Showing papers on "Fluorescence spectrometry published in 2003"
TL;DR: Aromatic carbon and the presence of specific aromatic compounds resulted in EEMs that aided in differentiating wastewater effluent DOM from drinking water DOM, and the highest cumulative EEM volume was observed for hydrophobic neutral DOM fractions.
Abstract: Excitation−emission matrix (EEM) fluorescence spectroscopy has been widely used to characterize dissolved organic matter (DOM) in water and soil. However, interpreting the >10,000 wavelength-dependent fluorescence intensity data points represented in EEMs has posed a significant challenge. Fluorescence regional integration, a quantitative technique that integrates the volume beneath an EEM, was developed to analyze EEMs. EEMs were delineated into five excitation−emission regions based on fluorescence of model compounds, DOM fractions, and marine waters or freshwaters. Volumetric integration under the EEM within each region, normalized to the projected excitation−emission area within that region and dissolved organic carbon concentration, resulted in a normalized region-specific EEM volume (Φi,n). Solid-state carbon nuclear magnetic resonance (13C NMR), Fourier transform infrared (FTIR) analysis, ultraviolet−visible absorption spectra, and EEMs were obtained for standard Suwannee River fulvic acid and 15 h...
4,407 citations
TL;DR: In this article, the authors present a dedicated investigation and practical description of how to apply PARAFAC modeling to complicated fluorescence excitation-emission measurements, including choosing the right number of components, handling problems with missing values and scatter, detecting variables influenced by noise and identifying outliers.
Abstract: This paper presents a dedicated investigation and practical description of how to apply PARAFAC modeling to complicated fluorescence excitation-emission measurements. The steps involved in finding the optimal PARAFAC model are described in detail based on the characteristics of fluorescence data. These steps include choosing the right number of components, handling problems with missing values and scatter, detecting variables influenced by noise and identifying outliers. Various validation methods are applied in order to ensure that the optimal model has been found and several common data-specific problems and their solutions are explained. Finally, interpretations of the specific models are given. The paper can be used as a tutorial for investigating fluorescence landscapes with multi-way analysis.
561 citations
TL;DR: This work has shown that sequence-specific fluorescence labeling of short RNA motifs is a first step toward genetically encodable fusion tags for imaging selected RNAs in vitro and in cells.
Abstract: MG and SRB aptamers, which are short RNA sequences originally selected only for binding to malachite green or sulforhodamine B, can greatly enhance the fluorescence of normally nonfluorescent triphenylmethane dyes. MG aptamer enhances the quantum yields of malachite green (MG) and a novel rigidized derivative, indolinyl malachite green (IMG) by >2000-fold. SRB aptamer brightens patent blue V and VF by >90-fold. These enhancements are specific because MG aptamer has no effect on patent blue dyes and SRB aptamer has little or no effect on MG and IMG. Such sequence-specific fluorescence labeling of short RNA motifs is a first step toward genetically encodable fusion tags for imaging selected RNAs in vitro and in cells.
446 citations
TL;DR: In this article, the degradation of a commercial environmentally degradable polyethylene was investigated in two stages: first by abiotic oxidation in an air oven to simulate the effect of the compost environment and secondly in the presence of selected microorganisms.
405 citations
TL;DR: The current study correlated early biochemical and histologic changes in oral tissue with spectral features in fluorescence, reflectance, and light scattering spectra acquired in vivo to diagnose early stages of oral malignancies.
Abstract: BACKGROUND
Understanding the development and progression of head and neck squamous cell carcinoma is key in the quest for the early diagnosis and prevention of this type of malignancy. The current study correlated early biochemical and histologic changes in oral tissue with spectral features in fluorescence, reflectance, and light scattering spectra acquired in vivo to diagnose early stages of oral malignancies.
