Complex materials via colloidal crystallization

The work presented in this thesis deals with complex materials, which were obtained by self-assembly of monodisperse colloidal particles, also called colloidal crystallization. Two main fields of interest were investigated, the first dealing with the fabrication of colloidal monolayers and nanostructures, which derive there from. The second turned the focus on the phononic properties of colloidal particles, crystals, and glasses. For the fabrication of colloidal monolayers a method is introduced, which is based on the sparse distribution of dry colloidal particles on a parent substrate. In the ensuing floating step the colloidal monolayer assembles readily at the three-phase-contact line, giving a 2D hexagonally ordered film under the right conditions. The unique feature of this fabrication process is an anisotropic shrinkage, which occurs alongside with the floating step. This phenomenon is exploited for the tailored structuring of colloidal monolayers, leading to designed hetero-monolayers by inkjet printing. Furthermore, the mechanical stability of the floating monolayers allows the deposition on hydrophobic substrates, which enables the fabrication of ultraflat nanostructured surfaces. Densely packed arrays of crescent shaped nanoparticles have also been synthesized. It is possible to stack those arrays in a 3D manner allowing to mutually orientate the individual layers. In a step towards 3D mesoporous materials a methodology to synthesize hierarchically structured inverse opals is introduced. The deposition of colloidal particles in the free voids of a host inverse opal allows for the fabrication of composite inverse opals on two length scales. The phononic properties of colloidal crystals and films are characterized by Brillouin light scattering (BLS). At first the resonant modes of colloidal particles consisting of polystyrene, a copolymer of methylmethacrylate and butylacrylate, or of a silica core-PMMA shell topography are investigated, giving insight into their individual mechanical properties. The infiltration of colloidal films with an index matching liquid allows measuring the phonon dispersion relation. This leads to the assignment of band gaps to the material under investigation. Here, two band gaps could be found, one originating from the fcc order in the colloidal crystal (Bragg gap), the other stemming from the vibrational eigenmodes of the colloidal particles (hybridization gap).

Spektroelektrochemische Untersuchungen mittels oberflächenverstärkter Infrarotabsorptionsspektroskopie (SEIRAS) an Multi-Redox-Center-Proteinen in einer biomimetischen Membranumgebung

Die optische Eigenschaften sowie der Oberflächenverstärkungseffekt von rauen Metalloberflächen sowie Nanopartikeln wurden intensiv für den infraroten Bereich des Spektrums in der Literatur diskutiert. Für die Präparation solcher Oberflächen gibt es prinzipiell zwei verschiedene Strategien, zum einen können die Nanopartikel zuerst ex-situ synthetisiert werden, der zweite Ansatz beruht darauf, dass die Nanopartikel in-situ hergestellt und aufgewachsen werden. Hierbei wurden beide Ansätze ausgetestet, dabei stellte sich heraus, dass man nur mittels der in-situ Synthese der Goldnanopartikel in der Lage ist nanostrukturierte Oberflächen zu erhalten, welche elektronisch leitfähig sind, nicht zu rau sind, um eine Membranbildung zu ermöglichen und gleichzeitig einen optimalen Oberflächenverstärkungseffekt zeigen. Obwohl keine ideale Form der Nanopartikel mittels der in-situ Synthese erhalten werden können, verhalten sich diese dennoch entsprechend der Theorie des Oberflächenverstärkungseffekts. Optimierungen der Form und Grösse der Nanopartikel führten in dieser Arbeit zu einer Optimierung des Verstärkungseffekts. Solche optimierten Oberflächen konnten einfach reproduziert werden und zeichnen sich durch eine hohe Stabilität aus. Der so erhaltene Oberflächenverstärkungseffekt beträgt absolut 128 verglichen mit dem belegten ATR-Kristall ohne Nanopartikel oder etwa 6 mal, verglichen mit der Oberfläche, die bis jetzt auch in unserer Gruppe verwendet wurde. Daher können nun Spektren erhalten werden, welche ein deutlich besseres Signal zu Rauschverhältnis (SNR) aufweisen, was die Auswertung und Bearbeitung der erhaltenen Spektren deutlich vereinfacht und verkürzt.rnNach der Optimierung der verwendeten Metalloberfläche und der verwendeten Messparameter am Beispiel von Cytochrom C wurde nun an der Oberflächenbelegung der deutlich größeren Cytochrom c Oxidase gearbeitet. Hierfür wurde der DTNTA-Linker ex-situ synthetisiert. Anschließend wurden gemischte Monolagen (self assembeld monolayers) aus DTNTA und DTP hergestellt. Die NTA-Funktionalität ist für die Anbindung der CcO mit der his-tag Technologie verantwortlich. Die Kriterien für eine optimale Linkerkonzentration waren die elektrischen Parameter der Schicht vor und nach Rekonstitution in eine Lipidmembran, sowie Elektronentransferraten bestimmt durch elektrochemische Messungen. Erst mit diesem optimierten System, welches zuverlässig und reproduzierbar funktioniert, konnten weitere Messungen an der CcO begonnen werden. Aus elektrochemischen Messungen war bekannt, dass die CcO durch direkten Elektronentransfer unter Sauerstoffsättigung in einen aktivierten Zustand überführt werden kann. Dieser aktivierte Zustand zeichnet sich durch eine Verschiebung der Redoxpotentiale um etwa 400mV gegenüber dem aus Gleichgewichts-Titrationen bekannten Redoxpotential aus. Durch SEIRAS konnte festgestellt werden, dass die Reduktion bzw. Oxidation aller Redoxzentren tatsächlich bei den in der Cyclovoltammetrie gemessenen Potentialen erfolgt. Außerdem ergaben die SEIRA-Spektren, dass durch direkten Elektronentransfer gravierende Konformationsänderungen innerhalb des Proteins stattfinden. rnBisher war man davon ausgegangen, aufgrund des Elektronentransfers mittels Mediatoren, dass nur minimale Konformationsänderungen beteiligt sind. Vor allem konnte erstmaligrnder aktivierte und nicht aktivierte Zustand der Cytochrom c Oxidase spektroskopisch nachweisen werden.rn

