@phdthesis{Bastian2022,
  author    = {Bastian, Philipp U.},
  title     = {Core-shell upconversion nanoparticles - investigation of dopant intermixing and surface modification},
  doi       = {10.25932/publishup-55160},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-551607},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XII, 108, xxiii},
  year      = {2022},
  abstract  = {Frequency upconversion nanoparticles (UCNPs) are inorganic nanocrystals capable to up-convert incident photons of the near-infrared electromagnetic spectrum (NIR) into higher energy photons. These photons are re-emitted in the range of the visible (Vis) and even ultraviolet (UV) light. The frequency upconversion process (UC) is realized with nanocrystals doped with trivalent lanthanoid ions (Ln(III)). The Ln(III) ions provide the electronic (excited) states forming a ladder-like electronic structure for the Ln(III) electrons in the nanocrystals. The absorption of at least two low energy photons by the nanoparticle and the subsequent energy transfer to one Ln(III) ion leads to the promotion of one Ln(III) electron into higher excited electronic states. One high energy photon will be emitted during the radiative relaxation of the electron in the excited state back into the electronic ground state of the Ln(III) ion. The excited state electron is the result of the previous absorption of at least two low energy photons. The UC process is very interesting in the biological/medical context. Biological samples (like organic tissue, blood, urine, and stool) absorb high-energy photons (UV and blue light) more strongly than low-energy photons (red and NIR light). Thanks to a naturally occurring optical window, NIR light can penetrate deeper than UV light into biological samples. Hence, UCNPs in bio-samples can be excited by NIR light. This possibility opens a pathway for in vitro as well as in vivo applications, like optical imaging by cell labeling or staining of specific organic tissue. Furthermore, early detection and diagnosis of diseases by predictive and diagnostic biomarkers can be realized with bio-recognition elements being labeled to the UCNPs. Additionally, "theranostic" becomes possible, in which the identification and the treatment of a disease are tackled simultaneously. For this to succeed, certain parameters for the UCNPs must be met: high upconversion efficiency, high photoluminescence quantum yield, dispersibility, and dispersion stability in aqueous media, as well as availability of functional groups to introduce fast and easy bio-recognition elements. The UCNPs used in this work were prepared with a solvothermal decomposition synthesis yielding in particles with NaYF4 or NaGdF4 as host lattice. They have been doped with the Ln(III) ions Yb3+ and Er3+, which is only one possible upconversion pair. Their upconversion efficiency and photoluminescence quantum yield were improved by adding a passivating shell to reduce surface quenching. However, the brightness of core-shell UCNPs stays behind the expectations compared to their bulk material (being at least μm-sized particles). The core-shell structures are not clearly separated from each other, which is a topic in literature. Instead, there is a transition layer between the core and the shell structure, which relates to the migration of the dopants within the host lattice during the synthesis. The ion migration has been examined by time-resolved laser spectroscopy and the interlanthanoid resonance energy transfer (LRET) in the two different host lattices from above. The results are presented in two publications, which dealt with core-shell-shell structured nanoparticles. The core is doped with the LRET-acceptor (either Nd3+ or Pr3+). The intermediate shell serves as an insulation shell of pure host lattice material, whose shell thickness has been varied within one set of samples having the same composition, so that the spatial separation of LRET-acceptor and -donor changes. The outer shell with the same host lattice is doped with the LRET-donor (Eu3+). The effect of the increasing insulation shell thickness is significant, although the LRET cannot be suppressed completely. Next to the Ln(III) migration within a host lattice, various phase transfer reactions were investigated in order to subsequently perform surface modifications for bioapplications. One result out of this research has been published using a promising ligand, that equips the UCNP with bio-modifiable groups and has good potential for bio-medical applications. This particular ligand mimics natural occurring mechanisms of mussel protein adhesion and of blood coagulation, which is why the UCNPs are encapsulated very effectively. At the same time, bio-functional groups are introduced. In a proof-of-concept, the encapsulated UCNP has been coupled successfully with a dye (which is representative for a biomarker) and the system's photoluminescence properties have been investigated.},
