Browsing by Subject "Gold"
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Item Assembly of colloidal nanocrystals into phospholipid structures and photothermal materials(2012-08) Rasch, Michael; Korgel, Brian Allan, 1969-There has been growing interest in developing colloidal metal and semiconductor nanocrystals as biomedical imaging contrast agents and therapeutics, since light excitation can cause the nanocrystals to fluoresce or heat up. Recent advances in synthetic chemistry produced fluorescent 2-4 nm diameter silicon and 1-2 nm diaemeter CuInSSe nanocrystals, as well as 16 nm diameter copper selenide (Cu₂₋[subscript x]Se) nanocrystals exhibiting strong absorbance of near infrared light suitable for biomedical applications. However, the syntheses yield nanocrystals that are stabilized by an adsorbed layer of hydrocarbons, making the nanocrystals hydrophobic and non-dispersible in aqueous solution. Encapsulating these nanocrystals in amphiphilic polymer micelles enables the nanocrystals to disperse in water. Subsequently, the Si nanocrystals were injected into tissue to demonstrate fluorescence imaging, the photothermal transduction efficiency of copper selenide nanocrystals was characterized in water, and the copper selenide nanocrystals were used enhance the photothermal destruction of cancer cells in vitro. The polymer-encapsulated copper selenide nanocrystals were found to have higher photothermal transduction efficiency than 140 nm diameter Au nanoshells, which have been widely investigated for photothermal therapy. Combining the optical properties of metal and semiconductor nanocrystals with the drug-carrying capability of lipid vesicles has received attention lately since it may create a nanomaterial capable of performing simultaneous drug delivery, optical contrast enhancement, and photo-induced therapy. Hydrophobic, dodecanethiol-coated Au nanocrystals were dispersed in water with phosphatidylcholine lipids and characterized using cryo transmission electron microscopy. 1.8 nm diameter Au nanocrystals completely load the bilayer of unsaturated lipid vesicles when the vesicles contain residual chloroform, and without chloroform the nanocrystals do not incorporate into the vesicle bilayer. 1.8 nm Au nanocrystals dispersed in water with saturated lipids to form lipid-coated nanocrystal agglomerates, which sometimes adhered to vesicles, and the shape of the agglomerates varied from linear nanocrystal chains, to flat sheets, to spherical clusters as the lipid fatty acid length was increased from 12 to 18 carbons. Including squalene formed lipid-stabilized emulsion droplets which were fully loaded with the Au nanocrystals. Results with 4.1 nm Au and 2-3 nm diameter Si nanocrystals were similar, but these nanocrystals could not completely load the bilayers of unsaturated lipids.Item Black Gold(2020-08-14) Exumé, Ahsjah Janiece; Smith, Ya'KeThis report summarizes the creation of Black Gold, a series pilot. It covers the writing process, pre-production, and post-production. Black Gold was produced as a graduate thesis project in partial fulfillment of a Master of Fine Arts degree in Film and Media Production in the Department of Radio-Television-Film.Item Carbonatites(2009-07) Barker, Daniel S.Item Catalytic chemistry of Pd−Au bimetallic surfaces(2015-08) Yu, Wen-Yueh; Mullins, C. B.; Henkelman, Graeme; Hwang, Gyeong S.; Korgel, Brian A.; Sitz, Greg O.Catalyst development is important to the contemporary world as suitable catalysts can allow chemical processes to proceed with reduced energy consumption and waste production. In order to design catalysts with improved performance, the fundamental studies that correlate catalytic properties with surface structures are essential as they can provide mechanistic insights into the reaction mechanism. Pd−Au bimetallic catalysts have shown exceptional performance for a number of chemical reactions, however, the interplay between the reactive species and surface properties are still unclear at the molecular level. In this dissertation, the catalytic chemistry of Pd−Au surfaces was investigated via model catalyst studies under ultrahigh vacuum conditions. A range of Pd−Au model surfaces were generated by annealing Pd/Au(111) surfaces and characterized/tested by surface science techniques. The findings in this dissertation may prove useful to enhance the fundamental understanding of structure-reactivity relation of Pd−Au catalysts in associated reactions.