Microfluidics has enabled many biological and biochemical applications such as high-throughput drug testing or point-of-care diagnostics. Dielectrophoresis (DEP) has recently achieved prominence as a powerful microfluidic technique for nanoparticle separation. Novel electric field-assisted insulator-based dielectrophoresis (iDEP) microfluidic devices have been employed to fractionate rod-shaped nanoparticles like Single-walled carbon nanotubes (SWNTs) and manipulate biomolecules like Deoxyribonucleic acid (DNA) and proteins. This dissertation involves the development of traditional as well as 3D-printed iDEP devices for the manipulation of nm-to-µm scale analytes. First, novel iDEP microfluidic constriction-based sorting devices were developed to introduce inhomogeneous electric field gradients to fractionate SWNTs by length. SWNTs possess length-specific optical and electrical properties, expanding their potential applications for future nanoscale devices. Standard synthesis procedures yield SWNTs in large-length polydispersity and chirality. Thus, an iDEP-based fractionation tool for desired lengths of SWNTs may be beneficial. This dissertation presents the first study of DEP characterization and fractionation of SWNTs using an iDEP microfluidic device. Using this iDEP constriction sorter device, two different length distributions of SWNTs were sorted with a sorting efficiency of >90%. This study provides the fundamentals of fractionating SWNTs by length, which can help separate and purify SWNTs for future nanoscale-based applications. Manipulation of nm-scale analytes requires achieving high electric field gradients in an iDEP microfluidic device, posing one of the significant challenges for DEP applications. Introducing nm-sized constrictions in an iDEP device can help generate a higher electric field gradient. However, this requires cumbersome and expensive fabrication methods. In recent years, 3D printing has drawn tremendous attention in microfluidics, alleviating complications associated with complex fabrication methods. A high-resolution 3D-printed iDEP device was developed and fabricated for iDEP-based manipulation of analytes. A completely 3D-printed device with 2 µm post-gaps was realized, and fluorescent polystyrene (PS) beads, λ-DNA, and phycocyanin protein trapping were demonstrated. Furthermore, a nm-resolution 3D-printed iDEP device was successfully printed. In the future, these high-resolution 3D-printed devices may lead to exploring DEP characteristics of nanoscale analytes like single protein molecules and viruses. The electric field-assisted unique fractionation phenomena in microfluidic platforms will become a critical solution for nanoparticle separation and manipulating biomolecules.

Understanding cellular processes can provide insight into disease pathogenesis and reveal critical information for prevention, diagnosis, and treatment. As key executors and signaling regulators, proteins carry relevant information not available from genomics and transcriptomics. Cell-to-cell differences significantly affect disease incidence and drug responses, generating a need for protein analysis at the single-cell level. However, quantitative protein analysis at the single-cell level remains challenging due to the low protein amount in a single cell and the proteome complexity. It requires sensitive detection techniques and appropriate sample preparation and delivery to the detection area. Here, a microfluidic platform in tandem with matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) has been developed for targeted intracellular protein analysis. The elastomeric multi-layer microfluidic platform, termed MIMAS, was designed as a series of 8.75 nL wells separated by pneumatic valves. The MIMAS platform allows cell loading, sample processing on-chip, and further in situ mass spectrometry analysis. The sample processing includes cell lysis, immunocapture, tryptic digestion and MALDI matrix solution loading for co-crystallization. This work demonstrates that the MIMAS approach is suitable for protein quantification by assessing the apoptotic protein Bcl-2 from MCF-7 breast cancer cells using an isotope-labeled peptide. The limit of detection was determined as 11.22 nM, equivalent to 5.91 x 10^7 protein molecules per well. Moreover, the MIMAS platform design was improved, allowing the successful quantification of Bcl-2 protein in small cell ensembles down to ~10 cells in 4 nL wells. Furthermore, the MIMAS platform was integrated with laser capture microdissection (LCM) for protein analysis from post-mortem human tissues. Intracellular amyloid-β peptide (Aβ), a hallmark of Alzheimer’s Disease, was assessed from human brain tissue using the LCM-MIMAS. The successful detection of Aβ from small cell ensembles (20 sliced pyramidal cells) demonstrated the LCM-MIMAS capability of assessing intracellular proteins from specific tissue cell subpopulations. The MIMAS approach is a promising tool for intracellular protein analysis from small cell ensembles, with the potential for single-cell analysis. It allows for protein analysis towards the understanding of biological phenomena for clinical and biological research.

