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- Title
- Catalytic Role of Boron Nitride in the Thermal Decomposition of Ammonium Perchlorate.
- Creator
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Grossman, Kevin, Seal, Sudipta, Coffey, Kevin, Heinrich, Helge, University of Central Florida
- Abstract / Description
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The decomposition of Ammonium Perchlorate (AP), a strong oxidizer used in solid rocket propellant, is widely studied in an attempt to increase the burn characteristics of propellants. Many materials have been shown to catalyze its decomposition, but little is known about the mechanism by which AP decomposition becomes catalyzed. In this study, Boron Nitride (BN) nanostructures, a material previously unknown to act as a catalyst, is studied. The decomposition reaction is studied by thermo...
Show moreThe decomposition of Ammonium Perchlorate (AP), a strong oxidizer used in solid rocket propellant, is widely studied in an attempt to increase the burn characteristics of propellants. Many materials have been shown to catalyze its decomposition, but little is known about the mechanism by which AP decomposition becomes catalyzed. In this study, Boron Nitride (BN) nanostructures, a material previously unknown to act as a catalyst, is studied. The decomposition reaction is studied by thermo-gravimetric analysis / differential scanning calorimetry, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The goal of this study is to discover the activation energy of this catalyst reaction, intermediary products of the reaction, mechanism of reaction and end state of the boron nitride nanostructures (ie, if the BN acts as a true catalyst, or participates on the overall reaction and has some end state that's different from the initial state). Four variations of BN have been synthesized using a hydrothermal process; BN nanoribbons, Boron Rich BN, Nitrogen-Rich BN, and high surface area BN. It is shown that the decomposition of AP is significantly altered when in the presence of BN and the mechanism through which BN catalyzes the decomposition is most likely the presence of oxidized nitrogen species on the BN material.
Show less - Date Issued
- 2015
- Identifier
- CFE0005801, ucf:50027
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005801
- Title
- Highly-Sensitive Stoichiometric Analysis of YAG Ceramics Using Laser-Induced Breakdown Spectroscopy (LIBS).
- Creator
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Kazemi Jahromi, Ali, Gaume, Romain, Richardson, Martin, Seal, Sudipta, University of Central Florida
- Abstract / Description
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Transparent ceramics are an important class of optical materials with applications in high-strength windows, radiation detectors and high-power lasers. Despite the many successful developments of the past decades, their challenging fabrication still needs to be perfected to achieve a better consistency in optical quality. In particular, ternary phase materials such as Yttrium Aluminum Garnet (YAG, Y3Al5O12), a long standing high-power laser host, require a precise control of stoichiometry,...
Show moreTransparent ceramics are an important class of optical materials with applications in high-strength windows, radiation detectors and high-power lasers. Despite the many successful developments of the past decades, their challenging fabrication still needs to be perfected to achieve a better consistency in optical quality. In particular, ternary phase materials such as Yttrium Aluminum Garnet (YAG, Y3Al5O12), a long standing high-power laser host, require a precise control of stoichiometry, often beyond the precision of current analytical techniques, in order to reduce scattering losses and the presence of deleterious point defects. This work explores the potential of Laser-Induced Breakdown Spectroscopy (LIBS) for the quantitative analysis of ceramic compositions near stoichiometry. We have designed a compact and automated LIBS system to determine the plasma composition of sintered mixtures of Y2O3-Al2O3 near the garnet composition. The performance of our setup is evaluated and compared to conventional techniques. Optimized conditions for the acquisition of plasma emission spectra are discussed and the intensity ratios of Y+ and Al in the 300 to 400nm spectral range are analyzed using simple plasma models. The results show that, for the selected parameters of our experiments, the fluctuations in plasma temperature are minimal, and the stability of the plasma is improved. Current results show that ceramic compositions can be resolved within 1 at% in oxide and several suggestions are proposed to further increase the accuracy and precision of the method.
Show less - Date Issued
- 2014
- Identifier
- CFE0005191, ucf:50624
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005191
- Title
- Real time monitoring of Cell-Nanoparticles interaction and tracking internalization process by mechanical probing using Atomic Force Microscopy.
- Creator
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Ly, Anh, Seal, Sudipta, Zhai, Lei, Heinrich, Helge, University of Central Florida
- Abstract / Description
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With extensive development of nanotechnology in last few years, scientists have discovered that nanoparticles (NPs) can be used as an efficient Drug Delivery System (DOS). In order to develop better NPs based drug delivery tool, it is imperative to understand the interaction between the NPs and the cell membrane. In our earlier studies, cerium oxide nanoparticles (CNPs) have been reported to have therapeutic properties, specifically against abnormalities associated with oxidative stress....
Show moreWith extensive development of nanotechnology in last few years, scientists have discovered that nanoparticles (NPs) can be used as an efficient Drug Delivery System (DOS). In order to develop better NPs based drug delivery tool, it is imperative to understand the interaction between the NPs and the cell membrane. In our earlier studies, cerium oxide nanoparticles (CNPs) have been reported to have therapeutic properties, specifically against abnormalities associated with oxidative stress. Therefore, CNPs with different sizes and morphology were selected to understand the interaction with cell. We analyzed the mechanical property of human nasal septum tumor cells membranes using Atomic Force Microscopy (AFM) with and without CNPs. In particular, Force-Distance spectroscopy mode was used to estimate the elasticity of cells membrane. Different concentrations (0, 50, 125 and 250 ?M) of CNPs were added to the cells (squamous cells; CCL30) and incubated for different time periods (0, 15, 30 and 60 minutes). Cell membrane elasticity/Young's modulus was calculated using a modified Hertz model. Changes in the cell elasticity were observed in high concentration of CNPs when treated with one hour. Significant changes in cell elasticity were observed at high concentration of CNPs for one hour of incubation. No significant change in cell elasticity was observed over one hour time period for 50 ?M of CNPs. Moreover, by using selected inhibitors to block different cell mediated internalization pathways, we also investigated the correlation between the cellular uptake and the tracking of NPs with their size. Specifically, similar change in cell elasticity was observed after blocking the cell energy production for CNPs with smaller diameter (3-5 nm). On the other hand, bigger size NPs (20-30 nm) showed no change in cell elasticity after blocking the cell energy production. These results indicate that 3-5 nm particles internalize cell by non-energy dependent pathway i.e. passive diffusion whereas 20-30 nm particles entered in cell by energy dependent pathways i.e. endocytosis of particles. Further, we have also identified the cellular uptake of 20-30 nm particles is by enclosing those CNPs in membrane vesicles in caveolae-mediated endocytosis mechanism. In summary, these results indicate that the nanoparticles-cell interaction has pronounced influence on the shape and size of the nanoparticles. These interactions can be further monitored by real time mechanical property measurement of cell membrane.
