共查询到20条相似文献,搜索用时 0 毫秒
1.
The blood-brain barrier (BBB), a unique selective barrier for the central nervous system (CNS), hinders the passage of most compounds to the CNS, complicating drug development. Innovative in vitro models of the BBB can provide useful insights into its role in CNS disease progression and drug delivery. Static transwell models lack fluidic shear stress, while the conventional dynamic in vitro BBB lacks a thin dual cell layer interface. To address both limitations, we developed a microfluidic blood-brain barrier (μBBB) which closely mimics the in vivo BBB with a dynamic environment and a comparatively thin culture membrane (10 μm). To test validity of the fabricated BBB model, μBBBs were cultured with b.End3 endothelial cells, both with and without co-cultured C8-D1A astrocytes, and their key properties were tested with optical imaging, trans-endothelial electrical resistance (TEER), and permeability assays. The resultant imaging of ZO-1 revealed clearly expressed tight junctions in b.End3 cells, Live/Dead assays indicated high cell viability, and astrocytic morphology of C8-D1A cells were confirmed by ESEM and GFAP immunostains. By day 3 of endothelial culture, TEER levels typically exceeded 250 Ω cm(2) in μBBB co-cultures, and 25 Ω cm(2) for transwell co-cultures. Instantaneous transient drop in TEER in response to histamine exposure was observed in real-time, followed by recovery, implying stability of the fabricated μBBB model. Resultant permeability coefficients were comparable to previous BBB models, and were significantly increased at higher pH (>10). These results demonstrate that the developed μBBB system is a valid model for some studies of BBB function and drug delivery. 相似文献
2.
Wen Guo Brigitte J. Engelman Tajay L. Haywood Neil B. Blok Daniel S. Beaudoin Sherine O. Obare 《Talanta》2011
Organophosphorus (OP) based pesticides are known powerful inhibitors of cholinesterases, thus the toxicity of this class of compounds causes serious environmental and human health concerns. We report that benzodipyrido[3,2-a:2′,3′-c]phenazine (BDPPZ) and 3,6-dimethylbenzodipyrido-[3,2-a:2′,3′-c]phenazine (DM-BDPPZ) provide independent fluorescent and electrochemical signal transductions in the presence of the organophosphorus (OP) pesticides; fenthion, malathion and ethion. The presence of the methyl groups at the 3 and 6 positions in DM-BDPPZ was found to significantly influence the sensor performance. The difference in the fluorescence and electrochemical signals produced by the interaction of the sensor compound with each of the OP pesticides provides a means for differentiating between the three pesticides. Detection limits of 10?8 M, 10?9 and 10?12 M were obtained for fenthion, malathion and ethion, respectively. Due to the high sensitivity and ability to minimize false positives these new sensors will be useful for potential integration for future environmental use. 相似文献
3.
Victor A. GalievskyAuthor Vitae Alexander S. StasheuskiAuthor VitaeSergey N. Krylov 《Analytica chimica acta》2016
Capillary electrophoresis with Laser-Induced Fluorescence (CE-LIF) detection is being applied to new analytical problems which challenge both the power of CE separation and the sensitivity of LIF detection. On-capillary LIF detection is much more practical than post-capillary detection in a sheath-flow cell. Therefore, commercial CE instruments utilize solely on-capillary CE-LIF detection with a Limit of Detection (LOD) in the nM range, while there are multiple applications of CE-LIF that require pM or lower LODs. This tutorial analyzes all aspects of on-capillary LIF detection in CE in an attempt to identify means for improving LOD of CE-LIF with on-capillary detection. We consider principles of signal enhancement and noise reduction, as well as relevant areas of fluorophore photochemistry and fluorescent microscopy. 相似文献
4.