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 Correlating Cu-Fe sulfides and Au mineralization in the Ertsberg-Grasberg District of Papua, Indonesia using volumetric analysis and trace element geochemistry(2017-08-09) Wright, Kylie Anne; Kyle, J. Richard; Ketcham, Richard Alan, 1965-The Ertsberg-Grasberg District in Papua, Indonesia, hosts two of the world’s largest intrusion-related Cu-Au deposits: the Ertsberg Intrusive System, a hybrid porphyry-skarn deposit, and the Grasberg Igneous Complex, a high-grade porphyry deposit. Cu mineralization within the Grasberg porphyry and Ertsberg skarn systems consists primarily of bornite and chalcopyrite, whereas native gold occurs as inclusions within, or along boundaries of these minerals. Experimental studies by other researchers have shown that at hydrothermal ore-forming temperatures (~300-700°C) and elevated sulfur activity, bornite and chalcopyrite can host 1000s ppm Au within the sulfide lattice or as nano-inclusions. Upon retrograde cooling of the hydrothermal system, the capacity of the Cu-Fe sulfides to host Au significantly decreases to ~10 ppm, suggesting that the Au becomes unstable within the Cu-Fe sulfide matrix and may passively migrate out of the sulfides and coalesce to form native gold grains. These data suggest that Cu-Fe sulfides could exert a strong control on the gold contents of porphyry deposits. However, the traditional model for native gold deposition in large hydrothermal systems relies primarily on fluid pulses, and does not consider gold contributions from the exsolution of previously precipitated gold within Cu-Fe sulfides. To assess the role of Au-bearing Cu-Fe sulfides in the concentration of native gold in this setting, High Resolution X-ray Computed Tomography was used to measure the native gold grains’ shapes, textures, and occurrence modes, and map the extent of contiguous Cu-sulfides. HRXCT data were used to 3D modified Voronoi regions within the Cu-sulfides, as an estimate of diffusional domains that may have provided gold to the Au-grains during cooling. The modified Voronoi volumes are defined for each Au-grain as the set of points within the Cu-sulfide network that are closer to that Au-grain than any other, when measured along a path through the Cu-sulfide. HRXCT data for 11 Ertsberg-Grasberg District ore samples were processed with two different threshold criteria, which produced 16 linear correlation values between modified Voronoi volumes and gold grain volumes. Of these 16 correlation coefficients, none show statistically significant correlations. Because of the paucity of gold grains within our samples, calculated drainage regions commonly extended to the physical edge of the core samples, rendering their actual volumes ambiguous and the correlations associated with them un-interpretable. In cases where numerous gold grains were identified, correlation values were not statistically significant. In general, however, this analysis was impaired by the necessity of interpreting whether all grains in a sample were created by a single event and mechanism. Complementary Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was used to assess and compare trace element variation within the Cu-Fe sulfides in the district and to constrain spatial variation of Au within Cu-Fe sulfides that contain native gold grains. LA-ICP-MS data show a strong positive correlation between Bi and Ag, and a moderate, positive correlation between Bi and Au, throughout the data. Au occurrences are scattered rather than uniform, where Au concentrations appear in patches throughout the sulfides. This may imply that the majority of non-visible gold exists in Au nanoparticles, rather than solid solution with the Cu-Fe sulfides. Spot analyses and 2D maps indicate the presence of an “enrichment halo” of elevated Au contents in Cu-Fe sulfides surrounding the gold grains. This “enrichment halo” can be interpreted as evidence in support of a hybrid Ostwald-type ripening process that coarsens gold inclusions in chalcopyrite at high-temperatures in porphyry-skarn systems.Item Enzyme immobilization on gold surfaces : effects of surface chemistry and attachment strategies on binding and activity(2023-04-20) Correira, Joshua Manuel; Webb, Lauren J.; Samanta, Devleena; Baiz, Carlos R; Gordon, Vernita; Shear, Jason BFunctional enzymes are the basis for many biotechnological systems, including biosensors, bio-fuel cells, and heterogeneous biocatalysts. In these systems, enzymes are often immobilized on a solid support or surface to capture their catalytic activity. Immobilization has the advantage of improving enzyme stability and reusability but often results in a significant loss of catalytic activity (1-2 orders of magnitude) when compared to the native enzyme. This inactivation is due to direct interactions between the enzyme and the solid support. Here, we developed methods to study enzyme immobilization and resulting inactivation. The aim of this work was to identify optimal surface chemistries and attachment strategies that promote high