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This dissertation is about fabrication and functionalization of metal nanoparticles for use in plasmonic and nonlinear optical (NLO) applications. In the first two chapters, I describe a series of experiments, where I combined silver nanoparticles fabricated by nanosphere lithography with ionic self-assembled multilayer (ISAM) films, tuning the geometry of the particles to make their plasmonic resonances overlap with the frequency of optical excitation. The designed hybrid metallic/organic nanostructures exhibited large enhancements of the efficiency of second harmonic generation (SHG) compared to conventional ISAM films, causing a modified film with just 3 bilayers to be optically equivalent to a conventional 700-1000 bilayer film. SHG responses from Ag nanoparticle-decorated hybrid-covalent ISAM (HCISAM) films were investigated as the next logical step towards high-Ï ²⁺ ISAM films. I found that the plasmonic enhancement primarily stems from interface SHG. Interface effects were characterized by direct comparison of SHG signals from PAH/PCBS ISAM films and PAH/PB HCISAM films. Though interface &chi²⁺ is substantially smaller in PAH/PCBS than in PAH/PB, plasmonically enhanced PAH/PCBS films exhibit stronger NLO response. I propose that the structure of PAH/PB film makes its interface more susceptible to disruptions in the nanoparticle deposition process, which explains our observations. During the fabrication of monolayer crystals for nanosphere lithography, I developed a variation of the technique of convective self-assembly, where the drying meniscus is restricted by a straight-edge located approximately 100 μM above the substrate adjacent to the drying zone. This technique can yield colloidal crystals at roughly twice the growth rate compared to the standard technique. I attribute this to different evaporation rates in the thin wet films in the two cases. I also found that the crystal growth rate depends strongly on the ambient relative humidity. Finally, dithiocarbamate (DTC)-grafted polymers were synthesized and employed to functionalize surfaces of Au nanopartciles. PAH-DTC shows greater stability in different environments than PEI-DTC. I also investigated the stability of PAH-DTC coated particles in suspensions with UV-Vis spectroscopy and autotitration. The covalently bonded PAH-DTC enhances the colloidal stability of the Au nanoparticles and enables subsequent ISAM film deposition onto the particles. / Ph. D.

Interfaces are ubiquitous in our daily life. A good understanding of the interfacial properties between different materials, or a single material in different physical states is of critical importance for us to explore the current world and bring benefits to mankind. In this work, interfacial behavior was investigated with the help of surface analysis techniques, such as quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and atomic force microscopy (AFM), in order to gain better understanding on biofuel conversion, gene/drug delivery, and chemical fixation of CO2. Biomimetic chelator-mediated Fenton (CMF) non-enzymatic degradations on cellulose and chitin thin films was studied by liquid-phase QCM-D and AFM. QCM-D is a powerful tool to monitor the kinetics of hydrolysis of regenerated cellulose and chitin model surfaces. Results from QCM-D and AFM showed that the majority of the biomass of the two model surfaces can be hydrolyzed by the CMF system. The initial degradation rates for both model surfaces by the CMF system are faster than that of the corresponding enzyme systems. The CMF system, which is a good non-enzymatic pretreatment agent for cellulose and chitin, may work on a wide variety of polysaccharide systems. Adsorption of cationic cellulose derivatives onto self-assembled monolayer (SAM) surfaces was investigated using liquid-phase SPR. Results from SPR showed that depending upon the cellulose derivative structure, irreversible adsorption ranging from a monolayer to ~1.6 layers of cellulose derivative were formed on the SAM-COOH surface based upon a charge neutralization mechanism. At low salt concentrations, the long-range electrostatic attraction between the cationic cellulose derivatives (6-PyrCA