METHODS
A total of 91 tissue sites from 15 patients with varying degrees of malignancy (normal, dysplastic, and cancerous sites) and 8 healthy volunteers were analyzed with 3 spectroscopic techniques. Direct biochemical information regarding oral tissue native fluorophores was obtained with intrinsic fluorescence spectroscopy by fitting a linear combination of collagen and the reduced form of nicotinamide adenine dinucleotide (NADH) fluorescence spectra to the intrinsic tissue fluorescence spectra excited with 337 nanometer (nm) and 358-nm laser light. Diffuse reflectance spectroscopy was used to provide information regarding tissue absorption and structure, such as hemoglobin concentration and stroma density, by measuring the wavelength-dependent absorption and scattering coefficients. By subtracting the diffusely reflected component from the measured reflectance, light scattering spectroscopy (LSS) information resulting from single backscattering from epithelial cell nuclei was obtained. LSS provides information concerning the size distribution of cell nuclei.
RESULTS
These optically extracted tissue parameters provide biochemical or structural information in vivo without the need for tissue excision, and can be used to diagnose tissue abnormalities. By combining the information provided by the three techniques, a method known as trimodal spectroscopy, a sensitivity and specificity of 96% and 96%, respectively, in distinguishing cancerous/dysplastic (mild, moderate, and severe) from normal tissue was achieved. In addition, the authors were able to distinguish dysplastic from cancerous tissue with a sensitivity of 64% and a specificity of 90%.
CONCLUSIONS
The results of the current study demonstrated that Trimodal spectroscopy is a highly sensitive and specific technique with which to diagnose tissue abnormalities. Cancer 2003;97:1681–92. © 2003 American Cancer Society.
DOI 10.1002/cncr.11255
310 citations
TL;DR: The degradation kinetics of a near-infrared fluorescent, diagnostic, and photodynamic agent, indocyanine green (ICG), was investigated in aqueous solution by steady-state fluorescence technique and found to follow first-order kinetics.
307 citations
TL;DR: The basis of these fluorescent molecular thermometers is the decrease in the microenvironmental polarities near the main chains of theCopolymers with increasing temperature, as confirmed from the maximum emission wavelengths of the benzofurazan units in the copolymers.
Abstract: Poly(N-isopropylacrylamide) in aqueous solution undergoes a phase transition at ∼32 °C. The fluorescence properties of benzofurazans are affected by solvent polarity. We combine these two characteristics for the first time to develop sensitive fluorescent molecular thermometers. Five fluorescent monomers having a benzofurazan skeleton were synthesized, and the copolymers of N-isopropylacrylamide (NIPAM) and a small quantity of the fluorescent monomer were obtained to investigate their fluorescence properties. With increase in temperature, the copolymers in water showed the temperature-induced phase transition at ∼32 °C and the fluorescence intensities of the copolymers concurrently increased. Especially, for the copolymer of 4-N-(2-acryloyloxyethyl)-N-methylamino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole and NIPAM, the fluorescence intensity at 37 °C was 13.3-fold that seen at 29 °C. The sensitive range of temperature of these fluorescent molecular thermometers is changed by the replacement of the ...
276 citations
TL;DR: The photoinduced electron transfer rates and the rates of back electron transfer follow the Marcus parabolic dependence of electron transfer rate on the driving force, providing for the first time a quantitative basis for a rational design principle which has high efficiency in modulating fluorescence properties of fluorescein-based probes.
Abstract: Fluorescence properties of fluorescein-based probes are shown to be finely controlled by the rate of photoinduced electron transfer from the benzoic acid moiety (electron donor) to the singlet excited state of the xanthene moiety (electron acceptor fluorophore). The occurrence of photoinduced electron transfer is clearly evidenced by transient absorption spectra showing bands due to the radical cation of the electron donor moiety and the radical anion of the xanthene moiety, observed in laser flash photolysis experiments. The photoinduced electron transfer rates and the rates of back electron transfer follow the Marcus parabolic dependence of electron transfer rate on the driving force. Such a dependence provides for the first time a quantitative basis for a rational design principle which has high efficiency in modulating fluorescence properties of fluorescein-based probes.
247 citations
TL;DR: In this article, a series of ITO electrodes modified chemically with self-assembled monolayers (SAMs) of porphyrins was designed to provide valuable insight into the development of artificial photosynthetic devices.
