<p> </p><p>Control of protein immobilization at sensor surfaces is of great interest within various scientific fields, since it enables studies of specific biomolecular interactions. To achieve this, one must be able to immobilize proteins with retained native structure, while minimizing non-specific protein binding. The high affinity interaction between streptavidin (SA) and biotin is extensively used as a linker between a surface, where SA is immobilized, and the (biotinylated) molecule of interest. Self- assembled monolayers (SAMs) of poly- and oligo ethylene glycol (PEG and OEG) derivatives have been proven in literature to minimize non-specific protein binding, and biotin-exposing SAMs have been shown efficient for immobilization of SA.</p><p>The aim of this master's thesis project was to develop biotinylated gold surfaces for quartz crystal microbalance with dissipation monitoring (QCM-D) applications through the self-assembly of mixed monolayers of thiolated OEG (or PEG) derivatives with or without a terminal biotin head group. For this, different thiol compounds were to be compared and evaluated. For the systems under study, the required biotin density for maximum specific SA immobilization was to be established, while keeping the non-specific serum adsorption at a minimum. Model experiments with biotinylated proteins immobilized to the SA-functionalized surfaces were to be performed to evaluate the possibilities for commercialization.</p><p>A protocol for the preparation of a novel biotinylated surface was developed based on the immersion of gold substrates in an ethanolic incubation solution of dithiols with OEG chains (SS-OEG and SS-OEG-biotin, 99:1) and found to give reproducible results with respect to low non-specific protein binding and immobilization of a monolayer of SA. The modified surfaces allowed for subsequent immobilization of biotinylated bovine serum albumin (bBSA) and biotinylated plasminogen (bPLG). PLG was the subject of a challenging case study, using a combination of QCM-D and surface plasmon resonance (SPR), where the immobilized protein was subjected to low molecular weight ligands that were believed to induce conformational changes. The high control of the surface chemistry allowed for the interpretation of the increased dissipation shift upon ligand binding in terms of conformational changes.</p><p>An obstacle before commercialization of the described biotinylated surfaces is that they do not seem stable for storage > 7 days. The reasons for this have to be investigated further.</p>

Control of protein immobilization at sensor surfaces is of great interest within various scientific fields, since it enables studies of specific biomolecular interactions. To achieve this, one must be able to immobilize proteins with retained native structure, while minimizing non-specific protein binding. The high affinity interaction between streptavidin (SA) and biotin is extensively used as a linker between a surface, where SA is immobilized, and the (biotinylated) molecule of interest. Self- assembled monolayers (SAMs) of poly- and oligo ethylene glycol (PEG and OEG) derivatives have been proven in literature to minimize non-specific protein binding, and biotin-exposing SAMs have been shown efficient for immobilization of SA. The aim of this master's thesis project was to develop biotinylated gold surfaces for quartz crystal microbalance with dissipation monitoring (QCM-D) applications through the self-assembly of mixed monolayers of thiolated OEG (or PEG) derivatives with or without a terminal biotin head group. For this, different thiol compounds were to be compared and evaluated. For the systems under study, the required biotin density for maximum specific SA immobilization was to be established, while keeping the non-specific serum adsorption at a minimum. Model experiments with biotinylated proteins immobilized to the SA-functionalized surfaces were to be performed to evaluate the possibilities for commercialization. A protocol for the preparation of a novel biotinylated surface was developed based on the immersion of gold substrates in an ethanolic incubation solution of dithiols with OEG chains (SS-OEG and SS-OEG-biotin, 99:1) and found to give reproducible results with respect to low non-specific protein binding and immobilization of a monolayer of SA. The modified surfaces allowed for subsequent immobilization of biotinylated bovine serum albumin (bBSA) and biotinylated plasminogen (bPLG). PLG was the subject of a challenging case study, using a combination of QCM-D and surface plasmon resonance (SPR), where the immobilized protein was subjected to low molecular weight ligands that were believed to induce conformational changes. The high control of the surface chemistry allowed for the interpretation of the increased dissipation shift upon ligand binding in terms of conformational changes. An obstacle before commercialization of the described biotinylated surfaces is that they do not seem stable for storage &gt; 7 days. The reasons for this have to be investigated further.