Synthesis and characterisation of photoreactive silanes for the self-assembly on functionalised silica surfaces

The aim of this thesis was to investigate novel techniques to create complex hierarchical chemical patterns on silica surfaces with micro to nanometer sized features. These surfaces were used for a site-selective assembly of colloidal particles and oligonucleotides. To do so, functionalised alkoxysilanes (commercial and synthesised ones) were deposited onto planar silica surfaces. The functional groups can form reversible attractive interactions with the complementary surface layers of the opposing objects that need to be assembled. These interactions determine the final location and density of the objects onto the surface. Photolithographically patterned silica surfaces were modified with commercial silanes, in order to create hydrophilic and hydrophobic regions on the surface. Assembly of hydrophobic silica particles onto these surfaces was investigated and finally, pH and charge effects on the colloidal assembly were analysed. In the second part of this thesis the concept of novel, "smart" alkoxysilanes is introduced that allows parallel surface activation and patterning in a one-step irradiation process. These novel species bear a photoreactive head-group in a protected form. Surface layers made from these molecules can be irradiated through a mask to remove the protecting group from selected regions and thus generate lateral chemical patterns of active and inert regions on the substrate. The synthesis of an azide-reactive alkoxysilane was successfully accomplished. Silanisation conditions were carefully optimised as to guarantee a smooth surface layer, without formation of micellar clusters. NMR and DLS experiments corroborated the absence of clusters when using neither water nor NaOH as catalysts during hydrolysis, but only the organic solvent itself. Upon irradiation of the azide layer, the resulting nitrene may undergo a variety of reactions depending on the irradiation conditions. Contact angle measurements demonstrated that the irradiated surfaces were more hydrophilic than the non-irradiated azide layer and therefore the formation of an amine upon irradiation was postulated. Successful photoactivation could be demonstrated using condensation patterns, which showed a change in wettability on the wafer surface upon irradiation. Colloidal deposition with COOH functionalised particles further underlined the formation of more hydrophilic species. Orthogonal photoreactive silanes are described in the third part of this thesis. The advantage of orthogonal photosensitive silanes is the possibility of having a coexistence of chemical functionalities homogeneously distributed in the same layer, by using appropriate protecting groups. For this purpose, a 3',5'-dimethoxybenzoin protected carboxylic acid silane was successfully synthesised and the kinetics of its hydrolysis and condensation in solution were analysed in order to optimise the silanisation conditions. This compound was used together with a nitroveratryl protected amino silane to obtain bicomponent surface layers. The optimum conditions for an orthogonal deprotection of surfaces modified with this two groups were determined. A 2-step deprotection process through a mask generated a complex pattern on the substrate by activating two different chemistries at different sites. This was demonstrated by colloidal adsorption and fluorescence labelling of the resulting substrates. Moreover, two different single stranded oligodeoxynucleotides were immobilised onto the two different activated areas and then hybrid captured with their respective complementary, fluorescent labelled strand. Selective hybridisation could be shown, although non-selective adsorption issues need to be resolved, making this technique attractive for possible DNA microarrays.

