Browsing by Subject "Nanoparticles"
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Item Active three-dimensional protein microstructures(2006) Hill, Ryan Toler; Shear, Jason B.Direct-write multiphoton-excited photocrosslinking of chemically active threedimensional (3D) protein microstructures could potentially extend in situ cellular analysis to include more interactive studies of neural networks, signal transduction, and neural response to local chemical gradients. This dissertation presents a strategy that has been developed for highly specific functionalization of 3D protein microstructures with protein-coated nanoparticles, an approach that is demonstrated to be appropriate for imparting these materials with desired electronic and chemical/biochemical properties. Once targeted with protein-gold conjugates, these protein scaffolds can serve as conductive bio-wires after electroless deposition is used to fuse the nanoparticles together. Unlike earlier approaches for templating metals with biomolecules, the current strategy can be used to construct scaffolds with precise spatial control in three dimensions, offering new opportunities to construct advanced bioelectronic architectures. This protein-gold conjugate functionalization technique has also proven to be an excellent way to localize high concentrations of active molecules with minimal nonspecific adsorption. Sequential functionalization steps can be used in conjunction vii with direct crosslinking of active enzymes, such as cytochrome c (cyt c), to produce enzyme suites capable of quantifying substrates with low micromolar detection limits. Also presented here are detailed electrochemical and spectroscopic studies that are aimed at quantitatively characterizing the native heme integrity and enzyme activity of directly photocrosslinked cyt c. Finally, this work presents initial studies focused on adapting gold conjugate functionalization of protein microstructures for compatibility with cultures of neurons and other cell types, a goal that would substantially expand capabilities for constructing in situ bioelectronics, localized dosing sources, and biochemical sensors for monitoring and stimulating biological processes. Use of this electrostatically driven approach towards functionalization combined with direct crosslinking of active molecules offers flexibility in the creation of highly definable, 3D reactive regions that are capable of sensing chemical gradients and/or modifying electric fields in sensitive aqueous environments.Item Advanced characterization of 1-2 nm Au, Pd, and AuPd nanoparticles for applications in electrocatalysis(2022-12-02) Strasser, Juliette Wells; Crooks, Richard M. (Richard McConnell); Mullins, Charles B.; Warner, Jamie H.; Henkelman, GraemeNanoparticles (NPs) synthesized within and stabilized by a dendrimer template are known as dendrimer-encapsulated nanoparticles (DENs). Because DENs are small and generally monodisperse, they have been used as model catalysts, with structure/function relationships that can be directly compared to first principles theory. It is becoming increasingly clear, however, that electrochemical experiments may change the size or structure of NPs, which is further exacerbated for NPs < ~5 nm in diameter due to their inherent instability. The work in this dissertation emphasizes the importance of NP characterization before, during, and after electrochemical measurements, for accurate correlation of NP structure and function. First, we show that three electrochemical scans to modest positive potentials results in substantial growth of 1-2 nm Au DENS (Chapter 3). The observed growth of the DENs directly correlates to changes in their electrocatalytic oxygen reduction reaction (ORR) activity. The key point of Chapter 3 is that after just three electrochemical cleaning scans, the G6-NH₂(Au₁₄₇) and G6-NH₂(Au₅₅) DENs are essentially indistinguishable in terms of both physical and electrocatalytic properties. Second, we report the presence of small clusters of atoms (< 1 nm) (SCs) and single atoms (SAs) in solutions containing 1-2 nm DENs (Chapter 4). We have found that the presence or absence of SAs/SCs depend on both the terminal functional group of the dendrimer (-NH₂ or -OH) and the elemental composition of the DENs (Au or Pd). The observations discussed in Chapter 4 provide insights into the mechanisms for Au and Pd DEN synthesis and stability and demonstrate the need for careful characterization of systems containing NPs. Third, we report a systematic study of the electrocatalytic properties and stability of a series of 1-2 nm Au, Pd, and AuPd alloy DENs for the ethanol oxidation reaction (EOR) (Chapter 5). NP sizes and compositions were characterized both before and after EOR electrocatalysis using aberration-corrected scanning transmission electron microscopy (ac-STEM) and energy dispersive spectroscopy (EDS). The results discussed in Chapter 5 demonstrate the importance of post-catalytic ac-STEM/EDS characterization for fully evaluating NP activity and stability, especially for 1-2 nm NPs that may change in size or structure during electrocatalysis.Item Application of pharmaceutical technologies to improve the activity of cancer chemotherapeutic agents(2015-05) Ibrahim, Youssef Wahib Naguib; Cui, Zhengrong; Smyth, Hugh D; Williams, Robert O; Hursting, Stephen D; Stavchansky, SalomonCancer is a leading cause of death worldwide. Chemotherapy remains a major therapeutic modality in cancer treatment. Conventional chemotherapeutic agents usually have limited efficacy. Furthermore, chemotherapeutic agent- and/or excipient-related toxicities comprise a serious problem that may, in many cases, deteriorate the patient’s quality of life. In this dissertation, different pharmaceutical technology approaches, including nanotechnology and pharmaceutical chemistry, were utilized to improve the activity of chemotherapeutic agents. Docetaxel is a second generation taxane used as a single agent in breast cancer, non-small cell lung cancer, and other cancers. Side effects related to