Thesis (Ph. D.)--State University of New York at Binghamton, Dept. of Chemistry, 2006. / Includes bibliographical references.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Eric M. Furst, Dept. of Chemical Engineering. Includes bibliographical references.

This study assessed biofilm formation within sealer-dentin interfaces of root segments filled with gutta-percha and zinc oxide sealer incorporated with chitosan nanoparticles, without and with canal surface treatments. Bovine root segments were filled using Pulp Canal Sealer incorporating chitosan nanoparticles (CS), or after surface treatment with phosphorylated CS (PHCS), chitosan-conjugated Rose Bengal (CSRB) and a combination of both (RBPH). The control group used unmodified sealer. Specimens were aged 1- or 4-weeks. Enterococcus faecalis biofilms were grown on specimens for 7days and assessed with confocal laser scanning microscopy. In the 4-week aged specimens only, the mean biofilm areas were lower than the control for CS, PHCS and RBPH. Percentage of biofilm-covered interface was lower than the control for CS and PHCS. CS, PHCS and RBPH did not differ. Incorporating chitosan nanoparticles into sealer affected inhibition of biofilm formation within the sealer-dentin interface. This was maintained with PHCS, but moderated by CSRB.

This study assessed biofilm formation within sealer-dentin interfaces of root segments filled with gutta-percha and zinc oxide sealer incorporated with chitosan nanoparticles, without and with canal surface treatments. Bovine root segments were filled using Pulp Canal Sealer incorporating chitosan nanoparticles (CS), or after surface treatment with phosphorylated CS (PHCS), chitosan-conjugated Rose Bengal (CSRB) and a combination of both (RBPH). The control group used unmodified sealer. Specimens were aged 1- or 4-weeks. Enterococcus faecalis biofilms were grown on specimens for 7days and assessed with confocal laser scanning microscopy. In the 4-week aged specimens only, the mean biofilm areas were lower than the control for CS, PHCS and RBPH. Percentage of biofilm-covered interface was lower than the control for CS and PHCS. CS, PHCS and RBPH did not differ. Incorporating chitosan nanoparticles into sealer affected inhibition of biofilm formation within the sealer-dentin interface. This was maintained with PHCS, but moderated by CSRB.

Large and small nanospheres, large and small nanoplates, nanorods and nanostars have been synthesized and fabricated into SERS substrates consisting of sandwiched and aggregated structure. Using 633 nm laser as excitation, individual SERS spectra of each labeling molecules, benzenethiol, 4-nitrobenzenethiol and 4-quinolinethiol, have been successfully obtained and the combination of these three molecules have the least amount of overlapping and can all be identified from the reference multiplexed spectra. Among all the substrates that have analyzed, the substrate made from nanospheres with sandwiched structure is able to produce multiplexed SERS spectra with more details and higher reproducibility. Although multiplexed SERS spectra can also be observed from substrates made from small nanoplates, nanostars and nanorods substrates with sandwiched structures, the unique peaks representing the labeling molecules are less consistent in their intensity. In addition, substrates with micro sized plates in sandwiched configuration are found to exhibit much lower SERS activities and this can be due to the size of the plate being much greater than the light source, restraining the surface plasmon resonance effect. Most of the substrates fabricated with aggregated nanoparticles have very low reproducibilities and saturated signals with 633 nm excitation. The spectra peaks are much easier to identify and are much more reproducible when 785 nm excitation have been adopted. This can be due to the size of the aggregated nanoparticles are much bulkier which a deeper penetrating light source is required to induce more molecules labels to exhibit SERS activities. A novel SERS substrate has been fabricated with nanoparticle-thiol-microplate sandwiched configuration by using a double ended thiol molecules, benzenedithiol, to strongly connect nanospheres and the plates together. However, the measurement of the SERS activity is limited by the overpowering of the light source, which has frequently melted and evaporated the plate samples once they have been exposed to the excitation radiation. In addition, instead of spreading evenly on the microplate surfaces, the nanoparticles have appeared to be aggregated which may have increased the difficulty in obtaining SERS activity.

This thesis describes some experiments developed to probe the fundamental aspects of the interfacial behaviour of proteins. The contents of this thesis can be broadly divided into two parts. In the first part, we studied how the size of the nanoparticles and other variables such as pH and bulk protein concentration affect the structure of the adsorbed protein layers. We also probed how these factors can influence the binding activity of adsorbed proteins. Study on the adsorption of IgG, Protein A and streptavidin on gold nanoparticles reveals that not all proteins are similarly affected by the size of the adsorbing surface. We found that though the optical properties of all the proteins vary with the size of the nanoparticle, their functionalities are not similarly affected by nanoparticle curvature. Protein A and streptavidin retain their binding capacity to IgG and biotin, respectively, irrespective of the size of the gold nanoparticle that they are attached to. On the other hand, a reduction/ loss in binding of adsorbed IgG to Protein A molecules is observed. The reduction in biological activity further depends on the radius of curvature of the adsorbing surface. The second part of the thesis describes how nanoparticles can used as a probe to study the complex interfacial behaviour of proteins. We have utilized the extreme sensitivity of localized surface plasmon resonance (LSPR) of gold nanoparticles to local refractive index to determine the optical properties of BSA adsorbed on various polymer surfaces. The dielectric properties of the adsorbed protein depend on the nature of the substrate. Further, we have developed a model to determine the refractive index profile of adsorbed protein as a function of the distance from the substrate.

