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Eingeladener Vortrag
- nein (6)
In dieser Arbeit werden die Grundlagen der Normung, die Entstehung einer Norm und die für die Gasanalytik relevanten Normungsgremien kurz dargestellt. Dazu werden die wichtigsten Normen zur Gasanalytik entlang des analytischen Prozesses gruppiert und aufgeführt. Schließlich wird als Anwendungsbeispiel aus der eigenen Praxis der Prozess von der Herstellung bis zur Zertifizierung eines Kalibriergases beschrieben.
Radiation therapy is a basic part of cancer treatment. To increase the DNA damage in carcinogenic cells and preserve healthy tissue at the same time, radiosensitizing molecules such as halogenated nucleobase analogs can be incorporated into the DNA during the cell reproduction cycle. In the present study 8.44 eV photon irradiation induced single strand breaks (SSB) in DNA sequences modified with the radiosensitizer 5-bromouracil (5BrU) and 8-bromoadenine (8BrA) are investigated. 5BrU was incorporated in the 13mer oligonucleotide flanked by different nucleobases. It was demonstrated that the highest SSB cross sections were reached, when cytosine and thymine were adjacent to 5BrU, whereas guanine as a neighboring nucleobase decreases the activity of 5BrU indicating that competing reaction mechanisms are active. This was further investigated with respect to the distance of guanine to 5BrU separated by an increasing number of adenine nucleotides. It was observed that the SSB cross sections were decreasing with an increasing number of adenine spacers between guanine and 5BrU until the SSB cross sections almost reached the level of a non-modified DNA sequence, which demonstrates the high sequence dependence of the sensitizing effect of 5BrU. 8BrA was incorporated in a 13mer oligonucleotide as well and the strand breaks were quantified upon 8.44 eV photon irradiation in direct comparison to a non-modified DNA sequence of the same composition. No clear enhancement of the SSB yield of the modified in comparison to the non-modified DNA sequence could be observed. Additionally, secondary electrons with a maximum energy of 3.6 eV were generated when using Si as a substrate giving rise to further DNA damage. A clear enhancement in the SSB yield can be ascertained, but to the same degree for both the non-modified DNA sequence and the DNA sequence modified with 8BrA.
DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7 - 2.3 x 10-16 cm2. The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies < 3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold.
BAM is currently building up a platform of novel nanoRMs relying on iron oxide nanoparticles of different shape, size and surface chemistry. Iron oxide was chosen as a core material because of its relevance to the material and life sciences.
As a first candidate of this series, we present cubic iron oxide nanoparticles with a nominal edge length of 8 nm. These particles were synthesized by thermal decomposition of iron oleate in high boiling organic solvents adapting well-known literature procedures. After dilution to a concentration suitable for electron microscopy (TEM and SEM) as well as for small-angle X-ray scattering (SAXS) measurements, the candidate nanoRM was bottled and assessed for homogeneity and stability by both methods following the guidelines of ISO 17034 and ISO Guide 35.
The particle sizes obtained by both STEM-in-SEM and TEM are in excellent agreement with a minimum Feret of 8.3 nm ± 0.7 nm. The aspect ratio (AR) of the iron oxide cubes were extracted from the images as the ratio of minimum Feret to Feret resulting in an AR of 1.18 for TEM to 1.25 for SEM. Alternatively, a rectangular bounding box was fitted originating from the minimum Feret and the longest distance through the particle in perpendicular direction. This led to AR values of 1.05 for TEM and 1.12 for SEM, respectively. The results confirm the almost ideal cubic shape.
The physico-chemical basis of DNA radiosensitization: Implications for cancer radiation therapy
(2018)
High-energy radiation is used in combination with radiosensitizing therapeutics to treat cancer. The most common radiosensitizers are halogenatednucleo-sides and cisplatin derivatives, and recently also metal nanoparticles have been suggested as potentialradiosensitizing agents. The radiosensitizingaction of these compounds can at least partly be ascribed to an enhancedreactivity towards secondary low-energy electrons generated along the radiation track of the high-energyprimary radiation, or to an additional emission of secondary reactive electrons close to the tumor tissue. This is referred to as physico-chem ical radiosensitization. In this Conceptarticle we presentcurrent experimental methodsused to study fundamentalprocesses of physico-chemical radiosensitization and discuss the most relevant classes of radiosensitizers. Open questions in the current discussions are identified and future directions outlined, which can lead to optimized treatment protocols or even novel therapeuticconcepts.