and 6-MeIMCA) and the SAM surfaces facilitates the formation of a 2-dimensional monolayer. While, for TMACE, the energy gained through the hydrophobic interaction between adjacent long polyelectrolyte branches may afford the electrostatic repulsion and chain entropy penalties, resulting in the formation of 3-dimensional adsorbed polyelectrolyte layers. Adsorption of 1,2-epoxybutane gas molecules onto/into VPI-100 metal–organic frameworks (MOFs) was studied by gas-phase QCM-D experiments. Results from QCM-D demonstrated that VPI-100 (Ni) MOFs have higher irreversible adsorption per unit cell (θ) and faster diffusion coefficients (D) than VPI-100 (Cu) MOFs. The presence of bound counter-balancing ions on the metallo-cyclam core was attributed as the cause of the higher θ and faster D through the Ni analogue, which suggests the MOF-epoxide interaction occurs at the metallo-cyclam. This study shed light upon tuning MOF structures for better CO2 sorption and epoxide activation to gain higher catalytic efficiency. Finally, in operando high energy X-ray diffraction (HEXRD) was used to monitor the phase transition of the NaxNi1/3Co1/3Mn1/3O2 cathode material during the sintering process. The first charge/discharge cycle of the NaxNi1/3Co1/3Mn1/3O2 cathode materials in different phases were also studied by in operando HEXRD. It was found that the intergrowth P2/O1/O3 cathode (NCM-Q cathode) can inhibit the irreversible P2–O2 phase transition and simultaneously improve the structural stability of the O3 and O1 phases during cycling. The NCM-Q cathode with triple-phase integration demonstrates highly reversible phase evolution during high voltage cycling, possibly leading to a highly reversible capacity and good cycle stability. / Doctor of Philosophy / Interfaces and surfaces are everywhere. Many critical processes, such as molecular recognition, catalysis, and charge transfer, take place at interfaces. The surfaces of plants and animals provide barriers from pathogens, prevent damage from mechanical impacts, detect external stimuli, etc. Inside the human body, nutrition and oxygen are adsorbed through interactions between substances and cell surfaces. Investigations of interfacial behaviors may help us understand our current world better and bring benefits to mankind. In this dissertation, the interface between bio-renewable natural polymers and biomimetic chelators, the interface between a self-assembled monolayer and cationic cellulose derivatives, and the interface between metal–organic frameworks (MOF) and 1,2-epoxybutane gas molecules, were studied with a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and atomic force microscopy (AFM), to gain insights into biofuel conversion, gene/drug delivery and chemical fixation of CO2, respectively. Additionally, thermally and electrochemically induced phase transitions in sodium-ion battery (SIB) cathode materials were probed via in operando high energy X-ray diffraction (HEXRD). Biomimetic chelator-mediated Fenton (CMF) non-enzymatic degradations of cellulose and chitin thin films were studied by liquid-phase QCM-D and AFM. It was found that the majority of the biomass of the two model surfaces can be degraded by the CMF system. Adsorption of cationic cellulose derivatives onto self-assembled monolayer (SAM) surfaces was investigated using liquid-phase SPR. It was found that both the absorbed layer conformation and the absorbed amount depend upon the interplay between long-range electrostatic interactions and short-range interactions. Adsorption of 1,2-epoxybutane gas molecules onto/into VPI-100 MOFs was studied by gas-phase QCM-D experiments. Data from QCM-D revealed the irreversible gas molecule absorption onto/into MOFs and shed light upon tuning MOF structures for better CO2 sorption and epoxide activation to gain higher catalytic efficiency. Finally, the in operando high energy X-ray diffraction (HEXRD) was used to probe thermally and electrochemically induced phase transitions in sodium-ion battery (SIB) cathode materials. It was found that the NCM-Q cathode with triple-phase integration demonstrates highly reversible phase evolution during high voltage cycling, possibly leading to a highly reversible capacity and good cycle stability.

