Ligand-stabilized metal nanoparticles (LSNPs) have garnered significant attention for use in applications including sensing, catalysis, and thin film fabrication. Many uses rely on the size-dependent properties of the metal nanoparticle core. Therefore, preservation of nanoparticle core size is of paramount importance. In other uses, the low processing temperatures afforded by metal LSNPs make them attractive as precursors for conductive thin films. In these distinctly different applications, understanding nanoparticle thermal stability is crucial. A key finding of this research is that nanoparticle sintering is dependent upon both core size and ligand functionality. Multi-technique analysis of four types of gold nanoparticles (AuNPs) with different ligand compositions and core sizes illustrates that more volatile ligands reduce the onset temperature for sintering. Also, AuNPs of larger core size with the same ligand composition exhibit lower sintering onset temperatures. Correlation between measurements reveals that only a small amount of ligand loss is necessary to trigger rapid sintering and that ligands are excluded to the surface of the porous gold films. AuNPs with ligand shells composed of two alkanethiols of different chain length and volatility indicate that the onset temperature of sintering can be tuned further through incorporation of a small amount of more volatile alkanethiol into a ligand shell of lower volatility. Mixed LSNPs further reveal that AuNP thermal stability depends upon the ligand shell composition and its intermolecular interactions, which can result in markedly different sintering behavior for different ligand compositions. Long-chain alkanethiol AuNPs sinter after only a small amount of ligand loss, whereas short-chain alkanethiol AuNPs sinter following complete ligand loss and the formation of metastable bare AuNPs. Heated AuNP films prepared with mixed-ligand AuNPs exhibit ligand-dependent differences in film morphology. To probe AuNP thermal stability in 2D-assemblies, self-assembly using larger ‘marker’ nanoparticles enables the study of small 1.5 nm AuNP arrays with successive TEM monitoring throughout ex situ heating. Monitoring images of the same area shows short-range (1-2 nm) nanoparticle migration/coalescence. In contrast to 3D assemblies, AuNP growth occurs at temperatures as low as 60 °C. This dissertation includes previously published and unpublished co-authored material. / 10000-01-01

Nanoscale colloidal particles display fascinating electronic, optical and reinforcement properties as a consequence of their dimensions. Stable dispersions of nanoscale colloids find applications in drug delivery, biodiagnostics, photonic and electronic devices, and polymer nanocomposites. Most nanoparticles are unstable in dispersions and polymeric surfactants are added generally to improve dispersability and control self-assembly. However, the effect of polymeric modifiers on nanocolloid properties is poorly understood and design of modifiers is guided usually by empirical approaches. Monte Carlo simulations are used to gain a fundamental molecular-level understanding of the effect of modifiers properties on the thermodynamics and interaction forces of nanoscale colloidal particles. A novel method based on the expanded ensemble Monte Carlo technique has been developed for calculation of the chemical potential of colloidal particles in colloid-polymer mixtures (CPM). Using this method, the effect of molecular parameters like colloid diameter, polymer chain length, colloid-polymer interaction strength, and colloid and polymer concentrations, on the colloid chemical potential is investigated for both hard-sphere and attractive Lennard-Jones CPM. The presence of short-chain polymeric modifiers reduces the colloid chemical potential in attractive as well as athermal systems. In attractive CPM, there is a strong correlation between polymer adsorption and colloid chemical potential, as both show a similar dependence on the polymer molecular weight. Based on the simulation results, simple scaling relationships are proposed that capture the functional dependence of the thermodynamic properties on the molecular parameters. The polymer-induced interaction forces between the nanoparticles have been calculated as a function of the above parameters for freely-adsorbing and end-grafted homopolymer modifiers. The polymer-induced force profiles are used to identify design criteria for effective modifiers. Adsorbing modifiers give rise to attractive interactions between the nanoparticles over the whole parameter range explored in this study. Grafted surface modifiers lead to attraction or repulsion based on the polymer chain length and grafting density. The polymer-induced attraction in both adsorbing and grafted modifiers is attributed primarily to polymer intersegmental interactions and bridging. The location of the thermodynamic minimum corresponding to the equilibrium particle spacing in nanoparticle-polymer mixtures can be controlled by tuning the modifier properties.