  language  = {en}
}
@phdthesis{Stete2020,
  author    = {Stete, Felix},
  title     = {Gold at the nanoscale},
  doi       = {10.25932/publishup-49605},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-496055},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 186},
  year      = {2020},
  abstract  = {In this cumulative dissertation, I want to present my contributions to the field of plasmonic nanoparticle science. Plasmonic nanoparticles are characterised by resonances of the free electron gas around the spectral range of visible light. In recent years, they have evolved as promising components for light based nanocircuits, light harvesting, nanosensors, cancer therapies, and many more. This work exhibits the articles I authored or co-authored in my time as PhD student at the University of Potsdam. The main focus lies on the coupling between localised plasmons and excitons in organic dyes. Plasmon-exciton coupling brings light-matter coupling to the nanoscale. This size reduction is accompanied by strong enhancements of the light field which can, among others, be utilised to enhance the spectroscopic footprint of molecules down to single molecule detection, improve the efficiency of solar cells, or establish lasing on the nanoscale. When the coupling exceeds all decay channels, the system enters the strong coupling regime. In this case, hybrid light-matter modes emerge utilisable as optical switches, in quantum networks, or as thresholdless lasers. The present work investigates plasmon-exciton coupling in gold-dye core-shell geometries and contains both fundamental insights and technical novelties. It presents a technique which reveals the anticrossing in coupled systems without manipulating the particles themselves. The method is used to investigate the relation between coupling strength and particle size. Additionally, the work demonstrates that pure extinction measurements can be insufficient when trying to assess the coupling regime. Moreover, the fundamental quantum electrodynamic effect of vacuum induced saturation is introduced. This effect causes the vacuum fluctuations to diminish the polarisability of molecules and has not yet been considered in the plasmonic context. The work additionally discusses the reaction of gold nanoparticles to optical heating. Such knowledge is of great importance for all potential optical applications utilising plasmonic nanoparticles since optical excitation always generates heat. This heat can induce a change in the optical properties, but also mechanical changes up to melting can occur. Here, the change of spectra in coupled plasmon-exciton particles is discussed and explained with a precise model. Moreover, the work discusses the behaviour of gold nanotriangles exposed to optical heating. In a pump-probe measurement, X-ray probe pulses directly monitored the particles' breathing modes. In another experiment, the triangles were exposed to cw laser radiation with varying intensities and illumination areas. X-ray diffraction directly measured the particles' temperature. Particle melting was investigated with surface enhanced Raman spectroscopy and SEM imaging demonstrating that larger illumination areas can cause melting at lower intensities. An elaborate methodological and theoretical introduction precedes the articles. This way, also readers without specialist's knowledge get a concise and detailed overview of the theory and methods used in the articles. I introduce localised plasmons in metal nanoparticles of different shapes. For this work, the plasmons were mostly coupled to excitons in J-aggregates. Therefore, I discuss these aggregates of organic dyes with sharp and intense resonances and establish an understanding of the coupling between the two systems. For ab initio simulations of the coupled systems, models for the systems' permittivites are presented, too. Moreover, the route to the sample fabrication - the dye coating of gold nanoparticles, their subsequent deposition on substrates, and the covering with polyelectrolytes - is presented together with the measurement methods that were used for the articles.},
  language  = {en}
}
@phdthesis{Kaergell2020,
  author    = {K{\"a}rgell, Martin},
  title     = {Layer formation from perovskite nanoparticles with tunable optical and electronic properties},
  doi       = {10.25932/publishup-47566},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475667},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 233},
  year      = {2020},