Disease prevention and personalized treatment will be impacted by the continued integration of protein biomarkers into medical practice. While there are already numerous biomarkers used clinically, the detection of protein biomarkers among complex matrices remains a challenging problem. One very important strategy for improvements in clinical application of biomarkers is separation/preconcentration, impacting the reliability, efficiency and early detection. Electrophoretic exclusion can be used to separate, purify, and concentrate biomarkers. This counterflow gradient technique exploits hydrodynamic flow and electrophoretic forces to exclude, enrich, and separate analytes. The development of this technique has evolved onto an array-based microfluidic platform which offers a greater range of geometries/configurations for optimization and expanded capabilities and applications. Toward this end of expanded capabilities, fundamental studies of subtle changes to the entrance flow and electric field configurations are investigated. Three closely related microfluidic interfaces are modeled, fabricated and tested. A charged fluorescent dye is used as a sensitive and accurate probe to test the concentration variation at these interfaces. Models and experiments focus on visualizing the concentration profile in areas of high temporal dynamics, and show strong qualitative agreement, which suggests the theoretical assessment capabilities can be used to faithfully design novel and more efficient interfaces. Microfluidic electrophoretic separation technique can be combined with electron microscopy as a protein concentration/purification step aiding in sample preparation. The integrated system with grids embedded into the microdevice reduces the amount of time required for sample preparation to less than five minutes. Spatially separated and preconcentrated proteins are transferred directly from an upstream reservoir onto grids. Dilute concentration as low as 0.005 mg/mL can be manipulated to achieve meaningful results. Selective concentration of one protein from a mixture of two proteins is also demonstrated. Electrophoretic exclusion is also used for biomarker applications. Experiments using a single biomarker are conducted to assess the ability of the microdevice for enrichment in central reservoirs. A mixture of two protein biomarkers are performed to evaluate the proficiency of the device for separations capability. Moreover, a battery is able to power the microdevice, which facilitates the future application as a portable device.

In this dissertation, micro-galvanic corrosion effects and passivation behavior of single-phase binary alloys have been studied in order to formulate new insights towards the development of “stainless-like” lightweight alloys. As a lightweight material of interest, Mg-xAl alloys were studied using aqueous free corrosion, atmospheric corrosion, dissolution rate kinetics, and ionic liquid dissolution. Polarization and “accelerated” free corrosion studies in aqueous chloride were used to characterize the corrosion behavior and morphology of alloys. Atmospheric corrosion experiments revealed surface roughness and pH evolution behavior in aqueous environment. Dissolution in absence of water using choline-chloride:urea ionic liquid allowed for a simpler dissolution mechanism to be observed, providing additional insights regarding surface mobility of Al. These results were compared with commercial alloy (AZ31B, AM60, and AZ91D) behavior to better elucidate effects associated with secondary phases and intermetallic particles often present in Mg alloys. Aqueous free corrosion, “accelerated” free corrosion and ionic liquid dissolution studies have confirmed Al surface enrichment in a variety of morphologies, including Al-rich platelet and Al nanowire formation. This behavior is attributed to the preferential dissolution of Al as the more “noble” element in the matrix. Inductively-coupled mass spectroscopy was used to measure first-order rate reaction constants for elemental Mg and Al dissolution in aqueous chloride environment to be kMg= 9.419 x 10-6 and kAl = 2.103 x 10-6 for future implementation in kinetic Monte Carlo simulations. To better understand how “stainless-like” passivation may be achieved, Ni-xCr alloys were studied using polarization and potential pulse experiments. The passivation potential, critical current density, and passivation current density were found to decay with increasing Cr composition. The measured average number of monolayers dissolved during passivation was found to be in good agreement with percolation theory, with a fitted 3-D percolation threshold of p_c^3D=0.118 compared with the theoretical value of 0.137. Using these results, possible approaches towards achieving passivation in other systems, including Mg-Al, are discussed.

