This thesis focuses on understanding implications of nanomaterial quality control and mass transport through internally etched silica coated nanoparticles for direct and quantitative molecular detection using surface enhanced Raman scattering (SERS). Prior to use, bare nanoparticles (partially or uncoated with silica) are removal using column chromatography to improve the quality of these nanomaterials and their SERS reproducibility. Separation of silica coated nanoparticles with two different diameters is achieved using Surfactant-free size exclusion chromatography with modest fractionation. Next, selective molecular transport is modeled and monitored using SERS and evaluated as a function of solution ionic strength, pH, and polarity. Molecular detection is achieved when the analytes first partition through the silica membrane then interact with the metal surface at short distances (i.e., less than 2 nm). The SERS intensities of unique molecular vibrational modes for a given molecule increases as the number of molecules that bind to the metal surface increases and are enhanced via both chemical and electromagnetic enhancement mechanisms as long as the vibrational mode has a component of polarizability tensor along the surface normal. SERS signals increase linearly with molecular concentration until the three-dimensional SERS-active volume is saturated with molecules. Implications of molecular orientation as well as surface selection rules on SERS intensities of molecular vibrational modes are studied to improve quantitative and reproducible SERS detection using internally etched Ag@Au@SiO2 nanoparticles. Using the unique vibrational modes, SERS intensities for p-aminothiophenol as a function of metal core compositions and plasmonics are studied. By understanding molecular transport mechanisms through internally etched silica matrices coated on metal nanoparticles, important experimental and materials design parameters are learned, which can be subsequently applied to the direct and quantifiable detection of small molecules in real samples without the need for lengthy separations and assays.

Le domaine des nanomatériaux joue un rôle de plus en plus important dans de nombreuses applications, qu'elles soient de natures biologique, médicales électroniques etc... Dans ce travail, nous présenterons des résultats concernant deux types de nanoparticules, le premier genre traite de nanoparticules hybrides confectionnées chimiquement pour des fins biologiques, le deuxième concerne des nanocristaux de silicium fabriqués par pyrolise laser pour des applications potentielles en optoélectronique. Les études sont menées en mettant en œuvre deux différentes techniques optiques, l'une en champ lointain, l'autre en champ proche. Dans le cas des nanohybrides, nous nous intéresserons à une caractérisation par microscopie en champ proche, qu'elle soit de nature spectroscopique ou d'imagerie simple, en utilisant en particulier une configuration optique guidante. Nous ferons un premier point à propos de l'émission de ses nanoparticules, puis discuterons des problèmes d'artefacts et de la résolution des images que nous pouvons atteindre avec notre montage. Nous prouverons l'importance essentielle du rôle des nanohybrides en tant que marqueur biologiques, et ceci dans deux différentes types de configuration de capteurs biologiques. Les nanoparticules de silicium de petites tailles (< 3 nm) seront étudiées essentiellement par microscopie confocale. Plus précisément, nous nous intéressons aux différents procédés de luminescence qui ont lieu lors de l'excitation d'une nanoparticule unique, en tenant compte des effets de taille et de surface. Nous chercherons à étudier l'influence de l'environnement des nanoparticules sur leurs propriétés spectrales en les plaçant dans des couches minces de natures diélectriques différentes. Nous conclurons enfin sur une brève description des différents effets Sark qui prennent lieu dans un tel système.

X-ray fluorescence is a well-understood phenomenon in which irradiation of certain materials, such as gold, with x-rays causes the emission of secondary x-rays with characteristic energies. By performing computed tomography using these fluorescence x-rays, the material of interest can be imaged inside an object. Our research group has already demonstrated that x-ray fluorescence computed tomography (XFCT) imaging using a typical 110 kVp microfocus x-ray tube is feasible for a small animal-sized object containing a distribution of a solution of low concentration gold nanoparticles. The primary goal of this thesis work was to study the effect of source x-ray energy spectra on gold fluorescence detection using the XFCT system. A computational approach using the Monte Carlo method was used. First, a computational model was created using the Monte Carlo N-Particle (MCNP) transport code based on the experimental setup of the pre-existing XFCT system. Simulations were run to verify the validity of the MCNP model as an accurate representation of the actual system by means of comparison with experimentally-obtained data. Finally, the model was used for further purely computational work. In the MCNP model, the source spectrum was changed to reflect several theoretical and experimentally obtained options. The effect of these changes on gold fluorescence production was documented and quantified using the signal-to-background ratio and other qualitative measures. The results from this work provided clues on how to improve the detection of fluorescence photons from gold nanoparticle-loaded objects using the XFCT system. This will benefit future research on the development of the XFCT system in the context of making it more feasible for gold nanoparticle-based preclinical molecular imaging applications.

