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Title: ROOM TEMPERATURE SYNTHESIS AND SYSTEMATIC CHARACTERIZATION OF ULTRA-SMALL CERIA NANOPARTICLES.
Creator: Patel, Chetak, Santra, Swadeshmukul, University of Central Florida
Abstract / Description: Cerium oxide (ceria, CeO2) is a rare earth oxide that has attracted wide-spread research interest because of its unique properties such as high mechanical strength, oxygen ion conductivity, oxygen storage capacity and autocatalytic property. In recent years, researchers have discovered that ceria nanoparticles (NPs) are capable of protecting cells from free radical induced damage. Interestingly, it was found that nanometer size (~ 5 nm) ceria can scavenge free radicals quite efficiently, thus...
Show moreCerium oxide (ceria, CeO2) is a rare earth oxide that has attracted wide-spread research interest because of its unique properties such as high mechanical strength, oxygen ion conductivity, oxygen storage capacity and autocatalytic property. In recent years, researchers have discovered that ceria nanoparticles (NPs) are capable of protecting cells from free radical induced damage. Interestingly, it was found that nanometer size (~ 5 nm) ceria can scavenge free radicals quite efficiently, thus acting as an anti-oxidant. This phenomenon has been explained based on the autocatalytic property of ceria NPs. Several methods have been developed for the synthesis of ceria NPs that include flame combustion, hydroxide co-precipitation, hydrothermal/solvothermal, microemulsion, sonochemical and microwave-assisted heating methods and sol-gel method. Ceria NPs synthesized by these methods are often highly aggregated. Furthermore, large scale synthesis of monodispersed CeO2 NPs is quite challenging. Therefore it is desirable to synthesize ceria NPs in bulk quantity keeping its important properties intact, specifically free-radical scavenging property. The main goal of this study is therefore to synthesize ultra-small (< 5.0 nm), high quality monodispersed ceria NPs in large quantities. In this thesis work, I present a couple of room temperature techniques, dilute sodium hydroxide (NaOH) assisted and ethylenediamine (EN) assisted for the synthesis of nearly mono-dispersed, ultra-small (< 5 nm) and water-dispersible ceria NPs. Morphology and particle size of the ceria NPs were investigated through high resolution transmission electron microscopy (HRTEM). The HRTEM analysis confirmed the formation of 3.0 ± 0.5 nm size and 2.5 ± 0.2 nm size highly-crystalline ceria NPs when synthesized using dilute NaOH and EN as solvents, respectively. The nanostructures were characterized by X-ray diffraction (XRD) studies to determine the crystal structure and phase purity of the products. The samples were also thoroughly characterized by X-ray photoelectron spectroscopy (XPS) to determine the oxidation state of cerium ions. The presence of the +3 and +4 oxidation states in the samples was also confirmed from the XPS analysis. The co-existence of these two oxidation states is necessary for their applications as free radical scavenger. The autocatalytic behaviors of the ceria NPs were investigated through a hydrogen peroxide test and monitored by UV-visible transmission spectroscopy.
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Date Issued: 2009
Identifier: CFE0002883, ucf:48043
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002883

Title: Development of enzyme-free hydrogen peroxide biosensor using cerium oxide and mechanistic study using in-situ spectro-electrochemistry.
Creator: Saraf, Shashank, Seal, Sudipta, Cho, Hyoung Jin, Zhai, Lei, Heinrich, Helge, Harper, James, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2016
Identifier: CFE0006498, ucf:51404
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006498

Title: Cerium oxide Nanoparticles: Their Phosphatase Activity and its Control.
Creator: Dhall, Atul, Self, William, Seal, Sudipta, Zervos, Antonis, University of Central Florida
Abstract / Description: Cerium oxide nanoparticles are established scavengers of reactive oxygen and nitrogen species. They have many potential biomedical applications that depend on their physicochemical properties and mode of preparation. Recent studies have found these nanoparticles possess phosphatase mimetic activity. Studying such catalytic activities will qualify their biomedical applications and render information on their bioavailability and potential toxicity.Two oxidation states of cerium exist in these...
Show moreCerium oxide nanoparticles are established scavengers of reactive oxygen and nitrogen species. They have many potential biomedical applications that depend on their physicochemical properties and mode of preparation. Recent studies have found these nanoparticles possess phosphatase mimetic activity. Studying such catalytic activities will qualify their biomedical applications and render information on their bioavailability and potential toxicity.Two oxidation states of cerium exist in these nanoparticles (3+ or 4+). It is hypothesized that the oxidation state of cerium in the nanoparticles determines the amount of adsorbed water on the crystal lattices. This in turn governs their activity as phosphatases. Nanoparticles with higher levels of cerium in the 4+ state exhibit phosphatase activity while those with higher levels of cerium in the 3+ state do not. This phosphatase activity may be controlled with the addition of inhibitory anions. It is hypothesized that anions with structures similar to phosphate can inhibit phosphatase activity by leading to the production of complexes on the surface of cerium oxide nanoparticles.Substrates that were used to test this activity include para-nitrophenyl phosphate (pNPP), 4-methylumbelliferyl phosphate (MUP) and adenosine triphosphate (ATP). To highlight the role of adsorbed water, we also performed experiments on pNPP with methanol as a solvent. The activity was measured by absorbance (pNPP and ATP) or fluorescence (MUP) and reported as nmol of phosphate/min. In some cases this rate was calculated through coupled reactions or by measuring the rate of formation of other colored products formed along with the release of phosphate such as pNP (para-nitrophenol).The phosphatase activity increased as the amount of adsorbed water increased implying that the abundance of adsorbed water makes the surface of 4+ ceria nanoparticles more active. Phosphatase activity for all the substrates exhibited Michaelis-Menten kinetics. Although the phosphatase activity of these nanoparticles is slow (turnover rate) as compared to real biological phosphatases, it can be used as a model catalytic activity to follow other catalytic activities that are associated with nanoparticles that have an abundance of cerium in the 4+ state, such as catalase activity. These results also provide information on the nature of the active sites involved in the catalytic activities associated with these nanoparticles.We identified three inhibitors, tungstate, molybdate and arsenate, which decreased the phosphatase activity of these nanoparticles in a dose dependent manner. Vmax, Km and Ki values were determined by varying substrate concentrations in the presence and absence of inhibitors. A partial mixed inhibition model was fit for each of these inhibitors.Summary: Phosphatase activity of cerium oxide nanoparticles with higher levels of cerium in the 4+ oxidation state was used as a model catalytic activity to study the nature of the active sites involved in catalysis. The study of inhibitors can reveal more information as to the surface binding of substrates in catalysis.
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Date Issued: 2014
Identifier: CFE0005603, ucf:50261
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005603

