Characteristic Emission Wavelengths Research Articles

Measuring Atomic Emission from Beacons for Long-Distance Chemical Signaling

In an effort to exploit chemistry for information science, we have constructed a system to send a message powered by a combustion reaction. Our system uses the thermal excitation of alkali metals to transmit an encoded signal over long distances. A message is transmitted by burning a methanol-soaked cotton string embedded with combinations of high, low, or zero levels of potassium, rubidium, and/or cesium ions. By measuring the intensities at the characteristic emission wavelengths of each metal in the near-infrared, 19 unique signals can be distinguished. We have built a custom telescope to detect these signals from 1 km away for nearly 10 min. The signal is isotropic, is self-powered, and has a low background. A potential application of this platform is for search and rescue signaling where another layer of information can be transmitted, in addition to the location of the beacon. This work, which seeks to encode and transmit information using chemistry instead of electronics, is part of the new field of "infochemistry".

Synthesis and properties study of new rare earth sodium borates Eu 3+ -doped Na 3 Y(BO 3 ) 2

The samples of ultraviolet (UV)-excited Eu3+-doped Na3Y(BO3)2 phosphor with different reaction temperatures and various concentrations of Eu3+ ions content are synthesised and their photoluminescence (PL) properties are investigated. It is found that the optimal reaction temperature and Eu3+-doped concentration are 800°C and 12.5%, respectively. The phosphor not only has stronger UV PL intensity but also shows excellent chromaticity and broader range of characteristic emission wavelength. Furthermore, a new phenomenon is observed. By altering the reaction temperatures, the peak positions of the highest intensity are divided into two types, which is due to the competition between two kinds of emission, resulting from the split of 5D0 level.

Pollution of Musts and Wines: A New Method for the Determination of Petroleum By-Products Using Fluorescence

Pollution of musts and wines by petroleum by-products may happen accidentally by mechanical machines, particularly during harvests. A new method for detecting and determining this type of pollutant, using fluorescence, has been developed in the present work. The principal pollutant investigated was diesel fuel which exhibits a characteristic fluorescence spectrum, whichever its origin. Fluorescence is principally emitted by traces of polycyclic aromatic compounds (PACs), principally polycyclic aromatic hydrocarbons (PAHs), contained in most petroleum by-products. The method involves a liquid-liquid extraction of PAHs using cyclohexane and fluorescence measurements were performed on the resulting “cyclohexane extracts.” Some natural compounds extracted from must and wine samples may also exhibit an intrinsic fluorescence emission which interferes with the characteristic fluorescence of pollutants. This is the case, in particular, of tannins contained in red wines and in wood. Thus, this prevents any reliable determination of pollutants. Natural compounds were efficiently separated from PAHs using solid phase extraction by elution of the cyclohexane solution on the florisil phase. The corresponding fluorescence was totally eliminated at the characteristic emission wavelength of pollutants. Thus, the presence of any pollution by diesel fuel could be characterized unambiguously and determined accurately. The limits of detection and quantification were determined to be around 0.3 and 1.0 μL L−1, respectively. Uncertainties on determinations were estimated at less than 20% for diesel fuel, provided a reference spectrum of the pollutant is available. If not, the pollutant concentration can be estimated within a factor two. The evolution of the pollution with time was also investigated over several weeks, particularly during the time of fermentation. The method is fairly simple to implement, quick and reliable.

Confirmatory analysis of non-steroidal anti-inflammatory drugs in bovine milk by high-performance liquid chromatography with fluorescence detection

HPLC with fluorescence detection is considered for confirmatory analysis of group B veterinary drugs by the European Union legislation. A procedure for confirming the presence of anti-inflammatory non-steroidal drug (NSAID) residues in bovine milk by reversed phase high-performance liquid chromatography with fluorescence detection is herein described. The native fluorescence of nine drugs belonging to different NSAID sub-classes, namely flurbiprofen, carprofen, naproxen, vedaprofen, 5-hydroxy-flunixin, niflumic acid, mefenamic acid, meclofenamic acid and tolfenamic acid, allowed for detection in bovine milk down to 0.25–20.0 μg/kg. Confirmation of the nine NSAIDs is attained by fluorescence detection at characteristic excitation and emission wavelengths. The procedure described is simple and selective. Limits of quantification (LOQs) ranging between 0.25 and 20 μg/kg were measured; satisfactory trueness and within-laboratory reproducibility data were calculated at LOQ spiking levels, apart from 5-hydroxy-flunixin. The procedure developed is used in our laboratory for confirmation of each one of the above mentioned NSAIDs in bovine milk, to support results after HPLC quantitative analysis with UV–vis detection.

