<p>This study firstly reports the development, characterisation, and application of thick-film acetylcholinesterase (AChE) biosensors based on a gold electrode modified with a mercaptobenzothiazole (MBT) self-assembled monolayer and either poly(omethoxyaniline) (POMA) or poly(2,5-dimethoxyaniline) (PDMA) in the presence of polystyrene(4-sulphonic acid) (PSSA). The Au/MBT/POMA-PSSA/AChE and Au/MBT/PDMA-PSSA/AChE biosensors were then applied to successfully detect standard organophosphorous and carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Secondly, it reports the construction of the Au/MBT/PANI/AChE/PVAc thick-film biosensor for the determination of certain organophosphate and carbamate pesticide solutions in selected aqueous organic solvent solutions.</p>

The surface of biomaterials can induce contacting blood to coagulate, similar to the response initiated by injured blood vessels to control blood loss. This poses a challenge to the use of biomaterials as the resulting coagulation can impair the performance of hemocompatible devices such as catheters, vascular stents and various extracorporeal tubings [1], what can moreover cause severe host reactions like embolism and infarction. Biomaterial induced coagulation processes limit the therapeutic use of medical products, what motivates the need for a better understanding of the basic mechanisms leading to this bio-incompatibility [2] in order to define modification strategies towards improved biomaterials [3]. Several approaches for the enhancement of hemocompatible surfaces include passive and active strategies for surface modifications. The materials’ chemical-physical properties like surface chemistry, wettability and polarity are parameters of passive modification approaches for improved hemocompatibility and are the focus of the present work. In the present study self assembled monolayers with different surface functionalities (-COOH, -OH, -CH3) were applied as well as two-component-layers with varying fractions of these, as they allow a defined graduation of surface wettability and charge. The ease of control over these parameters given by these model surfaces enables the evaluation of the influence of specific surface-properties on biological responses. To evaluate the effects of different surface chemistry on initial mechanisms of biomaterial induced coagulation, the surfaces were incubated with protein solution, human plasma, blood cell fractions or fresh heparinised human whole blood. Indicative hemocompatibility parameters were subsequently analysed focusing on protein adsorption, coagulation activation, contact activation (intrinsic/ enhancer pathway), impact of tissue factor (extrinsic/ activator pathway) and cellular systems (blood platelets and leukocytes).

Philosophiae Doctor - PhD / This study firstly reports the development, characterisation, and application of thick-film acetylcholinesterase (AChE) biosensors based on a gold electrode modified with a mercaptobenzothiazole (MBT) self-assembled monolayer and either poly(omethoxyaniline) (POMA) or poly(2,5-dimethoxyaniline) (PDMA) in the presence of polystyrene(4-sulphonic acid) (PSSA). The Au/MBT/POMA-PSSA/AChE and Au/MBT/PDMA-PSSA/AChE biosensors were then applied to successfully detect standard organophosphorous and carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Secondly, it reports the construction of the Au/MBT/PANI/AChE/PVAc thick-film biosensor for the determination of certain organophosphate and carbamate pesticide solutions in selected aqueous organic solvent solutions. / South Africa

xvii, 209 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Altering and controlling the properties of solid surfaces in aqueous or other liquid phase environments has been a sought after objective for decades. With the discovery of chemisorbed self-assembled monolayers, this dream has become a reality. Oxide and metal surfaces can now be readily coated with an array of commercially available products to produce a desired fnctionality. The presence of these coatings on solid surfaces affects properties of the interfacial region by altering interfacial electrostatic fields, changing the structure of interfacial water molecules and altering the interactions of adsorbed species. This dissertation reports on in situ studies of adsorption at several solid/aqueous interfaces using vibrational sum-frequency spectroscopy, a surface specific technique. These studies are augmented by the use of atomic force microscopy and contact angle goniometry to characterize the prepared surfaces and their interactions with adsorbates. The studies investigate how changes in the surface structure and chemistry, as well as the bulk aqueous phase, affect interfacial structure. The studies within are primarily focused on the interactions of water with bare and functionalized fused silica and the relationship between the aqueous phase composition and the structure of fluorocarbon and hydrocarbon self-assembled monolayers. The variations in aqueous structure are then examined in detail using ionic strength controlled experiments to understand the direct interactions of water hydrophobically coated silica. This analysis is followed by an investigation of the competitive adsorption of methanol and water at fluorocarbon and hydrocarbon monolayers which show spectroscopic signatures of the interaction strength between fluorocarbons and hydrocarbons. Further studies are performed using butylammonium chloride to verify these spectroscopic signatures and reveal different molecular structures of adsorbed species at chemically different hydrophobic surfaces. Lastly, specific ion effects on the CaF 2 /water interface are shown using equilibrium and time-resolved sum-frequency spectroscopy. The results of all these studies have implications for an array of surface chemical applications from mineral flotation to biocompatibility. This dissertation includes previously published co-authored material. / Committee in charge: Thomas Dyke, Chairperson, Chemistry; Geraldine Richmond, Advisor, Chemistry; James Hutchison, Member, Chemistry; Mark Lonergan, Member, Chemistry; Qusheng Jin, Outside Member, Geological Sciences

