Properties of nanoparticles can be engineered to exhibit desired properties for certain applications. In general, the surface area to volume ratio increases with the reduction of particle size. In some cases, this contributes to increase of surface defects available to the surrounding environment and hence reactivity. Changes in size, shape or coating of a nanoparticle can affect its properties. In this thesis, work was split into two main sections. The first part is an investigation into the antimicrobial and cytotoxicity effects of nano formulated N-acetyl cysteine coated zinc oxide (NAC-ZnO) as it can be encountered throughout the environment. NAC was used as a coating agent for its antimicrobial properties in terms of fighting against biofilm formation and its antioxidant properties. In this study, a comparative antimicrobial study of nano-size NAC-ZnO, nano-size NAC-ZnS, bulk ZnO (CR-41), and Zn(NO3)2 were conducted to understand the toxicity of these Zn based antimicrobials in the environment. The second part is a comprehensive investigation of Zinkicide®, a systemic nano formulated ZnO based antimicrobial for use in citrus trees to fight against bacterial diseases. Antimicrobial assays were performed for Zinkicide® on X. alfalfae, a gram-negative citrus phytopathogen surrogate, in efforts to find a solution to the citrus greening pandemic in Florida. Tests were also done to evaluate antimicrobial efficacy over time, to ensure that efficacy was not lost when stored or when used in the field by growers in their tank mixes. Hopefully, these results may help shed some light on how ZnO nanoparticles may react in the environment. This could lead to more nanotechnology-based products moving forward through the EPA & FDA pipeline to effectively make nanoparticle-based products more common place in agriculture.

Actin is an abundant and essential cytoskeletal protein that plays a central role in eukaryotic cell structure and motility. The intracellular environment where actin assembly occurs is crowded with various organelles, proteins, and macromolecules that limit the accessible volume for biomolecular reactions. Macromolecular crowding induces excluded volume effects influencing the activity of biological molecules as well as the shape and conformation of proteins. Crowding agents, such as polysaccharides or inert polymeric molecules, are used to mimic the conditions present in intracellular spaces and provide a better understanding of interactions inside the cell. Macromolecular crowding has been shown to affect actin filament assembly, however, how crowder size impacts actin assembly dynamics and kinetics is not well understood. In this thesis, we investigate how the excluded volume effects caused by crowding influences actin filament assembly kinetics by using synthetic polymeric crowder, polyethylene glycol (PEG), of various molecular weights. Using total internal reflection fluorescence (TIRF) microscopy, we directly visualized the assembly of individual actin filaments in various sizes of PEG crowded conditions. We quantified actin filament growth rates that depend on the size of crowder. Bulk fluorescence intensity was monitored to evaluate the effect of crowder size on actin assembly kinetics. These results demonstrate that the size of macromolecular crowding agents can modulate actin filament assembly kinetics, possibly by controlling the volume fractions. This work provides a foundation for a mechanism of how the dynamic cytoskeletal assembly occurs in living cells.

In recent years, peroxidase mimic nanostructures have attracted special interest due to their low cost, high stability, and high catalytic activity. Herein, we demonstrate the use of Pd-Pt nanocubes (NCs) to achieve the rapid and sensitive colorimetric detection of ascorbic acid (AA), commonly known as vitamin C. The colored signal generated by the catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by the decomposition of hydrogen peroxide (H2O2) is quenched in the presence of AA based on its antioxidant property. This colorimetric method attains a detection limit of 0.40 µM and a linear range from 0 to 15 µM, with good linearity. To the best of our knowledge, the method proposed in this work presents the fastest AA detection among all the other colorimetric methods, with only a 3-minute reaction time. Furthermore, this method offers a simple procedure, cost-effectiveness, room temperature conditions and stability. As a proof-of-concept demonstration, the Pd-Pt NCs detection of AA was applied in human serum to corroborate its applicability in the biomedical field with the analysis of biological samples.