Photocatalytic water splitting has been proposed as a promising way of generating carbon-neutral fuels from sunlight and water. In one approach, water decomposition is enabled by the use of functionalized nano-particulate photocatalyst composites. The atomic structures of the photocatalysts dictate their electronic and photonic structures, which are controlled by synthesis methods and may alter under reaction conditions. Characterizing these structures, especially the ones associated with photocatalysts’ surfaces, is essential because they determine the efficiencies of various reaction steps involved in photocatalytic water splitting. Due to its superior spatial resolution, (scanning) transmission electron microscopy (STEM/TEM), which includes various imaging and spectroscopic techniques, is a suitable tool for probing materials’ local atomic, electronic and optical structures. In this work, techniques specific for the study of photocatalysts are developed using model systems.

Nano-level structure-reactivity relationships as well as deactivation mechanisms of Ni core-NiO shell co-catalysts loaded on Ta2O5 particles are studied using an aberration-corrected TEM. It is revealed that nanometer changes in the shell thickness lead to significant changes in the H2 production. Also, deactivation of this system is found to be related to a photo-driven process resulting in the loss of the Ni core.

In addition, a special form of monochromated electron energy-loss spectroscopy (EELS), the so-called aloof beam EELS, is used to probe surface electronic states as well as light-particle interactions from model oxide nanoparticles. Surface states associated with hydrate species are analyzed using spectral simulations based on a dielectric theory and a density of states model. Geometry-induced optical-frequency resonant modes are excited using fast electrons in catalytically relevant oxides. Combing the spectral features detected in experiments with classical electrodynamics simulations, the underlying physics involved in this excitation process and the various influencing factors of the modes are investigated.

Finally, an in situ light illumination system is developed for an aberration-corrected environmental TEM to enable direct observation of atomic structural transformations of model photocatalysts while they are exposed to near reaction conditions.

This work describes the investigation of novel cathode and anode materials. Specifically, several mixed polyanion compounds were evaluated as cathodes for Li and Na-ion batteries. Clathrate compounds composed of silicon or germanium arranged in cage-like structures were studied as anodes for Li-ion batteries.

Nanostructured Cu4(OH)6SO4 (brochantite) platelets were synthesized using polymer-assisted titration and microwave-assisted hydrothermal methods. These nanostructures exhibited a capacity of 474 mAh/g corresponding to the full utilization of the copper redox in an conversion reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies were preformed to understand the mechanism and structural changes.

A microwave hydrothermal synthesis was developed to prepare a series compounds based on jarosite, AM3(SO4)2(OH)6 (A = K, Na; M = Fe, V). Both the morphology and electrochemical properties showed a compositional dependence. At potentials >1.5 V vs. Li/Li+, an insertion-type reaction was observed in Na,Fe-jarosite but not in K,Fe-jarosite. Reversible insertion-type reactions were observed in both vanadium jarosites between 1 – 4 V with capacities around 40 - 60 mAh/g. Below 1 V vs. Li/Li+, all four jarosite compounds underwent conversion reactions with capacities ~500 mAh/g for the Fe-jarosites.

The electrochemical properties of hydrogen titanium phosphate sulfate, H0.4Ti2(PO4)2.4(SO4)0.6 (HTPS), a new mixed polyanion material with NASICON structure was reported. A capacity of 148 mAh/g corresponding to2 Li+ insertion per formula unit was observed. XRD and XPS were used to characterize the HTPS before and after cycling and to identify the lithium sites. Evaluation of the HTPS in Na-ion cell was also performed, and a discharge capacity of 93 mAh/g was observed.