Dans le but de développer des matériaux et des dispositifs avec de nouvelles propriétés, l’élaboration de monocouches auto-assemblées (SAM) est un sujet d'intérêt croissant dans le domaine des nanosciences. Les SAM sont des agrégats bidimensionnels formés par des molécules régulièrement espacées sur une surface et liées entre elles par des forces non covalentes. Le domaine des biocapteurs électrochimiques pour la reconnaissance des brins d'ADN est parmi les applications les plus récentes des SAM. Dans ce cadre, nous avons mené une étude théorique des mécanismes fondamentaux engagés lors de l’adsorption de la molécule quinone Jug-C4-thiol sur la surface Au (111). Les résultats ont été confrontés aux mesures expérimentales accessibles réalisées par l’équipe « nano 2D » au laboratoire ITODYS (Université Paris7). Tout d’abord, la théorie de la fonctionnelle de la densité PBE et PBE-D2 a été utilisée pour étudier les mécanismes mis en jeu (physisorption ou chimisorption) lors de l’adsorption de la molécule isolée à la surface de Au (111) et déterminer le site le plus favorable pour chaque mécanisme. La nature de la liaison entre la molécule et la surface de a été finement analysée à l’aide de calculs de densité d’états (DOS) et de différences de densités de charge. Ensuite, l'assemblage de la molécule quinone Jug-C4-thiol sur la surface Au (111) a été étudié. Cet assemblage des molécules a été initié par la formation de configurations de dimère à travers la formation de liaisons intermoléculaires (liaison hydrogène et π-stacking, …). Les spectres infrarouges des configurations les plus stables ont été simulés et confrontés à l’expérience. Et enfin, le mécanisme d’échange entre des molécules « hôtes » (alcanethiols C12H25SH préalablement assemblés sur la surface) et « invitées » (Jug-C4-thiols) a été exploré avec les outils théoriques. L’analyse des résultats a mis en évidence des informations structurales et énergétiques importantes sur la formation de la monocouche moléculaire mixte. / In order to develop materials and devices with new properties, the development of self- In order to develop materials and devices with new properties, the development of self-assembled monolayers (SAM) is a topic of growing interest in the field of nanoscience. SAM are two-dimensional aggregates formed by molecules regularly spaced on a surface and bonded together by non-covalent forces. The field of electrochemical biosensors for DNA strand recognition is among the most recent applications of SAM. In this context, we conducted a theoretical study of the fundamental mechanisms involved in the adsorption of the quinone Jug-C4-thiol molecule on the Au (111) surface. The results were compared to the accessible experimental measurements from the "nano 2D" team at the ITODYS laboratory (Paris 7 University). First, the density functional theory at PBE and PBE-D2 levels was used to study the mechanisms involved (physisorption or chemisorption) during the adsorption of the isolated molecule on the surface of Au (111) and access to the most favorable site for each mechanism. The nature of the binding between the molecule and the surface was finely analyzed using density of states (DOS) calculations and differences in charge densities.Then, the assembly of the quinone Jug-C4-thiol molecule on the Au (111) surface was studied. This assembly of molecules was initiated by the formation of dimer configurations through the formation of intermolecular bonds (hydrogen bonding and π-stacking, etc.). The infrared spectra of the most stable configurations were simulated and compared with the experiment. And finally, the mechanism of exchange between "host" molecules (C12H25SH alkanethiols previously assembled on the surface) and "invited" molecules (Jug-C4-thiols) was explored with the theoretical tools. The analysis of the results revealed important structural and energetic informations on the formation of the mixed molecular monolayer.

Orientador: Lauro Tatsuo Kubota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-06T00:45:50Z (GMT). No. of bitstreams: 1 Carvalhal_RafaelaFernanda_M.pdf: 708037 bytes, checksum: ed89f8b11b63131a7f452b5191b27432 (MD5) Previous issue date: 2005 / Mestrado / Quimica Analitica / Mestre em Química

This licentiate thesis is focused on two methods for protein immobilization to biosensor surfaces for future applications in protein microarray formats. The common denominator is a surface chemistry based on a gold substrate with a self-assembled monolayer (SAM) of functionalized alkanethiolates. Both methods involve photochemistry, in the first case for direct immobilization of proteins to the surface, in the other for grafting a hydrogel, which is then used for protein immobilization. Paper I describes the development and characterization of Chelation Assisted Photoimmobilization (CAP), a three-component surface chemistry that allows for covalent attachment and controlled orientation of the immobilized recognition molecule (ligand) and thereby provides a robust sensor surface for detection of analyte in solution. The concept was demonstrated using His-tagged IgG-Fc as the ligand and protein A as the analyte. Surprisingly, as concluded from IR spectroscopy and surface plasmon resonance (SPR) analysis, the binding ability of this bivalent ligand was found to be more than two times higher with random orientation obtained by amine coupling than with homogeneous orientation obtained by CAP. It is suggested that a multivalent ligand is less sensitive to orientation effects than a monovalent ligand and that island formation of the alkanethiolates used for CAP results in a locally high ligand density and steric hindrance. Paper II describes the development of nanoscale hydrogel structures. These were photografted on a SAM pattern obtained by dip-pen nanolithography (DPN) and subsequent backfilling. The hydrogel grew fast on the hydrophilic patterns and slower on the hydrophobic background, which contained a buried oligo(ethylene glycol) (OEG) chain. Using IR spectroscopy, it was found that the OEG part was degraded during UV light irradiation and acted as a sacrificial layer. In this process other OEG residues were exposed and acted as new starting points for the self-initiated photografting and photopolymerization (SIPGP). A biotin derivative was immobilized to the hydrogel density pattern and interaction with streptavidin was demonstrated by epifluorescence microscopy.