Show less - Date Issued
- 2014
- Identifier
- CFE0005204, ucf:50637
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005204
- Title
- Regolith-Based Construction Materials for Lunar and Martian Colonies.
- Creator
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Grossman, Kevin, Seal, Sudipta, Florczyk, Stephen, Fang, Jiyu, Zhai, Lei, Leuenberger, Michael, University of Central Florida
- Abstract / Description
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Humankind's ambitions of exploring our solar system and parts beyond depend heavily on our ability to collect resources from local environments at our destinations rather than bringing materials on the journey. This is a concept known as in-situ resource utilization (ISRU) and it is one that has been understood by every explorer and settler in the history of humankind. Regolith on the moon and Mars has been shown to be a particularly useful resource and has the ability to provide humans with...
Show moreHumankind's ambitions of exploring our solar system and parts beyond depend heavily on our ability to collect resources from local environments at our destinations rather than bringing materials on the journey. This is a concept known as in-situ resource utilization (ISRU) and it is one that has been understood by every explorer and settler in the history of humankind. Regolith on the moon and Mars has been shown to be a particularly useful resource and has the ability to provide humans with resources including water, oxygen, construction material, fabric, radiation shielding, metals, and may more. This dissertation focuses on construction materials derived from standard regolith simulant JSC-1A, including bricks, composites, metals and modified powder materials. Sintering processes with JSC-1A were studied to determine optimal heating profiles and resulting compressive strengths. It was determined that the temperature profiles have an optimal effect on smaller particle sizes due to the larger surface area to volume ratio of small particles and sintering being a surface event. Compressive strengths of sintered regolith samples were found to be as high as 38,000 psi, which offers large utility for martian or lunar colonies. This study also investigates a method for extracting metals from regolith known as molten regolith electrolysis. The alloy of the two major metallic components of regolith, iron and silicon, has been investigated as a structural metal for colonies and a potential feedstock for novel metallic 3D printers. Parallel to these efforts, a new additive manufacturing technique designed to print metal parts in low and zero gravity environments is developed. The mechanical properties from metal parts from this technique are examined and it is determined how the printing process determines a microstructure within the steel that impacts the utility of the technology.
Show less - Date Issued
- 2018
- Identifier
- CFE0007331, ucf:52144
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007331
- Title
- Development of in vitro point of care diagnostics (IVPCD) based on Aptamers integrated Biosensors.(&)nbsp;.
- Creator
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Saraf, Nileshi, Seal, Sudipta, Fang, Jiyu, Florczyk, Stephen, Dong, Yajie, Self, William, University of Central Florida
- Abstract / Description
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The global market for the medical diagnostic industry is worth 25 billion dollars in the United States and is expected to grow exponentially each year. Presently available methods for biodetection, such as immunoassays, chemiluminescence and fluorescent based assays are expensive, time consuming and require skilled labor with high-end instruments. Therefore, development of novel, passive colorimetric sensors and diagnostic technologies for detection and surveillance is of utmost importance...
Show moreThe global market for the medical diagnostic industry is worth 25 billion dollars in the United States and is expected to grow exponentially each year. Presently available methods for biodetection, such as immunoassays, chemiluminescence and fluorescent based assays are expensive, time consuming and require skilled labor with high-end instruments. Therefore, development of novel, passive colorimetric sensors and diagnostic technologies for detection and surveillance is of utmost importance especially in resource constrained communities. The present work focusses on developing novel and advanced in vitro biodiagnostic tools based on aptamer integrated biosensors for an early detection of specific viral proteins or small biomolecules used as potential markers for deadly diseases. Aptamers are short single stranded deoxyribonucleic acid (DNA) which are designed to bind to a specific target biomolecule. These are readily synthesized in laboratory and offers several advantages over antibodies/enzymes such as stable in harsh environment, easily functionalized for immobilization, reproducibility etc. These undergo conformational changes upon target binding and produces physical or chemical changes in the system which are measured as colorimetric or electrochemical signals. Here, we have explored the aptamer-analyte interaction on different platforms such as microfluidic channel, paper based substrate as well as organic electrochemical transistor to develop multiple compact, robust and self-contained diagnostic tools. These testing tools exhibit high sensitivity (detection limit in picomolar) and selectivity against the target molecule, require no sophisticated instruments or skilled labor to implement and execute, leading a way to cheaper and more consumer driver health care. These innovative platforms provide flexibility to incorporate additional or alternative targets by simply designing aptamers to bind to the specific biomolecule.
Show less - Date Issued
- 2018
- Identifier
- CFE0007766, ucf:52388
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007766
- Title
- Rare Earth Oxide Coating with Controlled Chemistry Using Thermal Spray.