Superparamagnetic iron oxide nanoparticles (SPIONs), due to their controllable sizes, relatively long in vivo half-life and limited agglomeration are ideal for biomedical applications such as magnetic labeling, hyperthermia cancer treatment, targeted drug delivery and for magnetic resonance imaging (MRI) as contrast enhancement agents. However, very limited studies exist on detecting and characterizing these SPIONs in vitro in physiologically relevant conditions. It would be of interest to localize and characterize individual SPIONs at the nanoscale in physiologically relevant conditions. MFM offers great potential for this purpose. We evaluate the applicability of Magnetic Force Microscopy (MFM) in air as well as in liquid to characterize bare and SiO2 coated SPIONs on mica .The magnetic properties of bare and SiO2 coated SPIONs are compared on the nanoscale using MFM. MFM phase- shift dependence on scan height is investigated using SPION samples that have been coated in hydrophobic polymers, polystyrene (PS) and poly (methyl methacrylate) (PMMA). The polymers are used to spin-coat SPION samples and mimic cell lipid bilayers. Nanoscale MFM images of SPIONs in a liquid environment, covered with these hydrophobic polymers are also presented for the first time. The use of 3-merceptopropyltrimethoxysilane (3-MPTS) to covalently attach SiO2 SPIONs to gold substrates for the potential purpose of MFM imaging in liquid is also briefly addressed. These results will allow us to understand the feasibility of detecting magnetic nanoparticles within cell membranes without any labeling or modifications and present MFM as a potential magnetic analogue for fluorescence microscopy. These results could be applied to cell studies and will lead to a better understanding of how SPIONs interact with cell membranes and have a valuable impact for biomedical applications of all types of magnetic nanoparticles.

From catalytic studies in surface science, it has been shown that the catalytic activity is dependent on the type of metal facet used. Nanocrystals of different shapes have different facets. This raises the possibility that the use of metal nanoparticles of different shapes could catalyze different reactions with different efficiencies. The catalytic activity is found to correlate with the fraction of surface atoms located on the corners and edges of the tetrahedral, cubic, and spherical platinum nanoparticles. It is observed that for nanoparticles of comparable size, the tetrahedral nanoparticles have the highest fraction of surface atoms located on the corners and edges and also have the lowest activation energy, making them the most catalytically active. Nanoparticles have a high surface-to-volume ratio, which makes them attractive to use compared to bulk catalytic materials. However, their surface atoms are also very active due to their high surface energy. As a result, it is possible that the surface atoms are so active that their size and shape could change during the course of their catalytic function. It is found that dissolution of corner and edge atoms occurs for both the tetrahedral and cubic platinum nanoparticles during the full course of the mild electron transfer reaction and that there is a corresponding change in the activation energy in which both kinds of nanoparticles strive to behave like spherical nanoparticles. When spherical palladium nanoparticles are used as catalysts for the Suzuki reaction, it is found that the nanoparticles grow larger after the first cycle of the reaction due to the Ostwald ripening process since it is a relatively harsh reaction due to the need to reflux the reaction mixture for 12 hours at 100 oC. When the tetrahedral Pt nanoparticles are used to catalyze this reaction, the tetrahedral nanoparticles transform to spherical ones, which grow larger during the second cycle. In addition, studies on the effect of the individual reactant have also provided clues to the surface catalytic process that is taking place. In the case of the electron transfer reaction, the surface catalytic process involves the thiosulfate ions binding to the nanoparticle surface and reacting with the hexacyanoferrate (III) ions in solution. In the case of the Suzuki reaction, the surface catalytic mechanism of the Suzuki reaction involves the phenylboronic acid binding to the nanoparticle surface and reacting with iodobenzene via collisional processes.

This thesis consists of two distinct components: (1) Spin-polarized electron transport through aluminum array nanoparticles, (2) A single electric relaxation process in Barium Strontium Titanate (BST) nanoparticles. In the first chapter, we summarize our main results and new finding, and we also present our motivation. For the first component (chapters 2-5), we studied electron spin transport in nanometer scale aluminum grains as embedded in a ferromagnet tunneling junction. We observed tunnelling-magnetoresistance (TMR) and spin valve effects. From the TMR strong asymmetry with bias voltage, we explored spin relaxation effects. Additionally we also obtained the spin-coherence time on the order of nanoseconds by using the Hanle effect. For the second component (chapters 6-9), we investigated the dielectric response of BST and Barium Titanate (BTA) (high dielectric constant ferroelectrics) nanoparticles. The results were found to be quite unusual when compared with the dielectric response of film or bulk. The dielectric response is Debye relaxation with only a single relaxation time, and the relaxation time exhibits the Arrhenius Law at temperatures below 200 Kelvin.

Magnetic particles offer attractive features, so its development in a wide range of disciplines, including medical applications, has been very fruitful. As a result of the special physical properties of magnetic nanoparticles, many potential applications are made available in biomedicine. The most important feature of these particles is its magnetic forces, and it has been utilized in applications such as magnetic separation, drug delivery, hyperthermia and magnetic resonance imaging contrast agent. The important properties of magnetic particles for biomedical applications are nontoxicity, biocompatiblilty, injectability, and high-level accumulation in the target tissue or organ to two most important property among those mentioned above are nontoxicity and biocompatiblilty for available clinical trials. Some researchers have used polymers or polysaccharides coating on these surface of the magnetic material to improve the material's nontoxicity and biocompatiblilty. Common materials are dextran, polyethylene glycol, polyvinyl alcohol, starch and chitin and so on. We embedd Fe3O4 magnetic nanoparticles into agar hydrogels in the experiment, then made into powder by drying and grinding, using XRD, FTIR, TEM, SQUID, TGA and zeta potential identification of material properties. We examined its toxicity and the possibility for large scale production. This method can make use of simple and inexpensive way to mass-produce synthetic these biocompatible magnetic materials.