Title: ANALYSIS OF THE PREVENTION OF BIOCORROSION CAUSED BY DESULFOVIBRIO ALASKENSIS G20.
Creator: Boring, Michael, Self, William, University of Central Florida
Abstract / Description: Desulfovibrio alaskensis G20 and other sulfate-reducing bacteria cause significant damage to metal pipelines and other infrastructure through a metabolic pathway that releases toxic hydrogen sulfide into their surroundings. The biocorrosion that results from the release of hydrogen sulfide creates significant economic burden, and can pose health risks for those exposed to this chemical. They are commonly present in the form of biofilms, an extracellular matrix composed of bacterial cells,...
Show moreDesulfovibrio alaskensis G20 and other sulfate-reducing bacteria cause significant damage to metal pipelines and other infrastructure through a metabolic pathway that releases toxic hydrogen sulfide into their surroundings. The biocorrosion that results from the release of hydrogen sulfide creates significant economic burden, and can pose health risks for those exposed to this chemical. They are commonly present in the form of biofilms, an extracellular matrix composed of bacterial cells, polysaccharides, proteins, nucleic acids, and other materials. These biofilms are difficult to remove, and they provide protection to the bacteria within from anti-bacterial treatments. Desulfovibrio alaskensis G20 is a strain derived from a wild-type bacterium collected from an oil well corrosion site and is a model organism for understanding biofilm formation of sulfate-reducing bacteria and how these biofilms can be prevented or inhibited by techniques such as cerium oxide nanoparticle coating. To this end, samples of Desulfovibrio alaskensis G20 were grown anaerobically in 24-well and 96-well plates, and the resultant biofilm growth was measured through spectrophotometry. Several different environmental parameters were tested, including temperature, electron donor molecules, basal and enriched growth media, and oxidative stress, revealing several affinities for production of biofilm growth.
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Date Issued: 2017
Identifier: CFH2000263, ucf:45942
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000263

Title: CERIUM OXIDE NANOPARTICLES FOR THE DETECTION OF ANTIMICROBIAL RESISTANCE.
Creator: Noll, Alexander, Perez, J. Manuel, University of Central Florida
Abstract / Description: The rise of antimicrobial resistance demands the development of more rapid screening methods for the detection of antimicrobial resistance in clinical samples to both give the patient the proper treatment and expedite the treatment of patients. Cerium oxide nanoparticles may serve a useful role in diagnostics due to their ability to exist in a mixed valence state and act as either oxidizing agents or reducing agents. Considering that cerium oxide nanoparticles have been shown to shift in...
Show moreThe rise of antimicrobial resistance demands the development of more rapid screening methods for the detection of antimicrobial resistance in clinical samples to both give the patient the proper treatment and expedite the treatment of patients. Cerium oxide nanoparticles may serve a useful role in diagnostics due to their ability to exist in a mixed valence state and act as either oxidizing agents or reducing agents. Considering that cerium oxide nanoparticles have been shown to shift in absorbance upon oxidation, a useful method of antimicrobial resistance detection could be based on the oxidation of cerium oxide nanoparticles. Herein, an assay is described whereby cerium oxide nanoparticle oxidation is a function of glucose metabolism of bacterial samples in the presence of an antimicrobial agent. Cerium oxide nanoparticles were shown to have an absorbance in the range of 395nm upon oxidation by hydrogen peroxide whereas mixed valence cerium oxide nanoparticles lacked an absorbance around 395nm. In the presence the hydrogen peroxide-producing glucose oxidase and either increasing concentrations of glucose or bacterial medium supplemented with increasing concentrations of glucose, cerium oxide nanoparticles were shown to increase in absorbance at 395nm. This oxidation assay was capable of measuring differences in the absorbance of E. coli and S. aureus samples grown in the presence of inhibitory and non-inhibitory concentrations of ampicillin in as little as six hours. Therefore, this cerium oxide nanoparticle oxidation assay may be very useful for use in clinical laboratories for the detection of antimicrobial resistance due to the relatively low cost, no requirement for specialized equipment and, most importantly, the reduced incubation time of the assay to as little as six hours compared to current gold standard antimicrobial resistance detection methods that require 24 hours. This assay may thus also help partially circumvent the issue of knowledge of antimicrobial resistance in infected patients before prescribing improper regimens.
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Date Issued: 2011
Identifier: CFH0003760, ucf:44780
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0003760