Self-assembled monolayers (SAMs) on plasmonic substrates play a significant role applications of surface-enhanced Raman scattering (SERS). At the same time, localized surface plasmon resonances (LSPRs) can be employed for a broad range of plasmon-supported chemical modifications. Here, micropatterning using the derivatization of SAMs on gold nanosubstrates for rewritable SERS-based security labels or as the basis for sensing arrays functionalized with biomolecules is demonstrated using different plasmon-catalyzed reactions. The formation of 4,4′-dimercaptoazobenzene (DMAB) from p-aminothiophenol (PATP) as well as from p-nitrothiophenol (PNTP) and the reduction of PNTP to PATP are used to change the functionality of the substrate in specified positions. Employing LSPR, the reactions are started by illumination using visible laser light at a high intensity in a focal spot of a microscope objective and yield microscopic patterns of the reaction product. The obtained molecular patterns can be erased by other reactions, enabling different strategies for rewriting, encryption, or stepwise functionalization.
One of the most commonly used bonds between two biomolecules is the bond between biotin and streptavidin (SA) or streptavidin homologues (SAHs). A high dissociation constant and the consequent high-temperature stability even allows for its use in nucleic acid detection under polymerase chain reaction (PCR) conditions. There are a number of SAHs available, and for assay design, it is of great interest to determine as to which SAH will perform the best under assay conditions. Although there are numerous single studies on the characterization of SAHs in solution or selected solid phases, there is no systematic study comparing different SAHs for biomolecule-binding, hybridization, and PCR assays on solid phases. We compared streptavidin, core streptavidin, traptavidin, core traptavidin, neutravidin, and monomeric streptavidin on the surface of microbeads (10–15 μm in diameter) and designed multiplex microbead-based experiments and analyzed simultaneously the binding of biotinylated oligonucleotides and the hybridization of oligonucleotides to complementary capture probes. We also bound comparably large DNA origamis to capture probes on the microbead surface. We used a real-time fluorescence microscopy imaging platform, with which it is possible to subject samples to a programmable time and temperature profile and to record binding processes on the microbead surface depending on the time and temperature. With the exception of core traptavidin and monomeric streptavidin, all other SA/SAHs were suitable for our investigations. We found hybridization efficiencies close to 100% for streptavidin, core streptavidin, traptavidin, and neutravidin. These could all be considered equally suitable for hybridization, PCR applications, and melting point analysis. The SA/SAH–biotin bond was temperature-sensitive when the oligonucleotide was mono-biotinylated, with traptavidin being the most stable followed by streptavidin and neutravidin. Mono-biotinylated oligonucleotides can be used in experiments with temperatures up to 70 °C. When oligonucleotides were bis-biotinylated, all SA/SAH–biotin bonds had similar temperature stability under PCR conditions, even if they comprised a streptavidin variant with slower biotin dissociation and increased mechanostability.
Small variations in the isotopic composition of some elements have been used as proof of provenance of mineral and biological samples, to describe geological processes, and to estimate a contamination source. Routinely, isotope compositions are measured by mass spectrometry; the working horse of the isotope analysis. However, mass spectrometric methods are expensive, time-consuming and they require a high qualified analyst.
Here, an alternative faster and low-cost optical method for isotope ratio determination is investigated: high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Stable isotope amount composition of X = Li, B, Mg, Ca and Sr have been determined by monitoring the absorption spectra of their in situ generated hydrides (XH) in graphite furnace HR-CS-MAS. For example, the system of two stable isotopes of boron (10B and 11B) was studied via its hydride for the electronic transition X1Σ+ → A1Π (Fig. 1a). The spectrum of a given sample is a linear combination of the 10BH molecule and its isotopologue 11BH. Therefore, isotopic composition of samples and reference materials are calculated by a partial least square regression (PLS). For this, a spectral library is built by using samples with known isotope composition. Results are metrologically compatible with those reported by mass spectrometric methods. [1] Similar results are obtained for n isotope systems like Mg (24Mg, 25Mg, and 26Mg), where isotope shift of their isotopologues can be resolved as shown in Fig.1 b. The extension of this methodology to other elements like Li, Ca and Sr is discussed [2].
References:
[1] C. Abad, S. Florek, H. Becker-Ross, M.-D. Huang, H.-J. Heinrich, S. Recknagel, J. Vogl, N. Jakubowski, U. Panne, Determination of boron isotope ratios by high-resolution continuum source molecular absorption spectrometry using graphite furnace vaporizers, Spectrochim. Acta, Part B, 136 (2017) 116-122.
[2] C. Abad et al., unpublished results, 2018.