Ultra-Small Silver Nanoparticles - Dynamic Behavior in Aqueous and Biological Environments

The utilization of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a plethora of products ranging from cosmetics and textiles to medical instruments. Thus, investigations on nanoscale silver are attracting increasing interest in many fields, such as biomedicine or catalysis. Unfortunately, the results of these studies are diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. A major flaw is the usage of non-uniform and inadequate characterized particles with broad size distributions. To elucidate this problem this thesis deals with the synthesis and thorough characterization of a versatile silver nanoparticle system in a size at the lower end of the nanoscale. Poly(acrylic acid) (PAA)-stabilized silver nanoparticles with a nominal radius of 3 nm are synthesized using two methods. Firstly, they are produced in a classical batch synthesis and secondly in a microwave-assisted synthesis. The comparison of these two routes applying the same reaction conditions provides the opportunity to reveal whether non-thermal microwave effects, which are still under debate in literature, are present. The synthesized particles exhibit a high stability and are used in an inter-laboratory comparison proving their suitability for application in nanometrology, such as determination of nanoparticle sizes, size distribution widths, and particle concentrations. Furthermore, the high versatility of the silver nanoparticle system enables an easy ligand exchange to tune the surface of the particles on demand and improve their biocompatibility. Exemplarily, transfunctionalizations with albumin, glutathione, and tyrosine are performed and characterized by small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), UV/Vis and IR spectroscopy. These differently coated silver nanoparticles are used firstly in a catalytic application: the reduction of 4-nitrophenol. Therein, a dependence of the catalytic activity on the corresponding coating is observed and reveals that the PAA-stabilized silver nanoparticles exhibit an exceptionally high activity. As a preliminary study for future biological applications the binding behavior, especially the adsorption and desorption, of biocompatible, fluorescent ligands is investigated. It is demonstrated that a fluorescent labelling with appropriate binding properties can be provided, which is subsequently used in an initial investigation on lung and intestinal cells regarding particle transport. Subsequently, the PAA-stabilized particles are employed in an artificial digestion. The monitoring of the size and size distribution throughout the three steps of digestion (saliva, stomach, intestine) shows that the silver nanoparticles pass the digestion under transformation in size, but still remain nano-sized. Since silver is known for the continuous release of silver ions, the digestion of silver nanoparticles leads naturally to the question of the behavior of ionic silver in an artificial digestion. The investigation of this topic with the help of small and wide-angle X-ray scattering and IR spectroscopy reveals that silver thiocyanate nanoparticles are formed during in vitro digestion. The release of silver ions from the surface of silver nanoparticles is a crucial point in the risk assessment of silver nanoparticles, since the ions can undergo complex transformations in biological environments. In this work, enhanced ion release was observed for the interaction of PAA-stabilized silver nanoparticles with glutathione. New small silver clusters were formed during this process. The diverse applications of the silver nanoparticle system in this work demonstrate the high versatility and stability of the system, which is a promising candidate for further comparable biological and catalytic applications.Die Verwendung von Silbernanopartikeln in Konsumgütern des täglichen Lebens hat in den letzten zehn Jahren deutlich zugenommen, insbesondere aufgrund ihrer antimikrobiellen Eigenschaften. Heute werden sie in einer Vielzahl von Produkten