A systematic investigation of the role of the processing steps, such as ball-milling and acid/base etching, on the electrochemical properties of a silicon clathrate compound with nominal composition of Ba8Al16Si30 was performed. According to the transmission electron microscope (TEM), XPS, and electrochemical analysis, very few Li atoms can be electrochemically inserted, but the introduction of disorder through ball-milling resulted in higher capacity, while the oxidation layer made by the acid/base treatment prevented the reation. The electrochemical property of germanium clathrate was also investigated, unlike the silicon clathrate, the germanium one underwent a conversion reaction.

Studying charge transport through single molecules is of great importance for unravelling charge transport mechanisms, investigating fundamentals of chemistry, and developing functional building blocks in molecular electronics.

First, a study of the thermoelectric effect in single DNA molecules is reported. By varying the molecular length and sequence, the charge transport in DNA was tuned to either a hopping- or tunneling-dominated regimes. In the hopping regime, the thermoelectric effect is small and insensitive to the molecular length. Meanwhile, in the tunneling regime, the thermoelectric effect is large and sensitive to the length. These findings indicate that by varying its sequence and length, the thermoelectric effect in DNA can be controlled. The experimental results are then described in terms of hopping and tunneling charge transport models.

Then, I showed that the electron transfer reaction of a single ferrocene molecule can be controlled with a mechanical force. I monitor the redox state of the molecule from its characteristic conductance, detect the switching events of the molecule from reduced to oxidized states with the force, and determine a negative shift of ~34 mV in the redox potential under force. The theoretical modeling is in good agreement with the observations, and reveals the role of the coupling between the electronic states and structure of the molecule.

Finally, conclusions and perspectives were discussed to point out the implications of the above works and future studies that can be performed based on the findings.

Over the last few decades, homogeneous molybdenum catalysis has been a center of interest to inorganic, organic, and organometallic chemists. Interestingly, most of the important advancements in molybdenum chemistry such as non-classical dihydrogen coordination, dinitrogen reduction, olefin metathesis, and water reduction utilize diverse oxidation states of the metal. However, employment of redox non-innocent ligands to tune the stability and reactivity of such catalysts have been overlooked. With this in mind, the Trovitch group has developed a series of novel bis(imino)pyridine (or pyridine diimine, PDI) and diimine (DI) ligands that have coordinating phosphine or amine arms to exert coordination flexibility to the designed complexes. The research described in this dissertation is focused on the development of molybdenum catalysts that are supported by PDI and DI chelates and their application in small molecule activation.

Using the phosphine containing PDI chelate, Ph2PPrPDI, several low-valent molybdenum complexes have been synthesized and characterized. While the zerovalent monocarbonyl complex, (Ph2PPrPDI)MoCO, catalyzes the reduction of aldehyde C=O bonds, the C-H activated Mo(II) complex, (6-P,N,N,N,C,P-Ph2PPrPDI)MoH was found to be the first well-defined molybdenum catalyst for reducing carbon dioxide to methanol. Along with low- oxidation state compounds, a Mo(IV) complex, [(Ph2PPrPDI)MoO][PF6]2 was also synthesized and utilized in electrocatalytic hydrogen production from neutral water. Moreover, with the proper choice of reductant, an uncommon Mo(I) oxidation state was stabilized and characterized by electron paramagnetic resonance spectroscopy and single crystal X-ray diffraction.

While the synthesized (PDI)Mo complexes unveiled versatile reduction chemistry, varying the ligand backbone to DI uncovered completely different reactivity when bound to molybdenum. Unlike PDI, no chelate-arm C-H activation was observed with the propyl phosphine DI, Ph2PPrDI; instead, a bis(dinitrogen) Mo(0) complex, (Ph2PPrDI)Mo(N2)2 was isolated. Surprisingly, this complex was found to convert carbon dioxide into dioxygen and carbon monoxide under ambient conditions through a novel tail-to-tail CO2 reductive coupling pathway. Detailed experimental and theoretical studies are underway to gain further information about the possible mechanism of Mo mediated direct conversion of CO2 to O2.