Aquesta tesi engloba la síntesi i la caracterització estructural i magnètica de dos tipus de nanopartícules polymagnètiques: estructures nucli-escorça (core|shell, CS) i tipus ceba (onion-like). El primer sistema està format per un nucli-MnO|escorça-Mn 3O4 ( -Mn2O3) amb doble inversió, on el nucli i l'escorça mostren un comportament AFM i FiM, respectivament . Es de neix com estructuralment inversa ja que l'AFM es localitza al nucli i el FiM a l'escorça; a més, també es troba magnèticament invertida, és a dir, la temperatura de Néel de l'AFM presenta valors més elevats que la temperatura de Curie del FiM. Les nanopartícules nucli-escorça de MnO|Mn3O4 ( -Mn2O3) s'han obtingut a través de la passivació controlada de l'escorça de nanopartícules de MnO prèviament sintetitzades. Aquest procés permet controlar tant la grandària del nucli com el gruix de l'escorça. Es va con rmar que la composició de l'escorça un cop passivada depèn de la grandària inicial de les nanopartícules; conseqüentment, les nanopartícules més grans estan formades principalment per Mn3O4. No obstant, a mesura que es disminueix la grandària, la densitat de defectes augmenta obtenint, d'aquesta manera, una escorça més estable formada per la fase -Mn2O3. D'altra banda, nuclis AFM de MnO relativament petits poden induir un efecte magnètic de proximitat (magnetic proximity e ects) a l'escorça de FiM -Mn2O3 tot mantenint el seu ordre magnètic molt per sobre de la seva temperatura de Curie, TC; a més, aquest sistema presenta un augment de la temperatura de Néel de l'AFM. El segon sistema es basa en la síntesi de nanopartícules d'òxid de manganès i ferro del tipus nucli-escorça i ceba. Nanopartícules de dos òxids de ferro diferents (FeO|Fe3O4 CS i Fe3O4 monofàsica) s'han utilitzat com a llavors per a la posterior deposició d'òxid de manganès. A partir de les llavors nucli-escorça d'òxid de ferro s'han sintetitzat dos tipus de nanopartícules ceba (tres-components FeO|Fe 3O4|Mn3O4 i quatre-components FeO|Fe3O4|MnO|Mn3O4). D'altra banda, nanopartícules d'òxid de ferro monofàsiques han estat utilitzades com a llavors per a dipositar una capa na de manganès al seu voltant amb l'objectiu d'incentivar l'interdifusió del manganès-ferro i formar nanopartícules nucli-escorça de MnxFe3 ��xO4|FexMn3 ��xO4 amb una interfase graduada. S'ha observat que l'òxid de manganès creix epitaxialment en els plans (111) sobre les cares truncades del llavors cúbiques d'oxid de ferro. Finalment, nanopartícules nucli-escorça de MnxFe3 ��xO4|FexMn3 ��xO4 formades per una estructura tou-FiM/dur- FiM amb una composició gradual a l'interfase demostren un bon l'acoblament magnètic entre ambdues, tova i dura, fases FiM. / This thesis deals with the synthesis and magnetic and structural characterization of two di erent systems based in polymagnetic nanoparticles with core|shell (CS) and onion-like architectures. The rst system is formed by a double inverted core-MnO|shell- Mn3O4 ( -Mn2O3) where core and shell display an antiferromagnetic (AFM) and ferrimagnetic (FiM) behavior, respectively. It is de ned as structurally inverted since the AFM is placed in the core and the FiM in the shell (in contrast to conventional ferromagnetic( FM)/AFM CS systems); in addition, it is, also, magnetically inverted because the Néel temperature of the AFM is larger than the Curie temperature of the FiM (contrarily to standard exchange bias systems). MnO|Mn3O4 ( -Mn2O3) CS nanoparticles have been synthesized through the controlled shell passivation of pre-made MnO nanoparticles. This procedure allows reaching a good control over the nal core size and shell thickness. It was con rmed that the passivated shell composition depends on the nanoparticle size, where the larger nanoparticles presenting mainly Mn3O4. However, when the size diminishes, the density of defects in the MnO core increases and consequently -Mn2O3 is the more stable shell phase. Besides, small AFM MnO cores can induce a magnetic proximity e ect to the FiM -Mn2O3 shell, maintaining its magnetic order well above its Curie temperature, TC. Moreover, surface e ects in the MnO core can also lead an increase of the Néel temperature of the AFM. Further, given the AFM/FiM exchange coupling the system exhibits large coercivities and loop shifts along the eld axis, i.e., exchange bias. The second type of system comprises the synthesis of CS and onion-like nanoparticles based in manganese and iron oxides. Two di erent iron oxide nanoparticles (FeO|Fe3O4, AFM|FiM, CS and single phase FiM Fe3O4) have been used as seeds for the posterior manganese oxide deposition. From iron oxide CS seeds two di erent onion-like nanoparticles (three-components FeO|Fe3O4|Mn3O4 and four-components FeO|Fe3O4|MnO|Mn3O4) have been synthesized. The temperature dependence of the magnetization of these onion nanoparticles exhibits several magnetic transitions, in concordance with the presence of diverse magnetic phases. In addition, single phase iron oxide seeds were employed to deposit a manganese thin shells at high temperatures forcing a manganese-iron interdi usion to form the nal MnxFe3 �xO4|FexMn3 �xO4 CS nanoparticles with a graded interphase. The structural results show that the (111) planes of the manganese oxide grow epitaxially onto the (111) planes of the truncated faces of the initial cubic iron oxide seeds. Finally, the CS MnxFe3 �xO4|FexMn3 �xO4 nanoparticle, formed by soft-FiM|hard-FiM structure with a graded interphase composition, shows a strong exchange coupling between the hard and soft FiM phases.