Functionalized surfaces and surface functionalization of nanomaterials

Nature leads, we follow. But nanotechnologists are in hot pursuit, in designing controllable structures that can mimic naturally occurring and artificially synthesized materials on a common platform. The supramolecular chemistry concerns the investigation of nature principles to produce fascinating complexed and functional molecular assemblies, as well as the utilization of these principles to generate novel devices and materials, potentially useful for sensing, catalysis, transport and other applications in medical or engineering science. The work presented in this thesis is a compilation of different synthetic methods to achieve inorganic-organic hybrid nanomaterials. Silicatein, a protein enzyme, which acts both as a catalyst and template for the formation of silica needles in marine sponges, has been used for the biosynthesis of semiconductor metal oxides on surfaces. Silicatein was immobilized on gold (111) surfaces using alkane thiol, as well as on a novel self-assembly of NTA on top of a “cushion” of reactive ester polymer has been successfully employed to make functionalised surfaces. The immobilization of silicatein on surfaces was monitored by surface plasmon spectroscopy, atomic force microscopy and confocal laser scanning microscopy. Surface bound silicatein retains its biocatalytic activity, which was demonstrated by monitoring its hydrocatalytic activity to catalyse the synthesis of biosilica, biotitania, and biozirconia. The synthesis of semiconductor metal oxides was characterized using scanning electron microscopy. This hydrolytic biocatalyst is used to synthesize the gold nanoparticles. The gold nanoparticles are formed by reduction of tetrachloroaurate, AuCl4-, by the action of sulfhydryl groups hidden below the surface groups of the protein. The resulting gold nanoparticles which are stabilized by surface bound silicatein further aggregate to form Au nanocrystals. The shape of the nanocrystals obtained by using recombinant silicatein is controlled through chiral induction by the protein during the nucleation of the nanocrystals. As an extension of this work, TiO2 nanowires were functionalized using polymeric ligand which incorporates the nitrilotriacetic acid (NTA) linker in the back bone to immobilize His-tagged silicatein onto the TiO2 nanowires. The surface bound protein not only retains its original hydrolytic properties, but also acts as a reductant for AuCl4- in the synthesis of hybrid TiO2/silicatein/Au nanocomposites. Functionalized, monocrystalline rutile TiO2 nanorods were prepared from TiCl4 in aqueous solution in the presence of dopamine. The surface bound organic ligand controls the morphology as well as the crystallinity and the phase selection of TiO2. The surface amine groups can be tailored further with functional molecules such as dyes. As an example, this surface functionality is used for the covalent binding of a fluorescent dye,4-chloro-7- nitrobenzylurazene (NBD) to the TiO2 nanorods. The polymeric ligands have been used successfully for the in-situ and post-functionalization of TiO2 nanoparticles. Besides to chelating dopamine anchor group the multifunctional ligand system presented here incorporates a modifier molecule which allows the binding of functional molecules (here the dyes pyrene, NBD, and Texas Red) as well as additional entities which allow tailoring the solubility of inorganic nanocrystals in different solvents. A novel method for the surface functionalization of fullerene-type MoS2 nanoparticles and subsequently binding these nanoparticles onto TiO2 nanowires has been reported using polymeric ligands. The procedure involves the complexation of IF-MoS2 with a combination of Ni2+ via an umbrella-type nitrilotriacetic acid (NTA) and anchoring them to the sidewalls of TiO2 nanowires utilizing the hydroxyl groups of dopamine present in the main contents of polymeric ligand. A convenient method for the synthesis of Au/CdS nanocomposites has been presented, which were achieved through the novel method of thiol functionalization of gold colloids. The thermodynamically most stable phase of ZrO2 (cubic) has been obtained at much lower temperature (180°C). These nanoparticles are highly blue fluorescent, with a high surface area.

Thin nanostructured crystalline TiO 2 films and their applications in solar cells