eingesetzt, die von Kosmetika und Textilien bis hin zu medizinischen Instrumenten reichen. So stoßen Untersuchungen an Nanosilber in vielen Bereichen wie der Biomedizin oder der Katalyse auf zunehmendes Interesse. Leider sind die Ergebnisse dieser Studien divers und führen nicht zu einer konsistenten Bewertung der Toxizität von Silbernanopartikeln. Eine große Schwachstelle ist die Verwendung von uneinheitlichen und unzureichend charakterisierten Partikeln mit breiten Größenverteilungen. Um dieses Problem zu beleuchten, beschäftigt sich diese Arbeit mit der Synthese und umfassenden Charakterisierung eines vielseitigen Silbernanopartikelsystems mit einer Größe am unteren Ende der Nanoskala. Poly(acrylsäure) (PAA)-stabilisierte Silbernanopartikel mit einem nominalen Radius von 3 nm werden mit zwei Methoden synthetisiert. Zum einen werden sie in einer klassischen Batch-Synthese und zum anderen in einer mikrowellengestützten Synthese hergestellt. Der Vergleich dieser beiden Verfahren bei gleichen Reaktionsbedingungen ermöglicht die Aufklärung, ob nicht-thermische Mikrowelleneffekte, die in der Literatur noch diskutiert werden, in diesem Fall vorhanden sind. Die synthetisierten Partikel weisen eine hohe Stabilität auf und werden in einem Ringversuch eingesetzt, um ihre Eignung für den Einsatz in der Nanometrologie, wie zum Beispiel der Bestimmung von Nanopartikelgrößen, Größenverteilungsbreiten und Partikel-konzentrationen, nachzuweisen. Darüber hinaus ermöglicht die hohe Vielseitigkeit des Silbernanopartikelsystems einen einfachen Ligandenaustausch, um die Oberfläche der Partikel nach Bedarf anzupassen und ihre Biokompatibilität zu verbessern. Beispielhaft werden Umfunktionalisierungen mit Albumin, Glutathion und Tyrosin durchgeführt und durch Röntgenkleinwinkelstreuung (SAXS), dynamische Lichtstreuung (DLS), UV/Vis- und IR-Spektroskopie charakterisiert. Diese unterschiedlich beschichteten Silbernanopartikel werden zunächst in einer katalytischen Anwendung eingesetzt: Der Reduktion von 4-Nitrophenol. Dabei wird die Abhängigkeit der katalytischen Aktivität von der entsprechenden Beschichtung beobachtet und es zeigt sich, dass die PAA-stabilisierten Silbernanopartikel eine außergewöhnlich hohe Aktivität aufweisen. Als Vorbetrachtung für zukünftige Anwendungen der Silbernanopartikel in biologischen Fragestellungen wird das Bindungsverhalten, insbesondere die Adsorption und Desorption, von biokompatiblen, fluoreszierenden Liganden untersucht. Es zeigt sich, dass eine Fluoreszenzmarkierung mit geeigneter Bindungswirkung bereitgestellt werden kann. Die fluoreszenzmarkierten Partikel werden anschließend in einer ersten Untersuchung hinsichtlich des Partikeltransports auf Lungen- und Darmzellen eingesetzt. Anschließend werden die PAA-stabilisierten Partikel in einem künstlichen Verdau untersucht. Die Verfolgung der Größe und Größenverteilung in den drei Verdaustufen (Speichel, Magen, Darm) zeigt, dass die Silbernanopartikel den Verdau unter Größenveränderungen passieren, aber dennoch nanoskalig bleiben. Da Silber für die kontinuierliche Freisetzung von Silberionen bekannt ist, führt der Verdau von Silbernanopartikeln zu der Frage nach dem Verhalten von ionischem Silber in einem künstlichen Verdau. Die Untersuchung dieses Themas mit Hilfe von Röntgenklein- und Röntgenweitwinkelstreuung, sowie IR-Spektroskopie zeigt, dass bei dem in vitro Verdau Silberthiocyanatnanopartikel entstehen. Die Freisetzung von Silberionen von der Oberfläche von Silbernanopartikeln ist ein entscheidender Punkt bei der Risikobewertung von Silbernanopartikeln, da die Ionen in biologischen Umgebungen komplexe Transformationen durchlaufen können. In dieser Arbeit wurde eine erhöhte Ionenfreisetzung für die Interaktion von PAA-stabilisierten Silbernanopartikeln mit Glutathion beobachtet. Dabei entstanden neue kleine Silbercluster. Die vielfältigen Anwendungen des Silbernanopartikelsystems in dieser Arbeit zeigen die hohe Vielseitigkeit und Stabilität des Systems, das ein vielversprechender Kandidat für weitere vergleichbare biologische und katalytische Anwendungen ist