This study focuses on preparing surface enhanced fluorescence (SEF) substrates for use in the enhancement of the emission signal of rhodamine B and fluorescein dyes. Fluorescence spectroscopy has been widely utilized owing to its high sensitivity. SEF is a process where the interactions of fluorophores with the localized surface plasmons of metal nanoparticles results in fluorescence enhancement, increased photostability and rates of system radiative decay which leads to a decreased lifetime. One of the most important factors of SEF studies is to provide a uniform distance between fluorophore and metal nanoparticle in a controlled manner / otherwise, F&ouml / rster resonance energy transfer takes place from fluorophore to metal nanoparticle and emission intensity of fluorophore is quenched. The spherical gold and silver nanoparticles were prepared using the well known and straightforward chemical reduction method, in which sodium citrate acted both as a reducing agent and a stabilizer around the formed nanoparticles. Silver and gold were chosen because of their high plasmon field enhancement. Since plasmon field strongly depends on the shape and size of the nanoparticles, the prepared nanoparticles were characterized using absorption spectroscopy and field emission scanning electron microscopy (FE-SEM). Prior to deposition of silver or gold nanoparticles on glass slides, the slides were derivatized by immersing them into an aqueous solution of 3-Aminopropylethoxysilane (APTES). Following derivatization, silver or gold nanoparticles were deposited by immersing the slides into the colloid mixture. Metal nanoparticle coated slides were characterized using absorption spectroscopy and field emission scanning electron microscopy (FE-SEM). Surface enhanced Raman scattering (SERS) measurements were carried out to observe the plasmon efficiency of the deposited nanoparticles. The SERS measurements were repeated for the duration of two weeks in order to check the stability of the plasmon efficiency. In this study, different types of materials (silica, zinc oxide, gold, stearic acid.) were employed as spacers to observe their effects on fluorescence enhancement. Physical vapor deposition (PVD) and Langmuir-Blodgett (LB) film deposition techniques were used for the formation of the spacer within the substrate. Fluorescence enhancement of rhodamine B and fluorescein was observed on the prepared SEF substrates. Obtained enhancement factors indicate that SEF substrates have the potential for sensitivity improvements of fluorescence sensing in many fields.

<p>Adsorption on solid surfaces from solution is a fundamental property of a surfactant. It might even be the most important aspect of surfactant behavior, since it influences many applications, such as cleaning, detergency, dispersion, separation, flotation, and lubrication. Consequently, fundamental investigations of surfactant adsorption are relevant to many areas.</p><p>The main aim of this thesis has been to elucidate the adsorption properties, primarily on the solid/water interface, of a particular class of polyhydroxyl based surfactants: the alkyl glucosides. By the use of ellipsometry, the equilibrium and kinetic aspects of adsorption on titanium dioxide with respect to structural effects has been studied. Furthermore, the effects of small amounts of cationic surfactant additives on the adsorption on silica have been investigated. The results have been compared with similar studies for other nonionic surfactants.</p><p>We have found that the surfactant structure has a strong effect on the adsorption properties. An increase in the surfactant chain length increases the cooperativity of the system. An increase in the head group polymerization decreases the cooperativity and the plateau adsorbed amount at equilibrium. The effect of surfactant structure on the adsorption kinetics depends on the concentration relative to the cmc, while the there is a decrease in the rate of desorption with increasing hydrophobic chain length independent of the concentration. The adsorption/desorption process is concluded to be diffusion driven, as suggested by the model used. When comparing these results with studies on ethylene oxide based surfactants, we conclude that the two types of surfactants exhibit similar trends on surfaces onto which they adsorb.</p><p>Adsorption from binary surfactant solutions is even more interesting than adsorption from single surfactant solutions, since it brings us one step closer to the systems used in applications. In addition, adsorption from a mixture can be very different from adsorption from any of the single surfactants in the mixture. Alkyl glucosides alone do not adsorb on silica, but addition of small amounts of a cationic surfactant to the alkyl glucoside solution allows for adsorption on silica. A comparison between the adsorption and bulk properties has shown that mixed micellization explains most, but not all, effects of the coadsorption properties. Changing the pH in the mixed systems reveals that a surfactant with a pH-dependent charge and the ability to adapt its charge to the environment, e.g. a surface, enhances the adsorbed amount over a wider range of pH values than a purely cationic surfactant.</p><p>It is well known that alkyl glucosides and ethylene oxides adsorb differently on different types of hydrophilic surfaces. As a consequence, replacing ethylene oxides with alkyl glucosides might not be all straight-forward; however, we have shown that the effect of the surface can be eliminated by the use of a cosurfactant.</p>