Research on thin nanostructured crystalline TiO2 films has attracted considerable interests because of their intriguing physical properties and potential applications in photovoltaics. Nanostructured TiO2 film plays an important role in the TiO2 based dye-sensitized solar cells because they act as a substrate for the adsorption of dye molecules and a matrix for the transportation of electrons as well. Thus they can influence the solar cell performance significantly. Consequently, the control of the morphology including the shape, size and size distribution of the TiO2 nanostructures is critical to tune and optimize the performance of the solar cells. To control the TiO2 morphology, a strategy using amphiphilic block copolymer as templating agent coupled with sol-gel chemistry has been applied. Especially, a good-poor solvent pair induced phase separation process has been developed to guide the microphase separation behavior of the block copolymers. The amphiphilic block copolymers used include polystyrene-block-poly (ethylene oxide) (PS-b-PEO), poly (methyl methacrylate)-block-poly (ethylene oxide) (PMMA-b-PEO), and poly (ethylene oxide)-block-polystyrene-block-poly (ethylene oxide) (PEO-b-PS-b-PEO). The block copolymer undergoes a good-poor-solvent pair induced phase separation in a mixed solution of 1, 4-dioxane or N, N’-dimethyl formamide (DMF), concentrated hydrochloric acid (HCl) and Titanium tetraisopropoxide (TTIP). Specifically, in the system of PS-b-PEO, a morphology phase diagram of the inorganic-copolymer composite films was mapped by adjusting the weight fractions among 1, 4-dioxane, HCl, and TTIP in solution. The amorphous TiO2 within the titania-block copolymer composite films was crystallized by calcination at temperatures above 400C, where the organic block copolymer was simultaneously burned away. This strategy is further extended to other amphiphilic block copolymers of PMMA-b-PEO and PEO-b-PS-b-PEO, where the morphology of TiO2 films can also be controlled. The local and long range structures of the titania films were investigated by the combination of imaging techniques (AFM, SEM) and x-ray scattering techniques (x-ray reflectivity and grazing incidence small-angle x-ray scattering). Based on the knowledge of the morphology control, the crystalline TiO2 nanostructured films with different morphologies were introduced into solid state dye-sensitized solar cells. It has been found that all of the morphologies help to improve the performance of the solar cells. Especially, clustered nanoparticles, worm-like structures, foam-like structures, large collapsed nanovesicles show more pronounced performance improvement than other morphologies such as nanowires, flakes, and nanogranulars.

Nanoscale effects and applications of self-organized nanostructured thin films

A nanostructured thin film is a thin material layer, usually supported by a (solid) substrate, which possesses subdomains with characteristic nanoscale dimensions (10 ~ 100 nm) that are differentiated by their material properties. Such films have captured vast research interest because the dimensions and the morphology of the nanostructure introduce new possibilities to manipulating chemical and physical properties not found in bulk materials. Block copolymer (BCP) self-assembly, and anodization to form nanoporous anodic aluminium oxide (AAO), are two different methods for generating nanostructures by self-organization. Using poly(styrene-block-methyl methacrylate) (PS-b-PMMA) nanopatterned thin films, it is demonstrated that these polymer nanopatterns can be used to study the influence of nanoscale features on protein-surface interactions. Moreover, a method for the directed assembly of adsorbed protein nanoarrays, based on the nanoscale juxtaposition of the BCP surface domains, is also demonstrated. Studies on protein-nanopattern interactions may inform the design of biomaterials, biosensors, and relevant cell-surface experiments that make use of nanoscale structures. In addition, PS-b-PMMA and AAO thin films are also demonstrated for use as optical waveguides at visible wavelengths. Due to the sub-wavelength nature of the nanostructures, scattering losses are minimized, and the optical response is amenable to analysis with effective medium theory (EMT). Optical waveguide measurements and EMT analysis of the films’ optical anisotropy enabled the in situ characterization of the PS-b-PMMA nanostructure, and a variety of surface processes within the nanoporous AAO involving (bio)macromolecules at high sensitivity.