the drug itself and one of the excipients (i.e. Tween 80) are extensive. I designed a solid lipid nanoparticle (DCX-SLNs) formulation to improve the delivery of docetaxel into solid tumors and to avoid excipient-related side effects associated with the current Tween 80-based docetaxel formulation. The DCX-SLNs showed improved in vitro cytotoxicity in various cell lines and significantly inhibited tumor growth in an aggressive mouse model of lung cancer, while the Tween 80-based docetaxel formulation was not effective at the dose and dosing frequency tested. Higher drug accumulation in tumor tissues was achieved when the DCX-SLNs were injected intravenously, as compared to the Tween 80-based docetaxel formulation. Gemcitabine (2̕, 2̕-difluorodeoxycytidine, dFdC) is the first line treatment for advanced pancreatic cancer. It is also used in other cancers (e.g. ovarian and breast cancers). In this dissertation, docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, was conjugated to gemcitabine in the 4(N)-amine group to synthesize a new compound (DHA-dFdC). DHA-dFdC shows potent and broad spectrum cytotoxicity against all NCI/DTP60 human cancer cell lines. DHA-dFdC is also 100000-fold more cytotoxic than gemcitabine against human and mouse pancreatic cancer cells. In addition, DHA-dFdC shows high accumulation in mouse pancreas following intravenous injection, prompting the evaluation of its antitumor activity in mouse models of pancreatic cancer. In nude mice with subcutaneous or orthotopic human Panc-1 tumors, DHA-dFdC is more effective than the molar equivalent dose of gemcitabine in inhibiting the tumor growth. In conclusion, the activity of cancer chemotherapeutic agents can be significantly improved by formulating them with innovative pharmaceutical technologies.Item Application of superparamagnetic nanoparticle-based heating for non-abrasive removal of wax deposits from subsea oil pipelines(2015-08) Mehta, Prachi; Daigle, Hugh; Huh, ChunFlow assurance is a critical problem in the oil and gas industry, as an increasing number of wells are drilled in deep water and ultra-deep water environments. High pressures and temperatures as low as 5°C in these environments hinder flow of hydrocarbon-based fluids by formation of methane hydrate and wax deposits on the inner surface of pipelines. Commonly used methods for removal of deposits from pipelines are chemical injection and foam or gel pigs, which face several limitations. In our work, an application to use superparamagnetic nanoparticle-based heating for flow assurance, in the form of a magnetic nanopaint is presented. Superparamagnetic nanoparticle-based heating has been extensively researched in the biomedical industry for cancer treatment by hyperthermia. Superparamagnetic nanoparticles in dispersions generate heat by application of an oscillating magnetic field as explained by Neel’s relaxation theory. In our application, superparamagnetic Fe₃O₄ nanoparticles are embedded in a thin layer of cured epoxy termed ‘nanopaint’. This nanopaint coating on the internal surface of subsea pipelines could generate heat and thus remove formation of methane hydrates and wax. In our work, the role of key parameters affecting heating performance of superparamagnetic nanoparticles such as particle size, and magnetic field is quantified. Rigorous characterization of physical and magnetic properties of nanoparticles and nanopaint is performed. This is correlated to and used to optimize the heating performance. Heating performance of several samples of Fe₃O₄ nanoparticles varying in size distribution is evaluated in static experiments. Two samples having similar physical and magnetic properties are compared in terms of the correlation between their size distribution and their heating performance. Performance of nanopaint to heat static fluids, flowing fluids and wax deposit is evaluated. Heating performance of superparamagnetic nanoparticles in dispersions and in nanopaint is found to be similar and so it is concluded that Neel’s relaxation theory is applicable to nanopaint. Heating performance of nanopaint in flow experiment is found to be better than in static experiments by a factor greater than 5. A correlation of heating performance of nanopaint at magnetic fields of 100 to 1000 A/m is developed. Finally, implementation issues of nanopaint are addressed. The effect of low ambient temperatures on nanopaint heating performance is evaluated. The theoretical feasibility of generating a magnetic field inside a pipeline is studied. A COMSOL model is used to verify the feasibility of magnetic field propagation inside a steel pipeline and is subsequently used to evaluate nanopaint heating of wax deposits in pipeline. Material and power requirements are analyzed and optimized using the COMSOL model.Item Biomedical photoacoustics beyond thermal expansion : photoacoustic nanoDroplets(2012-05) Wilson, Katheryne Elizabeth; Emelianov, Stanislav Y.; Fowlkes, Brian; Hamilton, Mark; Sokolov, Konstantin; Williams, RobertThe recent increase in survival rates of most cancers is due to early detection greatly aided by medical imaging modalities. Combined ultrasound and photoacoustic imaging provide both morphological and functional/molecular information which can help to detect and diagnose cancer in its earliest stages. However, both modalities can benefit from the use of contrast agents. The objective of this thesis was to design, synthesize, and test a nano-sized, dual contrast agent for combined ultrasound and photoacoustic imaging named Photoacoustic nanoDroplets. This agent consists of liquid perfluorocarbon nanodroplets with encapsulated plasmonic nanoparticles. These dual contrast agents utilize optically triggered vaporization for photoacoustic signal generation, providing significantly higher signal amplitude than that from the traditionally used mechanism, thermal expansion. Upon pulsed laser irradiation, liquid perfluorocarbon undergoes a liquid-to-gas phase transition generating giant photoacoustic transients from these dwarf nanoparticles. Once