Johannes H. Sterba Frans Munnik Nick J. G. Pearce 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(1):25-35
Provenancing of ancient ceramics is a highly important scientific tool for archaeological studies. In general, ceramics are
not made from the original clay as it is found in deposits. To produce the needed physical properties in the finished product,
the clay has to be either tempered by adding sands or biological materials, or levigated, to remove the coarse fraction. Thus,
the chemical composition of the finished ceramic differs from the composition of the original clay bed. To overcome this obfuscation,
any information that can be gained about the temper is useful. In a small series, several pieces of ceramic were produced
from known clay and tempers and the resulting ceramics analysed by neutron activation analysis (NAA). As many attempts to
physically separate the temper from the clay matrix have failed, μ-spot analysis of temper inclusions was performed at the
microbeam particle induced X-ray Emission (μ-PIXE) facility in Rossendorf and with laser ablation inductively coupled plasma
mass spectroscopy (LA-ICP-MS) at the Aberystwyth University in Wales. It could be shown that from a small number of measurements,
a general impression of the temper used could be gained. Furthermore the μ-spot methods and the bulk data gained from INAA
are highly comparable, extending the set of elements that can be measured. With this information, the influence of the temper
on the bulk composition of the finished product can be estimated, which potentially adds crucial information to subsequent
dilution calculations. 相似文献
5.
Jean-Jacques Aaron Belkacem Laassis M. Carmen Mahedro Arsenio Muñoz de la Peña F. Salinas 《Journal of inclusion phenomena and macrocyclic chemistry》1994,18(1):69-79
The photo-oxidation reaction of phenothiazine has been studied in the presence of-cyclodextrin (-CD) and 2-hydroxypropyl-cyclodextrin (HP -CD). The influence of these organized media on the formation of the oxidation photoproduct upon UV irradiation has been investigated. Phenothiazine forms an inclusion complex with the cyclodextrins. The stoichiometry and formation constant of the complex formed with 2-hydroxypropyl -CD have been calculated using the changes of the fluorescence emission signal and of the absorbance of the drug upon inclusion. An increase of the fluorescence intensity of the photogenerated product is attained when it becomes included inside the cyclodextrin cavity. 相似文献
6.
《Journal of Photochemistry》1986,32(1):49-57
While the fluorescence of xanthone, thioxanthone and N-methylacridone shows the customary red shift with increasing solvent polarity, as measured by a polarization function, indicating an increase in dipole moment on excitation, the triplet-triplet (T1Tn) absorption spectra are strongly blue shifted, indicating a decrease in dipole moment on excitation. 相似文献
7.
Manju Bhargavi Gumpu Noel Nesakumar Bhat Lakshmishri Ramachandra John Bosco Balaguru Rayappan 《Journal of Analytical Chemistry》2017,72(3):316-326
We report for the first time a cyclic voltammetric nitrate sensor with a low detection limit based on the immobilization of zinc oxide nanoparticles on the surface of the platinum working electrode using chitosan membrane. Cyclic voltammetric data demonstrated that zinc oxide nanoparticles can electrochemically reduce nitrate ions to ammonium ions with high conductivity. In order to estimate electroanalytical parameters for each of the nitrate concentrations, Gaussian and Lorentzian curve fitting algorithms were performed on cyclic voltammetric data. Among them, the best analytical performance results were obtained with Gaussian calibration linear model. The zinc oxide modified platinum electrode showed a linear response to nitrate ions over a concentration range from 0.1 to 2.0 mM with a low detection limit and high sensitivity of 10 nM and 39.91 μA/cm2 mM, respectively. The nitrate ion concentrations in drinking water samples were determined using Gaussian calibration linear model and the predicted, added nitrate ion concentration values showed good correlation. 相似文献
8.
Macroscopic and microscopic dissipative structural patterns formed in the course of drying a series of the colloidal silica spheres ranging from 29 nm to 1 m in diameter have been observed in the aqueous deionized suspension on a cover glass. The broad ring patterns of the hill accumulated with the silica spheres are formed around the outside edges in the macroscopic scale for all spheres examined. The spoke-like cracks are also observed in the macroscopic scale and their number decreases sharply as sphere size increases. The pattern area and the time for the dryness have been discussed as a function of sphere size and concentration. The convection flow of water accompanied with that of the silica spheres and interactions among the silica spheres and substrate are important for the macroscopic pattern formation. The microscopic fractal structures of the wave-like patterns and branched strings are formed. Their fractal dimensions are determined. Microscopic patterns form in the narrow range of sphere sizes and concentrations and are determined mainly by the electrostatic and polar interactions between the spheres and/or between the sphere and substrate in the course of solidification. 相似文献
9.