Les propriétés d'une nouvelle classe de chimie de surface basée sur les monocouches auto-assemblées de liquides ioniques (ILs-SAMs), ont été étudiées pour une utilisation dans la construction de biocapteurs basés sur la résonance des plasmons de surface (SPR). Les biocapteurs sont utiles pour détecter des biomolécules spécifiques dans une matrice biologique complexe. Cependant, le signal analytique de la biomolécule spécifique peut être masqué par l’adsorption non spécifique de la matrice biologique, produisant une réponse faussement positive. Par ailleurs, l'activité des récepteurs moléculaires est souvent réduite par des techniques d'immobilisation chimique. Ainsi, il est essentiel de déterminer une surface idéale pour la préparation de biocapteurs. Les liquides ioniques sont bien connus pour favoriser l'activité des récepteurs moléculaires et cette étude enquête si cette propriété importante peut se traduire sur des capteurs SPR. Différents liquides ioniques ont été utilisés pour former des monocouches auto-assemblées sur une surface d'or. Les ILs-SAMs sont tous basés sur les sels de mercapto-(chaîne alkyle)nCH2-méthylimidazolium avec différentes chaînes alkyles (n = 3, 6, 9, 12) et différents contre-anions (Br-, BF4-, PF6-, NTf2-). Des études cinétiques de l'adsorption non spécifique de sérum bovin ont été réalisées sur des capteurs SPR avec un instrument construit sur mesure, basé sur l'interrogation des longueurs d’ondes SPR sur un prisme d’inversion d’image (dove). Par la suite, l’anti-IgG de chèvre sélective à l’IgG humain a été utilisé en tant que modèle pour la confection de biocapteurs sur les ILs-SAMs. En solution, il est possible d’effectuer des échanges du contre-anion des liquides ioniques pour un contre-anion de plus en plus hydrophobe. Cependant, l’échange inverse, soit vers des anions de plus en plus hydrophile, s’avère impossible. Toutefois, il a été observé par les travaux présentés dans ce mémoire, que les liquides ioniques immobilisés sur une surface d'or ont la capacité d'échanger leurs contre-anions réversiblement, procurant une méthode simple de moduler leurs propriétés physico-chimiques. Ce phénomène a été observé par la mesure d’angles de contacts et par les techniques spectroscopiques de l’infrarouge moyen (mid-IR), des photoélectrons de rayon-X (XPS) et par la diffusion Raman exaltée par les surfaces (SERS) ii ainsi que par la spectrométrie de masse (MS). La connaissance des propriétés d’échange d’anion est importante pour prédire le comportement de ces surfaces de liquides ioniques dans les tampons et fluides biologiques. / The properties of a novel class of surface chemistry based on ionic liquid self-assembled monolayers (IL-SAM) were investigated for use with surface plasmon resonance (SPR) biosensors. Biosensors are useful to detect specific biomolecules in a complex biological matrix. However, the analytical signal of a specific biomolecule can be masked by nonspecific adsorption of the biological matrix, resulting in a false positive response. Moreover, the activity of molecular receptors is often reduced by current immobilization chemistry. Thus, it is essential to determine an ideal surface for the preparation of biosensors. Ionic liquids are well-known to promote the activity of molecular receptors and this study investigates if this important property translates to SPR sensors. Different ionic liquids were used to form self-assembled monolayers on a gold surface. IL-SAM were based on mercapto(alkyl chain)n methylimidazolium salts with different alkyl chain (n = 3, 6, 9, 12) and counter anions (Br-, BF4-, PF6-, NTf2-). Kinetic studies of the nonspecific adsorption of bovine serum were carried on SPR sensors with a custom built instrument based on wavelength interrogation SPR on a dove prism. Thereafter, anti-goat IgG selective to human IgG was used as a model for biosensor employing ILs-SAM surface chemistry. Exchange of counter anion of ionic liquids was believed impossible for most hydrophobic counter anions. However, it was observed that ionic liquids immobilized on a gold surface have the ability to exchange their counter anions reversibly, allowing a simple method to modulate their physico-chemical properties. This phenomenon was observed by contact angle technique and by attenuated total reflectance mid-infrared (ATR mid-IR), X-ray photoelectron spectroscopy (XPS), surface enhanced raman spectroscopy (SERS) and mass spectrometry (MS). Better understanding of the anion exchange properties is crucial in predicting the behaviour of IL-SAM in presence of biological buffers and fluids.