Many vaccines require an adjuvant to induce a strong immune response. Aluminum–containing adjuvants have been approved by the United States Food and Drug Administration for human use for many years. There are two main aluminum-containing adjuvants, aluminum hydroxide and aluminum phosphate. Due to their favorable safety profile, aluminum-containing adjuvants have been widely used in human vaccines for decades. Many currently licensed and commercially available vaccines contain aluminum-containing adjuvants. However, aluminum-containing vaccine adjuvants suffer from two major limiting factors: (1) aluminum-containing adjuvants can only weakly or moderately potentiate antigen-specific antibody responses and are generally considered incapable of inducing cellular immune responses; (2) vaccines that contain aluminum-containing adjuvants require cold-chain refrigeration for storage and distribution, and may not be frozen, because freezing of the vaccine in dispersion causes irreversible coagulation that damages vaccines (e.g., loss in potency and stability). In this dissertation, the first limitation was addressed by reducing the size of the aluminum hydroxide from micrometers (3-10 micrometer) to nanometers of less than 200 nm, and the second limitation mentioned above was addressed by freeze-drying vaccines that contain aluminum salts as adjuvants into a dry powder using thin-film freeze-drying. In addition, using an improved experimental design, the vaccine adjuvant activities of nanoparticles of around 200 nm was compared to that of the nanoparticles of around 700 nm. The smaller 200 nm nanoparticles showed a more potent adjuvant activity than the larger nanoparticles. When dispersed in an aqueous medium, both aluminum hydroxide and aluminum phosphate are physically 1–20 micrometer particulates. There are data showing that particulate vaccine carriers of around 200 nm (or less) may be optimal in potentiating the immunogenicity of vaccines. Based on this finding, aluminum hydroxide nanoparticles of 112 nm were synthesized, and its adjuvant activity was compared to that of the traditional aluminum hydroxide adjuvant, which have particulates of 3-20 micrometer. Using ovalbumin and Bacillus anthracis protective antigen protein as model antigens, it was found that protein antigens adsorbed on the aluminum hydroxide nanoparticles induced stronger antigen-specific antibody responses than the same protein antigens adsorbed on the traditional aluminum hydroxide microparticles of around 9.3 µm. Importantly, the inflammation reactions induced by aluminum hydroxide nanoparticles in the injection sites were milder than that induced by microparticles. Simply reducing the particle size of the traditional aluminum hydroxide adjuvant in suspension from micrometers into nanometers represents a novel and effective approach to improve its potency. The second limitation was addressed by converting vaccines that contain an aluminum salt as an adjuvant from an aqueous dispersion into a dried powder using thin-film freeze-drying. There is evidence that aluminum-containing vaccines can be lyophilized to dry powders using high speed freezing methods. Thin-film freezing is a high speed freezing method with a freezing rate between 100 to 10,000 K/s, but the feasibility of using thin-film freeze-drying to freeze-dry vaccines that contain aluminum salts as adjuvants has not been tested before. In this dissertation, Using ovalbumin as a model protein antigen and aluminum hydroxide or aluminum phosphate as an adjuvant, it was confirmed that vaccines that are adjuvanted with aluminum hydroxide or aluminum phosphate can be freeze-dried with as low as 2% (w/v) of trehalose as a cryoprotectant by thin-film freeze-drying without causing vaccine aggregation while preserving the immunogenicity of the vaccine. Finally, the feasibility of using the thin-film freeze-drying method to freeze-drying vaccines that contain aluminum salts as adjuvants was further confirmed by drying a commercial aluminum salt-adjuvanted tetanus toxoid vaccine. Vaccines that contain aluminum salts as adjuvants may be converted to a dry powder using the thin-film freeze-drying method to avoid loss of potency due exposure to freezing conditions during transport and storage. / text

Optical manipulation of nanoscale objects is studied with particular emphasis on the role of plasmon resonance for enhancement of optical forces. The thesis provides an introduction to plasmon resonance and its role in confinement of light to a sub-diffraction volume. The strong light confinement and related enhancement of optical forces is then theoretically studied for a special case of nanoantenna supporting plasmon resonances. The calculation of optical forces, based on the Maxwell stress tensor approach, reveals relatively weak optical forces for incident powers that are used in typical realisations of trapping with nanoantenna. The optical forces are so weak that other non-optical effects should be considered to explain the observed trapping. These effects include heating induced convection, thermoporesis and chemical binding. The thesis also studies the optical effects of plasmon resonances for a fundamentally different application - size-based optical sorting of gold nanoparticles. Here, the plasmon resonances are not utilised for sub-diffraction light confinement but rather for their ability to increase the apparent cross-section of the particles for their respective resonant sizes. Exploiting these resonances, we realise sorting in a system of two counter-propagating evanescent waves, each at different wavelength that selectively guide gold nanoparticles of different sizes in opposite directions. The method is experimentally demonstrated for bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture. We conclude the thesis with a numerical study of the optimal beam-shape for optical sorting applications. The developed theoretical framework, based on the force optical eigenmode method, is able to find an illumination of the back-focal plane of the objective such that the force difference between nanoparticles of various sizes in the sample plane is maximised.