Title: ADSORPTION BEHAVIOUR OF POLYACRYLIC ACID ON CERIUM OXIDE NANOSTRUCTURES: EXPERIMENTAL AND PREDICTIVE MODEL.
Creator: Haghighat Mesbahi, Ali, Seal, Sudipta, Fang, Jiyu, Bai, Yuanli, University of Central Florida
Abstract / Description: Cerium oxide-based slurries are crucial for chemical mechanical polishing (CMP) in electronic industry. For these slurry systems, poly(acrylic acid) (PAA) is heavily utilized to provide colloidal stability. Some of the important parameters in the colloid stability are molecular weight (MW) and concentration of stabilizer, size of the nanoparticle in the slurry and the pH of system. By determining the colloidal stability of a discrete number of slurry formulations and relating these to certain...
Show moreCerium oxide-based slurries are crucial for chemical mechanical polishing (CMP) in electronic industry. For these slurry systems, poly(acrylic acid) (PAA) is heavily utilized to provide colloidal stability. Some of the important parameters in the colloid stability are molecular weight (MW) and concentration of stabilizer, size of the nanoparticle in the slurry and the pH of system. By determining the colloidal stability of a discrete number of slurry formulations and relating these to certain slurry component parameters, a possible model can be produced to predict the influence of these parameters on the particle stability. Direct quantification of colloidal stability is difficult, however, polymer adsorption has been well established to correlate with the stability and therefore it can be used to quantify the colloidal stability.For the current thesis, surface area of cerium oxide, molecular weight of PAA, and the relative weight fraction of PAA were varied in two different nanomaterial systems, such as nanocubes and nanorods. To obtain the best fit of these variables, as they relate to polymer adsorption, fittings were performed using two advanced modeling techniques; namely, artificial neural network and adaptive neuro-fuzzy inference system. The precision of these techniques were compared each other and with the more simple, though largely imprecise, multi-variable linear regression. It was determined that the GENFIS-3 model shows the best performance for describing polymer adsorption on the nanocube and nanorod systems with an average relative deviation of only 6.5%. Additionally, these models suggest that the relative fraction of PAA has the most significant effect on the stability of cerium oxide-based CMP slurries. The greater precision of these advanced modeling methods can explain the better slurry performance with greater colloidal stability.
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Date Issued: 2015
Identifier: CFE0006315, ucf:51542
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006315