This article has been published online on 21st May 2014, in Journal of Vacuum Science & Technology A: Vac (Vol.32, Issue 4): http://scitation.aip.org/content/avs/journal/jvsta/32/4/10.1116/1.4878815?aemail=author DOI: 10.1116/1.4878815 This article may be accessed via the issue's table of contents at this link: http://scitation.aip.org/content/avs/journal/jvsta/32/4?aemail=author The surface chemistry of the bis(tri-n-butylphosphane) copper(I) acetylacetonate, [(nBu3P)2Cu(acac)], and the thermal atomic layer deposition (ALD) of Cu2O using this Cu precursor as reactant and wet oxygen as co-reactant on SiO2 substrates are studied by in-situ X-ray photoelectron spectroscopy (XPS). The Cu precursor was evaporated and exposed to the substrates kept at temperatures between 22 °C and 300 °C. The measured phosphorus and carbon concentration on the substrates indicated that most of the [nBu3P] ligands were released either in the gas phase or during adsorption. No disproportionation was observed for the Cu precursor in the temperature range between 22 °C and 145 °C. However, disproportionation of the Cu precursor was observed at 200 °C, since C/Cu concentration ratio decreased and substantial amounts of metallic Cu were present on the substrate. The amount of metallic Cu increased, when the substrate was kept at 300 °C, indicating stronger disproportionation of the Cu precursor. Hence, the upper limit for the ALD of Cu2O from this precursor lies in the temperature range between 145 °C and 200 °C, as the precursor must not alter its chemical and physical state after chemisorption on the substrate. 500 ALD cycles with the probed Cu precursor and wet O2 as co reactant were carried out on SiO2 at 145 °C. After ALD, in situ XPS analysis confirmed the presence of Cu2O on the substrate. Ex-situ spectroscopic ellipsometry indicated an average film thickness of 2.5 nm of Cu2O deposited with a growth per cycle of 0.05 Å/cycle. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations depicted a homogeneous, fine, and granular morphology of the Cu2O ALD film on SiO2. AFM investigations suggest that the deposited Cu2O film is continuous on the SiO2 substrate.

The combination of analytical sensitivity and selectivity provided by time-of-flight secondary ion mass spectrometry (ToF-SIMS), with advanced statistical interrogation by principal component analysis (PCA), has allowed a significant advancement in the forensic discrimination of pen, pencil and glass materials based on trace characterisation.

Attractive particle interactions which lead to the hetero-aggregation or 'sliming' of silicate clay gangue and valuable sulphide mineral particles are encountered in a number of hydrometallurgical and flotation processes. Sliming leads to poor recovery of the valuable minerals and high recovery of the clay gangue minerals in flotation concentrates. In the present work, the hetero-aggregation mechanism of hydrophilic mica clay mineral sericite (or muscovite) and hydrophobic chalcocite was investigated by probing the particle interactions and the prevailing interfacial chemistry under dispersion conditions where the individual chalcocite and sericite particles displayed negative zeta potentials. The mitigation/suppression of the hetero-aggregation was examined via the prudent control of dispersion conditions and pulp chemistry (i.e., pH modification and solution speciation control) and the use of two, anionic, polymeric dispersants with different molecular weight and functionality (carboxylate-substituted polyacrylamide, Cyquest 3223 and sulphonate-substituted polymaleic acid, P80 co-polymers) as dispersants. The adsorption behaviour of both polymers onto both minerals under industrially relevant suspension conditions have been quantified in terms of the polymer adsorption density and the adsorbed layer characteristics. These interfacial layer properties which impact on the mineral particles' zeta potentials and interactions, and also underpin the dispersion efficacy of polymers were characterized, using interfacial and solution analytical methods and TM-AFM imaging analysis.