High throughput single molecule detection for monitoring biochemical reactions.

The design, performance and application of a novel optical system for high throughput single molecule detection (SMD) configured in a continuous flow format using microfluidics is reported. The system consisted of a microfabricated polymer-based multi-channel fluidic network situated within the optical path of a laser source (lambda(ex) = 660 nm) with photon transduction accomplished using an electron-multiplying charge coupled device (EMCCD) operated in a frame transfer mode that allowed tracking single molecules as they passed through a large field-of-view (FoV) illumination zone. The microfluidic device consisted of 30 microchannels possessing dimensions of 30 microm (width) x 20 microm (depth) with a 25 microm pitch. Individual molecules were electrokinetically driven through the fluidic network and excited within the wide-field illumination area with the resulting fluorescence collected via an objective and imaged onto the EMCCD camera. The detection system demonstrated sufficient sensitivity to detect single DNA molecules labeled with a fluorescent tag (AlexaFluor 660) identified through their characteristic emission wavelength and the burst of photons produced during their transit through the excitation volume. In its present configuration and fluidic architecture, the sample processing throughput was approximately 4.02 x 10(5) molecules s(-1), but could be increased dramatically through the use of narrower channels and a smaller pitch. The system was further evaluated using a single molecule-based fluorescence quenching assay for measuring the population differences between duplexed and single-stranded DNA molecules as a function of temperature for determining the duplex melting temperature, T(m).

Solvatofluorochromism of N-[2-(2-hydroxylethylamino)-ethyl]-1,8-naphthalimide in protic solvent

A N-substituted naphthalimide derivative N-[2-(2-hydroxylethylamino)-ethyl]-1,8-naphthalimide ( HEAN), which contains potential acceptors for hydrogen bond, was synthesized and fully characterized. The fluorescence and UV/vis behaviors of HEAN in different solvents were investigated, and its Stokes shift value and fluorescence quantum yield ( Φ f) in each solvent were determined. A remarkable fluorescence enhancement of HEAN in protic–polar solvents but a great quenching effect in apolar, less–polar and aprotic–polar solvents were observed, suggesting the key role of the proticity of solvents. In the protic–polar solvents, the fluorescence intensity and the quantum yield of HEAN increased along with a slight red-shift of the characteristic emission wavelength ( λ em) with the increase of solvent polarity. Maximum Φ f value of 0.453 for HEAN was found in water solvent with a Stokes shift of 4636 cm −1. The inhibition of the photoinduced electron transfer (PET) by the intermolecular hydrogen-bonding interactions between protic solvents and HEAN was proposed to be responsible for its strong fluorescence enhancement. Such solvatofluorochromic property of HEAN may make it as a prospective fluorescent chemosensor to distinguish a protic solvent from aprotic solvents.

Sequential Inactivation of Bacillus Subtilis Spores with Ultraviolet Radiation and Iodine

Bacillus subtilis spores were used as an indicator organism to characterize the effects of UV radiation and iodine, alone and in combination, as disinfectants for water. Spore exposures to UV radiation were conducted in shallow, well-mixed batch reactors under collimated beams. Three (essentially) monochromatic collimated UV sources were used in these experiments, with characteristic emission wavelengths of 222, 254, and 282 nm . Iodine exposures were conducted in well-mixed batch reactors. Synergism was demonstrated when UV (at certain doses) and iodine were used as sequential disinfectants; synergism was attributed to UV-induced damage that enhanced the susceptibility of spores to iodine.

