two-dimensional reaction landscapes at low forces is readily applicable to other nucleic acid systems and their interactions with proteins and enzymes.
245 citations
TL;DR: In this article, the phase change behavior of organic phase change materials (PCMs) in porous building materials was investigated using differential scanning calorimetry (DSC) and phase change composites.
243 citations
TL;DR: A simple, rapid and specific method for Hg(II) determination was proposed and was successfully applied to the detection of trace Hg (II) in real samples.
236 citations
TL;DR: An updated overview of the recent uses and future prospects for the different analytical methods employed in food and environmental samples is presented and the most relevant issues that condition the analogies and the contrasts between food and environment matrices in the analysis of quinolones are summarized.
Abstract: Contamination of the environment by pharmaceuticals, quinolones among them, is recognized as an emerging issue of concern to scientists and the public. Literature on the environmental analysis of quinolones has addressed a very small percentage of these compounds, and the analytical methods developed to determine them are very scarce. By contrast, a large number of methods have been proposed for their analysis in food, which has classically been considered the source of these residues for human beings. Although both matrices, food and environment, differ, most of the information obtained from one field can be applied to the other. However, to be able to do this, there is need for critical discussion about how analytical determination is carried out in each case. This review summarizes the most relevant issues that condition the analogies and the contrasts between food and environmental matrices in the analysis of quinolones. We describe and compare the target analytes and their relevant levels. We also critically review the approaches to extraction (e.g., solvent extraction (SE), pressurized liquid extraction (PLE) and solid-phase extraction (SPE)), depending on the sample characteristics. We also detail the main analytical techniques (e.g., liquid chromatography (LC) and capillary electrophoresis (CE) combined with UV, fluorescence (FLD) and mass spectrometry (MS), immunoassays and biosensors) used to identify and to quantify quinolone residues in both matrices. We present an updated overview of the recent uses and future prospects for the different analytical methods employed in food and environmental samples.
216 citations
TL;DR: In this article, X-ray fluorescence spectrometry (XRF) was used for the identification of the Chivay obsidian source in southern Peru, where the same sixty-six artifacts from the site of Jiskairumoko were compared for consistency in terms of source determination and individual element concentrations.
TL;DR: Molecular docking calculations suggest that the benzopyran ring of EGCG penetrates deeply into the active site while the galloyl moiety anchors it to the cleft through interactions with its hydroxyl groups, which explains the higher activity of E GCG and ECG.
Abstract: Catechins are the main ingredients of green tea extracts and have been shown to possess versatile biological activities, including antimicrobial. We determined that the catechins inhibit bacterial DNA gyrase by binding to the ATP binding site of the gyrase B subunit. In the group of four tested catechins, epigallocatechin gallate (EGCG) had the highest activity, followed by epicatechin gallate (ECG) and epigallocatechin (EGC). Specific binding to the N-terminal 24 kDa fragment of gyrase B was determined by fluorescence spectroscopy and confirmed using heteronuclear two-dimensional NMR spectroscopy of the EGCG-15N-labeled gyrase B fragment complex. Protein residues affected by binding to EGCG were identified through chemical shift perturbation. Molecular docking calculations suggest that the benzopyran ring of EGCG penetrates deeply into the active site while the galloyl moiety anchors it to the cleft through interactions with its hydroxyl groups, which explains the higher activity of EGCG and ECG.
TL;DR: A novel calix[4]arene-based chemosensor 1 based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies.
Abstract: A novel calix[4]arene-based chemosensor 1 based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg2+ to a CH3CN solution of 1 gave a significantly enhanced fluorescence at ∼575 nm via energy transfer (FRET-ON) from the pyrenyl excimer to a ring-opened rhodamine moiety. In contrast, addition of Al3+ induced a distinct increase of pyrenyl excimer emission (∼475 nm), while no obvious FRET-ON phenomenon was observed. Different binding behaviors of 1 toward Hg2+ and Al3+ were also proposed for the interesting observation.
TL;DR: This paper summarizes the features and performances of optical detection systems currently applied in order to monitor separations on microchip devices, points out exciting new approaches, and provides future perspectives on this field.