binding efficiencies while minimizing activity losses. Subsequently, we studied this using three enzymes (acetylcholinesterase (AChE), β-galactosidase (β-gal), horseradish peroxidase (HRP)) immobilized on gold surfaces by direct adsorption, covalent attachment, and DNA-directed attachment. First, AChE was directly adsorbed onto a variety of gold surfaces modified with self-assembled monolayers (SAMs) terminated with -COO⁻, -NH₃⁺, -OH, and -CH₃ functional groups at varying mole % to study the effect of surface hydrophobicity and charge on binding and activity. We found that binding was directly proportional to surface hydrophobicity (r = 0.75) and activity was inversely proportional to surface hydrophobicity (r = -0.62). The highest binding observed was ~40% of a monolayer on the most hydrophobic surfaces and the lowest binding observed was ~10% of a monolayer on the most hydrophilic surfaces. Conversely, on the most hydrophobic surfaces AChE retained <10% of its native activity, and on the most hydrophilic surfaces AChE retained ~40% of its native activity. This illuminated an inherent problem with direct adsorption: high binding and high activity are mutually exclusive. Due to these findings, we next immobilized β-gal and HRP on DNA-functionalized gold surfaces using DNA-DNA interactions, to avoid direct interactions between the enzyme and surface. We found that β-gal retained 62% of its native activity following immobilization, a significant improvement over previous direct adsorption strategies.Item Fabrication of hierarchical gold nanoblades with high surface enhanced Raman scattering activity(2017-12) He, Jiawei, M.S. in Engineering; Fan, DongleiTo obtain high sensitivity, efficiency, reproducibility and specificity, has been the goal in biochemical detection. Surface enhanced Raman scattering (SERS), which utilizes localized surface plasmon resonance (LSPR) of noble metals to significantly enhance Raman signals of molecules, is one of the most promising techniques for bio-sensing. Silver has been the dominant substrates for SERS due to its ultrahigh sensitivity. Comparing to silver, gold has its advantages in better bio-compatibility, less toxicity, and more tunable surface plasmon resonance (SPR) properties for potential photothermal applications in cancer treatment. Developing spiky gold nanostructures with sharp tips and dense junctions is the key to making its SERS performance comparable to silver. In this study, the synthesis of Au nanoblades for SERS activity with high sensitivity has been explored. By utilizing the galvanic replacement reaction between chloroauric acid (HAuCl₄) and Ag nanocapsules with 3,4-dihydroxyphenylalanine (DOPA) as surfactant and reducing agent, a new spiky structure of Au nanoblades coated on Ag nanocapsules was successfully synthesized. The concentration of DOPA and reaction time can significantly affect the number and morphology of Au blades. The lengths of Au nanoblades can vary from 20 nm to 100 nm under different reaction conditions. The SEM and EDS results have demonstrated the mechanism of the growth of Au nanoblades and the role of DOPA. The formation of AgCl during galvanic reaction between HAuCl₄ and Ag nanoparticles can promote non-epitaxial growth of Au on the AgCl precipitates. DOPA serves as a reducing agent to reduce HAuCl₄ to Au and a capping agent to favor the growth of sharp tips. Raman test results showed that the Au nanoblades detected Raman spectra of Nile blue with a concentration as low as 10⁻¹⁰ M. The high sensitivity and detection limit can be attributed to the dense sharp tips and small junctions as hotspots along the whole surface of the nanocapsules, which is comparable to the state-of-the-art Ag SERS substratesItem Gold-catalyzed alcohol oxidation reactions : insights from surface science and classical catalysis studies(2016-12) Mullen, Gregory Michael; Mullins, C. B.; Henkelman, Graeme; Humphrey, Simon; Hwang, Gyeong; Korgel, BrianCatalysts play an extremely important role in shaping the world around us. Foods, plastics, fuels, medicines, and countless other materials that are integral to our way of life rely on catalysts for their production. Despite their importance, to this day catalysts are still mysterious materials with active sites and reaction mechanisms that often remain unknown despite decades of investigation. In this dissertation, we investigate the use of gold catalysts for selective oxidation of alcohols, an important class of reaction used in the agrochemical, pharmaceutical, and fine chemicals industries. Using surface science and classical catalysis techniques, we demonstrate that water plays important and previously undiscovered roles in these processes, altering reaction mechanisms and influencing the selectivity