The assembly of actin filaments into bundles plays an essential role in mechanical strength and dynamic reorganization of cytoskeleton. Divalent counterions at high concentrations promote bundle formation through electrostatic attraction between charged filaments. Although it has been hypothesized that specific cation interactions may contribute to salt-induced bundling, molecular mechanisms of how salt modulates bundle assembly and mechanics are not well established. Here we determine the mechanical and dynamic properties of actin bundles with physiologically relevant cations. Using total internal reflection fluorescence (TIRF) microscopy, we measure the bending stiffness of actin bundles determined by persistence length analysis. We characterize real-time formation of bundles by dynamic light scattering intensity and direct visualization using TIRF microscopy. Our results show that divalent cations modulate bundle stiffness as well as time-dependent average bundle size. Furthermore, molecular dynamic simulations propose specificity for cation binding on actin filaments to form bundles. The work suggests that cation interactions serve a regulatory function in bundle assembly dynamics, mechanics, and structure.

This study will reveal the fabrication and development of an enzyme-less biosensor for creatinine detection. The biosensor involves a periodically patterned nano-porous TiO2 deposited with Au nanoparticles via e-beam evaporation and a layer of Imprinted Polymer (IP) of acrylamide and bis-acrylamide to obtain a heterostructure of I-Au-TiO2. The detection methods of creatinine are based on electrochemical measurements using Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV). The IP-Au-TiO2 sensor shows a detection LOD of 0.0949ng/mL and 0. 0.218ng/mL for EIS and DPV measurements, respectively. The nanofabricated biosensor was tested in the presents of urea, glucose, lactose, L-valine, and Glutamic acid and shows high specificity for creatinine due to the specific binding of the analyte to the imprinted polymer on the electrode. A comparison test was performed between the imprinted IP-Au-TiO2 versus Non-Imprinted (NI) NI-Au-TiO2 biosensors. the results show no specificity for the creatinine using NI-Au-TiO2 biosensor for the varied concentration from 0.1ng/ml to 1µg/ml compared to the I-Au-TiO2. However, The N-Au-TiO2 show enhanced specificity for creatinine in the presence of Localized Surface Plasmon Resonance (LSPR) at the interface of the Au nanoparticles and TiO2. The generated LSPR on the surface of the biosensor increased the sensitivity for creatinine due to charge separation and solution resistance between the sensor and mixture. This detection platform provided a promising result which can be easily expanded to detecting a variety of biomarkers linked to human diseases or pathogens such as bacteria or viruses for point of care detection.

Antibiotic treatment of systemic bacterial plant pathogens is an established practice in many crops; however, in citrus it has only recently become available for growers to utilize against Huanglongbing disease. The preliminary efficacy of these treatments is uncertain due to the inability to track their presence in phloem. The need to monitor their movement in planta, especially their presence and translocation in vascular tissue, is a necessary step in clarifying their effectiveness. Previous work has shown the value of Fluorescence Lifetime Imaging (FLIM) in distinguishing between fluorescent probes and plant tissue autofluorescence, which is normally a barrier in photochemical studies in plants. Our aim in this thesis was the synthesis and characterization of a fluorescent antibiotic conjugate that could be utilized for tracking in citrus tissue, with the specific goal of identifying movement through citrus plant phloem. Conjugation of streptomycin sulfate, a commercially available antibiotic, to a modified tris(bipyridine) ruthenium (II) chloride, a dye with desirable photophysical properties, was achieved via EDC:NHS coupling. Further studies were performed illustrating the characteristics and kinetics of this conjugate in planta, which showed that the conjugate had an increase in excited state lifetime upon introduction to a biological environment. Subsequent translocation experiments yielded results indicating that the conjugated antibiotic moves systemically upwards after 48 hours but fails to move down towards the root system of the plant after 168 hours.

The chemical, physical, and biological properties of bacteria developing resistance have been explored in animal based bacteria while plant bacteria have been largely neglected. Thus, the ability to probe changes in stiffness, adhesion, binding interactions and molecular traits of bacteria causing plant diseases is of great interest to develop a new generation of more potent, yet sustainable, pesticides. Our study aims to investigate the physical and chemical properties of bacterial systems, in particular their cell walls. Building upon this fundamental understanding of the cells, we also investigate the physicochemical responses associated to multivalent nanoparticle-based bactericide treatments on bacterial systems identified as pathogens in plant diseases. Here our efforts focus on developing a protocol for the fundamental understanding of Xanthomonas perforans, a strain known for causing bacterial spot in tomatoes and causing close to 50% losses in production. To support the design and accelerate the development of pesticides and treatments against this disease, we evaluate the changes bacteria undergo in the presence of the treatment. Using a silica nanoparticle-based treatment designed with a shell containing multivalent copper and quaternary ammonium, we compare bacteria pre- and post-treatment with infrared spectroscopy, atomic force microscopy (AFM)-based techniques, and TIRF microscopy. Statistical data analysis enables the identification of attributes that can potentially serve as markers to track the bacterial responses to the treatment in the future. Finally, we will discuss the exciting implications of this work, such as potential clues for the development of more potent treatments for resistant bacteria.