Abstract: A systematic series of ITO electrodes modified chemically with self-assembled monolayers (SAMs) of porphyrins and porphyrin-fullerene dyads have been designed to provide valuable insight into the development of artificial photosynthetic devices. First the ITO and gold electrodes modified chemically with SAMs of porphyrins with a spacer of the same number of atoms were prepared to compare the effects of energy transfer (EN) quenching of the porphyrin excited singlet states by the two electrodes. Less EN quenching was observed on the ITO electrode as compared to the EN quenching on the corresponding gold electrode, leading to remarkable enhancement of the photocurrent generation (ca. 280 times) in the porphyrin SAMs on the ITO electrode in the presence of the triethanolamine (TEA) used as a sacrificial electron donor. The porphyrin (H(2)P) was then linked with C(60) which can act as an electron acceptor to construct H(2)P-C(60) SAMs on the ITO surface in the presence of hexyl viologen (HV(2+)) used as an electron carrier in a three electrode system, denoted as ITO/H(2)P-C(60)/HV(2+)/Pt. The quantum yield of the photocurrent generation of the ITO/H(2)P-C(60)/HV(2+)/Pt system (6.4%) is 30 times larger than that of the corresponding system without C(60): ITO/H(2)P-ref/HV(2+)/Pt (0.21%). Such enhancement of photocurrent generation in the porphyrin-fullerene dyad system is ascribed to an efficient photoinduced ET from the porphyrin singlet excited state to the C(60) moiety as indicated by the fluorescence lifetime measurements and also by time-resolved transient absorption studies on the ITO systems. The surface structures of H(2)P and H(2)P-C(60) SAMs on ITO (H(2)P/ITO and H(2)P-C(60)/ITO) have been observed successfully in molecular resolution with atomic force microscopy for the first time.
235 citations
TL;DR: A review of analytical use of LEDs that has been advanced in the last decade is presented in this article, where LED-based absorbance measurement and its use in pedagogy, titrations, in providing immunity to refractive index and turbidity effects, in field and process analysis, in capillary electrophoresis, in liquid-liquid extraction systems, in film and drop-based analytical systems and with liquid core waveguides (LCWs) are discussed.
227 citations
TL;DR: In this paper, an instrumental neutron activation analysis was performed to determine the transition metal content in three types of silicon material for cost-efficient solar cells: Astropower silicon-film sheet material, Baysix cast material, and edge-defined film-fed growth (EFG) multicrystalline silicon ribbon.
Abstract: Instrumental neutron activation analysis was performed to determine the transition metal content in three types of silicon material for cost-efficient solar cells: Astropower silicon-film sheet material, Baysix cast material, and edge-defined film-fed growth (EFG) multicrystalline silicon ribbon. The dominant metal impurities were found to be Fe (6×1014 cm−3 to 1.5×1016 cm−3, depending on the material), Ni (up to 1.8×1015 cm−3), Co (1.7×1012 cm−3 to 9.7×1013 cm−3), Mo (6.4×1012 cm−3 to 4.6×1013 cm−3), and Cr (1.7×1012 cm−3 to 1.8×1015 cm−3). Copper was also detected (less than 2.4×1014 cm−3), but its concentration could not be accurately determined because of a very short decay time of the corresponding radioactive isotope. In all samples, the metal contamination level would be sufficient to degrade the minority carrier diffusion length to less than a micron, if all metals were in an interstitial or substitutional state. This is a much lower value than the actual measured diffusion length of these samples. Therefore, most likely, the metals either formed clusters or precipitates with relatively low recombination activity or are very inhomogeneously distributed within the samples. No significant difference was observed between the metal content of the high and low lifetime areas of each material. X-ray microprobe fluorescence spectrometry mapping of Astropower mc-Si samples confirmed that transition metals formed agglomerates both at grain boundaries and within the grains. It is concluded that the impact of metals on solar cell efficiency is determined not only by the total metal concentration, but also by the distribution of metals within the grains and the chemical composition of the clusters formed by the metals.
TL;DR: In water, the oligomers with longer side chain length show better energy transfer, as well as higher Stern-Volmer quenching constants (K(sv), largely due to a stronger hydrophobic attraction between the optically active components.