- Creator
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Singh, Virendra, Seal, Sudipta, Coffey, Kevin, Raghavan, Seetha, Heinrich, Helge, Zhai, Lei, University of Central Florida
- Abstract / Description
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Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent...
Show moreCerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray.This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86 (&)#177;3%.An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm 3+ and Gd 3+) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure.Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 oF) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 oF and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.
Show less - Date Issued
- 2012
- Identifier
- CFE0004230, ucf:49023
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004230
- Title
- Electrochemical Studies of Nanoscale Composite Materials as Electrodes in PEM Fuel Cells.
- Creator
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Anderson, Jordan, Zhai, Lei, Blair, Richard, Hampton, Michael, Zou, Shengli, Seal, Sudipta, University of Central Florida
- Abstract / Description
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Polymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels....
Show morePolymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels. Small organic molecules such as alcohols and formic acid have shown promise as alternatives to hydrogen in PEMFCs due to their higher stability at ambient conditions. The drawbacks for using these fuels in PEMFCs are related to their incomplete oxidation mechanisms, which lead to the production of carbon monoxide (CO). When carbon monoxide is released in fuel cells it binds strongly to the platinum anode thus limiting the adsorption and subsequent oxidation of more fuel. In order to promote the complete oxidation of fuels and limit poisoning due to CO, various metal and metal oxide catalysts have been used.Motivated by promising results seen in fuel cell catalysis, this research project is focused on the design and fabrication of novel platinum-composite catalysts for the electrooxidation of methanol, ethanol and formic acid. Various Pt-composites were fabricated including Pt-Au, Pt-Ru, Pt-Pd and Pt-CeO2 catalysts. Electrochemical techniques were used to determine the catalytic ability of each novel composite toward the electrooxidation of methanol, ethanol and formic acid. This study indicates that the novel composites all have higher catalytic ability than bare Pt electrodes. The increase in catalytic ability is mostly attributed to the increase in CO poison tolerance and promotion of the complete oxidation mechanism of methanol, ethanol and formic acid. Formulations including bi- and tri-composite catalysts were fabricated and in many cases show the highest catalytic oxidation, suggesting tertiary catalytic effects. The combination of bi-metallic composites with ceria also showed highly increased catalytic oxidation ability. The following dissertation expounds on the relationship between composite material and the electrooxidation of methanol, ethanol and formic acid. The full electrochemical and material characterization of each composite electrode is provided.
Show less - Date Issued
- 2012
- Identifier
- CFE0004510, ucf:49264
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004510
- Title
- Understanding the Role of Defects in the Radiation Response of Nanoceria.
- Creator
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Kumar, Amit, Seal, Sudipta, Heinrich, Helge, Cho, Hyoung, Leuenberger, Michael, Zhai, Lei, Devanathan, Ram, University of Central Florida
- Abstract / Description
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Nanoscale cerium oxide (nanoceria) have shown to possess redox active property , and has been widely studied for potential use in catalysis, chemical-mechanical planarization, bio-medical and solid oxide fuel cell (SOFC), etc. The redox state of nanoceria can be tuned by controlling the defects within the lattice and thus its physical and chemical properties. Perfect ceria lattice has fluorite structure and the research in last decade has shown that oxide and mixed oxide systems with...
Show moreNanoscale cerium oxide (nanoceria) have shown to possess redox active property , and has been widely studied for potential use in catalysis, chemical-mechanical planarization, bio-medical and solid oxide fuel cell (SOFC), etc. The redox state of nanoceria can be tuned by controlling the defects within the lattice and thus its physical and chemical properties. Perfect ceria lattice has fluorite structure and the research in last decade has shown that oxide and mixed oxide systems with pyrochlore and fluorite have better structural stability under high energy radiation. However, the current literature shows a limited number of studies on the effect of high energy radiation on nanoceria. This dissertation aims at understanding the phenomena occurring on irradiation of nanoceria lattice through experiments and atomistic simulation.At first, research was conducted to show the ability to control the defects in nanoceria lattice and understand the effect in tailoring its properties. The defect state of nanoceria was controlled by lower valence state rare earth dopant europium. Extensive materials characterization was done using high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to understand the effect of dopant chemistry in modifying the chemical state of nanoceria. The defects originating in the lattice and redox state was quantified with increasing dopant concentration. The photoluminescence property of the control and doped nanoceria were evaluated with respect to its defect state. It was observed that defect plays an important role in modifying the photoluminescence property and that it can be tailored in a wide range to control the optical properties of nanoceria.Having seen the importance of defects in controlling the properties of nanoceria, further experiments were conducted to understand the effect of radiation in cerium oxide thin films of different crystallinity. The cerium oxide thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE) growth. The thin films were exposed to high energy radiation over a wide range of fluence (1013 to 1017 He+ ions/cm3). The current literature does not report the radiation effect in nanoceria in this wide range and upto this high fluence. The chemical state of the thin film was studied using in-situ XPS for each dose of radiation. It was found that radiation induced defects within both the ceria thin films and the valence state deviated further towards non-stoichiometry with radiation. The experimental results from cerium oxide thin film irradiation were studied in the light of simulation. Classical molecular dynamics and Monte Carlo simulation were used for designing the model ceria nanoparticle and studying the interaction of the lattice model with radiation. Electronic and nuclear stopping at the end of the range were modeled in ceria lattice using classical molecular dynamics to simulate the effect of radiation. It was seen that displacement damage was the controlling factor in defect production in ceria lattice. The simulation results suggested that nanosized cerium oxide has structural stability under radiation and encounters radiation damage due to the mixed valence states. A portion of the study will focus on observing the lattice stability of cerium with increasing concentration of the lower valence (Ce3+) within the lattice. With this current theoretical understanding of the role of redox state and defects during irradiation, the surfaces and bulk of nanoceria can be tailored for radiation stable structural applications.