Review Article: Active scanning probes: a versatile toolkit for fast imaging and emerging nanofabrication

With the recent advances in the field of nanotechnology, measurement and manipulation requirements at the nanoscale have become more stringent than ever before. In atomic force microscopy, high-speed performance alone is not sufficient without considerations of other aspects of the measurement task, such as the feature aspect ratio, required range, or acceptable probe-sample interaction forces. In this paper, the authors discuss these requirements and the research directions that provide the highest potential in meeting them. The authors elaborate on the efforts toward the downsizing of self-sensed and self-actuated probes as well as on upscaling by active cantilever arrays. The authors present the fabrication process of active probes along with the tip customizations carried out targeting specific application fields. As promising application in scope of nanofabrication, field emission scanning probe lithography is introduced. The authors further discuss their control and design approach. Here, microactuators, e.g., multilayer microcantilevers, and macroactuators, e.g., flexure scanners, are combined in order to simultaneously meet both the range and speed requirements of a new generation of scanning probe microscopes

The Impact of Halogenated Phenylalanine Derivatives on NFGAIL Amyloid Formation

The hexapeptide hIAPP22–27 (NFGAIL) is known as a crucial amyloid core sequence of the human islet amyloid polypeptide (hIAPP) whose aggregates can be used to better understand the wild-type hIAPP’s toxicity to β-cell death. In amyloid research, the role of hydrophobic and aromatic-aromatic interactions as potential driving forces during the aggregation process is controversially discussed not only in case of NFGAIL, but also for amyloidogenic peptides in general. We have used halogenation of the aromatic residue as a strategy to modulate hydrophobic and aromatic-aromatic interactions and prepared a library of NFGAIL variants containing fluorinated and iodinated phenylalanine analogues. We used thioflavin T staining, transmission electron microscopy (TEM) and smallangle X-ray scattering (SAXS) to study the impact of side-chain halogenation on NFGAIL amyloid formation kinetics. Our data revealed a synergy between aggregation behavior and hydrophobicity of the phenylalanine residue. This study introduces systematic fluorination as a toolbox to further investigate the nature of the amyloid self-assembly process

Characterization of semiconductor materials using synchrotron radiation-based near-field infrared microscopy and nano-FTIR spectroscopy

We describe the application of scattering-type near-field optical microscopy to characterize various semiconducting materials using the electron storage ring Metrology Light Source (MLS) as a broadband synchrotron radiation source. For verifying high-resolution imaging and nano-FTIR spectroscopy we performed scans across nanoscale Si-based surface structures. The obtained results demonstrate that a spatial resolution below 40 nm can be achieved, despite the use of a radiation source with an extremely broad emission spectrum. This approach allows not only for the collection of optical information but also enables the acquisition of near-field spectral data in the mid-infrared range. The high sensitivity for spectroscopic material discrimination using synchrotron radiation is presented by recording near-field spectra from thin films composed of different materials used in semiconductor technology, such as SiO2, SiC, SixNy, and TiO2

Review Article: Active scanning probes: A versatile toolkit for fast imaging and emerging nanofabrication

With the recent advances in the field of nanotechnology, measurement and manipulation requirements at the nanoscale have become more stringent than ever before. In atomic force microscopy, high-speed performance alone is not sufficient without considerations of other aspects of the measurement task, such as the feature aspect ratio, required range, or acceptable probe-sample interaction forces. In this paper, the authors discuss these requirements and the research directions that provide the highest potential in meeting them. The authors elaborate on the efforts toward the downsizing of self-sensed and self-actuated probes as well as on upscaling by active cantilever arrays. The authors present the fabrication process of active probes along with the tip customizations carried out targeting specific application fields. As promising application in scope of nanofabrication, field emission scanning probe lithography is introduced. The authors further discuss their control and design approach. Here, microactuators, e.g., multilayer microcantilevers, and macroactuators, e.g., flexure scanners, are combined in order to simultaneously meet both the range and speed requirements of a new generation of scanning probe microscopes

Standardised Sampling Approach for Investigating Pathogens or Environmental Chemicals in Wild Game at Community Hunts

Wildlife may host pathogens and chemicals of veterinary and public health relevance, as well as pathogens with significant economic relevance for domestic livestock. In conducting research on the occurrence and distribution of these agents in wildlife, a major challenge is the acquisition of a sufficient number of samples coupled with efficient use of manpower and time. The aim of this article is to present the methodology and output of a sampling approach for game animals, which was implemented from 2017/18 to 2020/21 at drive hunts in Brandenburg, Germany. The central element was a framework agreement with the BImA, whereby federal forest officials and other hunters collected most of the samples during field dressing. Further samples of game carcasses were obtained by scientists during subsequent gathering at a collection point. Altogether, 3185 samples from 938 wild ungulates of four species were obtained for various studies analysing—in this case—food-borne agents in game animals. Sampling was representative and reflected the proportional distribution of ungulate species hunted in Brandenburg. Hunting district and hunting season strongly influenced hunting bag and hence sampling success. This sampling approach was demonstrated to be a suitable basis for monitoring programs, that can be adapted to other regions