The thesis focuses on elastic polymer material that is biodegradable and compatible with human cells and tissues. The presented research describes polymer synthesis, material processing, physico-chemical investigation and biological tests performed on this novel biomaterial.

The hydrophobicity of a surface is an important property in many areas of science and engineering. This is especially the case in mineral processing, where differences in surface hydrophobicity lie at the heart of the separation process of flotation. Chemicals are used to increase and decrease the natural hydrophobicity of minerals to attain a better separation between valuable and worthless material. Polymers are often used to reduce mineral surface hydrophobicity. Decades of empirically based decision making have produced a list of effective depressants. However the detailed study of how these polymer depressants affect surface hydrophobicity and mineral recovery lags behind applied investigations. The aim of this thesis was to study the adsorption of commonly used depressants on model surfaces and to interrogate the action of these polymers in reducing surface hydrophobicity. We have modelled the degree of hydrophobicity of common minerals in order to study polymer depressants with methods not commonly used in studies of surface characterisation in flotation. The model surfaces (self-assembled monolayers, SAMs) allowed us to use the quartz crystal microbalance with dissipation monitoring (QCM-D) to study the adsorption of polymers. The QCM-D can be used to obtain adsorption isotherms, adsorption kinetics, water content of adsorbed layers, and information on the conformation of the adsorbed polymer. The results from the QCM-D were correlated with the contact angle data from the captive bubble measurements, with which we assessed the hydrophobicity of the surface before and after polymer adsorption. Three of the polymers layers were probed with dynamic dewetting studies, in order to test other modes of depressant action. Three types of polymers were studied - a polyacrylamide (Polymer-H), a polyelectrolyte CMC (carboxymethyl cellulose) and a group of dextrins (Dextrin-TY, a phenyl succinate substituted dextrin (PS Dextrin) and a styrene oxide substituted dextrin (SO Dextrin)). These polymers are commonly used or have potential to be used in the depression of talc and graphite. Polymer-H was used to investigate the hydrophobic bonding between a non-ionic polymer depressant and chemically inert and non charged surfaces by probing the influence of substrate hydrophobicity on polymer adsorption and reduction of contact angle. Three different model surfaces were used (mixed self-assembled 0.5 SAM, 0.7 SAM or single self-assembled 1.0 SAM monolayers) with advancing contact angles between 75?? and 119??. The study of Polymer-H found that the substrate hydrophobicity is an important factor in adsorption of this polymer and the change in contact angle upon adsorption depends on adsorbed amount. The effectiveness of Polymer-H to reduce surface hydrophobicity was established to correlate with its conformation and morphology. CMC was investigated to find out how a stimulus responsive polymer depressant can be used in flotation. It was established that the adsorbed amount and rate of adsorption of CMC increase with decreasing of pH or increasing of ionic strength. It was shown that the surface hydrophobicity of a CMC pre-adsorbed layer changes with the environment and these alterations are fully reversible. A switch of ionic strength (from 10-2 M KCl to 10-1 M KCl) caused partial dehydration of the adsorbed layer and a decrease of the receding contact angle by 20??. A pH switch (pH = 9 to pH = 3) resulted in a 40?? change in receding contact angle. The CMC investigation showed that the use of a stimulus responsive polymer presents opportunities for exploiting solution conditions as a means to effect a better mineral separation in flotation The adsorption of three dextrin-based polymers on a model hydrophobic surface has been characterized using the quartz crystal microbalance with dissipation monitoring (QCM-D). The three polymers (one standard dextrin and two dextrins with different aromatic group substitutions) exhibited varying affinities and capacity for adsorption on the hydrophobic substrate. The effect of the three polymers on the static contact angle of the surface was studied using captive bubble contact angle measurements. The three polymers were seen to reduce the receding contact angle by similar amounts (approximately 14 degrees) in spite of having varying adsorbed amounts and differences in adsorbed layer water content. Although no differences were observed in the ability of the polymers to reduce the static contact angle, measurements of the dewetting dynamics between a rising air bubble and the polymer covered substrate yielded stark differences between the polymers, with one polymer slowing the dewetting dynamics by an order of magnitude more than the other two polymers. The differences in dewetting behaviour correlate with the adsorbed layer characteristics determined by QCM-D. / Thesis (PhD)--University of South Australia, 2010