triggered, the gaseous phase provides ultrasound contrast enhancement. Demonstrated in this work are the design, synthesis, characterization, and testing of Photoacoustic nanoDroplets in phantom and animal studies, and preliminary work into adapting these agents into targeted, drug delivery vehicles for simultaneous detection, diagnosis, and treatment of diseases.Item Carbon dioxide mobility and sweep alteration using surface-coated silica nanoparticles(2019-08-14) Alfakher, Ahmad; DiCarlo, David Anthony, 1969-Solvent flooding is a well-established method of enhanced oil recovery (EOR), CO₂ being the solvent most often used. CO₂ has also been injected into saline aquifers as a method of storage in an application of Carbon Capture and Storage (CCS). Both applications suffer from poor sweep efficiency. Creating in-situ CO₂ foam has previously been shown to improve the sweep efficiency of CO₂ floods. This study tested the use of surface-coated silica nanoparticles as an in-situ CO₂ foaming agent. In each experiment, the pressure drop was measured in five separate sections in the core, as well as along the whole core. In addition, the saturation in the core was measured periodically using a CT scanner. The experiments consisted of vertical core floods where liquid CO₂ displaced brine from the top to the bottom of the core, comparing the results in cases where surface-coated silica nanoparticles were suspended in the brine to cases with no nanoparticles. Pressure drop readings were analyzed to exclude capillary effects and calculate relevant flow parameters, such as CO₂ mobility. In these experiments, the mobility of CO₂ was on average 89% less in floods with nanoparticles compared to floods with no nanoparticles. This reduction in mobility was found to be long-lasting. Breakthrough occurred 45% later in foamed CO₂, and the final CO₂ saturation was also 45% greater than with un-foamed CO₂. The new measurements and mobility calculations in this study show how nanoparticles stabilize the CO₂ front. They can also be used to upscale the behavior observed from the core-scale to the reservoir scaleItem Characterization of biological hydrogel barriers(2014-12) Kaliki, Srimahitha; Smyth, Hugh D.C.,; Barr, Ronald; Milner, Thomas; Dunn, Andrew; Marek, StephenBiological hydrogel barriers include mucus, bacterial biofilms, fungal biofilms, and others. Biofilms are polysaccharide hydrogels. Biofilms are commonly found in the lungs of cystic fibrosis patients. Cystic fibrosis (CF) patients are susceptible to these types of chronic infections because their mucus barrier is abnormal. A common bacterial infection in these patients is caused by the bacterium Pseudomonas aeruginosa. While it is found that the bacteria can infect CF patients easily, the treatment of such infections by drugs had been found to be quite inefficient due to the structure of the biofilm itself and formidable mucus barrier. Mucus is a hydrogel which protects the gastrointestinal, genitor-urinal and respiratory tracts from pathogens and external environments. In our preliminary studies, topically applied nanoparticles disrupted these hydrogel barriers and resulted in the increase in permeability to solutes. The long term goal of this proposal is to understand and quantify the effects of the interaction between nanoparticles and biological hydrogel barriers. Discovering how nanoparticles disrupt the hydrogel barriers is important for understanding the health risks. The hypothesis of this research is that nanoparticles result in disruption of the hydrogel barrier structure that leads to increased exposures to co-deposited solutes. Quantifying the structural changes and diffusivity of such solutes using different novel techniques is the central object of my thesis. Bulk Rheological studies were performed using mucin samples treated with nanoparticles. It was noticed that the viscosities showed a negative trend with regards to the nanoparticle sizes which seemed to be contradictory to Einstein’s prediction. A possible mechanism of action was explained. Multiple particle tracking was performed to quantify viscosities of nanoparticles in mucin solution. Subsequently, drug diffusion studies were performed on similar samples to provide a relationship between the nanoparticle size and the drug permeability. Atomic force microscopy was performed in liquid cell using force mode on biofilms when treated with different sized nanoparticles. Micro-elasticity of these biofilms was calculated and compared.Item Coalescence and sintering in metallic nanoparticles : in-situ transmission electron microscopy (TEM) study(2012-05) Asoro, Michael Adewunmi, 1982-; Kovar, Desiderio; Ferreira, Paulo J. (Paulo Jorge); Rabenberg, Llewellyn K.; Meyers, Jeremy P.; Becker, Michael F.Nanoparticles possess unique physical, chemical, optical and electronic properties stemming from their nanoscale dimensions and are currently used in catalysis, microelectronics, drug delivery, as well as other applications. However, due to their large surface area-to-volume ratio, nanoparticles have a strong tendency to coalesce and sinter during processing or usage over short time scales and at low temperatures, which lead to significant changes in behavior and performance. In this work, in-situ transmission electron microscopy (TEM) heating has been used to investigate the effects of particle size, temperature and carbon capping layers on sintering in face-centered cubic (FCC) metallic nanoparticles. For the first time, we make direct and real-time measurements of nanoparticle size, neck growth, dihedral angle and grain boundary motion during sintering, which are then used to calculate fundamental material transport parameters such as surface diffusivity and grain boundary mobility. We observe that carbon surface coatings typically present on most commercial nanoparticles can significantly inhibit sintering in nanoparticles. Also, a new mechanism for coalescence in nanoparticles is shown where small clusters on the support can initiate neck growth by forming a bridge between the