exhibited by the catalysts for primary and secondary oxidation pathways. Additionally, we show that the structure and the composition of the support material both influence the activity and selectivity of gold catalysts for alcohol oxidation. Our results highlight the complexity that catalytic reaction mechanisms can exhibit and the structure-function relationships that can dictate their behavior. Knowledge of these factors is extremely valuable optimizing the design and implementation of catalytic processes. By leveraging knowledge like this, we will be able to mitigate the generation of industrial waste make better use of our natural resources.Item Gold-surface-mediated hydrogenation chemistry(2013-05) Pan, Ming, active 2013; Mullins, C. B.High surface area catalysts have been studied and applied in a wide range of chemical reactions and processes. The related microscopic details of surface chemistry are important and can be effectively explored employing surface science techniques. My dissertation focuses on investigations of catalytic properties of gold, primarily using vacuum molecular beam techniques, temperature programmed desorption (TPD) measurements, reflection-absorption infrared spectroscopy (RAIRS), and density functional theory (DFT) calculations. I conducted fundamental studies of hydrogenation reactions on a H atoms pre-covered Au(111) single crystal surface with co-adsorption of various chemical compounds, including acetaldehyde (CH₃CHO), acetone (CH₃COCH₃), propionaldehyde (CH₃CH₂CHO), water (H₂O), and nitrogen dioxide (NO₂). These studies allow better understanding of hydrogenative conversions facilitated by gold catalysts, which show great promise in hydrogenation applications but for which relevant fundamental studies are lacking. The experimental results unravel the unique and remarkable catalytic activity of gold in hydrogenation reactions: i) H atoms weakly absorb on the Au(111) surface and have a low desorption activation energy of ~ 28 kJ/mol; ii) acetaldehyde can be hydrogenated to ethanol at a low temperature of < 200 K; iii) propionaldehyde can be hydrogenated to 1-proponal (CH₃CH₂CH₂OH) on H pre-covered Au(111) whereas 2-propanol (CH₃CH(OH)CH₃) cannot be formed in the reaction of acetone with hydrogen atoms; iv) a coupling reaction of aldehyde-aldehyde or aldehyde-alcohol is observed on the H pre-covered Au(111) surface at temperatures lower than 200 K and this reaction can produce various ethers (symmetrical or unsymmetrical) from aldehydes and alcohols with the corresponding chain length; v) co-adsorbed H atoms have a strong interaction with water on the gold model surface and induce the dissociation of the O-H bond in water, which cannot be dissociated on the clean surface; vi) we observed a facile reaction of NO₂ reduction on H covered Au(111) and NO is produced at 77 K, yielding high NO₂ (100 %) conversion and selectivity towards NO (100 %) upon heating the surface to ~ 120 K. These studies indicate the exceptional catalytic activity of gold and enhance the understanding of surface chemistry of classical supported Au-based catalysts at the molecular scale.Item Growth, structure, and chemistry of 1B metal nanoclusters supported on TiO₂(110)(2006) Pillay, Devina; Hwang, Gyeong S.Cu, Ag, and Au nanoclusters dispersed on TiO2(110) surfaces are utilized in a wide variety of applications ranging from microelectronics to heterogeneous catalysis. The unique chemical reactivity of these clusters is largely dependent on their size, shape, spatial distribution, and interfacial interaction with the oxide support. This implies that atomic level control of these properties can offer great opportunities in the development of novel devices based on supported metal nanoclusters. It is therefore necessary to understand how formation and restructuring of these clusters alter their geometric and electronic characteristics. This thesis involves the development of a theoretical foundation for studying the growth, structure, and chemistry of Cu, Ag, and Au on TiO2(110) surfaces. Using density functional theory calculations, we have identified factors that control the chemical reactivity of these supported metal nanoclusters. First we investigated the electronic and geometric structures of the stoichiometric and reduced rutile TiO2(110) surfaces. Then we examined the surface chemistry of TiO2 towards gaseous CO and O2, as well as the structure and growth of 1B metal nanoclusters on TiO2(110). We also examined how the electronic and geometric properties of mixed metal nanoclusters, CuAun(n≤ 3), differ versus their single metal counterparts, Cum and Aum (m ≤ 4). Finally, we considered CO oxidation reactions on TiO2(110)-supported small Au clusters. While current experimental techniques are