Cell-semiconductor hybrid systems are a potential centerpiece in the scenery of biotechnological applications. The selection and study of promising crystalline semiconductor materials for bio-sensing applications is at the basis of the development of such hybrid systems. In this work we introduce crystalline SiC as an extremely appealing material for bio-applications. For the first time we report biocompatibility studies of different SiC polytypes whose results document the biocompatibility of this material and its capability of directly interfacing cells without the need of surface functionalization. Since the successful implementation of biosensors requires a good understanding and versatile control of the semiconductor surface properties, the chemistry, crystallography and electronic status of different SiC surfaces are extensively studied while their surface morphologies are thoroughly controlled via hydrogen etching. Also, investigations of the effect of cell surface charge on the electronic status of SiC surfaces are attempted adopting a contactless surface potential monitoring technique. The results obtained from these contactless measurements lead to the development of theoretical models well-suited for the description of cell-semiconductor hybrid systems electronic interactions.

Abstract not available

Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 146-156). Also available for download via the World Wide Web; free to University of Oregon users.

Graduation date: 1994

Im Fokus dieser Arbeit stand der Aufbau einer auf DNA basierenden Nanostruktur. Der universelle Vier-Buchstaben-Code der DNA ermöglicht es, Bindungen auf molekularer Ebene zu adressieren. Die chemischen und physikalischen Eigenschaften der DNA prädestinieren dieses Makromolekül für den Einsatz und die Verwendung als Konstruktionselement zum Aufbau von Nanostrukturen. Das Ziel dieser Arbeit war das Aufspannen eines DNA-Stranges zwischen zwei Fixpunkten. Hierfür war es notwendig, eine Methode zu entwickeln, welche es ermöglicht, Funktionsmoleküle als Ankerelemente ortsaufgelöst auf eine Oberfläche zu deponieren. Das Deponieren dieser Moleküle sollte dabei im unteren Mikrometermaßstab erfolgen, um den Abmaßen der DNA und der angestrebten Nanostruktur gerecht zu werden. Das eigens für diese Aufgabe entwickelte Verfahren zum ortsaufgelösten Deponieren von Funktionsmolekülen nutzt das Bindungspaar Biotin-Neutravidin. Mit Hilfe eines Rasterkraftmikroskops (AFM) wurde eine zu einem „Stift“ umfunktionierte Rasterkraftmikroskopspitze so mit der zu deponierenden „Tinte“ beladen, dass das Absetzen von Neutravidin im unteren Mikrometermaßstab möglich war. Dieses Neutravidinmolekül übernahm die Funktion als Bindeglied zwischen der biotinylierten Glasoberfläche und dem eigentlichen Adressmolekül. Das somit generierte Neutravidin-Feld konnte dann mit einem biotinylierten Adressmolekül durch Inkubation funktionalisiert werden. Namensgebend für dieses Verfahren war die Möglichkeit, Neutravidin mehrmals zu deponieren und zu adressieren. Somit ließ sich sequenziell ein Mehrkomponenten-Feld aufbauen. Die Einschränkung, mit einem AFM nur eine Substanz deponieren zu können, wurde so umgangen. Ferner mußten Ankerelemente geschaffen werden, um die DNA an definierten Punkten immobilisieren zu können. Die Bearbeitung der DNA erfolgte mit molekularbiologischen Methoden und zielte darauf ab, einen DNA-Strang zu generieren, welcher an seinen beiden Enden komplementäre Adressequenzen enthält, um gezielt mit den oberflächenständigen Ankerelementen binden zu können. Entsprechend der Geometrie der mit dem AFM erzeugten Fixpunkte und den oligonukleotidvermittelten Adressen kommt es zur Ausbildung einer definierten DNA-Struktur. Mit Hilfe von fluoreszenzmikroskopischen Methoden wurde die aufgebaute DNA-Nanostruktur nachgewiesen. Der Nachweis der nanoskaligen Interaktion von DNA-bindenden Molekülen mit der generierten DNA-Struktur wurde durch die Bindung von PNA (peptide nucleic acid) an den DNA-Doppelstrang erbracht. Diese PNA-Bindung stellt ihrerseits ein funktionales Strukturelement im Nanometermaßstab dar und wird als Nanostrukturbaustein verstanden. / The main aim of this work was the development of a DNA-based nanostructure. The universal four-letter code of DNA allows addressing bonds at the molecular level. The chemical and physical property of DNA makes this macromolecule an ideal candidate as a construction element for nanostructures. The aim of this work was to span a DNA strand between two fixed points. For this purpose it was necessary to develop a method which makes it possible to deposit functional molecules as anchoring elements with highly spatial resolution on a surface. These molecules should be immobilized on the lower micrometer scale to meet the requirements of the desired nanostructure. The method that has been developed for this task, which enables to deposit functional molecules, uses the binding pair biotin-neutravidin. Using the tip of an atomic force microscope (AFM), which can be uses like a pen, it was possible to deposit neutravidin on the lower micrometer scale. This neutravidin molecule is the linking element between the biotinylated glass surface and the actual address molecule. The thus generated neutravidin field could then be functionalized with a biotinylated molecule by incubation. The method has been published as sequential spotting method because it enables a sequential functionalization of neutravidin after it has been deposited. It was so possible to build up a multi-component array. The limitation of being able to deposit only one single substance with an AFM has been circumvented. It also was necessary to create anchor elements in order to immobilize the DNA at defined positions. The processing of the DNA was carried out using molecular biological methods and aimed at generating a DNA strand, which at both ends has a complementary sequence for binding to the surface bound anchor elements. The defined structure is a result of the geometry of the fixed points, generated by the AFM. Using fluorescence microscopy, the constructed DNA nanostructure was detected. The proof of the interaction of DNA-binding molecules with the DNA structure was carried out by the binding of PNA (peptide nucleic acid), which is capable of binding to double stranded DNA. The PNA and its DNA-interaction is a functional building block in the nanometer scale and can be regarded as a promising nanostructure.

