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 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.

Thermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of producing a variety of customizable microstructures as well as non-line-of-sight deposition, which allows more complex geometries to be coated, or even multiple parts at once. The pseudo-columnar microstructure that can be produced with PS-PVD is a possible alternative to EB-PVD. However, before PS-PVD can be used to its full potential, its mechanical properties and behavior must be understood. This work contributes to this understanding by characterizing PS-PVD TBCs that have been thermally cycled to simulate multiple lifetimes (0, 300, and 600 thermal cycles). Residual stress in the thermally grown oxide (TGO) layer is characterized by photoluminescence piezospectroscopy as TGO residual stress is correlated with the lifetime of the coating. Residual stress in the top coat is characterized by Raman spectroscopy, because this stress drives cracking in the top coat that can lead to failure. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are performed to observe microstructural and phase evolution to provide context and possible explanations for the stress results. In addition, EB-PVD samples of the same thermal cycling history are characterized in the same way so that PS-PVD can be benchmarked against the industry standard. The compressive residual stress in the TGO in both coatings was relieved with thermal cycling due to the TGO lengthening as well as microcracking. The PS-PVD samples had slightly lower TGO stress than the EB-PVD, which is attributed to the greater extent of cracking within the TGO, whereas cracking in the EB-PVD samples was at the TGO/topcoat interface. The PS-PVD cycled samples had significant cracking within the topcoat near the TGO due to both greater porosity than EB-PVD samples and regions of unmelted particles that provide little resistance to cracking. The greater convolution of the TGO in the PS-PVD samples results in greater out-of-plane tensile stresses that cause crack initiation, as well as diverts cracks away from the difficult-to-follow interface. The TGO stress results agree with existing literature and extend the thermal cycling beyond what has previously been reported for PS-PVD coatings, revealing a trend of stress relief and stress values similar to that of EB-PVD coatings in this study and in the literature. Residual stress in the topcoat for both coating types became increasingly compressive with thermal cycling, indicating loss of strain tolerance by sintering. The trend of the YSZ stress for both coating types to become more compressive with cycling and with depth agrees with the literature, and the thermal cycling is longer than has been previously reported for PS-PVD. The two coating types had quite different microstructures and crack modes as well as different as-deposited residual stresses, but after thermal cycling had similar stresses in both the TGO and top coat. No samples experienced spallation. These results indicate that, while PS-PVD coatings have different properties and behavior from EB-PVD coatings, they had comparable levels of damage to EB-PVD coatings of the same lifetime and are a viable alternative to EB-PVD. Further tuning of the processing parameters may result in PS-PVD coatings with even more similar behavior to EB-PVD coatings.

Lithium ion batteries (LIBs) have been used in various applications such as portable electronics, grid storages, and electric vehicles (EVs). Despite its commercial success, further advancement of the battery is necessary to satisfy the increasing demands for low-cost and high- performance energy storage devices as LIB is reaching its theoretical limits. Lithium sulfur battery (LSB) is one of the promising candidates for the next generation energy storage technologies. LSB uses sulfur cathode which is a low-cost and earth abundant material with an extremely high theoretical capacity of 2600 Wh kg-1. Although there have been numerous researches aiming to establish the LSB technology, it is still in a development stage. Some of the major challenges are; low-electric conductivity, dissolution of the intermediate lithium-polysulfide reactants, and the low Coulombic efficiency. These issues must be overcome before LSBs can become practical. The objective of this work is to develop an LSB cathode that solves the above issues and contributes to advancing the development of the LSB technology. We focus on improving the electrical conductivity while reducing the shuttle effect, a parasitic reaction of the polysulfides at the anode lithium surface. To achieve this goal, we developed a carbon black coated free-standing carbon cloth. It is infiltrated with a Li2S8-containing catholyte as an active material, and its carbon framework serves as an entrapment of the polysulfides. The electrode composite enabled high- sulfur-loading, and its high surface area increased the reaction sites allowing the effective utilization of the sulfur that lead to the high capacity. It also showed high capacity retention by successfully trapping the polysulfides within the electrode. This facile and low-cost solution contributes to the realization of the LSBs.

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 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¯ and Cl¯ 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.