Title: The Study of Physiochemical Properties of Cerium Oxide Nanoparticles and its Application in Biosensors.
Creator: Barkam, Swetha, Seal, Sudipta, Heinrich, Helge, Gaume, Romain, University of Central Florida
Abstract / Description: Biosensors continue to get smaller and faster with the advancement in nanotechnology through the use of nanomaterials to achieve high sensitivity and selectivity. However, the continued reliance on biomolecules or enzymes in the biosensor assembly poses the problem of reproducibility, storage and complexity. This dissertation research address some of the challenges by investigating the physiochemical properties of nanoparticles to understand its interaction with biological systems and develop...
Show moreBiosensors continue to get smaller and faster with the advancement in nanotechnology through the use of nanomaterials to achieve high sensitivity and selectivity. However, the continued reliance on biomolecules or enzymes in the biosensor assembly poses the problem of reproducibility, storage and complexity. This dissertation research address some of the challenges by investigating the physiochemical properties of nanoparticles to understand its interaction with biological systems and develop enzyme free biosensors. In this study, we have demonstrated a novel strategy to integrate cerium oxide nanoparticles (CNPs) as an efficient transducer through rigorous screening for developing enzyme/label free biosensors for detecting analytes such as dopamine associated with neurodegenerative diseases and limonin for fruit quality management. CNPs have been proven to exhibit antioxidant properties attributed to its dynamic change in surface oxidation states (Ce4+ to Ce3+ and vice versa) mediated at the oxygen vacancies on the surface of the CNPs. It is also well-established that nanoparticles are resourceful novel materials with a plethora of applications in the field of nanomedicine.It is of significant importance to study the changes in physiochemical properties of different synthesized CNPs for effective use in biomedical applications. In one of the studies, the effects of different anions in the precursor of the cerium salts used for synthesizing CNPs using the same synthesis method, were extensively studied. It has been demonstrated that the physicochemical properties such as dispersion stability, hydrodynamic size, and the signature surface chemistry, antioxidant catalytic activity, oxidation potentials of different CNPs have been significantly altered with the change of anions in the precursor salts. . The increased antioxidant property of CNPs prepared using the precursor salts containing NO3(&)#175; and Cl(&)#175; ions have been extensively studied using in-situ UV-Visible spectroscopy which reveal that the change in oxidation potentials of CNPs with the change in concentration of anions. Thus, this work demonstrated that the physicochemical and antioxidant properties of CNPs can be tuned by anions of the precursor during the synthesis process.After standardizing the synthesis process, CNPs have been immobilized on highly ordered polymer nanopillars to develop an optical sensor for dopamine detection. Dopamine, is one of the main neurotransmitters which plays a significant role in central nervous system and its deficiency leads to neurological disorders such as Parkinson's disease, schizophrenia etc. Current biosensors in the literature use invasive detection techniques and lacks sensitivity to detect physiological clinically relevant concentrations of dopamine. The interaction between CNPs and dopamine have been extensively studied using UV-visible spectro-electrochemical studies to achieve the right surface chemistry (35-70% Ce4+). The sensor exhibits high sensitivity (1fM detection in simulated body fluid), high selectivity (in acetic acid, sheep plasma) and increased robustness with several cycles of usage.Furthermore, we have developed a CNPs based biosensor by integrating it on a transistor platform for improved sensitivity and better adhesion by immobilizing in silk fibroin matrix. In the final study, CNPs integrated in silk fibroin (SF) polymer electrospun nanofibers incorporated on an organic electrochemical transistor platform, is used to develop a limonin sensor. It has been established that the concentration of limonin in citric fruit predicts the quality in terms of bitter taste from the HLB bacteria infected fruits. A unique in-house electrospinning set-up using drum as collector was used to develop SF (extracted from cocoon) nanofibers used as CNP (synthesized in-situ in fibers) transducer carrier, both of which have a specific interaction with limonin. This novel biosensor has exhibited high sensitivity (100nM in PBS) and selectivity (citric acid, sugar etc.) with improved robustness in terms of reuse. The broader impact of the study is to develop holistic diagnostic non-invasive biosensors that can directly be used to detect the analytes using samples from humans and/or on field for fruit quality determination, which is a huge stepping stone in the advancement of nanotechnology based biosensors. This will fuel future generation of enzyme free biosensors which can utilize similar concepts for the detection of other analytes. The biosensor could be printed on a flexible substrate to advance wearable smart biosensor and could eventually enable users to wirelessly monitor the analyte concentrations using smartphones.
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Date Issued: 2017
Identifier: CFE0006931, ucf:51662
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006931

Title: The Study of Photo-reduction of Cerium Oxide Nanoparticles in Presence of Dextran: An Attempt in Understanding the Functionality of the System.
Creator: Barkam, Swetha, Seal, Sudipta, Heinrich, Helge, Gaume, Romain, University of Central Florida
Abstract / Description: Malignant melanoma cancer is the sixth common cancer diagnosed in the United States. Surgery, chemotherapy and radiation are some of the successful techniques in killing tumor cells. However, in these techniques, it is not easy to distinguish tumor cells from the healthy once which inadvertently get exposed to chemical agent/radiation. Therefore it is required to develop an anti-cancer agent which selectively kills the cancer cells, while still protecting the normal tissues. In our...
Show moreMalignant melanoma cancer is the sixth common cancer diagnosed in the United States. Surgery, chemotherapy and radiation are some of the successful techniques in killing tumor cells. However, in these techniques, it is not easy to distinguish tumor cells from the healthy once which inadvertently get exposed to chemical agent/radiation. Therefore it is required to develop an anti-cancer agent which selectively kills the cancer cells, while still protecting the normal tissues. In our preliminary work, we have shown that Dextran (1000Da) coated Cerium oxide nanoparticles (Dex-CNPs) selectively kills the cancer cells (50% killing at a concentration of 150?M) without inducing toxicity to the normal cells. However, the mechanism involved on how CNPs/Dex-CNPs attain the selectivity and efficiently kill the tumor cells is still unknown. In this study we have synthesized Dextran coated ceria nano particles (Dex- CNPs) with different surface oxidation state ratio (Ce4+/Ce3+). This will provide an in depth understanding of the key chemical and physical properties of the system that can improve its efficacy. The varied surface oxidation of the particles is achieved by exposing Dex-CNPs to light which initiates a color change from dark to pale yellow indicating the reduction of Ce4+ to Ce3+. Interestingly we have found that the Dex-CNPs exposed to light have reduced cytotoxicity towards squamous cell carcinoma cell line (CCL30) compared to the protected once. Characterization of the same revealed that Dex- CNPs exposed to light have decreased Ce4+ /Ce3+ surface oxidation ratio compared to the other. This provides more insight in useful synthesis of Dex-CNPs in terms of storage and handling. In summary, higher Ce4+ /Ce3+ surface oxidation ratio is more efficient in hindering tumor growth by effectively hindering the tumor-stoma interaction.
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Date Issued: 2013
Identifier: CFE0005301, ucf:50508
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005301

