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Self-assembly of organothiols (OTs) and thiolated biomolecules onto gold nanoparticle (AuNP) surfaces remains one of the most intense areas of nanoscience research and understanding molecular interfacial phenomena is crucial. Investigation of OT adsorption onto AuNPs, including OT structure and orientation on nanoparticle surfaces, is of fundamental importance in understanding the structure and function relationship of functionalized nanoparticles. Despite the great importance of the interfacial interaction of AuNPs, the exact mechanism of OT interactions with AuNPs has remained unclear and quantitative investigation of OT adsorption has been very limited. The research reported here focused on developing a fundamental and quantitative understanding of OT interactions with AuNPs in water. In studies of OT interactions with AuNPs in water, we found that the OTs form an adsorbed monolayer on AuNPs by releasing the sulfur-bound hydrogen as a proton and acidifying the ligand binding solution. The pH measurements suggest that there is a substantial fraction (up to 45%) of the protons derived from the surface adsorbed OTs retained close to the gold surface, presumably as the counter-ion to the negatively- charged, thiolate-covered AuNPs. Charge-transfer between the surfacesorbed thiolate and the AuNPs is demonstrated by the quenching of the OT UV-vis absorption when the OTs are adsorbed onto the AuNPs. Using a combination of surface enhanced Raman spectroscopy (SERS), density function calculations, and normal Raman spectroscopy, the pH dependence of mercaptobenzimadazole (MBI) adsorption onto AuNPs was systematically studied. By using the ratiometric SERS ligand quantification technique, MBI adsorption isotherms were constructed at three different pHs (1.4, 7.9, and 12.5). The Langmuir isotherms indicate that MBI thione has a higher saturation packing density (~­631 pmol/cm2) than MBI thiolate (~­568 pmol/cm2), but its binding constant (2.14 x 106 M-1) is about five times smaller than the latter (10.12 x 106 M-1). The work described in this dissertation provides a series of new insights into AuNP-OT interaction, and structure and properties of OTs on AuNPs.

Scanning electrochemical microscopy (SECM) is used to deposit gold nanoparticles on a glassy carbon electrode (GCE). Deposition conditions, including the tip-substrate distance, current density, substrate potential, and addition of Ag ions in the electrolyte are changed to study the effects on gold spot size and particle morphology. Atomic force microscopy (AFM) is used to analyze the gold nanoparticles. The size and shape of the nanoparticle can be controlled by different SECM experimental conditions. OMSOL Multiphysics software is used to simulate the results of SECM deposition. By comparing the simulation results and experimental results, the deposition process can be understood better. Heterogeneous irreversible reaction rate constant of the reaction happened on GCE can be estimated.

Nanoparticles are important tools in biotechnology and biomedical research. Gold nanoparticles (AuNPs) have emerged as a particularly important class of nanobiotechnological tools as a result of a number of unique and useful attributes. These attributes include the high degree of biocompatibility of AuNP cores, the similarity in size of AuNPs and biomacromolecules, and the great chemical flexibility of AuNP surface design. One of the most promising applications of AuNPs in biotechnology and biomedicine is their use as drug delivery vehicles. Drug delivery vehicles provide therapeutics with desired delivery properties by targeting them specifically to the environments in which their therapeutic activity is sought and by overcoming solubility barriers. The drug delivery properties of AuNPs are a function of their sizes and surface chemistries. The nanometer scale of AuNPs allows these three-dimensional and diffusible self-assembled monolayers to act as substructures for supramolecular assemblies, to extravasate from tumor-supplying endothelia, and to undergo cellular uptake by endocytosis. AuNPs have become a versatile platform for the creation of multifunctional delivery vehicles. This work represents a collection of studies in which AuNPs have been used as probes in fundamental biological research and delivery systems for small molecules and biologics. In these studies, precision control of surface chemistry on the nanometer scale, made possible by AuNPs, has been used to find solutions to the problems of unraveling the role of hydrophobicity in immune system activation, delivering proteins past mammalian cell membranes, development of a sustained release drug delivery platform, and condensation and cellular delivery of siRNA.