Show less - Date Issued
- 2012
- Identifier
- CFE0004396, ucf:49375
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004396
- Title
- Nanoarchitectured Energy Storage Devices.
- Creator
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Yu, Zenan, Thomas, Jayan, Seal, Sudipta, Zhai, Lei, Fang, Jiyu, Sundaram, Kalpathy, University of Central Florida
- Abstract / Description
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Supercapacitors, the devices that connect the gap between batteries and conventional capacitors, have recently attracted significant attention due to their high specific capacitance, substantially enhanced power and energy densities, and extraordinary cycle life. In order to realize even better performance with supercapacitors, rejuvenated effort towards developing nanostructured electrodes is necessary. In this dissertation, several strategic directions of nanoarchitecturing the electrodes...
Show moreSupercapacitors, the devices that connect the gap between batteries and conventional capacitors, have recently attracted significant attention due to their high specific capacitance, substantially enhanced power and energy densities, and extraordinary cycle life. In order to realize even better performance with supercapacitors, rejuvenated effort towards developing nanostructured electrodes is necessary. In this dissertation, several strategic directions of nanoarchitecturing the electrodes to enhance the performance of supercapacitors are investigated. An introduction and background of supercapacitors, which includes motivation, classification and working principles, recent nanostructured electrode materials studies, and devices fabrication, are initially presented. A facile method, called Spin-on Nanoprinting (SNAP), to fabricate highly ordered manganese dioxide (MnO2) nanopillars is introduced. The SNAP method that is further modified to develop carbon nanoarray electrodes is also discussed. Subsequently, a template-free method to develop high aspect ratio copper oxide nanowhiskers on copper substrate is presented, which boosts the surface area by 1000 times compared to non-nanostructured copper substrate. Electrochemically deposited MnO2 on the nanostructured substrate provided a specific capacitance of about 1379 F g-1 which is very close to the theoretical value (~ 1400 F g-1) due to this efficient nanostructure design. In addition, a novel method to decorate metal nanoparticles on graphene aerogel, which considerably enhances the electronic conductivity and the corresponding specific capacitance, is demonstrated. Moreover, ferric oxide (Fe2O3) nanorods prepared by a simple hydrothermal method is discussed. Asymmetric devices assembled based on Fe2O3 nanorods and MnO2 nanowhiskers show excellent electrochemical properties. The devices not only display the capability to store energy but also transmit electricity through the inner copper core. These two functions are independent and do not interfere with each other. Finally, a summary of this dissertation as well as some potential future directions are presented.
Show less - Date Issued
- 2015
- Identifier
- CFE0006062, ucf:50995
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006062
- Title
- Design of surface chemical reactivity and optical properties in glasses.
- Creator
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Lepicard, Antoine, Richardson, Kathleen, Seal, Sudipta, Gaume, Romain, Dussauze, Marc, Kuebler, Stephen, University of Central Florida
- Abstract / Description
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Thermal poling is a technique which involves the application of a strong DC electric field to a glass substrate heated below its glass transition temperature (Tg). Following the treatment, a static electric field is frozen inside the glass matrix, effectively breaking its centrosymmetry. Historically, this treatment has been used as a way to gain access to second order non-linear optical properties in glasses. However, recent efforts have shown that the treatment was responsible for...
Show moreThermal poling is a technique which involves the application of a strong DC electric field to a glass substrate heated below its glass transition temperature (Tg). Following the treatment, a static electric field is frozen inside the glass matrix, effectively breaking its centrosymmetry. Historically, this treatment has been used as a way to gain access to second order non-linear optical properties in glasses. However, recent efforts have shown that the treatment was responsible for structural changes as well as surface property modifications. Our study was focused on using this technique to tailor surface properties in oxide (borosilicate and niobium borophosphate) and chalcogenide glasses. A strong emphasis was put on trying to control all changes at the micrometric scale. After poling, property changes were assessed using a set of characterization tools: the Maker fringes technique (a Second Harmonic Generation ellipsometry technique), micro-Second Harmonic Generation ((&)#181;-SHG), vibrational spectroscopy and Secondary Ion Mass Spectroscopy (SIMS). Surface reactivity in borosilicate glasses was effectively changed while in niobium borophosphate and chalcogenide glasses, the optical properties were controlled linearly and nonlinearly. Finally, property changes were effectively controlled at the micrometric scale. This opens up new applications of thermal poling as a mean to design glass substrate for integrated photonics and lab-on-a-chip devices.
Show less - Date Issued
- 2016
- Identifier
- CFE0006471, ucf:51435
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006471
- Title
- Development of enzyme-free hydrogen peroxide biosensor using cerium oxide and mechanistic study using in-situ spectro-electrochemistry.
- Creator
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Saraf, Shashank, Seal, Sudipta, Cho, Hyoung Jin, Zhai, Lei, Heinrich, Helge, Harper, James, University of Central Florida
- Abstract / Description
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During recent development, it has been demonstrated that cerium oxide nanoparticles (CNPs) have exhibited catalytic activity which mimics naturally existing enzymes such as superoxide dismutase (SOD) and catalase. The underlying mechanism is attributed to the modulation of oxygen vacancies on CNPs lattice by dynamic switching of the oxidation states between Ce3+ and Ce4+ due to the electron transfer resulting from the redox reaction between CNPs and reactive oxygen species such as hydrogen...