The mechanism of ion channel (mimetic) sensors (ICSs) consisting of (poly)electrolyte type alkane thiol, protein or dendrimer self assembled monolayers (SAMs) at gold electrodes as a sensing layer and highly charged redox-active marker ions in solution was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and rotating disk voltammetry (RDV) in the presence of a series of analytes, i.e, suppressor and enhancer ions, leading to the following general statements: (i) electrostatic binding of marker ions to the sensing layer is a prerequisite for an electrochemical current and (ii) charge propagation through the layer consists of electron hopping between surface-confined marker ions and solution born marker ions. It is further shown that there exists (iii) competition between equally charged ions for coordination sites at the oppositely charged sensing layer. An apparent charge inversion (iv) by surface confinement of multiple charged counter ions occurs. Thereby an existing electron transfer (ET) path can be cut or a new one can be induced. Build up of a second layer of multiple charged electroactive ions (v) can take place on top of the charge inverted layer. Competing ET (vi) through the inner and outer redox layer can take place. In addition to fundamental insight into the mechanism of charge propagation, valuable information for the design, optimization, and tailoring of new biosensors based on the ICS concept, the possibilities of exploiting layer-by-layer electrostatic SAMs and dendrimer-DNA interaction for bioanalytical applications are demonstrated by the current findings.

In this paper SAM (self-assembled monolayers) is used to passivate cobalt microbumps for 3D-stacking of Si chips. The SAM deposition process is optimized, using input from characterization techniques such as water contact angle measurement, ATR, AFM and XPS analysis in order to form a monolayer of Thiols-SAM on cobalt microbumps. A 3D stacked Si chips test vehicle was used to demonstrate the effectiveness of the SAM coating on cobalt bumps by measuring the electrical continuity of daisy chains.

The functionalization of surfaces has received attention because the process allows the design and tailoring of substrate surfaces with a new or improved function. "Host-guest" thin film complexes are composed of "host" molecules attached the substrate surface, either through physisorption or covalent bonds, with cavities for the inclusion of desired "guest" molecules for the functionalization of the surface. Two methods for fabricating functional "host-guest" thin films were investigated: Langmuir-Blodgett (LB) deposition and self-assembly monolayer (SAM). Langmuir films were created at the air-water interface using octadecanesulfonic acid (C18S) as the amphiphilic "host" molecules separated by hydrophilic guanidinium (G) spacer molecules, which created a cavity allowing the inclusion of desired "guest" molecules. Surface pressure-area isotherms of the (G)C18S, with and without guests, are characterized by the lift-off molecular areas and are use to determine the proper deposition surface pressure. "Host-guest" Langmuir films are deposited onto silicon substrates using the LB deposition technique. The LB films were then subjected to stability testing using different solvents over increasing periods of time. Grazing-angle incidence X-ray diffraction (GIXD), specular X-ray reflectivity (XRR) and transfer ratio measurements were used to characterize the crystallinity, film thickness, overall film stability and film coverage. The GIXD data revealed that the crystallinity of the deposited film varies with the "guest" molecules and can be disrupted by the functional group on the "guest" molecule through hydrogen bonding. After modeling the XRR data using StochFit, it was discovered that the more polar solvent, tetrahydrofuran (THF), removed the film completely while the nonpolar solvent, hexane, compacted the thin film and increased the electron density. With transfer ratios around 0.95 to 1.05, the deposited films were homogenous. The second method used was self-assembly monolayers, which differs from Langmuir films in that they are created by a spontaneous chemical synthesis from immersing a substrate into a solution containing an active surfactant. Octadecyltrichlorosilane (OTS) was used initially as a molecule to study the self-assembled monolayer procedure. To study a "host-guest" self-assembled monolayer system, a compound is being synthesized from 9-bromoanthracene. This compound would already contain the cavity necessary for the inclusion of "guest" molecules. The solution that contained OTS was composed of a 4:1 mixture of anhydrous octadecane: chloroform. Silicon substrates with a deposited oxide layer were hydroxylated for the surfactant binding chemical reaction to occur. The OTS SAMs were exposed to the same stability tests as the LB films. Surface contact angle measurements were taken of the OTS SAMs before and after the stability tests. The contact angle prior to the stability tests was 110° (±2°). The contact angle after immersion in THF was 101° (±2°) while the contact angle resulting from immersion in hexane was 105° (±2°). From the contact angle measurements, the degradation of the OTS SAMs was less extensive than that of the (G)C18S LB films. / Master of Science