Single polymers at surfaces: adsorption and detachment

This thesis is concerned with the adsorption and detachment of polymers at planar, rigid surfaces. We have carried out a systematic investigation of adsorption of polymers using analytical techniques as well as Monte Carlo simulations with a coarse grained off-lattice bead spring model. The investigation was carried out in three stages. In the first stage the adsorption of a single multiblock AB copolymer on a solid surface was investigated by means of simulations and scaling analysis. It was shown that the problem could be mapped onto an effective homopolymer problem. Our main result was the phase diagram of regular multiblock copolymers which shows an increase in the critical adsorption potential of the substrate with decreasing size of blocks. We also considered the adsorption of random copolymers which was found to be well described within the annealed disorder approximation. In the next phase, we studied the adsorption kinetics of a single polymer on a flat, structureless surface in the regime of strong physisorption. The idea of a ’stem-flower’ polymer conformation and the mechanism of ’zipping’ during the adsorption process were used to derive a Fokker-Planck equation with reflecting boundary conditions for the time dependent probability distribution function (PDF) of the number of adsorbed monomers. The numerical solution of the time-dependent PDF obtained from a discrete set of coupled differential equations were shown to be in perfect agreement with Monte Carlo simulation results. Finally we studied force induced desorption of a polymer chain adsorbed on an attractive surface. We approached the problem within the framework of two different statistical ensembles; (i) by keeping the pulling force fixed while measuring the position of the polymer chain end, and (ii) by measuring the force necessary to keep the chain end at fixed distance above the adsorbing plane. In the first case we treated the problem within the framework of the Grand Canonical Ensemble approach and derived analytic expressions for the various conformational building blocks, characterizing the structure of an adsorbed linear polymer chain, subject to pulling force of fixed strength. The main result was the phase diagram of a polymer chain under pulling. We demonstrated a novel first order phase transformation which is dichotomic i.e. phase coexistence is not possible. In the second case, we carried out our study in the “fixed height” statistical ensemble where one measures the fluctuating force, exerted by the chain on the last monomer when a chain end is kept fixed at height h over the solid plane at different adsorption strength ε. The phase diagram in the h − ε plane was calculated both analytically and by Monte Carlo simulations. We demonstrated that in the vicinity of the polymer desorption transition a number of properties like fluctuations and probability distribution of various quantities behave differently, if h rather than the force, f, is used as an independent control parameter.

New sensing platforms based on nanoscopic devices for probing protein-membrane interactions

A novel nanosized and addressable sensing platform based on membrane coated plasmonic particles for detection of protein adsorption using dark field scattering spectroscopy of single particles has been established. To this end, a detailed analysis of the deposition of gold nanorods on differently functionalized substrates is performed in relation to various factors (such as the pH, ionic strength, concentration of colloidal suspension, incubation time) in order to find the optimal conditions for obtaining a homogenous distribution of particles at the desired surface number density. The possibility of successfully draping lipid bilayers over the gold particles immobilized on glass substrates depends on the careful adjustment of parameters such as membrane curvature and adhesion properties and is demonstrated with complementary techniques such as phase imaging AFM, fluorescence microscopy (including FRAP) and single particle spectroscopy. The functionality and sensitivity of the proposed sensing platform is unequivocally certified by the resonance shifts of the plasmonic particles that were individually interrogated with single particle spectroscopy upon the adsorption of streptavidin to biotinylated lipid membranes. This new detection approach that employs particles as nanoscopic reporters for biomolecular interactions insures a highly localized sensitivity that offers the possibility to screen lateral inhomogeneities of native membranes. As an alternative to the 2D array of gold nanorods, short range ordered arrays of nanoholes in optically transparent gold films or regular arrays of truncated tetrahedron shaped particles are built by means of colloidal nanolithography on transparent substrates. Technical issues mainly related to the optimization of the mask deposition conditions are successfully addressed such that extended areas of homogenously nanostructured gold surfaces are achieved. Adsorption of the proteins annexin A1 and prothrombin on multicomponent lipid membranes as well as the hydrolytic activity of the phospholipase PLA2 were investigated with classical techniques such as AFM, ellipsometry and fluorescence microscopy. At first, the issues of lateral phase separation in membranes of various lipid compositions and the dependency of the domains configuration (sizes and shapes) on the membrane content are addressed. It is shown that the tendency for phase segregation of gel and fluid phase lipid mixtures is accentuated in the presence of divalent calcium ions for membranes containing anionic lipids as compared to neutral bilayers. Annexin A1 adsorbs preferentially and irreversibly on preformed phosphatidylserine (PS) enriched lipid domains but, dependent on the PS content of the bilayer, the protein itself may induce clustering of the anionic lipids into areas with high binding affinity. Corroborated evidence from AFM and fluorescence experiments confirm the hypothesis of a specifically increased hydrolytic activity of PLA2 on the highly curved regions of membranes due to a facilitated access of lipase to the cleavage sites of the lipids. The influence of the nanoscale gold surface topography on the adhesion of lipid vesicles is unambiguously demonstrated and this reveals, at least in part, an answer for the controversial question existent in the literature about the behavior of lipid vesicles interacting with bare gold substrates. The possibility of formation monolayers of lipid vesicles on chemically untreated gold substrates decorated with gold nanorods opens new perspectives for biosensing applications that involve the radiative decay engineering of the plasmonic particles.