Bashar R. M. Al-Gailani Gillian M. Greenway 《International journal of environmental analytical chemistry》2013,93(6):425-436
A miniaturized flow-injection-analysis system constructed from glass and polydimethylsiloxane was employed for the determination of ammonium in river water. The sample was filtered and delivered to the reactor chip electro-osmotically using a disposable fritted capillary, while reagents were delivered to the system by gravity. Ammonia was mixed with the hypochlorite, to form a monochloramine. Once the alkaline luminol (3-aminophthalhydrazide) was delivered to the system, it was oxidized by the unconsumed hypochlorite emitting a bright blue light (λ max?~?440?nm) that was detected using a miniaturized photomultiplier tube (PMT) located directly under the chip. The calibration model for ammonium standards was linear up to 0.1?µg?mL?1 (y?=??8.96x?+?1.02; correlation coefficient, r 2?=?0.9715) over a working range of 0.0–0.5?µg?mL?1. A detection limit of 10?±?6?µg?mL?1 was achieved with a precision value of (RSD ≤ 6.4%), for n?=?5. A direct and standard addition method were used to determine the concentration of ammonium in a river-water sample (from the Humber Estuary, UK) which was found to be 0.075?±?0.005?µg?mL?1, with a precision value of (RSD?≤?3.7%), for n?=?9. The results obtained showed good agreement with the average concentration 0.065?µg?mL?1 (provided by the local environmental agency), for the analysis of ammonia at different sample points on the estuary. 相似文献
10.
《Spectrochimica Acta Part B: Atomic Spectroscopy》2001,56(11):2157-2164
Total reflection X-ray fluorescence spectrometry (TXRF) offers many advantages for the identification of trace elements in biological samples like proteins, enzymes, tissues or plants. Because of difficult and time consuming isolations and cleaning procedures enzyme samples are often available in small amounts only. Using TXRF without any preliminary treatment, a ‘screening’ of such samples to determine the element composition is of interest and importance. Transition metals like Fe, Ni, Cu, Mo and the alkaline earth metal Ca may be determined with high accuracy. A further aspect of the investigation of enzymes is the simple and simultaneous determination of light elements. Sulfur, especially, is of interest. This element is a component of two amino acids, methionine and cysteine, and of iron–sulfur clusters and may be used for easy and simultaneous calculation of the protein concentration. Hence quantitative determination of sulfur by TXRF allows a cross-check regarding of conventional quantitative determination of protein concentration by, e.g. the Lowry method. On the basis of two selected enzymes of different origins and molecular weights this paper will demonstrate the influence of bio-organic matrix and different buffer media on sulfur determination by TXRF. The influence of layer thicknesses of the dry residues and absorption or scattering effects will be discussed. The results indicate that in enzymes with low molecular weights and minor amounts of buffer components a reliable determination of sulfur is possible. By contrast, for enzymes stored in higher buffer concentrations poorer results are given on account of the matrix effects described. 相似文献
11.
Schaeffer N Tan B Dickinson C Rosseinsky MJ Laromaine A McComb DW Stevens MM Wang Y Petit L Barentin C Spiller DG Cooper AI Lévy R 《Chemical communications (Cambridge, England)》2008,(34):3986-3988
The synthesis of fluorescent water-soluble gold nanoparticles by the reduction of a gold salt in the presence of a designed polymer ligand is described, the size and fluorescence of the particles being controlled by the polymer to gold ratio; the most fluorescent nanomaterial has a 3% quantum yield, a 1.1 nm gold core and a 6.9 nm hydrodynamic radius. 相似文献
12.