limited to providing complementary atomic-level real space information, first principles-based atomic level simulations greatly contribute to elucidating the fundamental behavior and properties of Cu, Ag, and Au nanoclusters on TiO2(110). First principles modeling has paved the way for new catalyst development by investigating how the geometric, electronic, and chemical properties of TiO2-supported 1B metal nanoclusters vary with surface defects, adsorbates, and metal dopants before valuable time and manpower is invested in experimental synthesis and characterization.Item Leveraging the extracellular electron transfer pathway of Shewanella oneidensis for pollutant remediation(2021-06-29) Springthorpe, Sarah Katherine; Keitz, Benjamin K.; Humphrey, Simon M; Webb, Lauren J; Werth, Charles JShewanella oneidensis is an electroactive soil bacterium that has shown promise for environmental remediation of both inorganic and organic pollutants. The bacterium accomplishes this process through extracellular electron transfer (EET), which is capable of reducing both soluble and insoluble oxidized substrates. However, like many remediation platforms that rely on metabolic activity, S. oneidensis is sensitive to high concentrations of toxic pollutants and can demonstrate slow degradation kinetics. To improve the environmental remediation capacity of S. oneidensis, we used two strategies: a) activating a synergistic effect between metabolism and material effects and b) engineering of the EET pathway (MtrCAB) for increased enzymatic activity. For the first strategy, we combine the native respiration of S. oneidensis with the high adsorption capacities of metal-organic frameworks to generate a platform for the remediation of redox-active metals. In Chapter 2, we demonstrate that S. oneidensis can respire on Fe(III)-based metal-organic frameworks via the MtrCAB pathway and that, in conjunction with continued microbial respiration, these bio-functionalized materials can be leveraged for synergistic removal of Cr(VI). In Chapter 3, we extend this platform to the recovery of Au(III) using the metal-organic framework MIL-127. In Chapter 4, we demonstrate that exogenous proteins containing produced by the yeast Yarrowia lipolytica can be used to increase the Fe(III) reduction rate of S. oneidensis. The increased production of Fe(II) can be leveraged for improved bacteria-material remediation strategies. For the second strategy, we use directed evolution and rational design to increase the activity of the outer membrane cytochrome MtrC of S. oneidensis. In Chapter 5, we demonstrate that the directed evolution of S. oneidensis MtrC results in improved degradation performance of organic dyes. Together, this work demonstrates the advantage of increasing electron flux to redox-active substrates through both material effects and protein engineering. These strategies can be implemented to improve current remediation platforms that rely on adsorption or bacterial metabolism.Item Localized surface plasmon resonance spectroscopy of gold and silver nanoparticles and plasmon enhanced fluorescence(2011-12) Vokac, Elizabeth Anne; Willets, Katherine A.; Brodbelt, Jennifer S.This thesis presents spectroscopic studies of metallic nanoparticle localized surface plasmons and plasmon enhanced fluorescence. We investigated the dielectric sensitivity of silver nanoprisms to an external electric field and gold nanorods to the formation of a self-assembled surface monolayer. Dark field microscopy was used to image plasmonic scattering from single nanoparticles, and a liquid crystal tunable filter was used to construct corresponding spectra. The plasmon resonances of silver nanoprisms displayed both reversible red shifts and irreversible blue shifts along with drastic intensity changes upon exposure to an applied bias. The plasmon resonances of gold nanorods showed sensitivity to the presence of alkanethiol molecules adhered to the particle surface by a moderate red shift. An increase in the effective external dielectric caused a shift toward longer wavelengths. We imaged plasmon enhanced fluorescence in order to optimize experimental parameters for a developing project that can characterize nanoparticle structure on sub-wavelength dimensions. Preliminary controls were performed to account for the effect of O₂ plasma treatment, solvent and alkanethiol monolayer formation on surface plasmon resonances. We found that O₂ plasma treatment for different time intervals did not result in a plasmon shift compared to untreated nanoparticles exposed to N₂; however when exposed to solvent the surface plasmons of the treated particles shifted five times as far toward the red. Interestingly, the solvent effect only resulted in a plasmon shift when the