On moduli spaces of semistable sheaves on K3 surfaces

Ich untersuche die nicht bereits durch die Arbeit "Singular symplectic moduli spaces" von Kaledin, Lehn und Sorger (Invent. Math. 164 (2006), no. 3) abgedeckten Fälle von Modulräumen halbstabiler Garben auf projektiven K3-Flächen - die Fälle mit Mukai-Vektor (0,c,0) sowie die Modulräume zu nichtgenerischen amplen Divisoren - hinsichtlich der möglichen Konstruktion neuer Beispiele von kompakten irreduziblen symplektischen Mannigfaltigkeiten. Ich stelle einen Zusammenhang zu den bereits untersuchten Modulräumen und Verallgemeinerungen derselben her und erweitere bekannte Ergebnisse auf alle offenen Fälle von Garben vom Rang 0 und viele Fälle von Garben von positivem Rang. Insbesondere kann in diesen Fällen die Existenz neuer Beispiele von kompakten irreduziblen symplektischen Mannigfaltigkeiten, die birational über Komponenten des Modulraums liegen, ausgeschlossen werden.

A biomimetic model membrane system on oxidic surfaces designed for the investigation of cytochrome c oxidase and other membrane proteins by fluorescence and waveguide spectroscopy

Die transmembrane Potenzialdifferenz Δφm ist direkt mit der katalytischen Aktivität der Cytochrom c Oxidase (CcO) verknüpft. Die CcO ist das terminale Enzym (Komplex IV) in der Atmungskette der Mitochondrien. Das Enzym katalysiert die Reduktion von O2 zu 2 H2O. Dabei werden Elektronen vom natürlichen Substrat Cytochrom c zur CcO übertragen. Der Eleltronentransfer innerhalb der CcO ist an die Protonentranslokation über die Membran gekoppelt. Folglich bildet sich über der inneren Membrane der Mitochondrien eine Differenz in der Protonenkonzentration. Zusätzlich wird eine Potenzialdifferenz Δφm generiert.rnrnDas Transmembranpotenzial Δφm kann mit Hilfe der Fluoreszenzspektroskopie unter Einsatz eines potenzialemfindlichen Farbstoffs gemessen werden. Um quantitative Aussagen aus solchen Untersuchungen ableiten zu können, müssen zuvor Kalibrierungsmessungen am Membransystem durchgeführt werden.rnrnIn dieser Arbeit werden Kalibrierungsmessungen von Δφm in einer Modellmembrane mit inkorporiertem CcO vorgestellt. Dazu wurde ein biomimetisches Membransystem, die Proteinverankerte Doppelschicht (protein-tethered Bilayer Lipid Membrane, ptBLM), auf einem transparenten, leitfähigem Substrat (Indiumzinnoxid, ITO) entwickelt. ITO ermöglicht den simultanen Einsatz von elektrochemischen und Fluoreszenz- oder optischen wellenleiterspektroskopischen Methoden. Das Δφm in der ptBLM wurde durch extern angelegte, definierte elektrische Spannungen induziert. rnrnEine dünne Hydrogelschicht wurde als "soft cushion" für die ptBLM auf ITO eingesetzt. Das Polymernetzwerk enthält die NTA Funktionsgruppen zur orientierten Immobilisierung der CcO auf der Oberfläche der Hydrogels mit Hilfe der Ni-NTA Technik. Die ptBLM wurde nach der Immobilisierung der CcO mittels in-situ Dialyse gebildet. Elektrochemische Impedanzmessungen zeigten einen hohen elektrischen Widerstand (≈ 1 MΩ) der ptBLM. Optische Wellenleiterspektren (SPR / OWS) zeigten eine erhöhte Anisotropie des Systems nach der Bildung der Doppellipidschicht. Cyklovoltammetriemessungen von reduziertem Cytochrom c bestätigten die Aktivität der CcO in der Hydrogel-gestützten ptBLM. Das Membranpotenzial in der Hydrogel-gestützten ptBLM, induziert durch definierte elektrische Spannungen, wurde mit Hilfe der ratiometrischen Fluoreszenzspektroskopie gemessen. Referenzmessungen mit einer einfach verankerten Dopplellipidschicht (tBLM) lieferten einen Umrechnungsfaktor zwischen dem ratiometrischen Parameter Rn und dem Membranpotenzial (0,05 / 100 mV). Die Nachweisgrenze für das Membranpotenzial in einer Hydrogel-gestützten ptBLM lag bei ≈ 80 mV. Diese Daten dienen als gute Grundlage für künftige Untersuchungen des selbstgenerierten Δφm der CcO in einer ptBLM.