  abstract  = {Hybrid organic-inorganic perovskites have attracted attention in recent years, caused by the incomparable increase in efficiency in energy convergence, which implies the application as an absorber material for solar cells. A disadvantage of these materials is, among others, the instability to moisture and UV-radiation. One possible solution for these problems is the reduction of the size towards the nano world. With that nanosized perovskites are showing superior stability in comparison to e.g. perovskite layers. Additionally to this the nanosize even enables stable perovskite structures, which could not be achieved otherwise at room temperature. This thesis is separated into two major parts. The separation is done by the composition and the band gap of the material and at the same time the shape and size of the nanoparticles. Here the division is made by the methylammonium lead tribromide nanoplatelets and the caesium lead triiodide nanocubes. The first part is focusing on the hybrid organic-inorganic perovskite (methylammonium lead tribromide) nanoplatelets with a band gap of 2.35 eV and their thermal behaviour. Due to the challenging character of this material, several analysis methods are used to investigate the sub nano and nanostructures under the influence of temperature. As a result, a shift of phase-transition temperatures towards higher temperatures is observed. This unusual behaviour can be explained by the ligand, which is incorporated in the perovskite outer structure and adds phase-stability into the system. The second part of this thesis is focusing on the inorganic caesium lead triiodide nanocubes with a band gap of 1.83 eV. These nanocrystals are first investigated and compared by TEM, XRD and other optical methods. Within these methods, a cuboid and orthorhombic structure are revealed instead of the in literature described cubic shape and structure. Furthermore, these cuboids are investigated towards their self-assembly on a substrate. Here a high degree in self-assembly is shown. As a next step, the ligands of the nanocuboids are exchanged against other ligands to increase the charge carrier mobility. This is further investigated by the above-mentioned methods. The last section is dealing with the enhancement of the CsPbI3 structure, by incorporating potassium in the crystal structure. The results are suggesting here an increase in stability.},
  language  = {en}
}
@phdthesis{Dai2018,
  author    = {Dai, Xiaolin},
  title     = {Synthesis of artificial building blocks for sortase-mediated ligation and their enzymatic linkage},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-420060},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIV, 125},
  year      = {2018},
  abstract  = {Das Enzym Sortase A katalysiert die Bildung einer Peptidbindung zwischen der Erkennungssequenz LPXTG und einem Oligoglycin. W{\"a}hrend vielf{\"a}ltige Ligationen zwischen Proteinen und verschiedenen Biomolek{\"u}len, Proteinen und kleinen synthetischen Molek{\"u}len, sowie Proteinen und Oberfl{\"a}chen durchgef{\"u}hrt wurden, besteht das Ziel dieser Arbeit darin, die Sortase-katalysierte Verlinkung von synthetischen Bausteinen zu untersuchen. Dies k{\"o}nnte den Weg bereiten f{\"u}r die Anwendung von Sortase A f{\"u}r chemische Aufgabenstellungen und eventuell sogar in den Materialwissenschaften. F{\"u}r diese grunds{\"a}tzliche Untersuchung wurden die verwendeten Bausteine zun{\"a}chst so einfach wie m{\"o}glich gehalten und leicht zug{\"a}ngliche SiO2 Nanopartikel und kommerziell erh{\"a}ltliche Polymerbl{\"o}cke ausgew{\"a}hlt. Die Bausteine wurden als erstes mit den Peptidsequenzen f{\"u}r Sortase-vermittelte Ligationen funktionalisiert. SiO2 Nanopartikel wurden mit Durchmessern von 60 und 200 nm hergestellt und mit C=C Doppelbindungen oberfl{\"a}chenmodifiziert. Dann wurden Peptide mit einem terminalen Cystein kovalent durch eine Thiol-en Reaktion angebunden. An die 60 nm NP wurden Peptide mit einem Pentaglycin und an die 200 nm Partikel Peptide mit LPETG Sequenz gebunden. Auf die gleiche Art und Weise wurden Peptide mit terminalem Cystein an die Polymere Polyethylenglykol (PEG) und Poly(N Isopropylacrylamid) (PNIPAM), die beide {\"u}ber C=C Endgruppen verf{\"u}gen, gebunden und G5-PEG und PNIPAM-LPETG Konjugate erhalten. Mit den vier Bausteinen wurden nun durch Sortase-vermittelte Ligation NP-Polymer Hybride, NP-NP und Polymer-Polymer Strukturen hergestellt und die Produkte u. a. durch Transmissionselektronen-mikroskopie, MALDI-ToF Massenspektrometrie sowie Dynamische Lichtstreuung charakterisiert. Die Verlinkung dieser synthetischen Bausteine konnte eindeutig gezeigt werden. Das Verwenden von kommerziell erh{\"a}ltlichen Polymeren hat jedoch zu einem Gemisch der Polymer-Peptid Konjugate mit unmodifiziertem Polymer gef{\"u}hrt, welches nicht gereinigt werden konnte. Deswegen