Title: THE GENERATION AND SCAVENGING OF RADICALS VIA CERIUM AND NANOCERIA.
Creator: Heckert, Eric, self, william, University of Central Florida
Abstract / Description: Cerium is the most abundant of the rare earth metals, found on average at a level of 66 parts per million in the earth's crust. The unique redox properties of cerium and cerium oxide nanoparticles have led to its use in a wide variety of industrial and commercial uses such as oxygen sensors, fertilizers and as a catalyst to remove toxic gases in automobile exhaust. The use of cerium has also garnered interest in the nanotechnology field. Nanoceria has been generated in its oxide form as...
Show moreCerium is the most abundant of the rare earth metals, found on average at a level of 66 parts per million in the earth's crust. The unique redox properties of cerium and cerium oxide nanoparticles have led to its use in a wide variety of industrial and commercial uses such as oxygen sensors, fertilizers and as a catalyst to remove toxic gases in automobile exhaust. The use of cerium has also garnered interest in the nanotechnology field. Nanoceria has been generated in its oxide form as nanoparticles and nanorods. Recently, nanoceria has been shown to protect against oxidative stress in both animal and cell culture models. Although not fully understood, this observed protective effect of nanoceria is believed to be the result of recently identified SOD mimetic activity. Currently there is little understanding as to how nanoceria is capable of scavenging radicals or what properties makes nanoceria an effective SOD mimetic. Our data shows strong evidence that the oxidation state of nanoceria is directly related to its reported SOD mimetic activity. As such, future studies of nanoceria should be mindful of the oxidation state of nanoceria preparations as only nanoceria with a high concentration of cerium (III) have shown effective SOD mimetic activity. In addition to the characterization of nanoceria and its SOD mimetic activity, we have evidence that free cerium is capable of generating radicals and damaging DNA in vitro in the presence of hydrogen peroxide. These data strongly suggests that the rare earth inner-transition metal cerium is capable of generating hydroxyl radicals via a Fenton-like reaction. Based on these results the use of free cerium salts should be monitored to limit environmental exposure to cerium. Altogether our data would suggest that cerium by virtue of its unique redox chemistry is quite capable of accepting and donating electrons from its surroundings. In its free form cerium is able to redox cycle easily and can generate radicals. However, paradoxically nanoceria may not easily redox cycle due to the bound lattice structure of the particle. The unique nature of nanoceria and cerium leads to a unique circumstance where nanoceria is a radical scavenger while free cerium generates radicals. As such, further investigation is needed to insure that leeching or cerium from nanoceria does not abrogate any potential benefit nanoceria may provide.
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Date Issued: 2007
Identifier: CFE0001892, ucf:47417
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001892

Title: USE OF CERIUM OXIDE NANOPARTICLES FOR PROTECTION AGAINSTRADIATION-INDUCED CELL DEATH.
Creator: Colon, Jimmie, Kolattukudy, Pappachan, University of Central Florida
Abstract / Description: The ability of engineered cerium oxide nanoparticles to confer radioprotection was examined. Rat astrocytes were treated with cerium oxide nanoparticles to a final concentration of 10 nanomolar, irradiated with a single 10 Gy dose of ionizing radiation and cell death was evaluated by propidium iodine uptake at 24 and 48 hours after radiation insult. Treatment of rat astrocytes with nanoceria resulted in an approximate 3-fold decrease in radiation induced death. These results suggest that the...
Show moreThe ability of engineered cerium oxide nanoparticles to confer radioprotection was examined. Rat astrocytes were treated with cerium oxide nanoparticles to a final concentration of 10 nanomolar, irradiated with a single 10 Gy dose of ionizing radiation and cell death was evaluated by propidium iodine uptake at 24 and 48 hours after radiation insult. Treatment of rat astrocytes with nanoceria resulted in an approximate 3-fold decrease in radiation induced death. These results suggest that the nanoceria are conferring protection from radiation induced cell death. Further experiments with human cells were conducted. Human normal and tumor cells (MCF-7 and CRL8798) were treated with the same dosage of cerium oxide nanoparticles, irradiated and evaluated for cell survival. Treatment of normal cells (MCF-7) conferred nearly 99% protection from radiation-induced cell death while the same concentration of nanoceria showed almost no protection in tumor cells (CRL8798). TUNEL analysis results of similarly treated cells demonstrated that nanoceria reduced radiation-induced cell death by 3-fold in normal breast cells but not in MCF-7 tumor cell lines when cultured under the same conditions. We concluded that cerium oxide nanoparticles confer radioprotection in a normal human breast line (CRL 8798) but not in a human breast tumor line (MCF-7). It is hoped that the outcome of this study will guide future endeavors toward a better elucidation of the molecular pathways involved in the protection of cells with nanoceria against radiation-induced cell death, as well as the minimization of the bystander effect in radiation therapy.
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Date Issued: 2006
Identifier: CFE0001048, ucf:46823
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001048

Title: Rare Earth Oxide Coating with Controlled Chemistry Using Thermal Spray.
Creator: Singh, Virendra, Seal, Sudipta, Coffey, Kevin, Raghavan, Seetha, Heinrich, Helge, Zhai, Lei, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2012
Identifier: CFE0004230, ucf:49023
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004230

Title: Understanding the Role of Defects in the Radiation Response of Nanoceria.
Creator: Kumar, Amit, Seal, Sudipta, Heinrich, Helge, Cho, Hyoung, Leuenberger, Michael, Zhai, Lei, Devanathan, Ram, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2012
Identifier: CFE0004396, ucf:49375
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004396