nanoparticles consisting of individual atoms or small clusters of atoms. In-situ TEM experiments provide critical and valuable real-time dynamic information for direct investigation of the link between the evolution of sintering and controlling mechanisms, which conventional experiments such as post-mortem TEM observations are not capable of conveying.Item Colloidal nanoparticles : a new class of laser gain media(2009-12) Morgan, Robert Douglas; Ditmire, Todd R.; Keto, John; Downer, Michael; Sitz, Greg; Desidero Kovar, DesideroDevelopment of high average power lasers has historically been limited by the properties of available gain media. As a result it is either too costly or impractical to employ lasers in many applications for which they would otherwise be well suited. We have synthesized a new type of colloidal laser gain material that should possess many of the advantages of solid state media without their primary disadvantage: poor thermal performance. The colloid consisted of an emulsion of 20% Nd+3 doped phosphate glass nanoparticles suspended in nonanoic acid. The spectroscopic properties of the material were found to be consistent with those of bulk Nd+3 doped materials and suitable for laser development.Item Colloidal particles at fluid interfaces : from stabilizing emulsions to destabilizing them(2019-05) Griffith, Christopher Adam; Daigle, Hugh; Lake, Larry W; Mohanty, Kishore; Balhoff, Matthew T; Werth, Charles JThis work uses silica nanoparticles to stabilize oil-in-water and water-in-water emulsions. These emulsions are called Pickering emulsions and have potential use for enhanced oil recovery. There are two challenges with using nanoparticles for subsurface applications which are the high salinities and elevated temperatures of reservoir brines. These conditions are problematic because nanoparticles without surface modification are unstable, because of nanoparticle charge screening, which leads to particle agglomeration. Additionally, much of the current research on particle stabilized emulsions focuses on using nanoparticles modified with hydrophobic molecules or surfactants with the sole intent of getting particles to the oil/water interface. Because of this, many of these particles are not applicable for subsurface applications due to their lack of stability in brine. To address these challenges, I functionalize silica nanoparticles with different concentrations of a hydrophilic silane called (3-glycidyloxypropyl)trimethoxysilane (glymo) and stabilize Pickering emulsions with these particles. Glymo was selected as a nanoparticle surface modifier because of its ability to sterically stabilize particles in brine. I characterized the static stability of different Pickering emulsion formulations by using a centrifuge and by calculating the emulsion demulsification pressure. I correlate a critical demulsification pressure to emulsions that show little change in emulsion drop size while flowing, which I define as dynamically stable. The critical demulsification pressure is applied to several untested Pickering emulsion formulations to verify its applicability as an emulsion pre-screening tool. I perform a rheological characterization on emulsions stabilized with low and high surface coverage glymo-coated particles to establish relationships between nanoparticle bridging and the extent of glymo surface modification with different ionic strength brines. I use cryo-scanning electron microscopy to visually assess the bridging behavior of these different Pickering emulsions. I use fumed silica particles, with different wettabilities, and assess their ability to destabilize a model Pickering emulsion. I determine there is a strong correlation between the wettability of a fumed silica particle and its ability to destabilize a model emulsion. This work is relevant because most of the current research on Pickering emulsions focuses primarily on how to tune the properties of colloidal particles to generate stable emulsions with less overall emphasis on methods to destabilize them. Lastly, an aqueous, two phase system is stabilized with 6 nm and 50 nm silica particles modified with 2-(methoxy(polyethyleneoxy)6-9propyl)trimethoxysilane (PEG-silane). Stabilization of the water/water interface results in emulsions that have relatively good stability to shear. Water-in-water emulsions do not contain any oil which is often considered a major limitation of Pickering emulsions for EOR, therefore these emulsions are potential candidates for enhanced oil recoveryItem Composite nanogels for the triggerable release of chemotherapeutics(2015-12) Peters, Jonathan Thomas; Peppas, Nicholas A., 1948-; Freeman, Benny; Johnston, Keith; Sanchez, Isaac; Zoldan, JanetaThe development of external stimuli responsive nanoparticles has progressed greatly since its inception in the seventies. However, apart from some clinical success for slow release delivery via liposomes, the technology has stalled for the delivery of chemotherapeutics due to a myriad of problems with cytocompatibility and premature diffusion of drug payload. The solution to cytocompatibility has been the coating of the system with polyethylene glycol. New methods have been developed to attach polyethylene glycol (PEG) tethers to the surface of otherwise unreactive particles. Surface hydrolysis of acrylamide containing polymers can be used to produce carboxylic acid functional groups near the surface of the polymeric nanoparticles. These nanoparticles can then be functionalized with PEG via EDC/NHS chemistry. The use of surface hydrolysis not only allows for reaction with these neutral polymers, but also provides greater control of PEG localization and leads to an unintrusive method to add the much needed stealth coating. In order to address the issue with premature release, new polymer systems have been developed. These systems are based around theory of hydrophobic interaction in order to improve the polymer/drug interaction in order to limit the unwanted diffusional release of drug payload. This interaction was addressed in a number of