The relationship between the amount and conformation of apolymer at the solid-liquid interface, and the resultinginteraction forces between two such surfaces has beeninvestigated. With a degree of control of the polymerconformation, by varying the temperature, solvent quality,polymer charge density etc, it has been possible to measure andinterpret the resulting changes in the surface interactions.The recurring themes of dynamics and hydrodynamics have beencontinually considered due to the large range and viscoelasticnature of the polymeric systems. The polymeric systems investigated in this thesis are, poly(N-isopropylacrylamide), poly (12-hydroxystearate) and a seriesof AM-MAPTAC polyelectrolytes with variable chargedensities. Adsorption and conformation of polymers have beeninvestigated by the novel QCM instrument. By comparison tosimultaneously measured energy loss information, a greaterunderstanding of the conformation of the polymer has beengained, both as a function of layer build-up during initialadsorption, and as a result of induced conformational changes.Comparing the results toin situsurface plasmon resonance and subsequent x-rayphotoelectron spectroscopy measurements, the relativeconcentration of polymer within the layer is determined. Inaddition, efforts have been made to extend the scope of thetechnique, in such ways as measuring with QCM as a function oftemperature and deriving viscoelastic properties. The later isstill to be achieved in absolute terms for polymer layers inliquid environments, yet both the principle and experimentalcapabilities have been shown. Normal interaction forces have been measured as a functionof solvation of the polymer layer, for both adsorbed andgrafted polymer layers. For fully solvated (steric) polymerlayers, which can act as colloidal stabilisers, the dynamics ofthe repulsive force, including hydrodynamics have beeninvestigated. The same has been achieved for collapsed polymerlayers, in which the dynamic adhesion has also beeninvestigated. The effect on the adhesion of three differentdynamic mechanisms has been determined (which, like the surfaceforces, depend on the polymer conformation andviscoelasticity). These dynamic mechanisms are based onbridging forces, polymer entanglement and a viscoelastic‘bulk’response from the surface layers. Lateral or friction measurements have also been completed.The effect of load and rate have been investigated as afunction of both the polymer charge density and the underlyingsubstrate, which result in a variable conformation and bindingstrength to the substrate. This has resulted in a complexaddition of numerous mechanisms, the dominant mechanism beingdetermined by the binding strength to the surface, polymerconformation and viscoelasticity. The results have shown thatadsorbed polymer layers can be used to both increase anddecrease friction, and to change the direction of the ratedependence.