Fluorimetric determination of phytic acid in urine based on replacement reaction

A sensitive fluorimetric method for determination of phytic acid in human urine samples was described. The method was based on a fluorimetric replacement reaction, in which the added phytic acid replaced the Cu 2+ ion from Cu 2+–gelatin complex, liberating the fluorescent gelatin molecule. The fluorescence of the solution was accordingly recovered proportionally to the amount of the foreign phytic acid. The excitation wavelength was 273.5 nm and the characteristic emission wavelength was 305.0 nm, respectively. The calibration graph was obtained by plotting the recovered fluorescent intensity at maximum 305.0 nm against the added standard phytic acid, and was divided into two sections. One section was linear over the range of 0.40–2.40 mg L −1 with a linear regression equation of I f = −0.895 + 15.146 c ( R 2 > 0.9993), and the other over the range of 2.40–9.20 mg L −1 with a linear regression equation of I f = −29.526 + 26.113 c ( R 2 > 0.9996), respectively. The relative standard deviation (R.S.D.) at 95% confidence degree for a 2.0 mg L −1 of standard phytic acid within 1 month was less than 1.26% ( n = 5), indicating the procedure is reproducible. The detection and the quantification limits of phytic acid were estimated to be 0.23 and 0.40 mg L −1, respectively. The proposed method was applied to the determination of phytic acid in urine samples and the found concentrations of phytic acid in urine were in the range of 0.49–0.75 mg L −1 with recoveries of 96.2–108.8%. Comparison of the obtained results with the reported HPLC was performed, indicating the proposed method was reliable.

High-sensitivity integrated fluorescence analysis for microfluidic lab-on-a-chip

Microfluidics studies the behavior of fluids at the microscale and the design of systems to take advantage of such behavior. A multidisciplinary field encompassing physics, chemistry, engineering, and biotechnology, microfluidics integrates sensors, actuators, and other electronics to create new applications.1–3 Importantly, new principles of fluid manipulation have enabled detection and handling of nanoliter fluid samples. In recent years, these principles have been applied to the development of lab-on-a-chip (LOC) systems.4, 5 A substantial challenge for such miniaturized systems—the size of a credit card—for point-of-care and on-site analysis lies in developing their ability to effectively detect analytes of interest. Small sample volumes and low concentrations common to microfluidic LOCs make high-sensitivity detection of critical importance. While conventional microscopy tools can easily meet these demands in a laboratory, developing portable systems requires integrated miniaturized detectors. Fluorescence is one of the most commonly used analytic techniques in the biosciences. It is based on emission of a dye at one wavelength when it is illuminated by another, shorter wavelength. Lack of integrated fluorescence detection is a major roadblock for many biotechnological assays in portable LOC format. In a typical microfluidic fluorescence immunoassay assay, fluorescently labeled antibodies are used to tag a specific antigen (e.g., bacteria, viruses, or other organic molecules of interest) in a microfluidic device. The excitation light stimulates the dye to fluoresce, and the characteristic emission wavelength, or color, is observed through a filter that suppresses excitation light, enbling the dye emission to be seen clearly. As shown in Figure 1, the orange light represents the dye emission and the green light Figure 1. Schematic of a lab-on-a-chip (LOC) for fluorescence analysis. PDMS: Poly(dimethylsiloxane).

C-terminal lysines determine phospholipid interaction of sarcomeric mitochondrial creatine kinase.