Polyelectrolyte based hydrogel fibers can mimic extracellular matrix and have applications such as drug delivery and tissue scaffolding. Metal ions play a critical role in hydrogel fiber stability via electrostatic interactions, but knowledge of how they modulate mechanical properties of individual polyelectrolyte polymers is lacking. In this study, electrospun polyacrylic acid with chitosan is used as a model system to evaluate ferric ion effect on nanofiber mechanics. Using dark field microscopy imaging and persistence length analysis, we demonstrate that ferric ions modulate the bending stiffness of nanofibers. Young's modulus of individual nanofibers is estimated at values of a few kilopascals, suggesting that electrospun nanofibers possibly exist in a hydrated state. Furthermore, Fourier Transform Infrared (FTIR) spectra indicate the effect of ferric ions on polyacrylic acid molecular bonds. Our results suggest that metal ions can regulate single nanofiber stiffness, thereby providing designs to fabricate hydrogels in a tunable fashion.

Understanding interactions between nanoparticles and biological systems is fundamental for the development of emerging nano-biotechnology applications. In this thesis, I present an investigation of zinc oxide (ZnO) nanoparticles interactions with biomolecules in two separate studies. The first section of my thesis covers tracking and detection of ZnO nanoparticles using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). ZinkicideTM is a bactericidal ZnO nanoparticle which has been developed for agriculture. The characterization of Zinkicide in biological media and in solution has been difficult due to its high dispersibility and ultra-small size. SDS-PAGE is considered a golden standard for protein qualitative interpretations. In this study, we have modified this typical protein assay and developed protocols for quantifying Zinkicide concentration, fluorescence intensity, and relative molecular weight changes in aqueous solutions. We found that SDS-PAGE is a novel and fundamental approach for assessing ZnO nanoparticles. The second part of my thesis is focused on investigating biological toxicity induced by nanoparticles. Recent studies have shown that nanoparticles have the capabilities to induce abnormalities on cellular networks including actin cytoskeleton. We have studied the effects of ZnO nanoparticles on filamentous actin assembly dynamics utilizing total internal reflection fluorescence (TIRF) microscopy imaging and biophysical analysis. The combination of these studies has provided pertinent information for the future development of nanoparticles designed for biological applications.

Two dimensional (2D) materials-based nanostructures have attracted much attention due to their unique properties which exhibit promising prospects for application in catalysis and energy storage devices. Control growth method is important in synthesizing these nanostructures. Chemical vapor deposition (CVD) is a powerful method that provides scalability and controllable way to grow high quality 2D materials-based nanostructures. Here, we report a novel CVD growth method of 2D molybdenum disulfide (MoS2) based different structures in which thin film of molybdenum trioxide (MoO3) was used as the source of molybdenum (Mo), while sulfur (S) powder was used for the chalcogen precursor. Precise control of Mo precursor which is hard to achieve with MoO3 powder promotes high quality growth of MoS2 based nanostructures. In particular, we observed different MoS2-based nanostructures under different growth conditions. The structures were characterized by a variety of techniques to identify their chemical composition and structural nature. Scanning electron microscopy showed the morphology of the vertical plates, nanocrystals, and triangles structures. Raman spectroscopy indicated that the MoS2 based vertical plates are composed of MoO2 and MoS2. Transmission electron microscopy confirmed the multilayer shell of MoS2 with MoO2 core in the nanocrystal structures. We have successfully grown these nanostructures using precise control of the precursor concentration in confined vapor phase. These nanostructures could be relevant in the application of electrocatalytic materials with insufficient long-range conductivity, such as water oxidation catalysts consisting of poorly conducting metal oxides. Confined vapor phase paves the way to control surface structures of MoS2 at the nanoscale to ultimately develop effective catalyst-based materials with high densities of active edge sites at the surface.