wurden anschließend Synthesestrategien f{\"u}r reine Peptid-Polymer und Polymer-Peptid Konjugate als Bausteine f{\"u}r Sortase-vermittelte Ligationen entwickelt. Diese basieren auf der RAFT Polymerisation mit CTAs, die entweder an N- oder C-Terminus eines Peptids gebunden sind. GG-PNIPAM wurde durch das Anbinden eines geeigneten RAFT CTAs an Fmoc-GG in einer Veresterungsreaktion, Polymerisation von NIPAM und Abspalten der Fmoc Schutzgruppe synthetisiert. Weiterhin wurden mehrere Peptide durch Festphasen-Peptidsynthese erhalten. Die Anbindung eines RAFT CTAs (oder eines Polymerisationsinitiators) an den N-Terminus eines Peptids kann automatisiert als letzter Schritt in einem Peptid-Synthetisierer erfolgen. Die Synthese eines solchen Konjugats konnte in dem Zeithorizont dieser Arbeit noch nicht erreicht werden. Jedoch existieren mehrere vielversprechende Strategien, um diesen Ansatz mit verschiedenen Kopplungsreagenzien zur Anbindung des CTAs fortzusetzen. Solche Polymer Bausteine k{\"o}nnen in Zukunft f{\"u}r die Synthese von Protein-Polymer Konjugaten durch Sortase-Katalyse verwendet werden. Außerdem kann der Ansatz auch f{\"u}r die Synthese von Block-Copolymeren aus Polymerbl{\"o}cken mit Peptidmotiven an beiden Enden ausgebaut werden. Auch wenn bei der grunds{\"a}tzlichen Untersuchung im Rahmen dieser Arbeit Hybridstrukturen hergestellt wurden, die auch durch traditionelle chemische Synthesen erhalten werden k{\"o}nnten, wird ein Bausatz solcher Bausteine in Zukunft die Synthese neuer Materialien erm{\"o}glichen und kann auch den Weg f{\"u}r die Anwendung von Enzymen in den Materialwissenschaften ebnen. In Erg{\"a}nzung zu Nanopartikeln und Block-Copolymeren k{\"o}nnen dann auch Hybridmaterialien unter Einbezug von Protein-basierten Bausteinen hergestellt werden. Daher k{\"o}nnten Sortase Enzyme zu einem Werkzeug werden, welches etablierte chemische Verlinkungstechniken erg{\"a}nzt und mit den hoch spezifischen Peptidmotiven {\"u}ber funktionale Einheiten verf{\"u}gt, die orthogonal zu allen chemischen Gruppen sind.},
  language  = {en}
}
@phdthesis{Abouserie2018,
  author    = {Abouserie, Ahed},
  title     = {Ionic liquid precursors for multicomponent inorganic nanomaterials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418950},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 193},
  year      = {2018},
  abstract  = {Health effects, attributed to the environmental pollution resulted from using solvents such as benzene, are relatively unexplored among petroleum workers, personal use, and laboratory researchers. Solvents can cause various health problems, such as neurotoxicity, immunotoxicity, and carcinogenicity. As such it can be absorbed via epidermal or respiratory into the human body resulting in interacting with molecules that are responsible for biochemical and physiological processes of the brain. Owing to the ever-growing demand for finding a solution, an Ionic liquid can use as an alternative solvent. Ionic liquids are salts in a liquid state at low temperature (below 100 C), or even at room temperature. Ionic liquids impart a unique architectural platform, which has been interesting because of their unusual properties that can be tuned by simple ways such as mixing two ionic liquids. Ionic liquids not only used as reaction solvents but they became a key developing for novel applications based on their thermal stability, electric conductivity with very low vapor pressure in contrast to the conventional solvents. In this study, ionic liquids were used as a solvent and reactant at the same time for the novel nanomaterials synthesis for different applications including solar cells, gas sensors, and water splitting. The field of ionic liquids continues to grow, and become one of the most important branches of science. It appears to be at a point where research and industry can work together in a new way of thinking for green chemistry and sustainable production.},
  language  = {en}
}
@phdthesis{Schulze2017,
  author    = {Schulze, Nicole},
  title     = {Neue Templatphasen zur anisotropen Goldnanopartikelherstellung durch den Einsatz strukturbildender Polymere},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-409515},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 117, xv},
  year      = {2017},