High affinity interaction between octameric mitochondrial creatine kinase (MtCK) and the phospholipid cardiolipin in the inner mitochondrial membrane plays an important role in metabolite channeling between MtCK and inner membrane adenylate translocator, which itself is tightly bound to cardiolipin. Three C-terminal basic residues revealed as putative cardiolipin anchors in the x-ray structures of MtCK and corresponding to lysines in human sarcomeric MtCK (sMtCK) were exchanged by in vitro mutagenesis (K369A/E, K379Q/A/E, K380Q/A/E) to yield double and triple mutants. sMtCK proteins were bacterially expressed, purified to homogeneity, and verified for structural integrity by enzymatic activity, gel filtration chromatography, and CD spectroscopy. Interaction with cardiolipin and other acidic phospholipids was quantitatively analyzed by light scattering, surface plasmon resonance, and fluorescence spectroscopy. All mutant sMtCKs showed a strong decrease in vesicle cross-linking, membrane affinity, binding capacity, membrane ordering capability, and binding-induced changes in protein structure as compared with wild type. These effects did not depend on the nature of the replacing amino acid but on the number of exchanged lysines. They were moderate for Lys-379/Lys-380 double mutants but pronounced for triple mutants, with a 30-fold lower membrane affinity and an entire lack of alterations in protein structure compared with wild-type sMtCK. However, even triple mutants partially maintained an increased order of cardiolipin-containing membranes. Thus, the three C-terminal lysines determine high affinity sMtCK/cardiolipin interaction and its effects on MtCK structure, whereas low level binding and some effect on membrane fluidity depend on other structural components. These results are discussed in regard to MtCK microcompartments and evolution.

Coupling Reactions of End- vs Mid-Functional Polymers

Reactive compatibilization of immiscible polymer blends is typically accomplished by grafting reactions between functional groups distributed randomly on one polymer and end-functional groups on the other polymer. A number of model studies have focused on end coupling in polymer melts. In this work we compare directly reaction rate constants for an end-functional chain reacting with an end-functional chain, kE, vs reacting with a mid-functional chain, kM, using competitive reaction of phthalic anhydride end- and mid-functional poly(methyl methacrylate) (PMMA-eAn and PMMA-mAn) with amine terminal PMMA and polystyrene (PMMA-NH2 and PS-NH2). PMMA-eAn was labeled with 7-nitrobenz-2-oxa-1,3-diazole (NBD) while PMMA-mAn was labeled with anthracene. We measured the extent of coupling to block and graft copolymers selectively at the characteristic excitation and emission wavelengths of NBD and anthracene using a fluorescence detector coupled with GPC. We found that coupling with the mid-functional PMMA was slower under all reaction conditions investigated and had the increasing order of kE/kM: homogeneous melt (1.7), solution (2.8), heterogeneous blend prepared in the mixer (2.6−3.2), and static flat interface (>10). The kinetic excluded-volume effect and steric hindrance due to the polymer chain are considered to be the reasons for kE/kM > 1 in the homogeneous case. kE/kM in solution was in agreement with the value (2.1) predicted by the kinetic excluded-volume theory. The large value of kE/kM in the static flat interface was attributed to end-group segregation at the interface. Interestingly, we found that flow affected the interfacial reaction tremendously, resulting in over 1000 times higher rate constant in heterogeneous melt blending than that in the static bilayer film.

High efficiency light emitting devices in silicon

We report on the fabrication and performances of highly efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. They exhibit strong 1.54 μm electro-luminescence (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III–V semiconductors. Emission at different wavelengths has been achieved incorporating different rare earths (terbium (Tb) and ytterbium (Yb)) in the gate dielectric. The external quantum efficiency depends on the rare-earth ions incorporated and ranges from 10% (for a Tb doped MOS) to 0.1% (for an Yb doped MOS). RE excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light emitting MOS devices have been fabricated using Er-doped silicon rich oxide (SRO) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 0.2%. In these devices, Er pumping occurs partially by hot electrons and partially by energy transfer from the Si nanostructures to the rare-earth ions, depending on Si excess in the film. Si/SiO 2 Fabry–Perot microcavities have been fabricated to enhance the external quantum emission along the cavity axis and the spectral purity of emission from the films that are used as active media to fabricate a Si-based resonant cavity light emitting diode (RCLED). These structures are fabricated by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths (nm): 540, 980 and 1540 (characteristic emission wavelengths, respectively, for Tb, Yb and Er). The reflectivity of the microcavities is about 97% and the quality factor ranges from 60 (for the cavity tuned at 980 nm) to 95 (for the cavities tuned at 540 and 1540 nm).