As demand for food increases, rapid testing methods are becoming increasingly important. In the past few years, yogurt has become popular. Yeast species are the most common spoilage organism, costing consumers and food companies money. A novel lateral flow assay has been developed to detect yeast oligonucleotide sequences. Gold nanoparticles were used as the standard reporter and fluorescent nanoparticles were developed as the novel reporter. The fluorescent nanoparticles were ruthenium-doped silica nanoparticles synthesized using the modified Stöber method. Visual analysis of assays using standard reporters showed the limit of detection to be 10 femtomoles of target sequence. Analysis of the fluorescent nanoparticles using a plate reader showed the limit of detection to be 0.027 femtomoles. The fluorescent reporter’s limit of detection is 1000 fold lower due to a sophisticated, more sensitive analysis method. Gold nanoparticles are appropriate for presence or absence testing, but fluorescent nanoparticles are best for obtaining quantitative data with low detection limits. Pathogens have been used as biological warfare for centuries. A brief review of common biowarfare agents is included. Yersinia pestis, the causative agent of the Plague, and Bacillus anthracis, the causative agent of Anthrax, are the focus. Additional work using gold nanoparticles as reporter in a sandwich assay is also included. The novel dye covered reporter was compared to the control, which was a single dye molecule linked to the reporter sequence. Repeated testing showed the novel reporter had a lower limit of detection and higher sensitivity due to increased ability to bind target.

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Due to enhanced properties such as large surface area-to-volume ratio, metal nanoparticles are often employed as catalysts for various applications. However, most studies involving nanoparticle catalysts have been conducted on collections of particles rather than single nanoparticles. Results obtained for ensemble systems can be difficult to interpret due to variations in particle loading and interparticle distance, which are often challenging to control and characterize. In this study, two immobilization strategies for incorporating gold nanoparticles (AuNPs) on carbon fiber ultramicroelectrodes (UMEs) were compared with the goal of extending these techniques to nanoelectrodes for studies of single AuNPs. Both layer-by-layer deposition of AuNPs on natural carbon fiber UMEs and direct reduction of AuNPs on nitrided carbon fiber UMEs were explored. Although both methods proved feasible, the direct reduction method seemed to be more effective and should better enable direct comparisons of bare and capped AuNPs.

The study of ferritin includes a rich history of discoveries and scientific progress. Initially, the composition of ferritin was determined. Soon, it was shown that ferritin is a spherical, hollow protein. Eventually, over several decades of research, the structure and some function of this interesting protein was elucidated. However, the ferritin field was not completely satisfied. Today, for example, researchers are interested in refining the details of ferritin function, in discovering the role of ferritin in a variety of diseases, and in using ferritin for materials chemistry applications. The work presented in this dissertation highlights the progress that we have made in each of these three areas: 1) Mechanistic studies: The buffer used during horse spleen ferritin iron loading significantly influences the mineralization process and the quantity of iron deposited in ferritin. The ferrihydrite core of ferritin is crystalline and ordered when iron is loaded into ferritin in the presence of imidazole buffer. On the other hand, when iron is loaded into ferritin in the presence of MOPS buffer, the ferrihydrite core is less crystalline and less ordered, and a smaller amount of total iron is loaded in ferritin. We also show that iron can be released from the ferritin core in a non-reductive manner. The rate of Fe3+ release from horse spleen ferritin was measured using the Fe3+-specific chelator desferoxamine. We show that iron release occurs by three kinetic events. 2) Disease studies: In order to better understand iron disruption during disease states, we performed in vitro assays that mimicked chronic kidney disease. We tested the hypothesis that elevated levels of serum phosphate interrupted normal iron binding by transferrin and ferritin. Results show that phosphate competes for iron, forming an iron(III)-phosphate complex that is inaccessible to either transferrin or ferritin. Ferritin samples separated from the iron(III)-phosphate complex shows that as the phosphate concentration increases, iron loading into ferritin decreases. 3) Materials chemistry studies: Anion sequestration during ferritin core reduction was studied. When the core of horse spleen ferritin is fully reduced using formamidine sulfinic acid, a variety of anions, including halides and oxoanions, cross the protein shell and enter the ferritin interior. Efforts have been made to use ferritin to control the concentration of anions for reactions. In addition, the native ferrihydrite mineral core of ferritin is a semi-conductor capable of catalyzing oxidation/reduction reactions. Light can photo-reduce AuCl4- to form gold nanoparticles (AuNPs) with ferritin as a photocatalyst. The mechanism of AuNP formation using ferritin as a photocatalyst was examined. From this work, we propose that the ferrihydrite core of ferritin photo-reduces; the mineral core dissolves into a soluble iron(II) mineral. The iron(II) then re-oxidizes, and a new mineral forms that appears to be the new photocatalyst, as the lag phase is significantly decreased with this new mineral form of ferritin.