Title: TUNING THE PROPERTIES OF NANOMATERIALS AS FUNCTION OF SURFACE AND ENVIRONMENT.
Creator: Karakoti, Ajay, Seal, Sudipta, University of Central Florida
Abstract / Description: Nanotechnology has shaped the research and development in various disciplines of science and technology by redefining the interdisciplinary research. It has put the materials science at the forefront of technology by allowing the researchers to engineer materials with properties ranging from electronics to biomedical by using materials as diverse as ceramics to just plain carbon. These exceptional properties are achieved by minimizing the dimension of particles in such smaller domains that...
Show moreNanotechnology has shaped the research and development in various disciplines of science and technology by redefining the interdisciplinary research. It has put the materials science at the forefront of technology by allowing the researchers to engineer materials with properties ranging from electronics to biomedical by using materials as diverse as ceramics to just plain carbon. These exceptional properties are achieved by minimizing the dimension of particles in such smaller domains that the boundary between the individual atoms, ions or cluster of particles is very small. This results in a change in conventional properties of particles from continuum physics to quantum physics and hence the properties of nanoparticles can be tuned based upon their size, shape and dimensionality. One of the most apparent changes upon decreasing the particle size is the increase in surface area to volume ratio. Thus nanoparticles possess greater tendency to interact with the environment in which they are present and similarly the environment can affect the properties of nanomaterials. The environment here is described as the immediate solid, liquid or gaseous material in immediate contact with the external surface of the nanoparticles. In order to control the physico-chemical properties of nanoparticles it is important to control the surface characteristics of nanoparticles and its immediate environment. The current thesis emphasizes the role of tuning the surface of nanoparticles and/or the environment around the nanoparticles to control their properties. The current approach in literature uses nanoparticles as a platform that can be used for a myriad of applications by just changing the surface species which can tune the properties of nanoparticles. Such surface modification can provide nanomaterials with hydrophilic, hydrophobic, biocompatible, sensing, fluorescence and/or electron transfer properties. The current thesis demonstrates the interaction between nanoparticles and the environment by changing the surface characteristics of nanomaterials through the use of oxide nanoparticles as examples. The first part of the thesis discusses the synthesis, modification and properties of cerium oxide nanoparticles (CNPs), a versatile material used in wide range of applications from catalysis to glass polishing, for their potential use in biomedical applications as a function of medium. The thesis starts by projecting the effect of environment on the properties of nanomaterials wherein it is shown that simple medium, such as, water can influence the optical properties of nanoparticles. It was shown that the strong polarizing effect of water on the non-bonding f electrons can cause a blue shift in the optical properties of CNPs as a function of increase in trivalent oxidation state of cerium in CNPs. This phenomenon, contradictory to existing literature in solid state where a red shift is observed upon increasing the trivalent oxidation state of cerium in CNPs, is purely attributed to the medium-inflicted change in properties of nanoparticles. This concept is built upon in the first half of thesis by increasing the colloidal stability of nanoparticles by surface and/or medium modification. It is shown that the narrow range of pH in which the colloidal CNPs are stable can be extended by changing the medium from water to polyhydroxy compounds such as glucose and dextran. The synthesis was designed specially to avoid the traditional precipitation and re-dispersion strategy of synthesis of nanoparticles to preserve the surface activity. The complex forming ability of cerium with polysaccharides was employed to synthesize the CNPs in a one step process and the pH stability of the NPs was extended between 2.0 to 9.5. The difference in the complexing ability of the monomer - glucose and its anhydro glucose polymer - dextran is reflected in the ability of cerium to form super-agglomerates with the monomer while anhydro gluco polymer forms extremely disperse 3-5 nm nanoparticles through steric modification. It is shown that the antioxidant activity of nanoparticles remain unchanged by surface modification by demonstrating the cycling of the oxidation state of cerium in CNPs, with time, through hydrogen peroxide mediated transition of oxidation states of cerium. It is demonstrated that the polymeric coatings, generally considered as passive surface coatings, can also play an active role in tuning the properties of nanomaterials and increasing their biocompatibility as well as bio-catalytic activity. It is demonstrated that the antioxidant activity of CNPs can be increased as a function of polyethylene glycol (PEG) while the biocompatibility is unaltered due to the biocompatible nature of PEG. The antioxidant activity of CNPs involves an electron transfer (ET) from the CNPs to the reactive oxygen species or vice versa. This heterogeneous ET system is further complicated by the presence of surface adsorbed species. Interfacial charge/electron transfer (ET) between a particle and adsorbed (or covalently bonded) molecule presents significant complexity as it involves a solid state electron transfer over long distance. Unlike a free ion, in solid state, the conducting electrons can be temporarily trapped by the coupling lattice sites. Adsorption/attachment of surface species to nanoparticle can disturb the electronic levels by further polarizing the electron cloud thereby localizing the electron and facilitating the charge transfer. Such an interfacial electron transfer between NPs and adsorbed organic species can be compared to the single electron transfer carried by organometallic systems with a metal ion core modified with electron delocalizing porphyrin ligands. It is demonstrated that in this PEGyltaed CNPs system, the PEG essentially forms a complex with CNPs in the presence of hydrogen peroxide to facilitate this electron transfer process. The superoxide dismutase (SOD) and catalase mimetic ability of CNPs is described and special emphasis is given to its biocompatibility. The second half of the thesis emphasizes the role of synthesis and surface modification in influencing the catalytic performance of cerium oxide modified titanium dioxide catalysts for decomposition of methanol. Noble metals supported on oxide nanoparticles have been an area of active research in catalysis. It is demonstrated that the modification of surface of the oxide nanoparticles by noble metals is a function of the synthesis process. By keeping the size of the nanoparticles constant, it was demonstrated that the differences in the oxidation state of noble metals can lead to change in the activity of noble metals. This contribution adds to the already existing controversy in the open literature about the role of the oxidation state of platinum in catalysis. The core level shifts in the binding energy of the 4f electrons of platinum was used as a guide to the gauge the oxidation state. Results from an in-house built catalytic reactor coupled to mass spectrometer and in-situ diffuse reflectance infra-red spectroscopy are used to quantify the catalytic performance and identify the mechanism of reaction as well as products of methanol decomposition.
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Date Issued: 2010
Identifier: CFE0003189, ucf:48590
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003189