ways, focusing on both compartmentalization and copolymerization in order to develop nanogels that can entrap and withhold more drug from the surrounding area. An in depth look into the interactions that encourage drug uptake in these systems was performed by altering the copolymer chosen for these systems. This work looks into effects on phase transition, functional groups, hydrophobicity, and any structural changes that occur as a result of the polymerization scheme. After drawing conclusions on the interactions that encourage drug uptake, complex systems were devised to take advantage of these interactions. Core shell systems were designed to take advantage of the convective release of lower critical solution systems while still utilizing the mechanisms that improve drug retention. These systems were synthesized by two methods, emulsion polymerization and micelle crosslinking. These systems have been showed to improve the drug interaction and retention of doxorubicin as a model chemotherapeutic.Item Contrast and sensitivity enhanced molecular imaging using photoacoustic nanoamplifiers(2012-08) Chen, Yun-Sheng, active 2012; Emelianov, Stanislav Y.Molecular imaging is an emerging imaging principle which can visually represent the biological processes both spatially and temporally down to the sub-cellular level in vivo. The outcome of this research is expected to have a profound impact on facilitating the early diagnosis of diseases, accelerating the development of new drugs, and improving the efficacy of therapy. In general, molecular imaging highly relies on probes to sense the occurrence of molecular biological events, and to generate signals which could be picked up by diagnostic imaging modalities. The advances in the design of molecular probes not only have equipped traditional anatomical medical imaging with new capabilities but also, in some cases, stimulated developments of new imaging modalities and renaissance of existing medical imaging modalities. One of these is photoacoustic imaging, which as an emerging medical imaging modality, unites the merits from both optical imaging and ultrasound imaging. It shares with optical imaging, that it uses non-ionizing radiation and provides higher contrast and higher sensitivity than ultrasound imaging. Unlike optical imaging, which requires ballistic photons for imaging, photoacoustic imaging requires only diffusive photons to excite the ultrasound signal from the imaging target; therefore, it is capable of imaging much deeper into the tissue. In combination with molecular probes, photoacoustic molecular imaging has been demonstrated by several research groups using various photoacoustic molecular probes. However, the molecular probes used for most of these studies were contrast agents simply adopted from other optical imaging modalities. Our research on photoacoustic contrast agents indicated that the mechanism of photoacoustic signal generation from nanometer-sized contrast agents is distinct from that of optically homogeneous materials, such as tissue. We have discovered that, the amplitude of the photoacoustic signal generated from nano-contrast agents depends not only on the optical absorption of the particles, but more importantly, on the dynamic process of the heat conduction from the nanoparticles to the ambient, and the thermal properties of the surrounding materials. Based on our finding, we explored and further improved the photoacoustic response of the nanoparticles by exploiting the heat conduction process between the nanoparticle and its surrounding materials and by manipulating the excitations. This research allows to create optimized molecular specific contrast enhanced photothermal stable probes which can aid photoacoustic imaging and image guided photothermal cancer therapy.Item Controlled assembly of biodegradable gold nanoclusters for in vivo imaging(2015-12) Stover, Robert John; Johnston, Keith P., 1955-; Truskett, Thomas M; Fan, Donglei; Korgel, Brian; Sokolov, KonstantinGold nanoparticles are of interest in biomedical imaging applications due to their inert nature and ability to exhibit surface plasmon resonance. These phenomena can result in high near-infrared extinction (NIR) due to asymmetry or close interparticle spacings within gold structures, making these materials ideal for photoacoustic imaging. Using this imaging modality, these materials allow for high contrast compared to the body’s tissues which exhibit a transparent “window” between 700-1100 nm, making them perfect for early cancer detection. However many gold structures designed for this application fail to achieve high NIR-absorbance at the <5 nm sizes which are required for efficient kidney clearance. Therefore, we designed a system which assembles ~4 nm primary gold particles into closely-spaced clusters of controlled size using a biodegradable, weakly adsorbing polymer and balance of colloidal attractive and repulsive forces. Thus, when the polymer degrades in acidic environments – such as within cells – the residual charge on the primary particles leads to dissociation of the clusters back to renal-clearable constituents. Since proteins in the blood and cells can increase the diameter of the primary particles above the 5 nm threshold, nanoparticle surfaces were designed to have a mixture of charged and zwitterionic molecules to limit protein interactions through buried charges and increased particle hydration. Strongly-bound, zwitterionic thiol-containing ligands were also investigated to resist the intracellular exchange of biomolecules which could compromise the clearable nature of the particles. These decorated nanoparticles were then assembled into clusters through one of two methods which varied either gold and polymer concentrations through evaporation, or particle charge via electrolyte addition prior to quenching by dilution in DI water. Once assembled, clusters assembled with polymer showed dissociation behavior after incubation in pH 5 acidic solutions to mimic the cellular pH environment. In other cases, sintering of the gold