Moderne Analysemethoden zur Charakterisierung funktioneller Nanomaterialien

The core of this dissertation is concerned with the various measurement methods for the characterization of synthesized nanoparticles and nanofilms, above all with the atomic force microscope. The latter is a popular and useful tool for determining the electrical, electrostatic, magnetic, mechanical and topographic properties of a sample or a selected sample range with an edge length of up to 150 µm. Using the atomic force microscope, it is furthermore possible to achieve resolutions in the sub-nanometer range and thus to visualize individual atoms. The measuring principle of this microscope consists of a sharp tip which is moved over the sample surface at a small distance and deflected from its vertical rest position due to interactions with this surface. This deflection is detected, for example, by a laser reflected on the back of the cantilever. The measurement signal can be used to determine the forces acting between the sample and the tip. Simple sample preparation and the possibility of measuring in vacuum, air and liquid make atomic force microscopy a versatile tool in nanotechnology and bionanotechnology. In addition, other measuring methods will be presented, including the electron microscopy, which provides information on the shape and composition of a sample complementary to that obtained by atomic force microscopy. Two projects from several scientific papers that were developed in the course of the doctoral period are described in more detail here. In a first project, nanoparticles were synthesized by directing a pulsed laser beam at a piece of metal (target) located in a liquid. As a result, nanoparticles were formed which dissolved in the liquid. This method for the synthesis of soluble nanoparticles is known as Pulsed Laser Ablation in Liquids (PLAL). The nanoparticles are composed of components of the target and the solvent matrix. Concretely, gold was used as target, while the liquid consisted of distilled water, small amounts of sodium chloride and small amounts of sodium water glass. The nanoparticles could be characterized as core-shell nanoparticles, whereby the gold core was coated with a thin silicate shell. The synthesis of the nanoparticles was optimized by screening the laser pulse properties and composition of the solution. Subsequently, the electrostatic, topographic and mechanical properties and composition of the nanoparticles were investigated. In order to determine the mechanical properties, a software was developed within the scope of this dissertation which evaluates the recorded force-distance curves using current contact mechanics models. Afterwards, the toxicity of the particles to different cell types was investigated in vitro. At the Chinese Academy of Sciences, Ningbo, People's Republic of China, these particles were furthermore used to investigate cell toxicity in vitro on other types of cells as well as histology and determination of the biodistribution of nanoparticles in vivo on a mouse. In addition, the effectiveness of the conversion of laser radiation into heat was determined. The results provided valuable information on the application of nanoparticles in photothermal cancer therapy. They could serve as a starting point for further work in the future. In addition, the potential of this synthesis method for medical applications has been confirmed. In the second project, described in more detail here, an attempt was made to produce a monolayer of purple membrane (PM) on a thin substrate. The membrane can pump protons light-driven from one side to the other. A uniformly oriented monolayer could serve as a large, thin proton pump. The samples were characterized by atomic force microscopy and electron microscopy. The purple membrane was first diluted in buffer or distilled water and allowed to dry on various substrates. Both topography and electrostatic properties were analysed to determine the orientation of the membrane. To improve the result, an electric field was applied to deposit the PM on the substrate via electrosedimentation and electrophoretic sedimentation. After changing from the wild type of PM to a his-tagged variant, the electrophoretic sedimentation produced large fields in which the PM merged. The formation of these fields was investigated under variation of the experimental conditions. A possible mechanism was derived from these measurements.