Abstract: The synthesis of 1,4-bis(9,9'-bis(3"-(N,N,N-trimethylammonium)-propyl)-2'-fluorenyl)benzene tetrabromide (C3), 1,4-bis(9,9'-bis(4"-(N,N,N-trimethylammonium)-butyl)-2'-fluorenyl)benzene tetrabromide (C4), 1,4-bis(9,9'-bis(6"-(N,N,N-trimethylammonium)-hexyl)-2'-fluorenyl)benzene tetrabromide (C6), and 1,4-bis(9,9'-bis(8"-(N,N,N-trimethylammonium)-octyl)-2'-fluorenyl)benzene tetrabromide (C8) is reported. Fluorescence energy transfer experiments between C3-C8 and the acceptors pentasodium 1,4-bis(4'(2",4"-bis(butoxysulfonate)-styryl)styryl)-2-(butoxysulfonate)-5-methoxybenzene (3), fluorescein labeled single-stranded DNA and fluorescein labeled double-stranded DNA in water, buffer, and methanol reveal the importance of hydrophobic and electrostatic forces in determining chromophore-chromophore close proximity. In water, the oligomers with longer side chain length show better energy transfer, as well as higher Stern-Volmer quenching constants (K(sv)), largely due to a stronger hydrophobic attraction between the optically active components. In methanol, the differences in energy transfer are leveled, and the oligomers with shorter side chain lengths show higher K(sv) values. Compounds C3, C4, C6, and C8 were also used to dissect the different contributors to DNA hybridization assays based on cationic conjugated polymers.
TL;DR: A versatile fluorescent peptide reporter of protein kinase activity is introduced that can be modified to target a desired kinase by changing the kinase recognition motif in the peptide sequence and is shown to be good substrates for these enzymes.
Abstract: We introduce a versatile fluorescent peptide reporter of protein kinase activity. The probe can be modified to target a desired kinase by changing the kinase recognition motif in the peptide sequence. The reporter motif contains the Sox amino acid, which generates a fluorescence signal when bound to Mg2+ present in the reaction mixture. The phosphorylated peptide exhibits a much greater affinity for Mg2+ than its unphosphorylated analogue and, thus, a greater fluorescence intensity. Product formation during phosphorylation by the kinase is easily followed by the increase in fluorescence intensity over time. These probes exhibit a 3−5-fold increase in fluorescence intensity upon phosphorylation, the magnitude of which depends on the substrate. Peptides containing the reporter functionality are phosphorylated on serine by Protein Kinase C and cAMP-dependent protein kinase and are shown to be good substrates for these enzymes. The principle of this design extends to peptides phosphorylated on threonine and t...
TL;DR: Although the 2-mm-long valve was prepared from a polymerization mixture consisting of only a 5% aqueous solution of monomers, it resists pressures of up to 1.38 MPa (200 psi) without observable structural damage.
Abstract: Monolithic plugs of poly(N-isopropylacrylamide) cross-linked with 5% methylenebisacrylamide have been prepared by photoinitiated polymerization within the channel of a microfluidic device. The volume change associated with the polymer phase transition at its lower critical solution temperature of 32 °C allows both the rapid swelling and the deswelling of the monoliths enabling the polymer to close or open the channel as it functions as a nonmechanical valve. Thermoelectric elements capable of changing the temperature of the system between 17 and 57 °C were used to actuate the valve. Flow through the device was monitored by fluorescence measurements via the laser-triggered photobleaching of a dye contained in the liquid phase. Photobleaching occurs quickly once the flow is stopped, and the time required to open and close the valve was 3.5 and 5.0 s, respectively. No changes in function were observed even after 120 open−close cycles. Although the 2-mm-long valve was prepared from a polymerization mixture co...
TL;DR: FRET experiments show that the polymers with a more flexible structure are better donors to fluorescein-labeled double-stranded DNA and indicate that there is better spatial registry between the flexible conjugated polymers and the secondary structure of DNA.
Abstract: Cationic water-soluble conjugated polymers with a non “rigid-rod” aspect ratio can be prepared by Suzuki coupling condensation polymerization of 2,7-dibromo-9,9-bis(6'-bromohexyl)fluorene and varying ratios of p- and m-phenyl diboronic acids, followed by reaction with trimethylamine. The resulting polymers are designated MnPm+, where the subscripts in Mn and Pm correspond to the ratio of meta and para linkages, respectively. Absorption and fluorescence spectra indicate facile energy transfer via interachain or intrachain mechanisms. The emission of MnPm+ with m > 50 matches that of M0P100+. Excitations ultimately reside in the polymer segments with largest number of para linkages. FRET experiments show that the polymers with a more flexible structure are better donors to fluorescein-labeled double-stranded DNA. Similar results are obtained when intercalated ethidium bromide is used as the acceptor. These results indicate that there is better spatial registry between the flexible conjugated polymers and th...