  abstract  = {Ziel der vorliegenden Arbeit war die Synthese und Charakterisierung von anisotropen Goldnanopartikeln in einer geeigneten Polyelektrolyt-modifizierten Templatphase. Der Mittelpunkt bildet dabei die Auswahl einer geeigneten Templatphase, zur Synthese von einheitlichen und reproduzierbaren anisotropen Goldnanopartikeln mit den daraus resultierenden besonderen Eigenschaften. Bei der Synthese der anisotropen Goldnanopartikeln lag der Fokus in der Verwendung von Vesikeln als Templatphase, wobei hier der Einfluss unterschiedlicher strukturbildender Polymere (stark alternierende Maleamid-Copolymere PalH, PalPh, PalPhCarb und PalPhBisCarb mit verschiedener Konformation) und Tenside (SDS, AOT - anionische Tenside) bei verschiedenen Synthese- und Abtrennungsbedingungen untersucht werden sollte. Im ersten Teil der Arbeit konnte gezeigt werden, dass PalPhBisCarb bei einem pH-Wert von 9 die Bedingungen eines R{\"o}hrenbildners f{\"u}r eine morphologische Transformation von einer vesikul{\"a}ren Phase in eine r{\"o}hrenf{\"o}rmige Netzwerkstruktur erf{\"u}llt und somit als Templatphase zur formgesteuerten Bildung von Nanopartikeln genutzt werden kann. Im zweiten Teil der Arbeit wurde dargelegt, dass die Templatphase PalPhBisCarb (pH-Wert von 9, Konzentration von 0,01 wt.\%) mit AOT als Tensid und PL90G als Phospholipid (im Verh{\"a}ltnis 1:1) die effektivste Wahl einer Templatphase f{\"u}r die Bildung von anisotropen Strukturen in einem einstufigen Prozess darstellt. Bei einer konstanten Synthesetemperatur von 45 °C wurden die besten Ergebnisse bei einer Goldchloridkonzentration von 2 mM, einem Gold-Templat-Verh{\"a}ltnis von 3:1 und einer Synthesezeit von 30 Minuten erzielt. Ausbeute an anisotropen Strukturen lag bei 52 \% (Anteil an dreieckigen Nanopl{\"a}ttchen von 19 \%). Durch Erh{\"o}hung der Synthesetemperatur konnte die Ausbeute auf 56 \% (29 \%) erh{\"o}ht werden. Im dritten Teil konnte durch zeitabh{\"a}ngige Untersuchungen gezeigt werden, dass bei Vorhandensein von PalPhBisCarb die Bildung der energetisch nicht bevorzugten Pl{\"a}ttchen-Strukturen bei Raumtemperatur initiiert wird und bei 45 °C ein Optimum annimmt. Kintetische Untersuchungen haben gezeigt, dass die Bildung dreieckiger Nanopl{\"a}ttchen bei schrittweiser Zugabe der Goldchlorid-Pr{\"a}kursorl{\"o}sung zur PalPhBisCarb enthaltenden Templatphase durch die Dosierrate der vesikul{\"a}ren Templatphase gesteuert werden kann. In umgekehrter Weise findet bei Zugabe der Templatphase zur Goldchlorid-Pr{\"a}kursorl{\"o}sung bei 45 °C ein {\"a}hnlicher, kinetisch gesteuerter Prozess der Bildung von Nanodreiecken statt mit einer maximalen Ausbeute dreieckigen Nanopl{\"a}ttchen von 29 \%. Im letzten Kapitel erfolgten erste Versuche zur Abtrennung dreieckiger Nanopl{\"a}ttchen von den {\"u}brigen Geometrien der gemischten Nanopartikell{\"o}sung mittels tensidinduzierter Verarmungsf{\"a}llung. Bei Verwendung von AOT mit einer Konzentration von 0,015 M wurde eine Ausbeute an Nanopl{\"a}ttchen von 99 \%, wovon 72 \% dreieckiger Geometrien hatten, erreicht.},
  language  = {de}
}
@phdthesis{MbayaMani2017,
  author    = {Mbaya Mani, Christian},
  title     = {Functional nanoporous carbon-based materials derived from oxocarbon-metal coordination complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407866},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IV, 135},
  year      = {2017},
  abstract  = {Nanoporous carbon based materials are of particular interest for both science and industry due to their exceptional properties such as a large surface area, high pore volume, high electroconductivity as well as high chemical and thermal stability. Benefiting from these advantageous properties, nanoporous carbons proved to be useful in various energy and environment related applications including energy storage and conversion, catalysis, gas sorption and separation technologies. The synthesis of nanoporous carbons classically involves thermal carbonization of the carbon precursors (e.g. phenolic resins, polyacrylonitrile, poly(vinyl alcohol) etc.) followed by an activation step and/or it makes use of classical hard or soft templates to obtain well-defined porous structures. However, these synthesis strategies are complicated and costly; and make use of hazardous chemicals, hindering their application for large-scale production. Furthermore, control over the carbon materials properties is challenging owing to the relatively unpredictable processes at the high carbonization temperatures. In the present thesis, nanoporous carbon based materials are prepared by the direct heat treatment of crystalline precursor materials with pre-defined properties. This synthesis strategy does not require any additional carbon sources or classical hard- or soft templates. The highly stable and porous crystalline precursors are based on coordination compounds of the squarate and croconate ions with various divalent metal ions including Zn2+, Cu2+, Ni2+, and Co2+, respectively. Here, the structural properties of the crystals can be controlled by the choice of appropriate synthesis conditions such as the crystal aging temperature, the ligand/metal molar ratio, the metal ion, and the organic ligand system. In this context, the coordination of the squarate