This investigation is divided into two portions linked together by the momentous reaches of electrochemistry science, principles influencing everyday phenomena as well as innovative research in the field of energy transformation. The first portion explores the strategies for flue gas carbon dioxide capture and release using electrochemical means. The main focus is in the role thiolates play as reversible strong nucleophiles with the ability to capture CO2 and form thiocarbonates. Carbon dioxide in this form is transported and separated from thiocarbonate through electrochemical oxidation to complete the release portion of this catch-and-release approach. Two testing design systems play a fundamental role in achieving an efficient CO2 catch and release process and were purposely build and adapted for this work. A maximum faradaic efficiency of seventeen percent was attained in the first membrane tests whose analysis is presented in this work. An efficiency close to thirty percent was attained with the membrane cell in recent experiments but have not been included in this manuscript.

The second portion of this manuscript studies bulk stress evolution resulting from insertion/extraction of lithium in/from a lithium manganese oxide spinel cathode structure. A cantilever-based testing system uses a sophisticated, high resolution capacitive technique capable of measuring beam deflections of the cathode in the subnanometer scale. Tensile stresses of up to 1.2 MPa are reported during delithiation along with compressive stresses of 1.0 MPa during lithiation. An analysis of irreversible charge loss is attributed to surface passivation phenomena with its associated stresses of formation following patterns of tensile stress evolution.

The late first row transition metals, being inexpensive and environmentally benign, have become very attractive for sustainable catalyst development. However, to overcome the detrimental one electron redox processes exhibited by these metals, the employment of redox non-innocent chelates turned out to be very useful. The Trovitch group has designed a series of pentadentate bis(imino)pyridine ligands (pyridine diimine, PDI) that are capable of binding the metal center beyond their 3-N,N,N core and also possess coordination flexibility. My research is focused on developing PDI-supported manganese catalysts for organic transformations and renewable fuel production.

The thesis presents synthesis and characterization of a family of low valent (PDI)Mn complexes. Detailed electronic structure evaluation from spectroscopic and crystallographic data revealed electron transfer from the reduced metal center to the accessible ligand orbitals. One particular (PDI)Mn variant, (5-Ph2PPrPDI)Mn has been found to be the most efficient carbonyl hydrosilylation catalyst reported till date, achieving a maximum turnover frequency of up to 4950 min-1. This observation demanded a thorough investigation of the operative mechanism. A series of controlled stoichiometric reactions, detailed kinetic analysis, and relevant intermediate isolation suggest a mechanism that involves oxidative addition, carbonyl insertion, and reductive elimination. Noticing such remarkable efficiency of the (PDI)Mn system, it has been tested for application in renewable fuel generation. A modest efficiency for H2 production at an apparent pH of 8.4 have been achieved using a cationic Mn complex, [(Ph2PPrPDI)Mn(CO)]Br. Although, a detailed mechanistic investigation remained challenging due to complex instability, a set of relevant Mn(-I) intermediates have been isolated and characterized thoroughly.

The dissertation also includes synthesis, characterization, and electronic structure evaluation of a series of Triphos supported iron complexes. Using this pincer chelate and either 2,2’-bipyridine (bpy) or 1,3,5,7-cyclooctatetraene (COT), a set of electronically interesting complexes have been isolated. Detailed electronic structure investigation using spectroscopy, magnetometry, crystallography, and DFT calculations revealed redox non-innocent behavior in the Bpy and COT ligands. Additionally, CO binding to the (Triphos)Fe system followed by reaction with borohydride reagents allowed for the isolation of some catalytically relevant and reactive iron hydride complexes.