TL;DR: This prototype system presents an example of orthogonal self-assembly, that is, the independent formation of two different supramolecular structures, each with their own characteristics that coexist within a single system.
Abstract: The concurrent self-assembly of new 1,3,5-trisamide-cyclohexane-based low molecular weight hydrogelators and various surfactants in water leads to the formation of self-assembled fibrillar networks with encapsulated micelles. This prototype system presents an example of orthogonal self-assembly, that is, the independent formation of two different supramolecular structures, each with their own characteristics that coexist within a single system.
TL;DR: Properly substituted coumarin aldehydes can be used to detect amines and amino acids under neutral, high ionic strength conditions by the formation of highly fluorescent iminium ions by forming hydrogen bonding of the chromophore carbonyl by the acidicIminium proton.
Abstract: Properly substituted coumarin aldehydes can be used to detect amines and amino acids under neutral, high ionic strength conditions by the formation of highly fluorescent iminium ions. The fluorescence of one sensor increases by 26-fold upon the addition of glycine. This strong florescent response is attributed to hydrogen bonding of the chromophore carbonyl by the acidic iminium proton.
TL;DR: Monitoring of sewage inputs to the river demonstrated that > 10% of the rivers' discharge is provided by sewerage inputs and that these inputs could be grouped by their fluorescence and ammonia properties, suggesting that sewerage cross connections are occurring.
TL;DR: It is concluded that luminol ECL could be readily excited by various oxygen-containing species electrogenerated at different applied potentials and might be of a potential to improve analytical selectivity and sensitivity for the detection of some analytes.
Abstract: The behavior of luminol electrochemiluminescence (ECL) at a paraffin-impregnated graphite electrode (PIGE) at different applied potentials was studied. Five ECL peaks were observed at 0.31, 0.59, 1.09, 1.54, and −0.58 V versus SCE, respectively, being related to potential scan direction and ranges, N2, O2, pH of the solution, and KCl concentration. The emission spectra of various ECL peaks at different potentials showed that all ECL peaks were initiated by luminol reactions. X-ray diffraction demonstrated that a simple mixture was formed between graphite and paraffin. The fluorescence spectra on the surface of the PIGE suggested that certain groups on the graphite were oxidized when the positive potential was applied to the electrode. In the presence of O2, three main ECL peaks were obtained in 0.1 mol/L KCl at pH 12.2. The ECL peak at 0.59 V with a shoulder is likely due to the reaction of luminol radicals with O2 and further electrooxidation of luminol radicals. The ECL peak at 1.54 V was suggested to b...
TL;DR: A new cyclodextrin/porphyrin supramolecular sensitizer for zinc ion has been proposed based on the porphyrin dual fluorescence emission ratio, which shows high selectivity over biologically relevant cations and could be used for biomedical application.
Abstract: In the present paper, a new cyclodextrin/porphyrin supramolecular sensitizer for zinc ion has been proposed based on the porphyrin dual fluorescence emission ratio. In aqueous solution, meso-tetraphenylporphyrin shows weak fluorescence, while in the presence of alkylated beta-cyclodextrin, it exhibits significant fluorescence enhancement by forming a cyclodextrin/porphyrin inclusion complex. Furthermore, the formation of a supramolecular complex causes a remarkable increase of the porphyrin metalation rate following the porphyrin fluorescence emission changes at two different emission wavelengths. The fluorescence emission of tetraphenylporphyrin at 656-nm bands decreases while that at 606 nm increases upon zinc ion interaction. Thus, the inclusion complex can behave as a ratiometric fluorescent sensor. Theoretically derivative equations for fluorescent ratiometry have been proposed for the first time. The feasibility of the proposed method is demonstrated by the performance of fluorometric detection of zinc ion. With the optimum conditions described, zinc ion in aqueous solution can be determined from 5.0 x 10(-7) to 2.5 x 10(-4) M. As the porphyrin electronic absorption and fluorescence emission are located in the visible range, and the fluorescence changes upon zinc ion interaction show high selectivity over biologically relevant cations, the inclusion complex could be used for biomedical application.