Throughout the study of polymer adsorption at the air/water and solid/water interfaces, surface tension measurements and surface plasmon resonance (SPR) spectroscopy have been identified as key methods for the acquisition of structural and thermodynamic information. These techniques were used to determine air/water and cellulose/water interfacial properties of pullulan (P) and pullulan cinnamates (PCs), 2-hydroxypropyltrimethylammonium xylans (HPMAXs), and hydroxypropyl xylans (HPXs). Hydrophobic modification of pullulan with cinnamate groups promoted adsorption onto model surfaces of regenerated cellulose. In order to understand the relative contributions of hydrophilic and hydrophobic interactions towards PC adsorption, PC adsorption onto self-assembled monolayers (SAMs) with different functional groups was also studied. As the degree of cinnamate substitution increased, greater adsorption onto cellulose, methyl-terminated SAMs (SAM-CH3), and hydroxyl-terminated SAMs (SAM-OH) was observed. This study showed that hydrogen bonding alone could not provide a complete explanation for PC adsorption onto cellulose. The adsorption of cationic 2-hydroxypropyltrimethylammonium (HPMA) xylans with different degrees of substitution (DS) onto SAMs and regenerated cellulose was studied by SPR. Surface concentration (Р) exhibited a maximum (Рmax) for HPMAX adsorption onto carboxylic acid-terminated SAMs (SAM-COOH) at an intermediate HPMA DS of 0.10. This observation was indicative of a relatively flat conformation for adsorbed HPMAXs with higher HPMA DS because of higher linear charge densities along the polymer backbone. Рobserved for HPMAX adsorption onto regenerated cellulose and SAM-OH surfaces was relatively low compared to HPMAX adsorption onto SAM-COOH surfaces. Surface tension measurements for aqueous solutions of HPX by the Wilhelmy plate technique showed that surface tension changes ("γ = γwater " γHPX(aq)) increased and critical aggregation concentrations generally decreased with increasing hydroxypropyl (HP) DS. Hence, even though HP substitution was necessary to induce aqueous solubility, excessive hydroxypropylation promoted aggregation in water. SPR studies indicated that HPXs did not adsorb significantly onto regenerated cellulose or SAM-OH surfaces (submonolayer coverage). In contrast, HPX did adsorb (~monolayer coverage) onto SAM-CH3 surfaces. Collectively, these studies showed natural polymers could be chemically modified to produce surface modifying agents with sufficient chemical control, whereby the surface properties of the resulting systems could be explained in terms of chemical structure and intermolecular interactions. / Ph. D.

Surfactants, polymers, and their mixtures are widely used in commercial formulations of paints, water-based adhesives, detergents, food, and other products. This thesis describes measurements of the forces acting on colloidal particles in surfactant and polymer solutions. The change in force on addition of surfactants and polymers is usually caused by adsorption to an interface. In this thesis, I also describe the effect of surface charge density, surface crystallinity, surface heterogeneity, and preadsorbed polymer on surfactant adsorption. A new method for the stabilization of colloidal particles is introduced via the synthesis and adsorption of unnatural proteins. Unnatural proteins can be synthesized using the natural "machinery" of a bacterial cell with almost any primary sequence, and provide an environmentally friendly route to colloidal stabilization. As a model system, we study the stabilization of alumina, because alumina has a high Hamaker constant and is therefore difficult to stabilize. An unnatural protein with the sequence, thioredoxin-Pro39Glu10 is used. The Glu10 is anionic (pH > 3) and is designed to adsorb to positively charged alumina (pH<9). The thioredoxin-Pro39 is hydrophilic so it should remain in solution, thereby providing a steric barrier to the approach of two particles in a range of salt and pH conditions. Ellipsometry experiments show that thioredoxin-Pro39Glu10 adsorbs to alumina. Force measurements with the Atomic Force Microscopy (AFM) colloid probe technique show that adsorption of the unnatural protein leads to repulsive forces that decay exponentially with the separation between the surfaces, and are independent of salt concentration. The loss of a salt-dependent force shows that adsorption of the unnatural protein has effectively neutralized the charge on the alumina. Thus, I have shown that an unnatural protein can be used to control the stability of a colloidal system. In general, the same hydrophilic block can probably be added to a variety of anchoring blocks to stabilize different colloidal particles. Electrostatic forces are frequently responsible for the stabilization of colloidal