Core-shell particles and their application for superhydrophobic surfaces

During the last years great effort has been devoted to the fabrication of superhydrophobic surfaces because of their self-cleaning properties. A water drop on a superhydrophobic surface rolls off even at inclinations of only a few degrees while taking up contaminants encountered on its way. rnSuperhydrophobic, self-cleaning coatings are desirable for convenient and cost-effective maintenance of a variety of surfaces. Ideally, such coatings should be easy to make and apply, mechanically resistant, and long-term stable. None of the existing methods have yet mastered the challenge of meeting all of these criteria.rnSuperhydrophobicity is associated with surface roughness. The lotus leave, with its dual scale roughness, is one of the most efficient examples of superhydrophobic surface. This thesis work proposes a novel technique to prepare superhydrophobic surfaces that introduces the two length scale roughness by growing silica particles (~100 nm in diameter) onto micrometer-sized polystyrene particles using the well-established Stöber synthesis. Mechanical resistance is conferred to the resulting “raspberries” by the synthesis of a thin silica shell on their surface. Besides of being easy to make and handle, these particles offer the possibility for improving suitability or technical applications: since they disperse in water, multi-layers can be prepared on substrates by simple drop casting even on surfaces with grooves and slots. The solution of the main problem – stabilizing the multilayer – also lies in the design of the particles: the shells – although mechanically stable – are porous enough to allow for leakage of polystyrene from the core. Under tetrahydrofuran vapor polystyrene bridges form between the particles that render the multilayer-film stable. rnMulti-layers are good candidate to design surfaces whose roughness is preserved after scratch. If the top-most layer is removed, the roughness can still be ensured by the underlying layer.rnAfter hydrophobization by chemical vapor deposition (CVD) of a semi-fluorinated silane, the surfaces are superhydrophobic with a tilting angle of a few degrees. rnrnrn

Structured antibody surfaces for bio-recognition and a label-free detection of bacteria

Antibody microarrays are of great research interest because of their potential application as biosensors for high-throughput protein and pathogen screening technologies. In this active area, there is still a need for novel structures and assemblies providing insight in binding interactions such as spherical and annulus-shaped protein structures, e.g. for the utilization of curved surfaces for the enhanced protein-protein interactions and detection of antigens. Therefore, the goal of the presented work was to establish a new technique for the label-free detection of bio-molecules and bacteria on topographically structured surfaces, suitable for antibody binding.rnIn the first part of the presented thesis, the fabrication of monolayers of inverse opals with 10 μm diameter and the immobilization of antibodies on their interior surface is described. For this purpose, several established methods for the linking of antibodies to glass, including Schiff bases, EDC/S-NHS chemistry and the biotin-streptavidin affinity system, were tested. The employed methods included immunofluorescence and image analysis by phase contrast microscopy. It could be shown that these methods were not successful in terms of antibody immobilization and adjacent bacteria binding. Hence, a method based on the application of an active-ester-silane was introduced. It showed promising results but also the need for further analysis. Especially the search for alternative antibodies addressing other antigens on the exterior of bacteria will be sought-after in the future.rnAs a consequence of the ability to control antibody-functionalized surfaces, a new technique employing colloidal templating to yield large scale (~cm2) 2D arrays of antibodies against E. coli K12, eGFP and human integrin αvβ3 on a versatile useful glass surface is presented. The antibodies were swept to reside around the templating microspheres during solution drying, and physisorbed on the glass. After removing the microspheres, the formation of annuli-shaped antibody structures was observed. The preserved antibody structure and functionality is shown by binding the specific antigens and secondary antibodies. The improved detection of specific bacteria from a crude solution compared to conventional “flat” antibody surfaces and the setting up of an integrin-binding platform for targeted recognition and surface interactions of eukaryotic cells is demonstrated. The structures were investigated by atomic force, confocal and fluorescence microscopy. Operational parameters like drying time, temperature, humidity and surfactants were optimized to obtain a stable antibody structure.

Tailoring molecule nanostructures on insulating surfaces investigated by non-contact atomic force microscopy

Self-assembled molecular structures were investigated on insulating substrate surfaces using non-contact atomic force microscopy. Both, substrate preparation and molecule deposition, took place under ultra-high vacuum conditions. First, C60 molecules were investigated on the TiO2 (110) surface. This surface exhibits parallel running troughs at the nanometer scale, which strongly steer the assembly of the molecules. This is in contrast to the second investigated surface. The CaF2 (111) surface is atomically flat and the molecular assemblyrnwas observed to be far less affected by the surface. Basically different island structures were observed to what is typically know. Based on extensive experimental studies and theoretical considerations, a comprehensive picture of the processes responsible for the island formation of C60 molecules on this insulating surfaces was developed. The key process for the emergence of the observed novel island structures was made out to be the dewetting of molecules from the substrate. This new knowledge allows to further understand andrnexploit self-assembly techniques in structure fabrication on insulating substrate surfaces. To alter island formation and island structure, C60 molecules were codeposited with second molecule species (PTCDI and SubPc) on the CaF2 (111) surface. Depending on the order of deposition, quiet different structures were observed to arise. Thus, these are the first steps towards more complex functional arrangements consisting of two molecule species on insulating surfaces.