nanoparticle clusters prevented such dissociation. This thesis demonstrates the ability to not only create biocompatible nanoparticle surfaces, but to establish control size control over nanocluster assemblies which are capable of being used as NIR contrast agents.Item Defects and deformation in nanostructured metals(2009-12) Carlton, Christopher Earl; Ferreira, Paulo J. (Paulo Jorge)A better understanding of how the nanoscale environment affects the mechanical properties of materials, in particular metallic nanoparticles and nanocrystalline metals is vital to the development of next generation materials. Of special interest is obtaining a fundamental understanding of the inverse Hall-Petch Effect in nanocrystalline metals, and nanoindentation in individual nanoparticles. Understanding these subjects is critical to understanding how the mechanical properties of materials are fundamentally affected by nanoscale dimensions. These topics have been addressed by a combination of theoretical modeling and in-situ nanoindentation transmission electron microscopy (TEM) analysis. Specifically, the study of the inverse Hall-Petch effect in nanocrystalline metals will be investigated by a thorough review of the literature followed by a proposed novel theoretical model that better explains the experimentally observed behavior of nanocrystalline metals. On the other hand, the nanoindentation of individual nanoparticles is a very new research topic that has yet to aggregate a large body of experimental data. In this context, in-situ TEM nanoindentation experiments on silver nanoparticles will be first performed to determine the mechanisms of deformation in these nanostructures. A theoretical explanation for the observed deformation mechanisms will be then developed and its implications will be discussed. In addition to nanoparticles, this study will also provide unique and valuable insight into the deformation mechanisms of nanopillars, a growing area of research despite much controversy and speculation about their actual mechanisms of deformation. After studying the novel behavior of both nanocrystalline metals and nanoparticles, useful applications of both classes of materials will be explored. The discussion of applications will focus on utilizing the interesting behaviors explored in the dissertation. Of particular interest will be applications of nanoparticles and nanocrystalline materials to coatings, radiation resistance and super-plastic materials.Item Dendrimer-encapsulated nanoparticles : synthetic methods and characterization including extended X-ray absorption-fine structure(2010-12) Weir, Michael Glen; Crooks, Richard M. (Richard McConnell); Bard, Allen J.; Frenkel, Anatoly I.; Henkelman, Graeme; Johnston, Keith; Willets, KatherineThis work describes the synthesis of dendrimer-encapsulated nanoparticles (DENs) and the expansion of the characterization ability for these materials. The dendrimer-template method for the synthesis of nanoparticles allows precise control over the size, composition and structure of nanoparticles in the 40-250 atom range. In this size regime, the surface structure of the nanoparticles dominates their catalytic properties. The long term goal of this research is to correlate the structure of these nanoparticles to their catalytic activity, improving the ability to predict superior catalysts a priori. As a prerequisite for this analysis, the precise structure of the catalytically active nanoparticle must be determined. Characterization of nanoparticles in the 1-2 nm region is significantly more difficult than more commonly used nanoparticles of 3-5 nm diameter or larger. Typical characterization of these nanoparticles involves UV-vis spectroscopy for Mie absorbance and transmission electron microscopy for size analysis. This work involves the use of extended X-ray absorption-fine structure (EXAFS) to determine the local structure of the nanoparticles. For monometallic Pt DENs, EXAFS was combined with UV-vis, TEM, X-ray photoelectron spectroscopy (XPS) and electrochemistry to determine that the Pt system is not simply nanoparticles but a more complex, bimodal state. EXAFS has also been used to differentiate between different bimetallic structures. For PdAu DENs, there are two synthetic methods used. When both metals are reduced simultaneously, the resulting nanoparticles have a quasi-random alloy structure. These nanoparticles were then extracted from the dendrimer into an organic solvent by use of alkanethiols. The extraction process changed the alloy structure into Au-core/Pd-shell. When Pd and Au were reduced in sequence, the DENs were formed as a Au-core/Pd-shell material, regardless of the order of the reduction of the metals. The Au-core/Pd-shell structure was also present after extraction. In addition to structural analysis to determine the result of different synthetic methods, EXAFS was also used in situ to measure the structure of Pt DENs during the oxidation of absorbed CO. These in situ measurements are important for determining the structure of the actual catalyst rather than the precursor nanoparticle. In this case, the Pt DENs changed from a bimodal distribution into fully reduced nanoparticles by the application of a reducing potential. The binding of CO to the Pt DENs and subsequent oxidation did not cause measurable agglomeration of the nanoparticles. This reduction of the Pt system by electrochemical means was also explored as a synthetic method. The Pt-dendrimer complex was placed on a TEM grid for electrochemical treatment. A potential step was shown to reduce some of the Pt-dendrimer complexes into Pt nanoparticles of the expected size. However, most of the complexes were not reduced. Therefore, only the standard chemical reduction followed by electrochemical treatment is sufficient to fully reduce the nanoparticle samples. This work has explored additional synthetic methods for the synthesis of monometallic and bimetallic DENs. The use of EXAFS, as well as other advanced characterization techniques, has advanced knowledge of the structure