TL;DR: The microwave functionalization technique will permit a broad range of inorganic nanophase phosphors to be used in high-throughput assays for environmental monitoring.
Abstract: A method for simply and cheaply preparing inorganic phosphor nanoparticles of Eu2O3 as labels in biology has been demonstrated with a simple microwave-assisted surface chemistry. The capping process adds a silane layer to the surface of the particles and provides amine groups that can be used for biological conjugation. The surface layer also protects the particles during conjugation chemistry. The particles retain their desirable optical properties that are typical of europium, that is, a spectrally narrow, red emission and a long fluorescence lifetime. The application of the nanoparticle labels in an immunoassay yields very good sensitivity in an immunoassay for atrazine (sub-parts-per-billion detection limit) without optimization of the detection system. The microwave functionalization technique will permit a broad range of inorganic nanophase phosphors to be used in high-throughput assays for environmental monitoring.
TL;DR: This is the first study to demonstrate unambiguously that the endoplasmic reticulum and Golgi apparatus are preferential sites of Foscan® accumulation in the MCF-7 cell line.
Abstract: Intracellular photosensitiser localisation significantly influences the mechanism of response to photodynamic therapy (PDT), since the primary sites of damage are closely related to the specific sensitiser distribution Foscan subcellular localisation in the MCF-7 human adenocarcinoma cell line has been studied by means of confocal microscopy and microspectrofluorometry The fluorescence topographic profiles recorded after cells costained with Foscan and organelle-specific fluorescent probes revealed that Foscan presents low localisation in lysosomes and a weak accumulation in mitochondria Alternatively, the Foscan fluorescence topographic profile turned out to colocalise perfectly with that obtained for the endoplasmic reticulum (ER) and the Golgi apparatus The patterns of fluorescence derived from confocal microscopy studies were consistent with predominant localisation of Foscan in these organelles Furthermore, evaluation of enzymatic activity of selected organelles immediately after laser light irradiation (650 nm) indicated the Golgi apparatus and ER as the primary damaged sites resulting from Foscan-mediated PDT in the MCF-7 cell line To our knowledge, this is the first study to demonstrate unambiguously that the ER and the Golgi apparatus are preferential sites of Foscan accumulation
TL;DR: A homologous series of bis-silicon-bridged stilbenes has been synthesized on the basis of a new intramolecular reductive cyclization of bis(o-silyl)-diphenylacetylenes with excess lithium naphthalenide.
Abstract: A homologous series of bis-silicon-bridged stilbenes has been synthesized on the basis of a new intramolecular reductive cyclization of bis(o-silyl)-diphenylacetylene. Thus, the reaction of bis(o-silyl)-diphenylacetylenes with excess lithium naphthalenide undergoes the two-electron reduction at the acetylene moiety to produce a dianion intermediate, which further undergoes a double cyclization in a 5-exo mode to produce the bis-silicon-bridged stilbenes. This methodology can also be applied to the synthesis of tetrakis-silicon-bridged bis(styryl)benzenes. The silicon-bridged pi-conjugated systems thus prepared show intense fluorescence in the visible region. Comparison of a bis-silicon-bridged stilbene with its carbon analogue demonstrates the substantial effects of the silicon-bridges on the electronic structures and thus on the fluorescence properties.
TL;DR: The first method for quantitative trace analysis of peroxide-based explosives is described, and a reversed-phase high-performance liquid chromatography method with post-column UV irradiation and fluorescence detection for the analysis of triacetone triperoxide and HMTD has been developed.
Abstract: The first method for quantitative trace analysis of peroxide-based explosives is described. A reversed-phase high-performance liquid chromatography method with postcolumn UV irradiation and fluorescence detection for the analysis of triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) has been developed. After separation, the analytes are degraded photochemically to hydrogen peroxide, which is subsequently determined on the basis of the peroxidase-catalyzed oxidation of p-hydroxyphenylacetic acid to the fluorescent dimer. This two-step reaction scheme in combination with the respective blanks (photochemical reactor switched off) provides for high selectivity. The limits of detection were 2 × 10-6 mol/L for both TATP and HMTD, respectively. The method has been applied to the analysis of real samples.