Drainage of thin aqueous films between solid surfaces measured with the colloidal probe technique

Understanding liquid flow at the vicinity of solid surfaces is crucial to the developmentrnof technologies to reduce drag. One possibility to infer flow properties at the liquid-solid interface is to compare the experimental results to solutions of the Navier-Stokes equations assuming the no-slip boundary condition (BC) or the slip BC. There is no consensus in the literature about which BC should be used to model the flow of aqueous solutions over hydrophilic surfaces. Here, the colloidal probe technique is used to systematically address this issue, measuring forces acting during drainage of water over a surface. Results show that experimental variables, especially the cantilever spring constant, lead to the discrepancy observed in the literature. Two different parameters, calculated from experimental variables, could be used to separate the data obtained in this work and those reported in the literature in two groups: one explained with the no-slip BC, and another with the slip BC. The observed residual slippage is a function of instrumental variables, showing a trend incompatible with the available physical justifications. As a result, the no-slip is the more appropriate BC. The parameters can be used to avoid situations where the no-slip BC is not satisfied.

Atomic-scale characterization of diamond surfaces and fullerene self-assembly

In this thesis, elemental research towards the implantation of a diamond-based molecular quantum computer is presented. The approach followed requires linear alignment of endohedral fullerenes on the diamond C(100) surface in the vicinity of subsurface NV-centers. From this, four fundamental experimental challenges arise: 1) The well-controlled deposition of endohedral fullerenes on a diamond surface. 2) The creation of NV-centers in diamond close to the surface. 3) Preparation and characterization of atomically-flat diamondsurfaces. 4) Assembly of linear chains of endohedral fullerenes. First steps to overcome all these challenges were taken in the framework of this thesis. Therefore, a so-called “pulse injection” technique was implemented and tested in a UHV chamber that was custom-designed for this and further tasks. Pulse injection in principle allows for the deposition of molecules from solution onto a substrate and can therefore be used to deposit molecular species that are not stable to sublimation under UHV conditions, such as the endohedral fullerenes needed for a quantum register. Regarding the targeted creation of NV-centers, FIB experiments were carried out in cooperation with the group of Prof. Schmidt-Kaler (AG Quantum, Physics Department, Johannes Gutenberg-Universität Mainz). As an entry into this challenging task, argon cations were implanted into (111) surface-oriented CaF2 crystals. The resulting implantation spots on the surface were imaged and characterized using AFM. In this context, general relations between the impact of the ions on the surface and their valency or kinetic energy, respectively, could be established. The main part of this thesis, however, is constituted by NCAFM studies on both, bare and hydrogen-terminated diamond C(100) surfaces. In cooperation with the group of Prof. Dujardin (Molecular Nanoscience Group, ISMO, Université de Paris XI), clean and atomically-flat diamond surfaces were prepared by exposure of the substrate to a microwave hydrogen plasma. Subsequently, both surface modifications were imaged in high resolution with NC-AFM. In the process, both hydrogen atoms in the unit cell of the hydrogenated surface were resolved individually, which was not achieved in previous STM studies of this surface. The NC-AFM images also reveal, for the first time, atomic-resolution contrast on the clean, insulating diamond surface and provide real-space experimental evidence for a (2×1) surface reconstruction. With regard to the quantum computing concept, high-resolution NC-AFM imaging was also used to study the adsorption and self-assembly potential of two different kinds of fullerenes (C60 and C60F48) on aforementioned diamond surfaces. In case of the hydrogenated surface, particular attention was paid to the influence of charge transfer doping on the fullerene-substrate interaction and the morphology emerging from self-assembly. Finally, self-assembled C60 islands on the hydrogen-terminated diamond surface were subject to active manipulation by an NC-AFM tip. Two different kinds of tip-induced island growth modes have been induced and were presented. In conclusion, the results obtained provide fundamental informations mandatory for the realization of a molecular quantum computer. In the process it was shown that NC-AFM is, under proper circumstances, a very capable tool for imaging diamond surfaces with highest resolution, surpassing even what has been achieved with STM up to now. Particular attention was paid to the influence of transfer doping on the morphology of fullerenes on the hydrogenated diamond surface, revealing new possibilities for tailoring the self-assembly of molecules that have a high electron affinity.