Show moreDuring recent development, it has been demonstrated that cerium oxide nanoparticles (CNPs) have exhibited catalytic activity which mimics naturally existing enzymes such as superoxide dismutase (SOD) and catalase. The underlying mechanism is attributed to the modulation of oxygen vacancies on CNPs lattice by dynamic switching of the oxidation states between Ce3+ and Ce4+ due to the electron transfer resulting from the redox reaction between CNPs and reactive oxygen species such as hydrogen peroxide (H2O2). Thereby the redox potential of CNPs is dependent on the surface chemistry i.e. the surface concentration of Ce3+ and Ce4+ Currently, the ratio of Ce3+/ Ce4+ in CNPs is characterized ex-situ using XPS or TEM which involves sample drying and exposure to high energy X-rays and electron beam, respectively. Sample drying and high energy beam exposure could lead to sample deterioration. The goal of the study is to explore a technique to characterize CNPs in-situ and identify the surface chemistry of CNPs. The in-situ investigation of CNPs was carried using spectroelectrochemistry wherein the electrochemical and optical measurements are carried out simultaneously. Detailed optical characterization of two different CNPs having different catalytic activity were carried under oxidation and reduction environments. Analysis of spectra revealed widely different redox potential for CNPs which was a function of pH and composition of buffer solution. In second part of dissertation a suitable surface chemistry of CNPs is investigated to replace the enzyme in biosensor assembly to allow amperometric detection of H2O2 in physiological conditions. Upon electrochemical investigation of the physio-chemical properties of CNPs, it was found that CNPs having higher surface concentration of Ce4+ as compared to Ce3+ oxidation states, demonstrated increased catalytic activity towards H2O2. The addition of CNPs resulted in 5 orders of increment in amperometric current with a response time of 400 msec towards detection of H2O2 and exhibited excellent selectivity in presence of interfering species. Additionally, cerium oxide was successfully integrated into the biosensor assembly through the anodic electrodeposition, which allowed the transfer of electron generated from the CNPs in the redox reaction to the electrode and demonstrated successful sensing of H2O2. Furthermore, to achieve detection of H2O2 in physiological conditions, CNPs were integrated with nanoporous gold (NPG) which exhibited anti-biofouling properties. The anti-biofouling property of NPG was investigated using electrochemical techniques and showed excellent signal retention in physiological concentration of albumin proteins. The novel study targets at developing robust enzyme free biosensor by integrating the detection ability of CNPs with the anti-biofouling activity of NPG based electrode.
Show less - Date Issued
- 2016
- Identifier
- CFE0006498, ucf:51404
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006498
- Title
- Redox-Active Solid State Materials and its Biomedical and Biosensing Applications.
- Creator
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Gupta, Ankur, Seal, Sudipta, Dong, Yajie, Cho, Hyoung Jin, Zhai, Lei, Schulte, Alfons, University of Central Florida
- Abstract / Description
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Reactive oxygen species (ROS) are byproducts of physiological processes in human body, and strengthened production of ROS is known to cause acute conditions such as inflammation, aging, Alzheimer's disease, melanoma and ovarian cancer, fibrosis and multiple sclerosis. Therefore, early detection of ROS at nanomolar concentration (at cellular level) and developing more potent antioxidants is essential for regular health monitoring. As an example, ROS are also responsible for inflammation...
Show moreReactive oxygen species (ROS) are byproducts of physiological processes in human body, and strengthened production of ROS is known to cause acute conditions such as inflammation, aging, Alzheimer's disease, melanoma and ovarian cancer, fibrosis and multiple sclerosis. Therefore, early detection of ROS at nanomolar concentration (at cellular level) and developing more potent antioxidants is essential for regular health monitoring. As an example, ROS are also responsible for inflammation reactions at orthopedic implants-tissue interface triggered by wear debris. Inflammation induced by ROS results in revision surgery. Coatings of redox-active materials exhibiting antioxidant properties on implants have potential to mitigate the inflammation and delay the need of revision surgery. This dissertation focus on developing advanced functional nanomaterials by tailoring the surface chemistry of existing materials. Surface chemistry of materials can be altered by introducing surface and edge defects in the lattice structure Three materials system doped cerium oxide nanoparticles (d-CNPs), cerium oxide thin films (CeOx) and molybdenum disulfide (MoS2) nanoparticles, have been studied for its surface and edge contributions in potential biomedical and biosensing applications. Surface (d-CNPs and CeOx thin films) and edge chemistry (MoS2) have been tailored to understand its role and specific response.Surface Ce3+/Ce4+ oxidation state in CNPs controls the bio-catalytic activity. Higher superoxide dismutase (SOD) is demonstrated by high Ce3+/Ce4+ oxidation state. On the other hand, improved catalase mimetic activity is observed for low Ce3+/Ce4+ CNPs. Different CNPs preparation results in different Ce3+ to Ce4+ ratio, particle size, surface coating, and agglomeration, thus significantly varying the antioxidant properties of CNPs. In the first section of the dissertation, sustainable one-step room temperature synthesis of rare earth element (La, Sm, and Er) d-CNPs have been developed to effectively control the Ce3+ to Ce4+ ratio for specific biological application. Substitution of Ce4+ ions by trivalent dopants from ceria lattice increases the oxygen vacancies and density of catalytic sites. Uniform distribution of trivalent dopant in ceria lattice confirmed by EFTEM is attributed to enhanced SOD mimetic activity, ROS scavenging and tuning surface Ce3+/Ce4+ oxidation state in CNPs. Surface chemistry of redox-active cerium oxide coating on orthopedic implants also plays a vital role in scavenging ROS and mitigating inflammation. Thus, surface chemistry of CeOx thin films deposited by atomic layer deposited (ALD), have also been tailored by controlling the film thickness. CeOx film of 2 nm thickness has high Ce3+/Ce4+ (ratio 1) whereas higher thickness films (6-33 nm) have lower Ce3+/Ce4+ (ratio 0.30-0.37). These films have been further tested for catalase mimetic activity and hydrogen peroxide (H2O2) detection. Sensor selectivity is always a key issue. Most often, ascorbic acid found in the biological system, interfere in the electrochemical detection of H2O2 resulting in selectivity issue, thus protective Nafion layer is required to prevent cerium oxide-ascorbic acid interaction.To improve the selectivity of electrochemical sensors, Sulfur-deficient redox-active MoS2 have been utilized for electrochemical detection of pharmaceutically relevant chemical species. S-deficient MoS2 nanoparticles have been prepared by liquid exfoliation method to increase Mo-edge density and tested as sensing materials for detection of pharmaceutically relevant H2O2, hypochlorous acid (HOCl) and reactive nitrogen (NO*) species. The addition of ascorbic acid and uric acid have shown no interference during H2O2 detection. Change in S to Mo ratio have been studied using x-ray photoelectron spectroscopy. Density functional theory (DFT) have been employed to understand the detection mechanism and size-dependent sensitivity of MoS2. DFT study further reveals the role of S-deficiency and Mo- and S-edges in the higher catalytic activity of 5-7 nm MoS2 particles.Through these studies, the importance of defects in nanomaterials and their exotic properties at the nanoscale have been demonstrated. Understanding developed from these studies have provided the framework to develop more advanced functional nanomaterials for biomedical and biosensing applications.