of various DENs. Both the characterization toolset and the synthetic methods will provide a basis for investigations of catalytically active materials.Item The Design and Control of Stability and Magnetic Properties of Imaging Nanoparticles(2012-12) Yoon, Ki Youl; Johnston, Keith P., 1955-; Bryant, Steven L; Milner, Thomas E; Huh, Chun; Ruoff, Rodney S; Ferreira, Paulo JThere is significant interest in applying nanoparticle (NP) science to subsurface reservoirs to facilitate oil and gas recovery, image subsurface reservoirs, aid sequestration of CO2 and benefit environmental remediation. Imaging nanoparticles have been designed with long-term dispersion stability in brine and minimal retention in reservoir rock and with preferential adsorption at oil-water interfaces. Polymer-stabilized nanoparticles provide sufficient electrostatic repulsion for high colloidal stability, as characterized by the zeta potential. The small size of the clusters, superparamagnetic properties, and high salt tolerance are highly beneficial in various applications including magnetomotive and electromagnetic imaging and mapping of petroleum reservoirs. Superparamagnetic nanoclusters may be used in imaging in biomedicine and in mapping of petroleum reservoirs, by generating either ultrasonic or acoustic signals with oscillating magnetic motion. For a given magnetization per weight of iron oxide, nanoclusters with sub ~100 nm diameters experience a much larger magnetic force than that of the primary sub- 10 nm primary particles. Aqueous dispersions of 0.1-0.2 wt% superparamagnetic iron oxide nanoclusters were stabilized with citric acid, poly(acrylic acid) (PAA), or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) on the particle surface, with a high loading of ~90% iron oxide. For nanoclusters with only 12% (w/w) PSS-alt-MA electrosteric stabilization was sufficient even in 8 wt% NaCl. Both PAA and PSS-alt-MA were used to stabilize nanoclusters with controlled size during synthesis in aqueous media. To obtain a permanent coating on the surface of clusters cross-linking of the polymer for different cross-linking densities was applied. In this general and highly flexible approach, iron oxide nanoparticles may be formed with an adsorbed polymer stabilizer, which is then permanently bound to the surface via cross-linking. To investigate interfacial activity of nanoparticles, oil-in-water emulsions were stabilized with iron oxide nanoclusters or graphene oxide platelets. In each case, the stabilization was achieved by designing the hydrophilic/hydrophobic nature of surface coating. For oil/water emulsions, the droplet size was as low as ~1 micron diameter, and strongly shear-thinning rheology was observed. A series of sub-100 nm superparamagnetic iron oxide nanoparticles with amphiphilic poly(acrylic acid-b-butylacrylate), (PAA-b-PBA) copolymer shells was synthesized to investigate the effect of the polymer structure on the interfacial tension for nanoparticles adsorbed at the dodecane-water interface. Large reductions in interfacial tension of up to 27.6 mN/m were obtained for a 0.27 wt% nanoparticle concentration indicating significant nanoparticle adsorption and interaction with the oil and water molecules at the interface. The adsorption energy of the polymer-coated nanoparticles at the dodecane/water interface was determined from the interfacial tension and nanoparticle radius, and analyzed in terms of the structure of the polymer stabilizer. Furthermore, oil-in-water emulsions stabilized with graphene oxide nanoplatelets were found to remain stable for several months even at high salinity (up to 5 wt% NaCl, for pH = 2 to 10). The droplet sizes were as small as ~1 μm with a low nanoplatelet concentration of 0.2 wt%.Item Design and optimization of surfactants and surface-modified nanoparticles for mechanistic studies of foam stabilization and interfacial interactions(2021-05-06) Da, Chang; Johnston, Keith P., 1955-; Hirasaki, George J.; Bonnecaze, Roger T.; Rochelle, Gary T.Surfactants and/or nanoparticles (NP) are shown to stabilize carbon dioxide CO₂-in-water (C/W) foams and nitrogen N₂-in-water (N/W) foams with strong interfacial adsorption and interactions. The first two studies demonstrate that viscous C/W foams may be generated with either a single zwitterionic surfactant or a single switchable diamine surfactant, over a wide temperature range up to 150 °C even at high salinities. The foams have apparent viscosities in the right range to have potential in CO₂ mobility control based on the experimental results in porous media. Moreover, both surfactants are shown to have high thermal stability with negligible chemical degradation after incubation at 135 °C for 30 days, which benefits long-term applications in high temperature reservoir conditions. To another topic, the binary grafting of ether diol and dimethylsilyl ligands on silica NPs are then shown to provide steric stabilization in bulk phase of concentrated brine and raise the NP hydrophobicity to promote interfacial adsorption, producing an interface with a relatively strong surface elastic dilational modulus E'. The NP-laden interface also demonstrates moderate ductility with a relatively slow change in surface pressure Π and E' over a wide range of surface area variation during compression and expansion. Moreover, the combination of an anionic surfactant with NPs grafted with the binary ligands, each of which is interfacial-active, produces a highly viscoelastic air-brine interface at high salinity that enabled highly stable N/W foams from ambient temperature up to 80 °C. The ability to tailor the interfacial properties with surfactants and NPs with independently tunable surfaces is of broad scientific interest and great potential for various applications.Item Design and synthesis of surfactants and nanoparticles for mechanistic studies of foams, emulsions and wettability alteration(2019-08) Alzobaidi, Shehab; Johnston, Keith P. 1955-; Bonnecaze, Roger; DiCarlo, David; Lynd, Nathaniel; Prodanovic, MasaSurfactants or nanoparticles are shown