Title: Cerium Oxide Nanoparticles Sensitize Pancreatic Cancer Cells to Radiation by Promoting Acidic pH, ROS, and JNK Dependent Apoptosis.
Creator: Wason, Melissa, Zhao, Jihe, Self, William, Altomare, Deborah, Baker, Cheryl, University of Central Florida
Abstract / Description: Side effects of radiation therapy (RT) remain the most challenging issue for pancreatic cancer treatment. In this report we determined whether and how cerium oxide nanoparticles (CONPs) sensitize pancreatic cancer cells to RT. CONP pretreatment enhanced radiation-induced reactive oxygen species (ROS) production preferentially in acidic cell-free solutions as well as acidic human pancreatic cancer cells. In acidic environments, CONPs favor the scavenging of superoxide radical over the hydroxyl...
Show moreSide effects of radiation therapy (RT) remain the most challenging issue for pancreatic cancer treatment. In this report we determined whether and how cerium oxide nanoparticles (CONPs) sensitize pancreatic cancer cells to RT. CONP pretreatment enhanced radiation-induced reactive oxygen species (ROS) production preferentially in acidic cell-free solutions as well as acidic human pancreatic cancer cells. In acidic environments, CONPs favor the scavenging of superoxide radical over the hydroxyl peroxide resulting in accumulation of the latter whereas in neutral pH CONPs scavenge both. CONP treatment prior to RT markedly potentiated the cancer cell apoptosis both in culture and in tumors and the inhibition of the pancreatic tumor growth without harming the normal tissues or host mice. Mechanistically, CONPs were not able to significantly impact RT-induced DNA damage in cancer cells, thereby ruling out sensitization through increased mitotic catastrophe. However, JNK activation, which is known to be a key driver of RT-induced apoptosis, was significantly upregulated by co-treatment with CONPs and RT in pancreatic cancer cells in vitro and human pancreatic tumors in nude mice in vivo compared to CONPs or RT treatment alone. Further, CONP-driven increase in RT-induced JNK activation was associated with marked increases in Caspase 3/7 activation, indicative of apoptosis. We have shown CONPs increase ROS production in cancer cells; ROS has been shown to drive the oxidation of thioredoxin (TRX) 1 which results in the activation of Apoptosis Signaling Kinase (ASK) 1. The dramatic increase in ASK1 activation following the co-treatment of pancreatic cancer cells with CONPs followed by RT in vitro suggests that increased the c-Jun terminal kinase (JNK) activation is the result of increased TRX1 oxidation. The ability of CONPs to sensitize pancreatic cancer cells to RT was mitigated when the TRX1 oxidation was prevented by mutagenesis of a cysteine residue, or the JNK activation was blocked by an inhibitor,. Additionally, angiogenesis in pancreatic tumors treated with CONPs and RT was significantly reduced compared to other treatment options. Taken together, these data demonstrate an important role and mechanisms for CONPs in specifically killing cancer cells and provide novel insight into the utilization of CONPs as a radiosensitizer and therapeutic agent for pancreatic cancer.
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Date Issued: 2013
Identifier: CFE0005116, ucf:50725
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005116

Title: Redox-Active Solid State Materials and its Biomedical and Biosensing Applications.
Creator: Gupta, Ankur, Seal, Sudipta, Dong, Yajie, Cho, Hyoung Jin, Zhai, Lei, Schulte, Alfons, University of Central Florida
Abstract / Description: 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.
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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: Dowding, Janet, Self, William, Bossy-Wetzel, Ella, Zervos, Antonis, Seal, Sudipta, Santra, Swadeshmukul, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2012
Identifier: CFE0004782, ucf:49783
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004782

Title: TAILORING THE PROPERTIES OF POLYELECTROLYTE COATED CERIUM OXIDE NANOPARTICLES AS A FUNCTION OF MOLECULAR WEIGHT.
Creator: Saraf, Shashank, Seal, Sudipta, Cho, Hyoung, Zhai, Lei, Heinrich, Helge, Harper, James, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2013
Identifier: CFE0005410, ucf:50410
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005410