High Efficiency Light Emission Devices in Silicon

AbstractWe report on the fabrication and performances of the most efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1.54 μm electroluminescence at 300K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III-V semiconductors. Emission at different wavelenghts has been achieved incorporating different rare earths (Ce, Tb, Yb, Pr) in the gate dielectric. The external quantum efficiency depends on the rare earth ions incorporated and ranges from 10% (for an Tb doped MOS) to 0.1% (for an Yb doped MOS). RE excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light emitting MOS devices have been fabricated using Er-doped SRO (Silicon Rich Oxide) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 0.2%. In these devices Er pumping occurs part by hot electrons and part by energy transfer from the Si nanostructures to the rare earth ions, depending by Si excess in the film. Si/SiO2 Fabry-Perot microcavities have been fabricated to enhance the external quantum emission along the cavity axis and the spectral purity of emission from the films that are used as active media to realize a Si based RCLED (resonant cavity light emitting diode). These structures are realized by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths: 540nm, 980nm and 1540nm (characteristic emission wavelengths respectively for Tb, Yb and Er). The reflectivity of the microcavities is of 97% and the quality factor ranges from 60 (for the cavity tuned at 980nm) to 95 (for the cavities tuned at 540nm and 1540nm).

Modulation of Guest Partitioning Within Dendrimer–Surfactant Supramolecular Assemblies

ABSTRACT Electrostatic interactions are used to create a template-assisted supramolecular assembly consisting of a polymeric dendrimer at the core and amphiphilic substrates on the periphery. The dendrimer generation and the chemical structure of the amphiphiles are varied to construct multiple and distinct microenvironments within the dendrimer–ligand complex for encapsulation of small guest molecules. In particular, these investigations employ a guest molecule that is a neutral fluorescent probe that exhibits an emission wavelength with an extreme sensitivity to the polarity of its surroundings. Partitioning of the fluorophore within the various microregions of the dendrimer–surfactant supramolecular complex is distinguished by the characteristic emission wavelengths of the overlapping Gaussian functions comprising the overall fluorescence spectrum. The observed variations in the prodan emission spectrum suggest interaction of prodan at protonated amino groups (460-nm emission), within dendritic branches and surfactant tails (490-nm emission), and in interior regions of the dendrimer core (430-nm emission). We demonstrate that the positioning of the guest molecule within the supramolecular complex can be modulated through the selection of dendrimer generation, surfactant chain length, and dendrimer:surfactant concentration ratio.

Emission spectra of MgSO 4:Dy, MgSO 4:Tm and MgSO 4:Dy,Mn phosphors

MgSO 4:Dy, MgSO 4:Tm and MgSO 4:Dy,Mn thermoluminescence (TL) phosphors have been prepared and their emission spectra were measured using a linear heater and optical multichannel analyzer. Emission bands at about 480, 580 and 660 nm of MgSO 4 doped with Dy were observed in three dimension (3D) glow curve. Emission bands about 360, 460, and 660 nm were observed in a 3D glow curve of MgSO 4 doped with Tm. The emission spectra of MgSO 4:Dy and MgSO 4:Tm are attributed to the characteristic emission wavelengths from transitions of Dy 3+ and Tm 3+ respectively. The results show that the structures of traps in matrix materials determine the activation energy distribution and dopant energy levels of rare earth ions are related with the emission spectrum wavelengths of sulfate phosphors. The intensities of the glow peaks in both bands at about 480 and 580 nm in MgSO 4 doped Dy and Mn were dramatically reduced in comparison with that of MgSO 4 doped Dy except above 300°C. It means that the trapping structures of MgSO 4 :Dy phosphor has greatly been altered by the co-dopant Mn but no change is observed in wavelengths of the emission spectra.

Generalised Canonical Correlation Analysis for the interpretation of fluorescence spectral data

The paper reports an application of Generalised Canonical Correlation Analysis to fluorescence spectral data. Emission fluorescence spectra can be recorded for several excitation wavelengths and can be presented as 3-way data tables. The objec- tives of the data treatment are to describe and compare the samples by taking into account all the emission spectra, and to reve al characteristic excitation and emission wavelengths. Generalised Canonical Correlation Analysis has been tested on fluorescence emission spectra acquired for binary mixtures of raw materials in the food domain. The application of the method within the con - text of spectral data is presented.

