Analytische Chemie
Filtern
Erscheinungsjahr
- 2017 (201) (entfernen)
Dokumenttyp
- Zeitschriftenartikel (191)
- Beitrag zu einem Tagungsband (8)
- Buchkapitel (1)
- Posterpräsentation (1)
Sprache
- Englisch (201) (entfernen)
Referierte Publikation
- ja (201) (entfernen)
Schlagworte
- Fluorescence (17)
- Quantum yield (13)
- Nanoparticle (12)
- Nanoparticles (11)
- Mechanochemistry (10)
- Upconversion (9)
- NIR (8)
- SAXS (8)
- Small-angle X-ray scattering (7)
- IR (6)
Under the Comité Consultatif pour la Quantité de Matière (CCQM), a key comparison, CCQM-K104, was coordinated by the National Institute of Metrology (NIM). The comparison was designed to demonstrate a laboratory's performance in determining the mass fraction of the main component in a complex high purity organic material. Nine NMIs or DIs participated in the comparison. Eight participants reported their results. An additional impurity was resolved from the avermectin B1a peak and was tentatively identified as an unknown impurity by NMIA (National Measurement Institute (Australia)). It was subsequently identified by NIM as a diastereoisomer of avermectin B1a at the C-26 position. Final reference value (KCRV) = 924.63 mg/g, with uncertainty (k=1) = 3.89 mg/g, and expanded uncertainty = 8.97 mg/g. The degrees of equivalence with the avermectin B1a KCRV for each participant were reported. The measurement results and degrees of equivalence should be indicative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of high structural complexity (relative molecular mass range of 500 Da -1000 Da and low polarity (-log KOW ≤ -2).
Quantum dot (QD) based nanomaterials are very promising materials for the fabrication of optoelectronic devices like solar cells, light emitting diodes (LEDs), and photodetectors as well as as reporters for chemo- and biosensing and bioimaging. Many of These applications involve the monitoring of changes in photoluminescence intensity and energy transfer processes which can strongly depend on excitation wavelength or energy. In this work, we analyzed the excitation energy dependence (EED) of the photoluminescence quantum yields (PL QYs) and decay kinetics and the circular dichroism (CD) spectra of CdSe/CdS core/shell QDs with different thicknesses of the surface passivation shell. Our results demonstrate a strong correlation between the spectral position of local maxima observed in the EED of PL QY and the zero-crossing points of the CD profiles. Theoretical analysis of the energy band structure of the QDs with effective mass approximation suggests that these structures could correspond to exciton energy levels. This underlines the potential of CD spectroscopy for the study of electronic energy structure of chiroptically active nanocrystals which reveal quantum confinement effects.
The implementation of fluorescent methods is of outstanding importance in the field of optical chemical sensor Technology and biosciences. Their bioanalytical applications are manifold including fluorescence microscopy, fluorescence in situ hybridization, DNA sequencing, fluorescence-activated cell sorting, immunoassays, analysis of DNA and Protein microarrays, and quantitative PCR, just to name a few examples. Particularly, fluorescence microscopy is a valuable method in the versatile field of biomedical imaging methods which nowadays utilizes different fluorescence Parameters like emission wavelength/Color and lifetime for the discrimination between different targets. Sectional Images are available with confocal microscopes. Tissue, cells or single cellular compartments can be stained and visualized with fluorescent dyes and biomolecules can be selectively labeled with fluorescent dyes to Monitor biomolecular interactions inside cells or at Membrane bound receptors.
On the other hand , fluorophores can act as indicator (or "molecular probe") to visualize intrinsically colorless and non-fluorescent ionic and neutral analytes such as pH, Oxygen (pO2), metal ions, anions, hydrogen peroxide or bioactive small organic molecules such as Sugars or nucleotides. Thereby, their photoluminescent properties (fluorescence or phoporescence intensity, exitation and/or Emission wavelength, emission lifetime or anisotropy) respond to the presence of these species in their immediate Environment. In general, the use of luminescent probes has the advantage that they can be delivered directly into the sample, and detected in a contactless remote mode. By now, these probes are often encapsulated in different types of nanoparticles (NPs) made from (biodegradable) organic polymers, biopolymers or inorganic materials like silica or bound to their surface.
Despite their immense and rapidly increasing
importance as analytical tools or therapeutic drugs, the detailed
structural features of particular monoclonal antibodies are
widely unknown. Here, an antibody already in use for diagnostic
purposes and for molecular dosimetry studies in cancer therapy
with very high affinity and specificity for cisplatin-induced DNA
modifications was studied extensively. The molecular structure
and modifications as well as the antigen specificity were
investigated mainly by mass spectrometry. Using nano electrospray
ionization mass spectrometry, it was possible to characterize the antibody in its native state. Tandem-MS experiments not
only revealed specific fragments but also gave information on the molecular structure. The detailed primary structure was further
elucidated by proteolytic treatment with a selection of enzymes and high resolution tandem-MS. The data were validated by
comparison with known antibody sequences. Then, the complex glycan structures bound to the antibody were characterized in
all detail. The Fc-bound oligosaccharides were released enzymatically and studied by matrix-assisted laser desorption/ionization
mass spectrometry. Overall 16 different major glycan structures were identified. The binding specificity of the antibody was
investigated by applying synthetic single and double stranded DNA oligomers harboring distinct Pt adducts. The antibody−
antigen complexes were analyzed by mass spectrometry under native conditions. The stability of the complex with double
stranded DNA was also investigated.
Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanoprobes for a wide range of pharmaceutical, diagnostic, medical, and therapeutic applications. A key Parameter indicating the Formation and stability of micelles is the critical micelle concentration (CMC). In this respect, we determined the CMC of common anionic, cationic, and non-ionic surfactants fluorometrically using different fluorescent probes and fluorescence Parameters for Signal detection and ompared the results with conductometric and surface Tension measurements. Based upon These results, requirements, Advantages, and pitfalls of each methods are discussed. Our study underlines the versatility of fluorometric methods that do not impose specific requirements on surfactants and are especially suited for the quantification of very low CMC values. Conductivity and surface Tension measurements yield smaller uncertainties particularly for high CMC values, yet are more time- and substance consuming and not suitable for every surfactant.
Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy Transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-Efficiency issue by developing versatile core-Shell nanostructures, where high-concentration sensitizers and activators are confined in the core and Shell Region of representative hexagonal NaYF2:Yb,Er UCNPs. After Doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of Magnitude higher luminescence intesity than conventional homogeneously doped nanostructures. At the same time, the activator Ions located in the Shell enable a ~6 times more efficient resonant energy Transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly encrease the General applicability of upconversion nanotechnologies.
Modification of polyethylene and polypropylene surfaces by atmospheric-pressure plasmas using mixtures of nitrogen and hydrogen was studied using Fouriertransform infrared spectroscopy in the attenuated total reflection mode (FTIR-ATR) and by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) in order to shed some light on the chemical nature of nitrogen-containing functional Groups on the polymer surface. Using FTIR-ATR spectroscopy combined with hydrogendeuterium isotope exchange of active hydrogen atoms, it was shown that the direct treatment of PE foils by dielectric barrier discharges (DBDs) in N2/H2 mixtures and a subsequent exposure of the samples to the ambient air results in the formation of –NH2 moieties of primary amides on the polymer surface. Corresponding in situ experiments with streaming N2/H2 DBD post-discharges virtually free of H2O and O2, on the other hand, showing the absence of –NH2, proving that no primary amines or amides are formed by this treatment although substantial amounts of nitrogen are incorporated. Moreover, directly N2/H2-plasma-treated polymer surfaces, similar to afterglow-treated low-density polyethylene (LDPE), show amphiphilic character as to be seen by chemical derivatization with nucleophilic reagents 4-(trifluoromethyl) phenylhydrazine and 4-(trifluoromethyl)benzylamine, in addition to electrophilic aromatic aldehydes normally
used to derivatize such surfaces.
The presence of imines or other functional groups with CN moieties which may be invoked to explain the dual (amphiphilic) reactivity is proven by NEXAFS studies on ultrathin plasma-treated PE films, confirming significant amounts of nitrogen in CN bonds and carbon in CC bonds.
At the core of luminescence color and lifetime Tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the Impact of the particle architecture for commonly used sensitizer (S) and activator (A) Ions. In this respect, a series of core@Shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@..., ...@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-Shell NPs. As refealed by quantitative steady-state and time-resolved luminescence studies, the relative spatial Distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical Impact on ther luminescence characteristics. Although the increased amount of Yb3+ Ions boosts UCNP Performance by amplifying the Absorption, the Yb3+ ions can also efficiently dissipate the energy stored in the material through energy Migration to the surface, thereby reducing the Overall energy Transfer Efficiency to the activator ions. The results provide yet another proof that UC Phosphor chemistry combined with materials Engineering through intentional core@shell structures may help to fine-tune the luminescence Features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and Display technologies.
For in-service inspections on wheelset axles with a hollow drilling, mechanized ultrasound inspection systems with single element probes are typically used. The ultrasonic testing in the zones close to the external surface of the railway axles can be realized from the inside of the bore hole, without demounting the wheelset and without dismantling the wheels and the brake discs. The testing system must be able to find flaws in the external surface of the hollow shafts, whose surface lies in the radial-radial plane, these are called transversal flaw. Presently testing systems are used, where scanning is realized in the circumferential direction by mechanical rotation of the probe system in the actual drilling. The phased array probe system, which is presented here, can carry out the rotation scan electronically. The scan can be carried out by simply moving the system forward and backwards through the drilling without mechanical rotation. Manipulation becomes simpler and the inspection time can be shortened considerably. The ultrasonic beam can be inclined exactly and be focused in the plane vertical to the specimen axis.
The probe is designed with help of indispensable simulations using especially designed software developed by BAM. The feasibility and the alignment between the simulated and experimental results were shown in earlier projects reported by Boehm et al. (2006) and Völz et al. (2012). The main task here is to optimize a probe for bore holes with a diameter of 65 mm with an increase in sensitivity and a high spatial resolution. This development will be carried out by use of extensive simulations and result in certain changes of the relevant probe parameters.
A sealable ultrathin window sample cell for the study of liquids by means of soft X-ray spectroscopy
(2017)
A new sample cell concept for the analysis of liquids or solid-liquid interfaces using soft X-ray spectroscopy is presented, which enables the complete sealing of the cell as well as the Transport into vacuum via, for example, a load-lock system. The cell uses pressure monitoring and active as well as passive pressure regulation systems, thereby facilitating the full control over the pressure during filling, sealing, evacuation, and measurement. The cell design and sample preparation as well as the crucial sealing procedure are explained in detail. As a first proof-of-principle experiment, successful nitrogen K-edge fluorescence yield near-edge X-ray absorption fine structure experiments of a biomolecular solution are presented. For this purpose, it is shown that the careful evaluation of all involved parameters, such as window type or photon flux, is desirable for optimizing the experimental result.