With a number of advantages hitherto unrecognized, nanoparticle-stabilized emulsions and foams have recently been proposed for enhanced oil recovery (EOR) applications. Long-distance transport of nanoparticles is a prerequisite for any such EOR applications. The transport of the particles is limited by the degree to which the particles are retained by the porous medium. In this work, experiments that quantify the retention and provide insight into the mechanisms for nanoparticle retention in porous media are described. Sedimentary rock samples (Boise sandstone and Texas Cream limestone) were crushed into single grains and sieved into narrow grain size fractions. In some cases, clay (kaolinite or illite) was added to the Boise sandstone samples. These grain samples were packed into long (1 ft – 15 ft) slim tubes (ID = 0.93 cm) to create unconsolidated sandpack columns. The columns were injected with aqueous dispersions of silica-cored nanoparticle (with and without surface coating) and flushed with brine. The nanoparticle effluent concentration history was measured and the nanoparticle recovery was calculated as a percentage of the injected nanoparticle dispersion. Fifty experiments were performed in this fashion, varying different experimental parameters while maintaining others constant to allow direct comparisons between experiments. The parameters analyzed in this thesis are: specific surface area of the porous medium, lithology, brine salinity, interstitial velocity, residence time, column length, and temperature. Our results indicate that retention is not severe, with an 8% average of the injected amount, for all our experiments. From the parameters analyzed, specific surface area was the most influential variable, with a linear effect on nanoparticle retention independently of lithology. Salinity increased nanoparticle retention slightly and delayed nanoparticle arrival. Velocity, residence time and length are coupled parameters and were studied jointly; they had a minor effect on retention. Temperature had a marginal effect, as we observed an approximate 2% increase in retention at 80°C compared to 21°C. Both surface coated and bare silica nanoparticles were successfully transported, so surface coating does not appear to be a prerequisite for transport for the particle and rock systems studied. / text

Nanoparticle-functionalized electrodes have attracted attention in areas such as energy production and storage, sensing, and electrosynthesis. The electrochemical properties of these electrodes depend upon the nanoparticle properties, e.g., core size, core morphology, surface chemistry, as well as the structure of the nanoparticle/electrode interface, including the coverage on the electrode surface, choice of electrode support, and the interface between the nanoparticle and the electrode support. Traditionally used methods of producing nanoparticle-functionalized electrodes lack sufficient control over many of these variables, particularly the nanoparticle/electrode interface. Tethering nanoparticles to electrodes with molecular linkers is a strategy to fabricate nanoparticle-functionalized electrodes that provides enhanced control over the nanoparticle/electrode structure. However, many existing tethering methods are done on catalytically active electrode supports, which makes isolating the electrochemical activity of the nanoparticle challenging. Furthermore, previous work has focused on larger nanoparticles, yet smaller nanoparticles with core diameters less than 2.5 nm are of interest due to their unique structural and electronic properties. This dissertation addresses both of these gaps, exploring small nanoparticle electrocatalysts that are molecularly tethered to catalytically inert electrodes. This dissertation first reviews and compares the methods of fabricating nanoparticle-functionalized electrodes with a defined molecular interface in the context of relevant attributes for electrochemical applications. Next, a new platform approach to bind small gold nanoparticles to catalytically inert boron doped diamond electrodes through a defined molecular interface is described, and the influence of the nanoparticle/electrode interface on the electron transfer properties of these materials is evaluated. The next two studies build upon this platform to evaluate molecularly tethered nanoparticles as oxygen electroreduction catalysts. The first of these two describes the systematic study of atomically precise small gold clusters, highlighting the influence of atomic level differences in the core size and the electrode support material on the catalytic properties. The second study extends the platform approach to study small bimetallic silver-gold nanoparticles produced on the electrode surface and highlights the influence of the structural arrangement of the metals on the catalytic activity. Finally, future opportunities for the field of molecularly tethered nanoparticle-functionalized electrodes are discussed. This dissertation includes previously published and unpublished co-authored material. / 2019-01-27