Show less - Date Issued
- 2017
- Identifier
- CFE0006944, ucf:51655
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006944
- Title
- Cerium oxide nanoparticles act as a unique catalyst and scavenge nitric oxide and peroxynitrite and decrease RNS in vitro and in vivo.
- Creator
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Dowding, Janet, Self, William, Bossy-Wetzel, Ella, Zervos, Antonis, Seal, Sudipta, Santra, Swadeshmukul, University of Central Florida
- Abstract / Description
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Cerium oxide nanoparticles (CeO2 NPs)(nanoceria) have been shown to possess a substantial oxygen storage capacity via the interchangeable surface reduction and oxidation of cerium atoms, cycling between the Ce4+ and Ce3+ redox states. Reduction of Ce4+ to Ce3+ causes oxygen vacancies or defects on the surface of the crystalline lattice structure of the particles, generating a cage for redox reactions to occur. The study of the chemical and biological properties of CeO2 NPs has expanded...
Show moreCerium oxide nanoparticles (CeO2 NPs)(nanoceria) have been shown to possess a substantial oxygen storage capacity via the interchangeable surface reduction and oxidation of cerium atoms, cycling between the Ce4+ and Ce3+ redox states. Reduction of Ce4+ to Ce3+ causes oxygen vacancies or defects on the surface of the crystalline lattice structure of the particles, generating a cage for redox reactions to occur. The study of the chemical and biological properties of CeO2 NPs has expanded recently, and the methods used to synthesize these materials are also quite diverse. This has led to a plethora of studies describing various preparations of CeO2 NPs for potential use in both industry and for biomedical research. Our own work has centered on studies that measure the ability of water-based CeO2 NPs materials to reduce reactive oxygen and nitrogen species in biological systems, and correlating changes in surface chemistry and charge to the catalytic nature of the particles. The application in experimental and biomedical research of CeO2 NPs began with the discovery that water-based cerium oxide nanoparticles could act as superoxide dismutase mimetics followed by their ability to reduce hydrogen dioxide similar to catalase. While their ROS scavenging ability was well established, their ability to interact with specific RNS species, specifically nitric oxide (NO) or peroxynitrite (ONOO-) was not known. The studies described in this dissertation focus on the study of RNS and cerium oxide nanoparticles.Our in vitro work revealed that CeO2 NPs that have higher levels of reduced cerium sites (3+) at the surface (which are effective SOD mimetics) are also capable of accelerating the decay of peroxynitrite in vitro. In contrast, CeO2 NPs that have fewer reduced cerium sites at the particle surface (which also exhibit better catalase mimetic activity) have NO scavenging capabilities as well as some reactivity with peroxynitrite. Our studies and many others have shown cerium oxide nanoparticles can reduce ROS and RNS in cell culture or animal models. The accumulation of ROS and RNS is a common feature of many diseases including Alzheimer's disease (AD). Testing our CeO2 NPS in cortical neurons, we used addition of A? peptide as an AD model system. CeO2 NPs delayed A?-induced mitochondrial fragmentation and neuronal cell death. When mitochondrial ROS levels are increased, mitochondrial fission is activated by DRP1 S616 phosphorylation. Specifically, our studies showed the reduction of phosphorylated DRP1 S616 in the presence of CeO2 NPs. Results from our studies have begun to unravel the molecule mechanism behind the catalytic nature of how CeO2 NPs reduce ROS/RNS in biological systems and represents an important step forward to test the potential neuroprotective effects of CeO2 NPs in model systems of AD.A plethora of studies describing various preparations of CeO2 NPs for potential use in both industry and for biomedical research have been described in the past five years. It has become apparent that the outcomes of CeO2 NPs exposure can vary as much as the synthesis methods and cell types tested. In an effort to understand the disparity in reports describing the toxicity or protective effects of exposure to CeO2 NPs, we compared CeO2 NPs synthesized by three different methods; H2O2 (CNP1), NH4OH (CNP2) or hexamethylenetetramine (HMT-CNP1). Exposure to HMT-CNP1 led to reduced metabolic activity (MTT) at a 10-fold lower concentration than CNP1 or CNP2 and surprisingly, exposure to HMT-CNP1 led to substantial decreases in the ATP levels. Mechanistic studies revealed that HMT-CNP1 and CNP2 exhibited robust ATPase (phosphatase) activity, whereas CNP1 lacked ATPase activity. HMT-CNP1 were taken up into HUVECs far more efficiently than the other preparations of CeO2 NPs. Taken together, these results suggest the combination of increased uptake and ATPase activity of HMT-CNP1 may underlie the mechanism of the toxicity of this preparation of CeO2 NPs, and may suggest ATPase activity should be considered when synthesizing CeO2 NPs for use in biomedical applications. Overall the studies have uncovered two new catalytic activities for water-based CeO2 NPs (NO scavenging and accelerated decay of peroxynitrite), demonstrated their ability to reduce RNS in an AD cell culture model as well as identifying a catalytic activity (phosphatase) that may underlie the observed toxicity of CeO2 NPs reported in other studies.