TL;DR: A fluorescence depolarization technique was used to determine the molecular size of asphaltene solubility fractions of a petroleum resid asphaltee, and the population distribution was estimated from published LDMS results.
Abstract: A fluorescence depolarization technique was used to determine the molecular size of asphaltene solubility fractions of a petroleum resid asphaltene. The molecular size was determined at different emission wavelengths for each solubility fraction. For each subfraction the range of molecular size was found to vary considerably. However, at a given emission wavelength, the molecular sizes for the different asphaltene solubility subfractions are very similar, that is the subfractions differ from each other by different population distributions of the same set of molecules. The size variation among the different subfractions is due to the different molecular population distributions of the constituent components. The population distribution was estimated from published LDMS results.
TL;DR: The fluorescence-based CCOA method for determination of carbonyl group profiles in cellulosic substrates was employed to study the mechanisms of various oxidative and degradation processes involving celluloses in greater detail and allowed for the first time to distinguish thecarbonyl course in different molecular weight ranges.
TL;DR: In this article, a sensitive method was developed and validated for routine screening and confirmation of ractopamine residues in porcine and bovine muscle tissues, where muscle tissues were extracted with methanol and hydrolyzed with β-glucuronidase, followed by liquid extraction and solid phase clean up.
TL;DR: The aim of this study is to immobilize an enzyme, namely, organophosphorus hydrolase (OPH), and to detect the presence of paraoxon, which is an organophile compound, using the layer-by-layer (LbL) deposition technique.
Abstract: The aim of this study is to immobilize an enzyme, namely, organophosphorus hydrolase (OPH), and to detect the presence of paraoxon, which is an organophosphorus compound, using the layer-by-layer (LbL) deposition technique. To lift the OPH from the solid substrate, a pair of polyelectrolytes (positively charged chitosan (CS) and negatively charged poly(thiophene-3-acetic acid) (PTAA)) were combined. These species were made charged by altering the pH of the solutions. LbL involved alternate adsorption of the oppositely charged polyions from dilute aqueous solutions onto a hydrophilic quartz slide. This polyion cushion was held together by the electrostatic attraction between CS and PTAA. The growing process was monitored by fluorescence spectroscopy. OPH was then adsorbed onto the five-bilayer CS/PTAA system. This five-bilayer macromolecular structure compared to the solid substrate rendered stability to the enzyme by giving functional integrity in addition to the ability to react with paraoxon solutions. The ultimate goal is to use such a system to detect the presence of organophosphorus compounds with speed and sensitivity using the absorption and fluorescence detection methodologies.
TL;DR: A simple and sensitive fluorimetric method for the determination of ascorbic acid (AA) is described, based on the condensation reaction between AA and o-phenylenediamine in the absence of the oxidant.
TL;DR: A novel, intrinsically fluorescent nonadentate europium chelate with two chromophores and hydrophilic alpha-galactose side groups is synthesized, which facilitates short turnaround times and simple instrumentation due to the absence of all signal development steps, at the same time retaining an excellent immunoassay performance.
Abstract: New labels and assay techniques are needed to improve the sensitivity and quantitativeness of point-of-care immunotesting while sustaining the rapidity and ease of use of the assays. We synthesized a novel, intrinsically fluorescent nonadentate europium chelate with two chromophores and hydrophilic α-galactose side groups. The chelate is highly fluorescent, soluble in water, and provides effective shielding of Eu from water. The performance of the nonadentate chelate was compared with a heptadentate chelate in a dry reagent immunoassay for human chorionic gonadotropin (hCG). After 15-min incubation and washing, time-resolved fluorescence was measured directly from a wet or dried well surface. Contrary to the heptadentate label, the effect of aqueous quenching on the nonadentate label was found to be insignificant, with calculated analytical detection limits (background + 3 SD) of 0.9 and 0.7 IU/L hCG for wet and dry measurements, respectively, and a linear range up to 5000 IU/L. The CVs for the new label ...