In this study photocatalytic antibacterial and self-cleaning activities of TiO2-SiO2 thin films as a function of TiO2/SiO2 ratios were investigated. TiO2-SiO2 mixed oxides were synthesized by sol-gel method and coated over soda-lime glass plates by dip coating technique. Escherichia coli was used as a model microorganism for the photocatalytic antibacterial tests. Degradation rate of methylene blue (MB) molecules was used to characterize photocatalytic self-cleaning activities of thin film surfaces. The maximum antibacterial activity was achieved over 92 wt% SiO2 containing thin films. However, when the SiO2 content exceeds 92 wt%, photocatalytic antibacterial activity decreased considerably, which was explained by the dilution of TiO2 phase and inaccessibility of TiO2. Increase in photocatalytic antibacterial activity was attributed to increases in the relative surface area, roughness, hydroxyl (OH-) groups and bacterial adhesion. The favored bacterial adhesion enhanced direct contact of bacteria with TiO2 particles and surface reactive oxygen species. The highest initial decomposition rate of MB was obtained for 60 wt% SiO2 and the activity decreases as SiO2 concentration increases. The increase in photocatalytic activity by the SiO2 addition can be explained by the increase of the amount of MB per unit area of TiO2-SiO2 thin films. Different adsorption capability of thin films against MB molecule and E. coli cell was explained as the first reason why the antibacterial and self-cleaning activities reached their maximum values at different SiO2 ratios. The second reason could be related with the different control mechanisms of self-cleaning and antibacterial activities by different textural and surface properties.

This work outlines a series of developments and discoveries related to surface chemistry of controlled near-surface architectures. Through a combination of various X-ray spectroscopy techniques and innovative electrochemical fabrication techniques, valuable knowledge has been added to the fields of electrochemical fabrication, electrocatalysis, and fundamental surface chemistry. Described here is a specific new development in the technique of surface limited redox replacement (SLRR). This work, along with an accompanying journal publication1, reports the first-ever use of nickel as an intermediary for SLRR. In addition, this work identifies specific deviations from the nominal reaction stoichiometry for SLRR-grown films. This led to the proposal of a new reaction mechanism for the initial stages of the SLRR process, which will assist future fabrication attempts in this field. This work also discovered fundamental changes in Pt overlayer systems as the thickness of the overlayer on a gold support is increased from less than a single atomic monolayer to multilayer thicknesses. It was found that Pt overlayers below a certain threshold thickness exhibited increased affinity for hydroxyl groups, along with an increased propensity for formation of oxide and chloride species. These films were also studied for methanol, carbon monoxide, and ethylene glycol electro-oxidation. Finally, this work reports controlled surface architectures of Pt and Cu deposits on application-oriented TiO₂ nanotube arrays and Au-carbon supports.

In particle induced desorption-ionization mass spectrometry the strength of an analyte's signal under a given set of bombardment conditions is usually considered to be representative of the analytes relative surface activity. This rationale is generally used to explain differences in the technique's sensitivity between and within various classes of compound. In liquid matrix assisted secondary ion mass spectrometry (SIMS) sensitivity enhancement of ionic analytes by pairing with surface active counterions has been demonstrated by several groups. This technique has been utilized in this work to achieve a 10,000 fold enhancement in the signal for ATP on a double focusing magnetic sector instrument and to detect femtomole quantities of nucleoside monophosphates on a time-of-flight instrument. The analyte's signal, however, is dependent on both the analyte bulk concentration and that of the surfactant. Additionally, the surfactant concentration that produces the maximum analyte signal changes with the analyte concentration. In this study, this phenomenon has been modeled in terms of conventional solution equilibria and surface chemical principles. It is assumed that the initial surface composition and the bulk concentration are the boundary conditions of a steady state established by the competing processes of surface sputtering and surface replenishment from the bulk during analysis. Calculated surface excesses correlate well with observed relative ion intensities, suggesting that equilibrium conditions are approached in the sample matrices despite the outwardly dynamic nature of the sputtering processes. / Graduation date: 1994

Biomaterial surface energy, chemical composition, charge, wettability and roughness all play an important role in determining the degree of the direct bone-to-implant interface, termed osseointegration. Surface chemistry, which is influenced by surface energy, wettability, and composition, is another factor that determines osteoblast phenotype and regulates osteoblast maturation. Increased surface energy is desirable for bone implants due to enhanced interaction between the implant surface and the biological environment. The extent of bone formation in vivo is also increased with increasing water wettability of implants. The physiological role of implant surface chemistry is important in determining the success of implant osseointegration because of molecular rearrangements, surface reactions, contamination, and release of toxic or biologically active ions that are determined by the starting chemistry. However, the role of surface chemistry on osteoblast response is not fully studied. Therefore, the overall goal of this dissertation is to understand how the surface chemistry, including wettability, chemical composition, and charge density, of titanium biomaterials impacts osteoblast maturation (in vitro). This study focuses on the general hypothesis that modifications of surface chemistry of titanium surfaces with sterilization or polyelectrolyte coating on titanium surfaces regulate osteoblast response.