Title: PROBING AND TUNING THE SIZE, MORPHOLOGY, CHEMISTRY AND STRUCTURE OF NANOSCALE CERIUM OXIDE.
Creator: Kuchibhatla, Satyanarayana, Seal, Sudipta, University of Central Florida
Abstract / Description: Cerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be...
Show moreCerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be enhanced in the nanoceria. In most the practical scenarios, it is necessary to have a stable suspension of ceria nanoparticles (CNPs) over longer periods of time. However, the existing literature is confined to short term studies pertaining to synthesis and property evaluation. Having understood the need for a comprehensive understanding of the CNP suspensions, this dissertation is primarily aimed at understanding the behavior of CNPs in various chemical and physical environments. We have synthesized CNPs in the absence of any surfactants at room temperature and studied the aging characteristics. After gaining some understanding about the behavior of this functional oxide, the synthesis environment and aging temperature were varied, and their affects were carefully analyzed using various materials analysis techniques such as high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS). When the CNPs were aged at room temperature in as-synthesized condition, they were observed to spontaneously assemble and evolve as fractal superoctahedral structures. The reasons for this unique polycrystalline morphology were attributed to the symmetry driven assembly of the individual truncated octahedral and octahedral seed of the ceria. HRTEM and Fast Fourier Transform (FFT) analyses were used to explain the agglomeration behavior and evolution of the octahedral morphology. Some of the observations were supported by molecular dynamic simulations. Poly (ethylene glycol) (PEG) and ethylene glycol (EG) were used to control the kinetics of this morphology evolution. The ability to control the agglomeration of CNPs in these media stems from the lower dielectric constant and an increased viscosity of the EG and PEG based solvents. CNPs when synthesized and aged in frozen conditions, i.e. in ice, were found to form one dimensional, high aspect ratio structures. A careful analysis has provided some evidence that the CNPs use the porous channels in ice as a template and undergo oriented attachment to form nanorods. When the aging treatment was done near freezing temperature in solution, the nanorods were not observed, confirming the role of channels in ice. When synthesized in aqueous media such as DI water, PEG and EG; CNPs were observed to exhibit a reversible oxidation state switching between +3 and +4. Band gap values were computed from the optical absorption data. The changes in the band gap values observed were attributed to the changes in the oxidation state of CNPs as opposed to the quantum confinement effects, as expected in other nanoparticle systems. The work presented in this dissertation demonstrates, with evidence, that in order to obtain a comprehensive understanding of the properties of nanoscale materials it is of paramount importance to monitor their behavior over relatively longer periods of time under various ambient environments. While the solution based techniques offer a versatility and low cost route to study the fundamental properties of nanomaterials, they suffer some inherent problems such as precursor contamination and uncontrolled chemical reactions. Especially when analyzing the behavior of ceria-based materials for applications like solid oxide fuel cells, a great control in the density and crystalline quality are desired. In order to achieve this, as a first step pure ceria thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE). The ceria films were analyzed using various in situ and ex situ techniques to study the crystal structure, growth mode and epitaxial quality of the films. It was observed that the epitaxial orientation of the ceria films could be tuned by varying the deposition rate. When the films were grown at low deposition rate (< 8 Å/min) ceria films with epitaxial (200) orientation were observed where as the films grown at high deposition rates (up to 30 Å/min) showed (111) orientation. Theoretical simulations were used to confirm some of the experimental facts observed in both nanoparticles and thin films.
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Date Issued: 2008
Identifier: CFE0002163, ucf:47499
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002163

Title: The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests.
Creator: Pearman, Benjamin, Hampton, Michael, Blair, Richard, Clausen, Christian, Seal, Sudipta, Campiglia, Andres, Yestrebsky, Cherie, Mohajeri, Nahid, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2012
Identifier: CFE0004789, ucf:49731
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004789

Nanoparticles (4)	+ -
cerium oxide nanoparticles (4)	+ -
Cerium Oxide (3)	+ -
Cerium oxide nanoparticles (3)	+ -
cerium oxide (3)	+ -

Ceria (2)	+ -
Cerium Oxide Nanoparticles (2)	+ -
Cerium oxide (2)	+ -
Modeling (2)	+ -
biosensor (2)	+ -
catalysis (2)	+ -
nanoparticles (2)	+ -
phosphatase (2)	+ -
surface chemistry (2)	+ -
Accelerated durability (1)	+ -
Agglomeration (1)	+ -
Alzheimer's disease (1)	+ -
Angiogenesis (1)	+ -
Antimicrobial Resistance (1)	+ -
Apoptosis (1)	+ -
Atomic layer deposition (1)	+ -
Band Gap (1)	+ -
Characterization (1)	+ -
Coatings (1)	+ -
Corrosion (1)	+ -
Defects (1)	+ -
Degradation (1)	+ -
Degradation mechanisms (1)	+ -
Degradation mitigation (1)	+ -
Desulfovibrio alaskensis G20 (1)	+ -

ETD Collection (17)	+ -
Honors Collection (2)	+ -

University of Central Florida (19)	+ -
Seal, Sudipta (13)	+ -
Heinrich, Helge (6)	+ -
Zhai, Lei (5)	+ -
Self, William (4)	+ -

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