ions to Zn2+ yields porous 3D cube crystalline particles. The morphology of the cubes can be tuned from densely packed cubes with a smooth surface to cubes with intriguing micrometer-sized openings and voids which evolve on the centers of the low index faces as the crystal aging temperature is raised. By varying the molar ratio, the particle shape can be changed from truncated cubes to perfect cubes with right-angled edges. These crystalline precursors can be easily transformed into the respective carbon based materials by heat treatment at elevated temperatures in a nitrogen atmosphere followed by a facile washing step. The resulting carbons are obtained in good yields and possess a hierarchical pore structure with well-organized and interconnected micro-, meso- and macropores. Moreover, high surface areas and large pore volumes of up to 1957 m2 g-1 and 2.31 cm3 g-1 are achieved, respectively, whereby the macroscopic structure of the precursors is preserved throughout the whole synthesis procedure. Owing to these advantageous properties, the resulting carbon based materials represent promising supercapacitor electrode materials for energy storage applications. This is exemplarily demonstrated by employing the 3D hierarchical porous carbon cubes derived from squarate-zinc coordination compounds as electrode material showing a specific capacitance of 133 F g-1 in H2SO4 at a scan rate of 5 mV s-1 and retaining 67\% of this specific capacitance when the scan rate is increased to 200 mV s-1. In a further application, the porous carbon cubes derived from squarate-zinc coordination compounds are used as high surface area support material and decorated with nickel nanoparticles via an incipient wetness impregnation. The resulting composite material combines a high surface area, a hierarchical pore structure with high functionality and well-accessible pores. Moreover, owing to their regular micro-cube shape, they allow for a good packing of a fixed-bed flow reactor along with high column efficiency and a minimized pressure drop throughout the packed reactor. Therefore, the composite is employed as heterogeneous catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran showing good catalytic performance and overcoming the conventional problem of column blocking. Thinking about the rational design of 3D carbon geometries, the functions and properties of the resulting carbon-based materials can be further expanded by the rational introduction of heteroatoms (e.g. N, B, S, P, etc.) into the carbon structures in order to alter properties such as wettability, surface polarity as well as the electrochemical landscape. In this context, the use of crystalline materials based on oxocarbon-metal ion complexes can open a platform of highly functional materials for all processes that involve surface processes.},
  language  = {en}
}
@phdthesis{Schuermann2017,
  author    = {Sch{\"u}rmann, Robin Mathis},
  title     = {Interaction of the potential DNA-radiosensitizer 8-bromoadenine with free and plasmonically generated electrons},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407017},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 120},
  year      = {2017},
  abstract  = {In Germany more than 200.000 persons die of cancer every year, which makes it the second most common cause of death. Chemotherapy and radiation therapy are often combined to exploit a supra-additive effect, as some chemotherapeutic agents like halogenated nucleobases sensitize the cancerous tissue to radiation. The radiosensitizing action of certain therapeutic agents can be at least partly assigned to their interaction with secondary low energy electrons (LEEs) that are generated along the track of the ionizing radiation. In the therapy of cancer DNA is an important target, as severe DNA damage like double strand breaks induce the cell death. As there is only a limited number of radiosensitizing agents in clinical practice, which are often strongly cytotoxic, it would be beneficial to get a deeper understanding of the interaction of less toxic potential radiosensitizers with secondary reactive species like LEEs. Beyond that LEEs can be generated by laser illuminated nanoparticles that are applied in photothermal therapy (PTT) of cancer, which is an attempt to treat cancer by an increase of temperature in the cells. However, the application of halogenated nucleobases in PTT has not been taken into account so far. In this thesis the interaction of the potential radiosensitizer 8-bromoadenine (8BrA) with LEEs was studied. In a first step the dissociative electron attachment (DEA) in the gas phase was studied in a crossed electron-molecular beam setup. The main fragmentation pathway was revealed as the cleavage of the C-Br bond. The formation of