Show less - Date Issued
- 2012
- Identifier
- CFE0004782, ucf:49783
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004782
- Title
- Synthesis and Study of Chemo-Hydrothermally Derived Water-Soluble Chitosan and Chiosan-Metal Oxide Composites.
- Creator
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Basumallick, Srijita, Santra, Swadeshmukul, Kolpashchikov, Dmitry, Zou, Shengli, Ye, Jingdong, Seal, Sudipta, University of Central Florida
- Abstract / Description
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Chitosan (CS) is a man-made sugar based biopolymer derived from chitin, the second most abundant natural polymer after cellulose. Chitin is sourced from crustacean species such as shrimps and crabs. The chemical structure of chitin contains N-Acetyl D-glucosamine monomer units which forms CS upon deacetylation. In CS, ?-(1-4) linked D-glucosamine units are randomly distributed. Approximately 75% - 80% sugar units contains primary amine groups in commercially available low molecular weight CS....
Show moreChitosan (CS) is a man-made sugar based biopolymer derived from chitin, the second most abundant natural polymer after cellulose. Chitin is sourced from crustacean species such as shrimps and crabs. The chemical structure of chitin contains N-Acetyl D-glucosamine monomer units which forms CS upon deacetylation. In CS, ?-(1-4) linked D-glucosamine units are randomly distributed. Approximately 75% - 80% sugar units contains primary amine groups in commercially available low molecular weight CS. Biodegradability, low toxicity, mucoadhesive and transfecting properties of CS polymer are attractive for applications as oral and nasal drug delivery systems. Chitosan polymer is water insoluble at neutral pH. To solubilize CS, dilute mineral acid (such as hydrochloric acid and nitric acid) or organic acid (such as acetic acid) is often used. CS contains both hydroxyl and primary amine groups in its structure. In acidic solution, the amine functional groups become protonated (positively charged). Positively charged CS remains stable only in low pH condition due to electrostatic repulsion of charged polymer segments. Therefore, by using a suitable anionic (negatively charged) cross-linker, stable CS particles (such as nanoparticles and microspheres) can be prepared. This is popularly known as ionic gelation method. Extensive studies have been done on the synthesis of drug loaded CS particles where particle integrity is maintained by ionic gelation using tripolyphosphate (TPP, an anionic cross-linker). Drug encapsulated CS-TPP composite particles are shown to maintain biodegradability and biocompatibility. The CS-TPP composite particles exhibits very limited dispersibility at neutral pH conditions specifically in neutral buffered conditions. A number of biomedical applications (including systemic drug formulations) however demands buffer-stable CS composite particles for achieving optimal therapeutic outcome.To overcome the above dispersibility issues, CS polymer and CS particles units have been chemically modified using water soluble motifs (such as water soluble polymer or ligands). This approach is very cumbersome and usually involves multiple purification steps. Chemical modification of natural CS chain introduces risks of compromising biodegradability and biocompatibility. Therefore, there is a strong need for developing a straightforward method of making water soluble CS and CS particles.Chapter 1 of this dissertation presents an overview of the CS polymer, various applications of CS polymers, methods of making CS polymers and CS particles, current limitations of synthesis methods for preparing stable chitosan particles at neutral pH conditions and finally delineates the scope of the proposed research work.Chapter 2 describes development of chemo-hydrothermal synthesis method for producing water soluble CS polymer and water dispersible CS composite particles. In this method, a chemical (depolymerizing agent) is used to treat CS polymer in a hydrothermal (high temperature and high pressure) condition. Two types of depolymerizing agents have been used, an inorganic acid (e.g. hydrochloric acid, HCl) and a bicarboxylic organic acid (e.g. tartaric acid, TA). In both cases, 100% depolymerized CS polymer was obtained. Chemical characteristics of the depolymerized CS were comparable to acid solubilized CS. CS polymer exhibits weak fluorescence. Interestingly, hydrothermally depolymerized CS shows strong fluorescence properties irrespective of the nature of depolymerizing agent used. TA not only depolymerized CS but also formed CS-TA composite particulate structures in solution via self-assembly. The CS-TA composite particles are stable in a wide pH range from 5 to 11. Detailed spectroscopic and microscopic studies have been done to understand the basic mechanism of particle formation and increase in fluorescence properties (i.e. structure-property relationship). Usefulness of CS-TA in solubilizing water-insoluble cargos (such as fluorescein isothiocyanate, FITC) has been demonstrated.Chapter 3 is focused on hydrothermal synthesis of mixed-valence copper (Cu) oxide loaded CS-TA composite particles and their characterization. Crystalline Cu oxide nanoparticles were coated with the CS-TA layer. Water dispersibility of Cu oxide greatly improved upon coating with CS-TA material. To demonstrate catalytic activity of Cu-oxide loaded CS-TA film in sequestering carbon dioxide (CO2), an electrochemical setup was used. Electrochemical reduction of CO2 was successfully demonstrated. It was observed that CS-TA environment not only maintained catalytic properties of Cu oxide but also allowed solution processing of Cu-oxide film onto the electrode surface.Chapter 4 discusses a convenient method of making monodispersed water dispersible Cu loaded chitosan nanoparticles (Cu-CS) using HCl depolymerized CS polymer. The purpose of this study was to investigate if there was any improvement in antibacterial properties of Cu-CS nanoparticles prepared using hydrothermally treated CS polymer. Interestingly, it was observed that the antibacterial efficacy of Cu was not compromised in Cu-CS nanoparticles. Moreover, the materials exhibited improvement in antibacterial efficacy against both Gram-negative and Gram-positive bacteria species. A plausible mechanism has been proposed to explain antibacterial results.Chapter 5 summarizes major findings of this dissertation research and presents future research directions.