particles. The decay length of these forces is dictated by the electrolyte concentration. The relationship between the decay length and the concentration is well understood for fully dissociated 1:1 electrolytes. Here, I examine the decay-length in solutions where the ions associate strongly. The forces are measured between silica surfaces in aqueous carboxylic acid and surfactant solutions. The decay lengths of the electrostatic double-layer force in both these solutions are well described by the usual expression for decay length when the concentration of ions is obtained from an activity measurement. The effect of the surface properties of the solid substrate on surfactant adsorption is also described in this thesis. The adsorption characteristics of a charged surfactant onto fixed charged surfaces as a function of surface charge density is reported. This is the first time that a method has been introduced for making a series of known fixed charged surfaces. Investigating surfactant adsorption to these surfaces has improved our understanding of the role of charge density in surfactant adsorption and desorption. The desired surface charge density is achieved by the use of gold-thiol self-assembled monolayers (SAMs) of different Ï -groups ("OH and "N+(CH3)3). The mole fraction of "N+(CH3)3 on the mixed SAM dictates the surface charge density. The charge on "N+(CH3)3 is fixed and does not self-regulate. The adsorption of sodium dodecyl sulfate (SDS) to the interface between these model surfaces and aqueous solutions of SDS is investigated. Atomic Force Microscopy (AFM) of the adsorbed surfactant reveals no surface micelles above the critical micelle concentration, cmc, over a wide variety of "N+(CH3)3 densities. This shows that the lateral mobility of ions other than surfactant at the interface is important for the formation of surface micelles of ionic surfactants. Adsorption isotherms of SDS (with no added salt) measured by Surface Plasmon Resonance (SPR) show a plateau region in which the surface excess of SDS is equal to the known fixed surface charge. This demonstrates that the adsorption is electrostatically driven. There is no critical surface charge density at which adsorption rises rapidly. Thus there appears to be no 'hemimicelle concentration'. My work suggests that the formation of hemimicelles depends on the lateral mobility of the surface ions. Desorption experiments starting above the cmc show rapid desorption of SDS into water until the surface excess is equal to the surface charge density. The rapid desorption is followed by a much slower desorption. The elucidation of this fast-slow desorption pattern based on charge density is made possible by the preparation of a set of constant charge surfaces. / Ph. D.

Plant cell wall polysaccharides are abundant natural polymers making them potential sources for sustainable and biodegradable materials. Interfacial behavior, including adsorption and enzymatic degradation, of several plant cell wall polysaccharides and their derivatives were studied with a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and atomic force microscopy (AFM). Xyloglucan adsorption isotherms were obtained to probe how cellulose-hemicellulose interactions were affected by the type of cellulose substrate and molar mass of xyloglucan. Xyloglucan as small as a heptasaccharide still adsorbed irreversibly onto cellulose. Carboxymethyl cellulose (CMC) adsorption onto cellulose and viscoelastic properties and water contents of the adsorbed CMC layers were obtained from a combination of QCM-D and SPR data. The CMC samples formed hydrated and viscoelastic layers compared to the relatively rigid xyloglucan layer. Pectin model surfaces were prepared by pectin adsorption from citric phosphate buffer onto gold substrates. These pectin model surfaces were used for subsequent interaction studies with xyloglucan and enzymatic degradation behavior. There is a strong correlation between the degree of esterification (DE) and film resistance to degradation with the high DE being the most susceptible to degradation. The adsorption of two mixed linkage glucans (MLG), barley and lichen MLG, onto regenerated cellulose (RC) surfaces in the absence and presence of other matrix polysaccharides was studied. Viscoelastic properties of the resulting layer were compared as a function of the proprotion of '-(1''3) linkages with lichen MLG forming softer gel-like layers on RC. The lichen MLG layers were further used for enzymatic degradation studies with respect to enzyme concentration, temperature, pH and ionic strength. These studies show that polymer adsorption is a promising strategy to modify material surfaces and provides fundamental understanding of interactions and biodegradation of cell wall polysaccharides at solid/liquid interfaces. / Ph. D.