a stable parent anion was observed for electron energies around 0 eV. Furthermore, DNA origami nanostructures were used as platformed to determine electron induced strand break cross sections of 8BrA sensitized oligonucleotides and the corresponding nonsensitized sequence as a function of the electron energy. In this way the influence of the DEA resonances observed for the free molecules on the DNA strand breaks was examined. As the surrounding medium influences the DEA, pulsed laser illuminated gold nanoparticles (AuNPs) were used as a nanoscale electron source in an aqueous environment. The dissociation of brominated and native nucleobases was tracked with UV-Vis absorption spectroscopy and the generated fragments were identified with surface enhanced Raman scattering (SERS). Beside the electron induced damage, nucleobase analogues are decomposed in the vicinity of the laser illuminatednanoparticles due to the high temperatures. In order to get a deeper understanding of the different dissociation mechanisms, the thermal decomposition of the nucleobases in these systems was studied and the influence of the adsorption kinetics of the molecules was elucidated. In addition to the pulsed laser experiments, a dissociative electron transfer from plasmonically generated "hot electrons" to 8BrA was observed under low energy continuous wave laser illumination and tracked with SERS. The reaction was studied on AgNPs and AuNPs as a function of the laser intensity and wavelength. On dried samples the dissociation of the molecule was described by fractal like kinetics. In solution, the dissociative electron transfer was observed as well. It turned out that the timescale of the reaction rates were slightly below typical integration times of Raman spectra. In consequence such reactions need to be taken into account in the interpretation of SERS spectra of electrophilic molecules. The findings in this thesis help to understand the interaction of brominated nucleobases with plasmonically generated electrons and free electrons. This might help to evaluate the potential radiosensitizing action of such molecules in cancer radiation therapy and PTT.},
  language  = {en}
}
@phdthesis{Klier2016,
  author    = {Klier, Dennis Tobias},
  title     = {Upconversion luminescence in Er-codoped NaYF4 nanoparticles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98486},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 89},
  year      = {2016},
  abstract  = {In the context of an increasing population of aging people and a shift of medical paradigm towards an individualized medicine in health care, nanostructured lanthanides doped sodium yttrium fluoride (NaYF4) represents an exciting class of upconversion nanomaterials (UCNM) which are suitable to bring forward developments in biomedicine and -biodetection. Despite the fact that among various fluoride based upconversion (UC) phosphors lanthanide doped NaYF4 is one of the most studied upconversion nanomaterial, many open questions are still remaining concerning the interplay of the population routes of sensitizer and activator electronic states involved in different luminescence upconversion photophysics as well as the role of phonon coupling. The collective work aims to explore a detailed understanding of the upconversion mechanism in nanoscaled NaYF4 based materials co-doped with several lanthanides, e.g. Yb3+ and Er3+ as the "standard" type upconversion nanoparticles (UCNP) up to advanced UCNP with Gd3+ and Nd3+. Especially the impact of the crystal lattice structure as well as the resulting lattice phonons on the upconversion luminescence was investigated in detail based on different mixtures of cubic and hexagonal NaYF4 nanoscaled crystals. Three synthesis methods, depending on the attempt of the respective central spectroscopic questions, could be accomplished in the following work. NaYF4 based upconversion nanoparticles doped with several combination of lanthanides (Yb3+, Er3+, Gd3+ and Nd3+) were synthesized successfully using a hydrothermal synthesis method under mild conditions as well as a co-precipitation and a high temperature co-precipitation technique. Structural information were gathered by means of X-ray diffraction (XRD), electron microscopy (TEM), dynamic light scattering (DLS), Raman spectroscopy and inductively coupled plasma atomic emission spectrometry (ICP-OES). The results were discussed in detail with relation to the spectroscopic results. A variable spectroscopic setup was developed for multi parameter upconversion luminescence studies at various temperature 4 K to 328 K. Especially, the study of the thermal behavior of upconversion luminescence as well as time resolved area normalized emission spectra were a prerequisite for the detailed understanding