Show less - Date Issued
- 2014
- Identifier
- CFE0005461, ucf:50395
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005461
- Title
- TAILORING THE PROPERTIES OF POLYELECTROLYTE COATED CERIUM OXIDE NANOPARTICLES AS A FUNCTION OF MOLECULAR WEIGHT.
- Creator
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Saraf, Shashank, Seal, Sudipta, Cho, Hyoung, Zhai, Lei, Heinrich, Helge, Harper, James, University of Central Florida
- Abstract / Description
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The application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA)which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA...
Show moreThe application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA)which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analysed using the change in the Gibbs free energy computed by Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The Gibbs free energy was highest for PAA coated CNPs by 250 kg/mole indicating the most stable coating. The free energy for PAA 100 kg/mole coated CNPs is 85% lower than the PAA250 coated CNPs. This significant difference is caused by the strong adsorption of PAA100 on CNPs. Catalytic activity of PAA-CNPs is accessed by the catalase enzymatic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. Apart from PAA coating the catalase activity is also affected by the structure of the coating layer.
Show less - Date Issued
- 2013
- Identifier
- CFE0005410, ucf:50410
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005410
- Title
- Novel Immunogens of Cellular Immunity Revealed using in vitro Human Cell-Based Approach.
- Creator
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Schanen, Brian, Self, William, Warren, William, Khaled, Annette, Seal, Sudipta, Zervos, Antonis, University of Central Florida
- Abstract / Description
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Nanotechnology has undergone rapid expansion largely as a result of its enormous potential for applications as biomaterials, drug delivery vehicles, cancer therapeutics, and immunopotentiators. Despite this wave of interest and broad appeal for nanoparticles, evidence of their effect to the human immune system remains scarce. Concerns rise as studies on nanoparticle toxicology continue to emerge indicating that nanomaterials can be acutely toxic and can have long term inflammatory effects as...
Show moreNanotechnology has undergone rapid expansion largely as a result of its enormous potential for applications as biomaterials, drug delivery vehicles, cancer therapeutics, and immunopotentiators. Despite this wave of interest and broad appeal for nanoparticles, evidence of their effect to the human immune system remains scarce. Concerns rise as studies on nanoparticle toxicology continue to emerge indicating that nanomaterials can be acutely toxic and can have long term inflammatory effects as seen in animal models. Based on these findings and the rise in the development of nanoparticle technologies targeting in vivo applications, the urgency to characterize nanomaterial immunogenicity is paramount.Nanoparticles harbor great potential because they possess unique physicochemical properties compared to their larger counter parts as a result of quantum-size effects and their inherent large surface area to volume ratio. These physicochemical properties govern how a nanoparticle will behave in its environment. However, researchers have only just begun to catalogue the biological effect these properties illicit. We took it upon ourselves to investigate nanoparticle size-induced effects using TiO2, one of the most widely manufactured nanoparticles, as a model. We studied these effects in dendritic cells across a human donor pool. We examined dendritic cells because they have an inimitable functional role bridging the innate and adaptive arms of immunity. From this work we found that TiO2 nanoparticles can activate human dendritic cells to become pro-inflammatory in a size-dependent manner as compared to its micron-sized counterpart, revealing novel immune cell recognition and activation by a crystalline nanomaterial.Having identified nanomaterial size as a contributing feature of nanoparticle induced immunopotentiation, we became interested if additional physicochemical properties such as surface reactivity or catalytic behavior could also be immunostimulatory. Moreover, because we witnessed a stimulatory effect to dendritic cells following nanoparticle treatment, we were curious how these nanoparticle-touched dendritic cells would impact adaptive immunity. Since TiO2 acts as an oxidant we chose an antioxidant nanoparticle, CeO2, as a counterpart to explore how divergent nanoparticle surface reactivity impacts innate and adaptive immunity. We focused on the effect these nanoparticles had on human dendritic cells and TH cells as a strategy towards defining their impact to cellular immunity. Combined, we report that TiO2 nanoparticles potentiate DC maturation inducing the secretion of IL-12p70 and IL-1?, while treatment with CeO2 nanoparticles induced IL-10, a hallmark of suppression. When delivered to T cells alone TiO2 nanoparticles induced stronger proliferation in comparison to CeO2 which stimulated TReg differentiation. When co-cultured in allogeneic T cell assays, the materials directed alternate TH polarization whereby TiO2 drives largely a TH1 dominate response, whereas CeO2 was largely TH2 bias. Combined, we report a novel immunomodulatory capacity of nanomaterials with catalytic activity. While unintentional exposure to these nanomaterials could pose a serious health risk, development and targeted use of such immunomodulatory nanoparticles could provide researchers with new tools for novel adjuvant strategies or therapeutics.
Show less - Date Issued
- 2012
- Identifier
- CFE0004629, ucf:49927
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004629
- Title
- The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests.
- Creator
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Pearman, Benjamin, Hampton, Michael, Blair, Richard, Clausen, Christian, Seal, Sudipta, Campiglia, Andres, Yestrebsky, Cherie, Mohajeri, Nahid, University of Central Florida
- Abstract / Description
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Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of...
Show moreFuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications.Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work.Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states.In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests.The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 (-) 5 nm and 20 (-) 150 nm size, respectively, that did not change size or shape when incorporated into the membranes.At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.
Show less - Date Issued
- 2012
- Identifier
- CFE0004789, ucf:49731
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004789