to stabilize carbon dioxide (CO₂)-in-water (C/W) foams, nitrogen (N₂)-in-water (N/W) foams and CO₂-in-oil (C/O) emulsions and to alter the wettability of oil-wet calcite surfaces to water-wet. Chapter 2 focuses on developing an understanding of the aqueous and interfacial properties of single viscoelastic surfactants to stabilize C/W foams for extended time with highly viscous aqueous phases. Surface modified amphiphilic silica nanoparticles are then investigated as alternatives to surfactants to increase the stability of C/W and N/W foams. Here, the first examples of nanoparticles with known surface modification that stabilize foams in high salinity brines at elevated temperature are presented. The fundamental understanding gained from surfactant design for C/W foam studies is used to design stabilizers for C/O emulsions. Here, polymeric surfactants with polydimethylsiloxane backbones and pendant linear alkyl chains are designed to stabilize novel C/O emulsions despite the low interfacial adsorption driving force, given the low interfacial tension. Finally, silica nanoparticles with various modifications (anionic, cationic and nonionic) are used to mechanistically study wettability alteration of oil-wet calcite surface to water-wet, especially in high salinity environments.Item Detection of magneto-activated water/oil interfaces containing nanoparticles(2011-12) Ryoo, SeungYup; Huh, Chun; Milner, Thomas E.; Driga, Micea; Becker, Michael; Neikirk, Dean; Johnston, Keith P.Accurate, non-invasive determination of multiphase fluids distribution in reservoir rock can greatly help the evaluation and monitoring of oil reservoirs. This laboratory thesis research, carried but utilizing the biomedical engineering concepts and measurement facilities, is an important step in developing a novel magnetic field-based oil detection method. When paramagnetic nanoparticles are either adsorbed oil/water interface or dispersed in a fluid phase in reservoir rock pores, and exposed to external magnetic field, the resultant particle movements displace the interface. Interfacial tension acts as a restoring force, leading to interfacial fluctuation and a pressure (sound) save. As the first step, the motion of the interface between a suspension of paramagnetic nanoparticles and a non-magnetized fluid (placed in a cylindrical dish) is measured by phase-sensitive optical coherence tomography (PS-OCT). Experiments were carried out with a range of iron-oxide nanoparticles that were synthesized and surface-coated by our Chemical Engineering collaborators. The numerical method was improved to be volume conserving, and extended to 3D, for more quantitative matching. The measurements of interfacial motion by PS-OCT confirm theoretical predictions of the frequency doubling and importance of material properties, such as the particle size, for the interface displacements. The relative densities of the fluid phase(air/aqueous and dodecane/aqueous) strongly affect the interfacial displacement. Next, the acoustic responses to the external magnetic oscillation, from the rock samples into which different aqueous dispersions of nanoparticles were injected, were measured in terms of the magnetic frequency, nanoparticle concentration, and other process parameters. Subsequently, the PS-OCT displacements in response to the external magnetic oscillation, from the rock samples into which different aqueous dispersions of nanoparticles were injected, were also measured in terms of the magnetic frequency, nanoparticle concentration, and other process parameters. Conclusions and the recommendations for further study are then given.Item Detection of microRNA by electrocatalytically amplified nanoparticle collisions(2017-06-16) Castaneda, Alma Delia; Crooks, Richard M. (Richard McConnell); Shear, Jason B; Eberlin, Livia S; Webb, Lauren J; Hoffman, David WWe report a new and general approach that will be useful for adapting the method of electrocatalytic amplification (ECA) to biosensing applications. In ECA, individual collisions of catalytic nanoparticles with a noncatalytic electrode surface lead to bursts of current. In this dissertation, the current arises from catalytic electrooxidation of N₂H₄ at the surface of platinum nanoparticles (PtNPs). As described in Chapter 1, the problem with using ECA for biosensing applications heretofore, is that it is necessary to immobilize a receptor, such as DNA (as in the case here) or an antibody on the PtNP surface. This inactivates the colliding NP, however, and leads to very small collision signatures. In this work, we show that oligonucleotides bound on the PtNP surface can be detected using ECA following enzymatic digestion. Chapter 2 demonstrates the proof-of-concept of this general approach using ssDNA-modified PtNPs and Exonuclease I (Exo I), an enzyme specific to ssDNA. After PtNPs were passivated with ssDNA, we show that the presence of this DNA can be detected by selectively removing a fraction via enzymatic cleavage. About half of the electrocatalytic current is recovered from the PtNPs on both Au and Hg microelectrodes. In Chapter 3, we show the application of this enzyme approach for the specific detection of microRNA (miRNA). The targets are miRNA-203 and miRNA-21, miRNAs of interest for cancer biomarker detection. PtNPs were modified with ssDNA complementary to the target, incubated with the miRNA, and the ssDNA was cleaved by Duplex Specific Nuclease (DSN). This exposes the PtNP surface for ECA, and the signal frequency is correlated to concentration of miRNA. Chapter 4 introduces a technique whereby ECA signals are manipulated via electrostatic interactions by modifying the surface of Au microelectrodes with polyelectrolyte multilayer films (PEMs). We demonstrate that it is possible to control the frequency of the collisions by manipulating the net electrostatic charge on the outer surface of the PEM film, and that electrons are able to tunnel from the PtNPs to the electrode through films of thicknesses up to 5 nm. These results set the stage for future sensing applications