A new fluorescence−HPLC method was developed for the simultaneous determination of eight biogenic monoamines (histamine, methylamine,
tyramine, ethylamine, propylamine, tryptamine, 2-phenylethylamine, isoamylamine) and two biogenic diamines (putrescine, cadaverine)
in the presence of heptylamine as the internal standard. The amines were pre-column derivatized with naphthalene-2,3-dicarboxaldehyde
in the presence of cyanide ion as the nucleophile. The effect of the derivatization reaction conditions on the reaction yield
was investigated. The derivatives were separated on an Inertsil ODS-3 column (250 × 4mm i.d., 5 μm) using gradient elution
and detected fluorimetrically at excitation and emission wavelengths of 424 and 494 nm, respectively. Limits of detection
between 0.002 and 0.4 ng, injected on-column (10-μL loop), were achieved. The within- and between-day relative standard deviations
ranged between 0.2−3.4% and 0.3−4.8%, respectively. The utility of the method in assaying biogenic mono- and diamine mixtures
in Greek cheeses is demonstrated. Ultrasound-assisted liquid−liquid extraction was applied prior to derivatization. 相似文献
13.
Detection limit, reporting limit and limit of quantitation are analytical parameters which describe the power of analytical methods. These parameters are used for internal quality assurance and externally for competing, especially in the case of trace analysis in environmental compartments. The wide variety of possibilities for computing or obtaining these measures in literature and in legislative rules makes any comparison difficult. Additionally, a host of terms have been used within the analytical community to describe detection and quantitation capabilities. Without trying to create an order for the variety of terms, this paper is aimed at providing a practical proposal for answering the main questions for the analysts concerning quality measures above. These main questions and related parameters were explained and graphically demonstrated. Estimation and verification of these parameters are the two steps to get real measures. A rule for a practical verification is given in a table, where the analyst can read out what to measure, what to estimate and which criteria have to be fulfilled. In this manner verified parameters detection limit, reporting limit and limit of quantitation now are comparable and the analyst himself is responsible to the unambiguity and reliability of these measures. 相似文献
14.
Wada M Yokota C Ogata Y Kuroda N Yamada H Nakashima K 《Analytical and bioanalytical chemistry》2008,391(3):1057-1062
A sensitive high-performance liquid chromatography (HPLC)–fluorescence method for determination of morphine (Mor) in rat brain
and blood microdialysates was developed using 4-(4,5-diphenyl-1H-imidazol-2-yl)benzoyl chloride (DIB-Cl) as a label. Mor was labeled with DIB-Cl under mild reaction conditions (at room temperature
for 10 min). The separation of DIB-Mor was carried out on an octadecylsilica (ODS) column with CH3CN/0.1 M acetate buffer (pH 5.4) within 14 min. The detection limits of Mor in brain and blood microdialysates at a signal-to-noise
ratio of 3 were 0.4 and 0.6 ng mL−1, respectively. The proposed method was successfully applied to the preliminarily study of potential pharmacokinetic interaction
between Mor and diclofenac. 相似文献
15.
Water-soluble cadmium sulfide (CdS) quantum dots (QDs) capped by mercaptoacetic acid were synthesized by aqueous-phase arrested
precipitation, and characterized by transmission electron microscopy, spectrofluorometry, and UV-Vis spectrophotometry. The
prepared luminescent water-soluble CdS QDs were evaluated as fluorescence probes for the detection of highly reactive hydrogen
selenide ions (HSe− ions). The quenching of the fluorescence emission of CdS QDs with the addition of HSe− ions is due to the elimination of the S2− vacancies which are luminescence centers. Quantitative analysis based on chemical interaction between HSe− ions and the surface of CdS QDs is very simple, easy to develop, and has demonstrated very high sensitivity and selectivity
features. The effect of foreign ions (common anions and biologically relevant cations) on the fluorescence of the CdS QDs
was examined to evaluate the selectivity. Only Cu2+ and S2− ions exhibit significant effects on the fluorescence of CdS QDs. With the developed method, we are able to determine the
concentration of HSe− ions in the range from 0.10 to 4.80 μmol L−1, and the limit of detection is 0.087 μmol L−1. The proposed method was successfully applied to monitor the obtained HSe− ions from the reaction of glutathione with selenite. To the best of our knowledge, this is the first report on fluorescence
analysis of HSe− ions in aqueous solution.
Figure CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe- ions in aqueous
solution 相似文献
16.