particles were N₂ dried after solvent incubation. Gold nanorods incubated in ethanol showed no wavelength maximum shift in pure solvent over time, but shifted moderately to the red after incubation in a solution of alkanethiol molecules. Conditions for the plasmon enhanced fluorescence study were optimized using a dye conjugate of the same alkanethiol molecule used previously by formation from solution in a monolayer on the gold nanorod surface. The appropriate synthesis for dye functionalization, molecular concentrations, solvents and optical settings were determined.Item Loss compensation in a plasmonic nanoparticle array(2013-05) Miller, Shannon Marie; Alú, AndreaThe problem of heavy material and radiative losses in plasmonic devices has held back their implementation for compact and high-speed data storage and interconnects. One of the most interesting solutions to this problem currently under exploration is the addition of a gain material in close proximity to the metallic nanostructures for loss compensation. Here the physics of light transport in a nanoparticle array, and the operation of gain media in contact with the structure, are described and analytically modeled. A two-dimensional array of closely spaced gold nanoparticles has been fabricated by focused ion beam milling, and its electromagnetic response in the presence or absence of a dye coating has been simulated in preparation for pump-probe optical testing. The compensation of losses via a fluorophore coating has been proven for the first time in this geometry, for a physically realized sample.Item Magneto-plasmonic nanoparticle platform for detection of rare cells and cell therapy(2014-08) Wu, Chun-Hsien, active 21st century; Sokolov, Konstantin V. (Associate professor); Dunn, Andrew; Emelianov, Stanislav; Yeh, Hsin-Chih; Zal, TomaszMagnetic and plasmonic properties combined in a single nanostructure provide a synergy that is advantageous in a number of biomedical applications, such as contrast enhancement in multimodal imaging, simultaneous capture and detection of circulating tumor cells, and photothermal therapy of cancer. These applications have stimulated significant interest in development of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared region and a strong magnetic moment. In this dissertation, we addressed this need to create a novel immunotargeted magneto-plasmonic nanoparticle platform. The nanostructures were synthetized by self-assembly of primary 6 nm iron oxide core-gold shell particles, resulting in densely packed spherical nanoclusters. The close proximity of the primary particles in the nanoclusters generates a greatly improved response to an external magnetic field and strong near-infrared plasmon resonances. A procedure for antibody conjugation and PEGylation to the hybrid nanoparticles was developed for biomedical applications which require molecular and biocompatible targeting. Furthermore, we presented two biomedical applications based on the immunotargeted hybrid nanoparticle platform, including circulating tumor cell (CTC) detection and cell-based immunotherapy of cancer. In the CTC detection assays, rare cancer cells were specifically targeted by antibody-conjugated nanoparticles and efficiently separated from normal blood cells by a magnetic force in a microfluidic chamber. The experiments in whole blood showed capture efficiency greater than 90% for a variety of cancers. We also explored photoacoustic imaging to detect nanoparticle-labeled CTCs in whole blood. The results showed excellent sensitivity to delineate the distribution of hybrid nanoparticles on the cancer cells. Thus, these works paves the way for a novel CTC detection approach which utilizes immunotargeted magneto-plasmonic nanoclusters for a simultaneous magnetic capture and photoacoustic detection of CTCs. In another application, we introduced a novel approach to label cytotoxic T cells using the magnetic nanoparticles with an expectation to enhance T cell recruitment in tumor under external magnetic stimulus. A series of in vitro experiments demonstrated highly controllable manipulation of labeled T cells. Thus, these results highlight the promise of using our nanoparticle platform as a multifunctional probe to manipulate and track immune cells in vivo and further improve the efficacy of cell-based cancer immunotherapy.Item Model catalyst studies of the CO oxidation reaction on Titania supported gold nanoclusters(2004) Stiehl, James Daniel; Mullins, C. B.The chemical nature of gold has been determined to be much richer than previously thought. Recent discoveries that properly prepared gold catalysts (i.e. gold particle diameters in 2 – 5 nm size range) can catalyze the CO oxidation reaction at low temperature have spurned a renewed