Abstract: This paper summarizes the features and performances of optical detection systems currently applied in order to monitor separations on microchip devices. Fluorescence detection, which delivers very high sensitivity and selectivity, is still the most widely applied method of detection. Instruments utilizing laser-induced fluorescence (LIF) and lamp-based fluorescence along with recent applications of light-emitting diodes (LED) as excitation sources are also covered in this paper. Since chemiluminescence detection can be achieved using extremely simple devices which no longer require light sources and optical components for focusing and collimation, interesting approaches based on this technique are presented, too. Although UV/vis absorbance is a detection method that is commonly used in standard desktop electrophoresis and liquid chromatography instruments, it has not yet reached the same level of popularity for microchip applications. Current applications of UV/vis absorbance detection to microchip separations and innovative approaches that increase sensitivity are described. This article, which contains 85 references, focuses on developments and applications published within the last three years, points out exciting new approaches, and provides future perspectives on this field.
TL;DR: An updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development and considers the future outlook for SPR and SPR-associated BIA studies.
Abstract: Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright.
TL;DR: The authors' preliminary studies indicate that Al nanostructured substrates can potentially find widespread use in MEF applications particularly in the UV-blue spectral regime, and are very stable in buffers that contain chloride salts compared to usual silver colloid-based substrates for MEF, thus furthering the usefulness of these Al- based substrates in many biological assays where high concentration of salts are required.
Abstract: Particulate aluminum films of varied thicknesses were deposited on quartz substrates by thermal evaporation. These nanostructured substrates were characterized by scanning electron microscopy (SEM). With the increase of aluminum thickness, the films progress from particulate toward smooth surfaces as observed by SEM images. To date, metal-enhanced fluorescence (MEF) has primarily been observed in the visible−NIR wavelength region using silver or gold island films or roughened surfaces. We now show that fluorescence could also be enhanced in the ultraviolet-blue region of the spectrum using nanostructured aluminum films. Two probes, one in the ultraviolet and another one in the blue spectral region, have been chosen for the present study. We observed increased emission, decrease in fluorescence lifetime, and increase in photostability of a DNA base analogue 2-aminopurine and a coumarin derivative (7-HC) in 10-nm spin-casted poly(vinyl alcohol) film on Al nanostructured surfaces. The fluorescence enhancemen...
TL;DR: The use of spatially offset Raman spectroscopy (SORS) is demonstrated in the identification of counterfeit pharmaceutical tablets and capsules through different types of packaging because of excessive surface Raman or fluorescence signals emanating from the packaging, capsule shell, or tablet coating contaminating the much weaker subsurface Raman signals.
Abstract: We demonstrate the use of spatially offset Raman spectroscopy (SORS) in the identification of counterfeit pharmaceutical tablets and capsules through different types of packaging. The technique offers a substantially higher sensitivity than that available from conventional backscattering Raman spectroscopy. The approach is particularly beneficial in situations where the conventional Raman backscattering method is hampered or fails because of excessive surface Raman or fluorescence signals emanating from the packaging, capsule shell, or tablet coating contaminating the much weaker subsurface Raman signals of the active pharmaceutical ingredients and excipients held in the product. It is demonstrated that such interfering signals can be effectively suppressed by SORS.
TL;DR: Nucleophilic substitution of tetrabromo NDI with alkoxy, alkylthio, and alkylamino nucleophiles afforded a series of core-tetrasubstituted NDI chromophores that complete the series of previously reported di- and trifunctionalized NDI derivatives.
Abstract: 2,3,6,7-tetrabromonaphthalene dianhydride has been synthesized by the bromination of naphthalene dianhydride with dibromoisocyanuric acid in excellent yield. The condensation of this dianhydride with 2,6-diisopropylaniline yielded the corresponding tetrabromo-substituted naphthalene diimide (NDI), which is a versatile precursor for the synthesis of core-tetrafunctionalized NDIs. Nucleophilic substitution of tetrabromo NDI with alkoxy, alkylthio, and alkylamino nucleophiles afforded a series of core-tetrasubstituted NDI chromophores that complete the series of previously reported di- and trifunctionalized NDI derivatives. The effects of electronic nature and number of core substituents on the optical and electrochemical properties of NDIs have been investigated by UV-vis and fluorescence spectroscopy and cyclic voltammetry. The absorption maxima (629-642 nm) of tetraamino NDIs are strongly bathochromically shifted compared to those of other core-functionalized NDIs.