人工膜と生体膜の接点を探る 最近の膜研究の方法 環境感受性色素によるリポソームと細胞の膜物性のイメージング

The environment-sensitive fluorescent probes, such as prodan, acrylodan and laurdan, change their emission wavelength depending on the polarity of their environment. For example, laurdan changes its emission peak from 440 nm in the gel phase of lipid bilayer to 490 nm in the liquid-crystalline phase. Time-resolved fluorescence spectra of laurdan in liposomes suggested that the 490 nm component of fluorescence was a emission from dipolar-relaxed states of excited fluorophores and that the dipolar relaxation was due to water molecules penetrated into the hydrophobic region of membranes. The generalized polarization (GP), defined by two fluorescence intensities at these characteristic emission wavelengths, is a measure of membrane fluidity and polarity. We have constructed an imaging system which enables us to obtain spatial distribution of the GP. The system is composed of a fluorescence microscope, monochromatic filters, a cooled-CCD camera, and an image-analysis system. It was found that the average GP value in a liposome and its temperature dependence were almost the same as those obtained by a conventional fluorescence spectrometer, by appending only one instrumental constant which described the difference of relative sensitivity between the two wavelength channels. By using this apparatus to the study of membrane heterogeneity of CHO (chinese hamster ovary) cells, it was found that plasma membranes were less polar than the membranes of organelles.

Application of multi-wavelength fluorometry for monitoring wastewater treatment process dynamics

Much of the methodology employed for characterizing wastewater and in modeling wastewater treatment processes employs off-line analysis. Off-line analysis is time consuming and not ideally suited to developing process control strategies. Clearly a rapid, inexpensive and reliable method suitable for following organic consumption and biomass production on-line would be very useful. In this study multiple excitation—multiple emission fluorometry was examined as a method for monitoring wastewater treatment processes. Results were first obtained for defined protein solutions and activated sludge to identify characteristic excitation and emission wavelength pairs. These results were then used to develop a rapid off-line assay for measurement of synthetic feeds consisting of protein substrates for batch aerobic and anoxic wastewater treatment processes and for on-line monitoring of cellular metabolic states in an anoxic process. Step-wise multiple regression and principal component analysis were employed for data analysis. The former was used to determine the most informative excitation and emission wavelength pairs while the latter was applied to reduce fluorescent spectra dimensions. Analysis of the batch kinetics suggests that this approach is valid and revealed some dynamic features of protein utilization and biomass accumulation under aerobic and anoxic conditions. A correlation was developed between COD-removal rates and the fluorescence signals in the two processes using fluorescent emission spectra rather than single signals. The data suggests that this multiple excitation—multiple emission fluorometry may be a suitable method for following wastewater and activated sludge dynamics and could be used as the basis for the development of expert system based biosensors.

Interaction of influenza hemagglutinin amino-terminal peptide with phospholipid vesicles: a fluorescence study

We have studied tryptophan fluorescence from a 20-residue synthetic peptide corresponding to the amino terminal of the HA2 subunit of the influenza virus hemagglutinin protein, a putative "fusion" peptide. Decay-associated spectra have been obtained at pH 7.4 and at pH 5 (the optimal pH for influenza virus fusion) in the presence and absence of liposomes. We demonstrate that a blue shift in the total steady-state fluorescence spectrum upon binding to liposomes is due to a movement in characteristic emission wavelength and increased lifetime of one of the resolved spectral components. In contrast, a further shift after lowering the pH is the product of a redistribution in the relative amplitudes of spectral components. Also, each decay component is quenched by spin-labels or anthroxyl groups normally located within the hydrocarbon interior of the membranes. Calculations are presented leading to an estimate of the distance of the tryptophan residue from the bilayer center, suggesting that the tryptophan residues are at or near the hydrocarbon-polar interface. No gross positional change was detected between pH values. Rotational depolarization is shown to be retarded by liposome binding, more so at low pH.