interest in the chemistry of gold. Despite the extensive research that has been performed regarding CO oxidation on Au based catalysts, many issues still remain unresolved. The origin of the particle size dependence of the reaction is not well understood. Also, details concerning the reaction mechanism, specifically identification of the active oxygen species, remain unresolved. In the following studies, ultra high vacuum, molecular beam, surface science techniques are used to study the CO oxidation reaction on titania supported gold nanoclusters (Au/TiO2). Using a radio frequency generated plasma-jet, it is possible to simultaneously populate the Au/TiO2 samples with atomically adsorbed and molecularly chemisorbed oxygen species, allowing for the opportunity to investigate the reactivity of each respective species. The reaction of CO with atomically adsorbed oxygen has been studied over a range of temperatures from 65 – 250 K as a function of gold coverage and oxygen coverage. The reaction is observed to be a strong function of both of the sample temperature and the oxygen coverage. The reaction is also relatively independent of the gold coverage on the sample, in contrast to findings for the reaction employing gas-phase reactants under moderate pressures. The formation and reactivity of molecularly chemisorbed oxygen on the samples following exposure to the plasma-jet was also investigated. Evidence is presented showing that some molecularly chemisorbed oxygen is formed as a result of recombination of impinging atoms on the model catalyst surface. Evidence is also presented showing that adsorption of an oxygen atom on the sample influences the chemisorption of molecular species from the gas phase. Finally, evidence is presented showing that the molecularly chemisorbed oxygen species can participate in the CO oxidation reaction at 77 K. This finding reveals a reaction channel for CO oxidation on Au/TiO2 model catalysts that does not require the dissociation of oxygen.Item Molecular beam studies of low temperature CO oxidation on gold(2005) Kim, Tae Sang; Mullins, C. B.Gold is considered as noble among other metals because of its resistance to oxidation and corrosion. It is the most electronegative metal and its electron affinity is actually greater than that of oxygen. For this reason gold will not react directly with other electronegative elements such as molecular oxygen. As a result, gold has not been given much attention as a potential active ingredient for heterogeneous catalysis until it was discovered that gold particles that are 2-5 nm in diameter have exceptional catalytic activity towards many reactions. Among these reactions, low temperature CO oxidation is one of the most unique regarding gold catalysts in that it cannot be matched by other metals. Although it is widely accepted that gold particles which are 2-5 nm in diameter exhibit the greatest activity in CO oxidation, there is still much debate on the nature of the active sites for these catalysts and also the details of the reaction mechanism. Using molecular beams in conjunction with a radio frequency generated plasma jet, I have studied CO oxidation with atomically adsorbed oxygen on Au/TiO2 and Au(111). It is shown that CO reacts readily with pre-adsorbed oxygen atoms on a Au/TiO2 planar model catalyst and on Au(111) to produce CO2 even at temperatures as low as 77 K. The results presented show that gold particle size seems to have little effect on CO oxidation when oxygen adatoms are pre-adsorbed. This suggests that if reactive oxygen is primarily supplied through dissociation of oxygen molecules on the surface, the rate-limiting step in CO oxidation over gold is likely to be the dissociation of molecular oxygen. Another notable aspect of low temperature CO oxidation is that the addition of water in the feed stream is believed to enhance the reactivity by as much as two orders of magnitude. Here, evidence is shown that water can participate in CO oxidation on Au(111) surface populated with atomic oxygen by directly supplying its oxygen to CO to form CO2 at low temperatures. The results strongly suggest the direct involvement and promoting role of water in CO oxidation on oxygen covered Au(111).Item Oxidative chemistry on gold : unraveling molecular transformations at surfaces(2009-05) Gong, Jinlong, 1979-; Mullins, C. B.Gold has been considered catalytically inert due to its resistance to oxidation and corrosion. However, decades ago, it was discovered that gold nano-particles (<5nm) on metal oxides demonstrate superior chemical activity towards many reactions. These seminal findings spurred considerable interest in investigations of the mechanistic details of oxidative reactions on gold-based catalysts. However, the active