Emerging societal challenges such as the need for more sustainable energy and catalysis are requiring more sensitive and versatile measurements at the nanoscale. This is the case in the design and optimization of new materials for energy harvesting (solar cells) and energy storage devices (batteries and capacitors), or for the development of new catalysts for carbon sequestration or other reactions of interest. Hence, the ability to advance spectroscopy with nanoscale spatial resolution and high sensitivity holds great promises to meet the demands of deeper fundamental understanding to boost the development and deployment of nano-based devices for real applications. In this dissertation, the impact of nanoscale characterization on energy-related and catalytic materials is considered. Firstly an introduction of the current energy and environmental challenges and our motivations are presented. We discuss how revealing nanoscale properties of solar cell active layers and supercapacitor electrodes can greatly benefit the performance of devices, and ponder on the advantages over conventional characterization techniques. Next, we focus on two dimensional materials as promising alternative catalysts to replace conventional noble metals for carbon sequestration and its conversion to added-value products. Defect-laden hexagonal boron nitride (h-BN) has been identified as a good catalyst candidate for carbon sequestration. Theoretically, defects exhibit favorable properties as reaction sites. However, the detailed mechanism pathways cannot be readily probed experimentally, due to the lack of tools with sufficient sensitivity and time resolution. A comprehensive study of the design and material processes used to introduce defects in h-BN in view of improving the catalytic properties is presented. The processing-structure-property relationships are investigated using a combination of conventional characterization and advanced nanoscale techniques. In addition to identifying favorable conditions for defect creation, we also report on the first signs of local reactions at defect sites obtained with nanoscale spectroscopy. Next, we explore avenues to improve the sensitivity and time-resolution of nanoscale measurements using light-assisted AFM-based nanomechanical spectroscopy. For each configuration, we evaluate the new system by comparing its performance to the commercial capabilities. Lastly, we provide a perspective on the opportunities for state-of-the-art characterization to impact the fields of catalysis and sustainable energy, as well as the urge for highly sensitive functional capabilities and time-resolution for nanoscale studies.

In the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedance spectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150°C, as well as different annealing temperatures (1100-1400 °C). All spectra, regardless of temperature and bias, consist of two semi-circular arcs, corresponding to the free-carbon phase and the interface, respectively. The impedance of the free-carbon phase is independent of the bias, while that of the interface decreased significantly with increasing dc bias. It is shown that the change of the interfacial capacitance with the bias can be explained using the double Schottky barrier model. The charge-carrier concentration and potential barrier height were estimated by comparing the experimental data and the model. The results revealed that increasing testing temperature led to an increased charge-carrier concentration and a reduced barrier height, both following Arrhenius dependence, whereas the increase in annealing temperature resulted in increased charge-carrier concentration and barrier height. The phenomena were explained in terms of the unique bi-phasic microstructures of the material. The research findings reveal valuable microstructural information of temperaturedependent properties of polymer derived ceramics, and should contribute towards more precise understanding and control of the electrical as well as dielectric properties of polymer derived ceramics. Furthermore, the desalination performances and underlying mechanisms of two-dimensional CVD-grown MoS2 layers membranes have been experimentally assessed. Based on a successful large-area few-layer 2D materials growth, transfer and integration method, the 2D MoS2 layers membranes showed preserved chemical and microstructural integrity after integration. The few-layer 2D MoS2 layers demonstrated superior desalination capability towards various types of seawater salt solutions approaching theoretically-predicted values. Such performances are attributed to the dimensional and geometrical effect, as well as the electrostatic interaction of the inherently-present CVD-induced atomic vacancies for governing both water permeation and ionic sieving at the solution/2D-layer interfaces.

In the clinical setting, polyvinyl chloride (PVC) accounts for 25% of all polymers used in medical device applications. However, medical devices fabricated with PVC, such as endotracheal tubes, extracorporeal circuits (ECCs), or intravenous catheters suffer from thrombosis and infection. Mortality associated with hospital associated infections (HAIs) exceed 100,000 deaths each year. One method to overcome these challenges is to develop bioactive polymers with nitric oxide (NO) release. Nitric oxide exhibits many physiological roles including, antibacterial, antithrombic, anti-inflammatory activity. In this study, Tygon® PVC tubing was impregnated with a NO donor molecule, S-nitroso-N-acetylpenicillamine (SNAP), via a simple solvent-swelling-impregnation method, where polymer samples were submerged in a SNAP impregnation-solvent (methanol, acetone, plasticizer). An additional topcoat of a biocompatible CarboSil 2080A (CB) was applied to reduce SNAP leaching. The SNAP-PVC-CB were characterized for NO release using chemiluminescence, leaching with UV-Vis spectroscopy, surface characterization with scanning electron microscopy, tensile strength analysis, stability during storage and sterilization, and antimicrobial properties in vitro. The SNAP-PVC-CB exhibited NO flux of 4.29 ± 0.80 x 10-10 mol cm-2 min-1 over the initial 24 h under physiological conditions and continued to release physiological levels of NO for up 14 d (incubated in PBS at 37 °C). The addition of CB-topcoat reduced the total SNAP leaching by 86% during incubation. Mechanical properties and surface topography remained similar to original PVC after SNAP-impregnation and application of CB-topcoat. After ethylene oxide sterilization and 1-month storage, SNAP-PVC-CB demonstrated excellent SNAP stability (ca. 90% SNAP remaining). In a 24 h antibacterial assay, SNAP-PVC reduce viable bacteria colonization (ca. 1 log reduction) of S. aureus and E. coli compared to PVC controls. This novel method for SNAP-impregnation of medical grade plasticized PVC holds great potential for improving the biocompatibility of post-fabricated PVC medical devices.

Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities. An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop. An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.

No description available.

No description available.