In modern research and industrial applications, the importance of coatings can hardly be underestimated. Coatings are used extensively in optics, biomedical instruments, cutting tools, and solar panels to name a few. The primary purpose of any coating is to alter surface properties of the base material thus adding new functionality or improving the performance of the original product. A multitude of coating techniques has evolved over the years with spray coating being one of the more widely used. Some applications require deposition of materials that are either in the form of a solution or suspension. Therefore, before or during the deposition process small droplets of the said liquid are formed and transferred onto the substrate. Since differently sized droplets have different surface impact dynamics, droplet velocity at the impact plays an important role in the way it will adhere to the surface. Most spray coating techniques do not take into account the process of droplet-surface interaction which may result in overspray, poor coating thickness control, and material waste. The research presented in this dissertation outlines the supporting principles, design, fabrication and testing of an innovative spray coating system that provides the ability to fine tune coating parameters, including droplet impact velocities, to provide close to optimum deposition conditions. The core of the design consist of a dual velocity nozzle unit that ensures acceptable range of droplet velocities at the surface, while keeping droplets from accelerating excessively inside the system. Early experiments showed the system’s potential to produce nanoparticle coatings with particles uniformly distributed across the substrate. In addition, pigment coating for improved 3D scanning was also performed, thereby improving the surface definition and accuracy of the scanning results. Scalability of the system also led to experiments in applying this technology to microprinting. Preliminary microprinting results illustrated the system’s flexibility and opened new research avenues in micro-coating, microprinting, and, possibly rapid prototyping. Furthermore, thanks to the highly adaptable nature of the proposed design, seamless incorporation of a torch-like device into the nozzle unit was also possible. That provided the opportunity to perform in situ thermal processing or sintering of deposited material as well as production of a nanoparticle coating in a one-step process by thermally decomposing precursor solution. Technology developed during the research work presented in this dissertation demonstrated its ability to be adapted in a number of applications that can benefit both industry and engineering research alike. Large area coatings, nanoparticle production, micro-coating, and coatings for improved 3D scanning are just a few areas where the presented technique can already, or may, if developed further, outperform existing and widely accepted methods. Fine tuning of the system to a particular application, and tapping into its potential in other fields will be explored in future research. / Graduate

L'Héparane Sulfate (HS), un polysaccharide linéaire, module les activités biologiques de nombreuses protéines. Afin d'élucider les interactions entre l'HS et les protéines, la synthèse chimique d'HS est un outil précieux, mais elle peut être difficile. Notre équipe a montré que des mélanges combinatoires obtenus par auto-assemblage de différentes combinaisons de dérivés disaccharidiques (lactose et lactose persulfaté) sur surfaces planes d'or peuvent reconnaître spécifiquement certaines protéines se liant à l'HS, telles que les isoformes de la chimiokine CXCL12 ou IFNγ. Avec ces dérivés, nous avons réalisé un auto-assemblage sur des nanoparticules d'or. Mais à cause de la toxicité des nanoparticules d'or, nous avons aussi adapté cette méthode à des nanoparticules lipidiques. En utilisant les conditions qui ont déjà été améliorées pendant la synthèse des dérivés lactose et lactose persulfaté, nous avons préparé deux autres dérivés disaccharidiques plus proches de la structure réelle d'HS. Ces nouveaux dérivés sont utilisés pour réaliser des nanoparticules d'or et nanoparticules lipidiques afin de comparer les propriétés avec les lactose et lactose persulfaté. Les tests d'affinité avec différentes protéines sont en cours de réalisation. / Héparan Sulfate (HS) is a linear polysaccharide that modulates the biological activities of numerous proteins. In order to elucidate the interaction between HS and proteins, the synthesis of HS is an invaluable tool, but the synthesis is sometimes difficult. Our group has demonstrated that the combinatorial mixtures obtained by self-assembly of different combinations of disaccharide derivatives (lactose and persulfated lactose) on gold plan surfaces could recognize specifically some HS binding proteins, such as the isoforms of the chemokine CXCL12 or IFNγ. Because of the toxicity of gold nanoparticles, we have also adapted this method to lipid nanoparticles. Using the conditions that have already improved during the synthesis of lactose and persulfated lactose derivatives, we have synthesized two other disaccharide derivatives, which were closer to the real structure of HS. These new derivatives were used to prepare the gold and lipid nanoparticles at the aim of comparing the properties with lactose and persulfated lactose. The tests of affinities with different proteins are in progress.

Nanoparticles are currently finding increasing use as drug delivery systems in the treatment of cancer and other disorders. When nanoparticles are introduced into body fluids, they adsorb proteins forming a coating called protein corona. The protein corona is vital since it controls biological responses of nanoparticles through interactions with cells and biological barriers. Due to the dynamic behaviour of protein-protein and protein-nanoparticle interactions, the protein corona evolves during circulation in the body. This results in difficulties to predict the biological behaviour and outcome of nanoparticles. In this work, it is hypothesised that a nanoparticle-protein corona (NP-PC) enriched in specific proteins could serve as a model to determine if the design and formation of a patient-specific nanodrug-protein corona could offer a novel approach to control nanodrug-protein corona evolution. Through usage of a model nanoparticle and model plasmas and by applying shotgun proteomics and SUrface proteomics, Safety, Targeting, and Uptake (SUSTU), NP-PC proteins were identified and quantified. The results indicate that desirable proteins are maintained in the protein corona surface when nanoparticles with a pre-made corona are introduced into model plasma. This implies that a designed NP-PC would be a strategy to control nanodrug-protein corona evolution, offering a route to improve nanodrug targeting and uptake by cells.

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