site and structure of supported Au nanoclusters as well as the active oxygen species remains elusive. Achieving high selectivity toward partial oxidation products also remains a challenge. In this dissertation, an oxygen-covered Au(111) crystal under ultra vacuum conditions was used as a model system to gain insights into oxidative reactions in gold-based catalysis. I have been able to demonstrate that (i) surface-bound oxygen atoms are metastable at low temperature; (ii) the oxygen atoms participate in surface reactions as a Brønsted base or a nucleophilic base; and (iii) the acid-base reactions that have been observed on silver and copper may also occur on gold. Low temperature CO oxidation and the associated mechanistic aspects are investigated. CO reacts with hydroxyls formed from water-oxygen interactions to produce CO₂ on Au(111) populated with atomic oxygen at low temperatures. Directing an ¹⁶O beam toward C¹⁸O₂ pre-adsorbed Au(111), the formation of carbonate is significantly enhanced. This reaction is suggested to follow a hot-precursor-mediated mechanism. The identification of reaction pathways in oxidation of N-containing molecules such as ammonia and propylamine is presented. Abstraction of hydrogen from ammonia or propylamine by O atoms is the initial step in the surface decomposition of NHx (or RNHx-1) on Au(111). Atomic oxygen or hydroxyl-assisted dehydrogenation steps have lower barriers than the recombination steps under relevant conditions. 100% selectivity of N₂ or propionitrile can be obtained if the oxygen coverage is below the stoichiometric value. The surface oxidative chemistry of alcohols on Au(111) is also investigated. Except for methanol that is fully oxidized, alcohols initially undergo O-H bond cleavage (producing alcoxides) followed by selective β-C-H bond activation to form aldehydes or ketones. This finding reveals that the interaction of Au with the metal oxide support might not be essential to facilitate the reactions if active oxygen species are readily present, particularly at low temperatures.Item Phosphine-capped nanoparticles for electrocatalysis(2021-01-25) Baar, Kevin Thomas; Crooks, Richard M. (Richard McConnell); Humphrey, Simon M.In this work, a new method of synthesizing gold-rhodium alloyed nanoparticles (Au-Rh NPs), stabilized by triphenylphosphine (PPh₃) ligands is reported. This method has only previously been used to synthesize monometallic Au₅₅(PPh₃)₁₂Cl₆ (Au55) and Rh₅₅(PPh₃)₁₂Cl₆ (Rh55) nanoparticles. The NPs were characterized using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), nuclear magnetic resonance (NMR), and time-offlight secondary ion mass spectrometry (TOF-SIMS). It was observed that the synthesis produced NPs with the same size as Au55 and Rh55 and a wide range of alloy compositions as well as gold nanoparticles (AuNPs) and rhodium nanoparticles (RhNPs). The electrocatalytic activity for the oxygen reduction reaction (ORR) is explored for the AuRh NPs and compared with the activities of Au55 and Rh55 using cyclic voltammetry (CV) and rotating ring disk voltammetry (RRDV).Item Reaction controlled kinetic assembly of small gold nanoclusters with high NIR extinction(2011-08) Willsey, Brian William; Johnston, Keith P., 1955-; Milner, Thomas ENanoclusters with sizes of ~50nm with high NIR extinction at wavelengths beyond 800 nm are of interest in various fields including biomedical optical imaging, microelectronics, plasmonic sensors, and catalysis. Herein we report gold nanoclusters with hydrodynamic diameters of ~50 nm composed of ~10 nm primary particles. The kinetically controlled assembly of clusters occurs simultaneously with the reaction to synthesize the primary particles. The clustering is induced by attractive van der Waals forces that dominate over the steric and electrostatic repulsive forces present. Stability is provided using a single, biocompatible polysaccharide in either carboxymethyl dextran or dextran. High NIR shifts of the surface Plasmon resonance are achieved through close interparticle spacings of primary particles, deviations in morphology from that of a sphere of primaries, and the surface roughness that results from the clustering process. The cluster size is mediated by controlling the relative nucleation and growth rates of primary particles using a moderate reducing agent in NH2OH and glucose at pH 8.7. It will be shown that cluster size is also dependent on Au concentrations in solution. Maintaining low Au concentrations will allow for smaller clusters. In particular, the small size and high NIR extinction at longer wavelengths (800-1100 nm) makes these particles of interest for optical imaging applications in biology, as particles with a hydrodynamic diameter of ~50 nm have long blood lifetimes.