Wood is a complex biocomposite that exhibits a high work of fracture, making it an ideal model for multiphase man-made materials. Typically, man-made composites demonstrate interfacial fracture at failure due to abrupt transitions between neighboring phases. This phenomenon does not occur in wood because gradual phase transitions exist between regions of cellulose, hemicellulose, and lignin and therefore adhesion between adjacent phases is increased. The formation of interphases occurs as a consequence of the self-assembly process which governs the formation of wood. If this process was understood more thoroughly, perhaps tougher man-made, biobased composites could be prepared. To study self-assembly phenomena in wood, a system composed of a model copolymer (pullulan abietate, DS=0.027) representing the lignin-carbohydrate complex (LCC) and a model surface for cellulose fibers was used. The self-assembly of the polysaccharide pullulan abietate (DS=0.027) onto a regenerated cellulose surface prepared using the Langmuir-Blodgett (LB) technique was studied via surface plasmon resonance (SPR). Rapid, spontaneous, and desorption-resistant cellulose surface modification resulted when exposed to the model LCC. Adsorption was quantified using the de Feijter equation revealing that between 9-10 anhydroglucose units (AGUs) adsorb per nm&178; of cellulose surface area when cellulose is exposed to pullulan abietate (DS=0.027) compared to the adsorption of 6.6 AGUs per nm&178; of cellulose surface area when cellulose is exposed to unsubstituted pullulan. / Master of Science

Anisotropic plasmonic noble metallic nanoparticles (APMNs) have received enormous attention due to their distinct geometric features and fascinating physicochemical properties. Owing in large part to their tailored localized surface plasmon resonance (LSPR) and the intensive electromagnetic field at the sharp corners and edges, APMNs are exceptionally well suited for biomedical applications such as biosensing, bioimaging, diagnostics and therapeutics. Although a rich variety of surfactant-assisted colloidal routes have been developed to prepare well-defined APMNs, biomedical applications necessitate tedious and rigorous purification processes for the complete removal of toxic surfactants. In this dissertation, we aim to develop generic bioenabled green synthetic methodologies towards APMNs. By applying a series of thermodynamic, kinetic and seed quality control, a series of APMNs with varied morphologies such as branched nanostars and triangular nanoprisms have been successfully prepared. We first presented the preparation of gold nanostars (Au NSTs) through a two-step approach utilizing a common Good's buffer, HEPES, as a weak reducing agent. Single crystalline Au NSTs with tunable branches up to 30 nm in length were produced and the halide ions rather than the ionic strength played a significant roles on the length of the branches of Au NSTs. Then consensus sequence tetratricopetide repeat (CTPR) proteins with increasing number of repeats were used as model proteins to probe the effects of concentration as well as the protein shape on the morphology and resulting physicochemical properties of plasmonic gold nanoparticles. Since the underlying growth mechanism for the biomimetic synthesis of APMNs remains elusive and controversial, the other objective is to elucidate the molecular interactions between inorganic species and biopolymers during the course of NP evolution. Fluorescent quenching and 2D NMR experiments have confirmed the moderate binding affinity of CTPR to the Au(0) and Au(III). We observed that the initial complexation step between gold ions and CTPR3 is ionic strength dependent. Furthermore, we also found that NPs preferentially interact with the negatively charged face of CTPR3 as observed in 2D NMR. Knowledge of binding behavior between biospecies and metal ions/NPs will facilitate rational deign of proteins for biomimetic synthesis of metallic NPs. A modified seed-mediated synthetic strategy was also developed for the growth of silver nanoprisms with low shape polydispersity, narrow size distribution and tailored plasmonic absorbance. During the seed nucleation step, CTPR proteins are utilized as potent stabilizers to facilitate the formation of planar-twinned Ag seeds. Ag nanoprisms were produced in high yield in a growth solution containing ascorbic acid and CTPR-stabilized Ag seeds. From the time-course UV-Vis and transmission electron microscopy (TEM) studies, we postulate that the growth mechanism is the combination of facet selective lateral growth and thermodynamically driven Ostwald ripening. By incorporation of seeded growth and biomimetic synthesis, gold nanotriangles (Au NTs) with tunable edge length were synthesized via a green chemical route in the presence of the designed CTPR protein, halide anions (Br⁻) and CTPR-stabilized Ag seeds. The well-defined morphologies, tailored plasmonic absorbance from visible-light to the near infrared (NIR) region, colloidal stability and biocompatibility are attributed to the synergistic action of CTPR, halide