of intramolecular deactivation processes, structural changes upon annealing or Gd3+ concentration, and the role of phonon coupling for the upconversion efficiency. Subsequently it became possible to synthesize UCNP with tailored upconversion luminescence properties. In the end, the potential of UCNP for life science application should be enunciated in context of current needs and improvements of a nanomaterial based optical sensors, whereas the "standard" UCNP design was attuned according to the special conditions in the biological matrix. In terms of a better biocompatibility due to a lower impact on biological tissue and higher penetrability for the excitation light. The first step into this direction was to use Nd3+ ions as a new sensitizer in tridoped NaYF4 based UCNP, whereas the achieved absolute and relative temperature sensitivity is comparable to other types of local temperature sensors in the literature.},
  language  = {en}
}
@phdthesis{Olszewska2015,
  author    = {Olszewska, Agata},
  title     = {Forming magnetic chain with the help of biological organisms},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89767},
  school      = {Universit{\"a}t Potsdam},
  pages     = {101},
  year      = {2015},
  abstract  = {Magnetite nanoparticles and their assembly comprise a new area of development for new technologies. The magnetic particles can interact and assemble in chains or networks. Magnetotactic bacteria are one of the most interesting microorganisms, in which the assembly of nanoparticles occurs. These microorganisms are a heterogeneous group of gram negative prokaryotes, which all show the production of special magnetic organelles called magnetosomes, consisting of a magnetic nanoparticle, either magnetite (Fe3O4) or greigite (Fe3S4), embedded in a membrane. The chain is assembled along an actin-like scaffold made of MamK protein, which makes the magnetosomes to arrange in mechanically stable chains. The chains work as a compass needle in order to allow cells to orient and swim along the magnetic field of the Earth. The formation of magnetosomes is known to be controlled at the molecular level. The physico-chemical conditions of the surrounding environment also influence biomineralization. The work presented in this manuscript aims to understand how such external conditions, in particular the extracellular oxidation reduction potential (ORP) influence magnetite formation in the strain Magnetospirillum magneticum AMB-1. A controlled cultivation of the microorganism was developed in a bioreactor and the formation of magnetosomes was characterized. Different techniques have been applied in order to characterize the amount of iron taken up by the bacteria and in consequence the size of magnetosomes produced at different ORP conditions. By comparison of iron uptake, morphology of bacteria, size and amount of magnetosomes per cell at different ORP, the formation of magnetosomes was inhibited at ORP 0 mV, whereas reduced conditions, ORP - 500 mV facilitate biomineralization process. Self-assembly of magnetosomes occurring in magnetotactic bacteria became an inspiration to learn from nature and to construct nanoparticles assemblies by using the bacteriophage M13 as a template. The M13 bacteriophage is an 800 nm long filament with encapsulated single-stranded DNA that has been recently used as a scaffold for nanoparticle assembly. I constructed two types of assemblies based on bacteriophages and magnetic nanoparticles. A chain - like assembly was first formed where magnetite nanoparticles are attached along the phage filament. A sperm - like construct was also built with a magnetic head and a tail formed by phage filament. The controlled assembly of magnetite nanoparticles on the phage template was possible due to two different mechanism of nanoparticle assembly. The first one was based on the electrostatic interactions between positively charged polyethylenimine coated magnetite nanoparticles and negatively charged phages. The second phage -nanoparticle assembly was achieved by bioengineered recognition sites. A mCherry protein is displayed on the phage and is was used as a linker to a red binding nanobody (RBP) that is fused to the one of the proteins surrounding the magnetite crystal of a magnetosome. Both assemblies were actuated in water by an external magnetic field showing their swimming behavior and potentially enabling further usage of such structures for medical applications. The speed of the phage - nanoparticles assemblies are relatively slow when compared to those of microswimmers previously published. However, only the largest phage-magnetite assemblies could be imaged and it is therefore still unclear how fast these structures can be in their smaller version.},
  language  = {en}
}