TL;DR: It was found that both static quenching and non-radiation energy transfer were the main reasons for the fluorescence quenched, and the interaction of puerarin and BSA was driven mainly by hydrophobic forces.
TL;DR: The experimental results showed that the fluorescence quenching of BSA by silicotungstic acid is a result of the formation of SiW-BSA complex; staticQuenching and non-radiative energy transferring were confirmed to result in the fluorescent quenched.
TL;DR: Municipal solid waste (MSW) compost contains a significant amount of humic substances, and mixed inoculation of MSW with complex microorganisms and lingo-cellulolytic during composting gave a greater degree of HA aromatization than inoculation with complexmicroorganisms or lingospecifics alone, indicating that inoculation in composting would improve the degree humification and maturation processes.
TL;DR: The maturity degree reached by different samples of several mixtures from winery and distillery residues composted using the Rutgers composting system is assessed by means of excitation-emission matrix (EEM) fluorescence spectroscopy by using the quantitative method of fluorescence regional integration (FRI).
TL;DR: An aptamer modified gold nanoparticles (Apt-AuNPs) based molecular light switching sensor has been demonstrated for the analysis of breast cancer markers (platelet-derived growth factors (PDGFs) and their receptors) in homogeneous solutions.
Abstract: An aptamer modified gold nanoparticles (Apt-AuNPs) based molecular light switching sensor has been demonstrated for the analysis of breast cancer markers (platelet-derived growth factors (PDGFs) and their receptors) in homogeneous solutions. The PDGF binding aptamer has a unique structure with triple-helix conformation that allows N,N-dimethyl-2,7-diazapyrenium dication (DMDAP) and PDGF bindings. The fluorescence of DMDAP is almost completely quenched by Apt-AuNPs when it intercalates with the aptamers. Owing to high magnitudes of increases (up to 40-fold) in the turn-on fluorescence signals of DMDAP/Apt-AuNP upon PDGFs binding, the approach is highly sensitive for the detection of PDGFs. The DMDAP/Apt-AuNP probe specifically and sensitively detected PDGFs under optimal concentrations of salts and DMDAP. We also demonstrated that the Apt-AuNPs are effective selectors for enrichment of PDGF-AA from large-volume samples. The approach allows detection of PDGF-AA at a concentration down to 8 pM, showing bette...
TL;DR: A new strategy to study methylase activity using fluorescent probes coupled with enzyme-linkage reactions that is easy, simple, and nonradioactive, yet as efficient as gel electrophoresis in detecting the activity of methylase.
Abstract: DNA methylation catalyzed by methylase plays an important role in many biological events. However, traditional methods of methylase activity analysis by gel electrophoresis were laborious and discontinuous. In this paper, we report a new strategy to study methylase activity using fluorescent probes coupled with enzyme-linkage reactions. A hairpin DNA probe is prepared with a fluorophore and a quencher linked at the 5'- and 3'-terminus of the probe. A disturbance of the stem sequence by DNA methylation would cause the separation of the fluorophore and the quencher, resulting in the restoration of the fluorescence. We used DNA adenine methylation (Dam) methyltransferase (MTase) and Dpn I endonuclease, both having a 5'-G-A-T-C-3' recognition sequence. Dam MTase catalyzed the methylation of the sequence of 5'-GATC-3', and Dpn I cut the sequence of 5'-G-Am-T-C-3'. The fluorescence of the hairpin probe was restored when it was cleaved by Dpn I endonuclease during the course of methylation. Unlike traditional methods, this assay was done in real time and could be used to monitor the dynamic process of methylation. Our method is easy, simple, and nonradioactive, yet as efficient as gel electrophoresis in detecting the activity of methylase. It also had the potential to screen suitable inhibitor drugs for Dam methylase.