ions, and CTPR-stabilized Ag seeds. We also ascertained that a vast array of biosustainable materials including negatively charged lignin and cellulose derivatives can serve as both a potent stabilizers and an efficient nanocrystal modifiers to regulate the growth of well-defined Ag nanoprisms using a one-pot or seeded growth strategy. The influential effects of reactants and additives including the concentration of sodium lignosulfonate, H2O2 and NaBH4 were studied in great detail. It implies that appropriate physicochemical properties rather than the specific binding sequence of biomaterials are critical for the shaped-controlled growth of Ag NTs and new synthetic paradigms could be proposed based on these findings. Last but not the least, we have demonstrated the resulting APMNs, particularly, Au NSTs and Ag NTs exhibit remarkable colloidal stability, enhanced SERS performance, making them promising materials for biosensing and photothermal therapy. Since the Ag nanoprisms are susceptible to morphological deformation in the presence of strong oxidant, they also hold great potential for the colorimetric sensing of oxidative metal cation species such as Fe3+, Cr3+, etc. / Ph. D. / When a beam of light impinges on the surface of noble metallic nanoparticle (NP), particularly gold (Au) and silver (Ag), the conduction electrons are excited which induces a collective oscillatory motion, resulting in an intense localized surface plasmon resonance (LSPR) absorbance as well as the amplified localized electromagnetic filed. Owing in large part to the tailored LSPR and the intensive electromagnetic field at the sharp corners and edges, anisotropic plasmonic noble metallic nanoparticles (APMNs) can be utilized to span an array of applications such as biosensing, bioimaging, diagnostics and therapeutics. Although great advancement has been made to prepare well-defined APMNs through versatile surfactant-assisted colloidal methodologies, biomedical applications necessitate tedious and rigorous purification processes for the complete removal of toxic surfactants. To address this ubiquitous challenge, biomimetic and bioinspired green synthesis have been extensively explored to fabricate APMNs under mild and ambient conditions. In this dissertation, we aim to develop generic bioenabled synthetic strategies towards APMNs, particularly, Au nanostars and Au/Ag nanoprisms. Herein, protein mediated shape-selective synthesis of APMNs were presented, in which consensus sequence tetratricopetide repeat (CTPR) proteins and biological Good’s buffers were employed as nanocrystal growth modifiers and mild reducing agents, respectively. The dramatic implications of repeat proteins on the morphological and optical properties of the Au NPs were explicitly discussed. The other objective of this dissertation is to elucidate the molecular interactions between inorganic species and biopolymers to further unravel the underlying growth mechanism during the course of APMNs evolution. By incorporation of seeded growth and biomimetic synthesis, Ag/Au nanotriangles (Au NTs) with tunable edge length were synthesized in the presence of the designed CTPR protein, halide anions (Br⁻) and CTPR-stabilized Ag seeds. The well-defined morphologies, tailored plasmonic absorbance from visible-light to the near infrared (NIR) region, colloidal stability and biocompatibility are attributed to the synergistic action of each components in the synthetic system. Last but not the least, we have demonstrated the resulting NPs exhibit remarkable colloidal stability, mitigated cytotoxicity and surface enhanced Raman spectroscopy (SERS) performance, making them good candidates for biosensing and photothermal therapy. This work might shed light on the roles biomolecules play in green synthesis of APMNs, along with rationalizing the design of biomimetic systems to bridge the gap between the bioenabled technique and traditional colloidal synthesis.

No / Widefield surface plasmon resonance (WSPR) microscopy provides high resolution imaging of interfacial interactions. We report the application of the WSPR imaging system in the study of the interaction between keratinocytes and liquid crystals (LC). Imaging of fixed keratinocytes cultured on gold coated surface plasmon substrates functionalized with a thin film of liquid crystals was performed in air using a 1.45 NA objective based system. Focal adhesion of the cells adhered to glass and LC were further studied using immunofluorescence staining of the vinculin. The imaging system was also simulated with 2 × 2 scattering matrix to investigate the optical reflection of the resonant plasmonic wave via the glass/gold/cell and glass/gold/LC/cell layers. WSPR imaging indicated that keratinocytes are less spread and formed distinct topography of cell–liquid crystal couplings when cultured on liquid crystal coated substrates. The simulation indicates that glass/LC shifted the surface plasmon excitation angle to 75.39° as compared to glass/air interface at 44°. The WSPR microcopy reveals that the cells remodelled their topography of adhesion at different interfaces.