Molecular dynamics simulations of mixtures of 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM+][PF6-]) and water have been performed in order to investigate how small amounts of water affect the translational and rotational dynamics of this ionic liquid (IL). We find that water is closely associated with the anions and that its presence enhances both the translational and rotational dynamics of the IL. In agreement with experiments, we find that the fluorescence spectra of Coumarin-153 is red-shifted because of the presence of water. Small amounts of water enhance the speed of relaxation of the solvent surrounding the solute probe after photoexcitation, but only at a "local environment" level. Interconversion between environments still occurs on a long time scale compared with the fluorescence lifetime of the probe. Excitation wavelength-dependent emission is observed both in the neat IL and in the IL+water mixture. 相似文献
17.
《Tetrahedron letters》2014,55(51):7076-7081
Comparison is made of the crystal structures of two different solvates of a molecule containing both H-bond donor and acceptor sites, which is found either as a monomer or a hexamer. The solid state features are analysed with respect to the behaviour seen in solutions in the same solvents as found in the crystal lattices. Dimethylsulfoxide appears to be particularly effective in preventing aggregation not only through H-bond acceptance but also through contacts at S which may block H-bond acceptor sites adjacent to donors. 相似文献
18.
Mbaye M Gaye Seye MD Aaron JJ Coly A Tine A 《Analytical and bioanalytical chemistry》2011,400(2):403-410
Flow injection analysis combined with photo-induced fluorescence (FIA-PIF) has been applied for the determination of α-cypermethrin
pesticide residues in Senegalese natural waters, using organic solutions and cyclodextrin (β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin)
aqueous media. The α-cypermethrin insecticide has a very weak natural fluorescence, but it is converted into strongly fluorescent
photoproduct(s) by UV irradiation. Cyclodextrins were found to enhance the PIF signal. FIA parameters, including mobile phase
flow rate, injected volume, and reactor length, were optimized. Analytical performances of the FIA-PIF method for the determination
of α-cypermethrin were satisfactory, with concentration linear dynamic ranges over one to two orders of magnitude and with
rather low limits of detection and limits of quantification, in the ng mL−1 range, and relative standard deviations comprised between 1.2% and 3.8%. Application of FIA-PIF for the analysis of fortified
natural water samples collected from Senegal yielded good recovery values (84–112%). Because of its high sampling rate, the
FIA-PIF method constitutes a rapid analytical tool, useful for quantification of α-cypermethrin residues in natural waters. 相似文献
19.
Moors SL Jonckheer A De Maeyer M Engelborghs Y Ceulemans A 《Current protein & peptide science》2008,9(5):427-446
We discuss the dynamics of tryptophan rotamers in the context of the non-exponential fluorescence decay in proteins. The central question is: how does the ground-state conformational heterogeneity influence the time evolution of tryptophan fluorescence? This problem is examined here from the theoretical perspective. Three methods at different levels of theory, and with different scopes and computational requirements are reviewed. The Dead-end elimination method is limited to side-chain dynamics and provides an efficient way to detect the stable tryptophan rotamers in a protein. Its application to the study of heterogeneous emission characteristics is illustrated. Molecular dynamics is aimed at the full phase space of the macromolecule in solution, but must rely on classical force fields and laws of evolution. We examine to what extent the molecular mechanics paradigm yields sufficiently accurate thermodynamic results, and what are the possible kinetic implications. Finally Quantum Chemistry is the only theoretical method that allows a direct assessment of the excited states. It is necessarily restricted to small molecular systems, and thus must be used in a hybrid combination with classical methods and electrostatic models. So far understanding of the emitting state has greatly progressed as a result of these calculations, but the actual treatment of the photophysical decay processes at the quantum level has not yet really started. 相似文献
20.
Alison E. Ashcroft 《Journal of the American Society for Mass Spectrometry》2010,21(7):1087-1096
A number of proteins are capable of converting from their soluble, monomeric form into highly-ordered, insoluble aggregates
known as amyloid fibrils. In vivo, these fibrils, which accumulate in organs and tissues, are associated with a wide range
of amyloid diseases for which there are currently no therapeutic solutions. The molecular details of the pathway from native
monomer through oligomeric intermediates to the final amyloid fibril remain a challenging enigma. Over the past few years,
mass spectrometry has been applied to investigate the various stages of amyloid fibril formation, and this report summarizes
the key steps achieved to date. 相似文献