TL;DR: Out of 100 biophenols previously reported in olive products, the on-line RPLC-DAD-ESI-MS was able to confirm the presence of 52 compounds in OMW, including a number of simple phenols, flavonoids and secoiridoids.
TL;DR: A modified version of the spatially offset Raman spectroscopy concept that permits the interrogation of a wide range of containers, including transparent, colored, and diffusely scattering plastic and glass beverage, medicine, and cosmetic bottles, with no change in experimental geometry.
Abstract: We present a Raman spectroscopic method for the noninvasive detection of liquid explosives within bottles, and other packaging, of substantially higher sensitivity and wider applicability than that currently available via conventional Raman spectroscopy. The approach uses a modification of the spatially offset Raman spectroscopy (SORS) concept, which permits the interrogation of a wide range of containers, including transparent, colored, and diffusely scattering plastic and glass beverage, medicine, and cosmetic bottles, with no change in experimental geometry. The enhanced sensitivity is achieved by the technique's inherent ability to effectively suppress fluorescence and Raman contributions originating from the wall of the container. The application is demonstrated on the noninvasive detection of hydrogen peroxide solution, a critical component of a number of liquid explosives. In contrast to conventional Raman spectroscopy, the modified SORS concept enables the detection of concealed hydrogen peroxide ...
TL;DR: The paper describes the development and characterization of analytical properties of quantum dot-based probes for enzymatic activity and for screening enzyme inhibitors and found that the quantum dot FRET probes were sufficiently bright to enable quantitative enzyme and enzyme inhibition assays.
Abstract: The paper describes the development and characterization of analytical properties of quantum dot-based probes for enzymatic activity and for screening enzyme inhibitors. The luminescent probes are based on fluorescence resonance energy transfer (FRET) between luminescent quantum dots that serve as donors and rhodamine acceptors that are immobilized to the surface of the quantum dots through peptide linkers. Peptide-coated CdSe/ZnS quantum dots were prepared using a one-step ligand exchange process in which RGDC peptide molecules replace trioctylphosphine oxide (TOPO) molecules as the capping ligands of the quantum dots. The peptide molecules were bound to the surface of the CdSe/ZnS quantum dots through the thiol group of the peptide cysteine residue. The peptide-coated quantum dots were labeled with rhodamine to form the FRET probes. The emission quantum yield of the quantum dot FRET probes was 4-fold lower than the emission quantum yield of TOPO-capped quantum dots. However, the quantum dot FRET probes ...
TL;DR: Results indicate that picomolar detection limits can be achieved with standard instrumentation and the use of an intercalating dye (ethidium bromide) as an acceptor to alleviate non-specific adsorption is described.
TL;DR: This work proposes a mathematical correction procedure based on the intensity of Raman scatter from water that was found to reduce the error after correction by up to 50% in comparison with two absorbance correction procedures.
TL;DR: It is proposed that synthetic "tuning" of the pKa of fluorescein and other pH-sensitive fluorophores provides a general means to optimize binding assays.
Abstract: The phenolic pKa of fluorescein varies depending on its environment. The fluorescence of the dye varies likewise. Accordingly, a change in fluorescence can report on the association of a fluorescein conjugate to another molecule. Here, we demonstrate how to optimize this process with chemical synthesis. The fluorescence of fluorescein-labeled model protein, bovine pancreatic ribonuclease (RNase A), decreases upon binding to its cognate inhibitor protein (RI). Free and RI-bound fluorescein−RNase A have pKa values of 6.35 and 6.70, respectively, leaving the fluorescein moiety largely unprotonated at physiological pH and thus limiting the sensitivity of the assay. To increase the fluorescein pKa and, hence, the assay sensitivity, we installed an electron-donating alkyl group ortho to each phenol group. 2‘,7‘-Diethylfluorescein (DEF) has spectral properties similar to those of fluorescein but a higher phenolic pKa. Most importantly, free and RI-bound DEF−RNase A have pKa values of 6.68 and 7.29, respectively,...