In this thesis two issues in nanotechnology have been addressed. The first is the comprehensive characterization of engineered nanomaterials prior to their examination in toxicology and environmental studies. The second is the development of a method to produce nanostructure arrays over large areas and for low cost. A major challenge when assessing nanomaterial’s risks is the robust characterization of their physicochemical properties, particularly in commercial products. Such data allows the critical features for biological outcomes to be determined. This work focused on the inorganic oxides that were studied in powdered and dispersed forms as well as directly in consumer sunscreen products. The most important finding was that the commercial sunscreens that listed titania or zinc oxide as ingredients contained nanoscale materials. Cell free photochemical tests revealed that ZnO particles without any surface coating were more active at generating ROS than surface coated TiO2 nanoparticles. These studies make clear the importance of exposure studies that examine the native form of nanomaterials directly in commercial products. The second part of this thesis presents the development of a new method to fabricate gold nanoring and nanocrescent arrays over large areas; such materials have unique optical properties consonant with those described as metamaterials. A new shaped nanosphere lithography approach was used to manipulate the form of silica nanospheres packed onto a surface; the resulting array of mushroom structures provided a mask that after gold evaporation and etching left either golden rings or crescents over the surface. The structures had tunable features, with outer diameters ranging from 200 to 350 nm for rings and crescent gap angles of ten to more than a hundred degrees. The use of a double mask method ensured the uniform coverage of these structured over 1 cm2 areas. Experimental and theoretical investigations of the optical properties of the arrays revealed the optical resonances in the infrared region. Finally, in the course of developing the nanorings, etch conditions were developed to deposit large area arrays of polystyrene nanodoughnuts with diameters from 128 to 242 nm. These non-conductive structures provide an ideal template for further attachment of magnetic of optically emissive nanoparticles.

No description available.

Gold nanoparticles strongly absorb and scatter visible and near infrared light because of the strongly enhanced electric fields at the surface. This provides the potential of designing novel optically active reagents for simultaneous molecular imaging and photothermal cancer therapy. In this thesis, gold nanospheres and nanorods conjugated with anti-epidermal growth factor receptor (anti-EGFR) antibodies that specifically target EGFR on the cell surface are shown to be used for dual diagnostics and therapy. Using micro-absorption spectroscopy and light scattering imaging, cancerous (HOC 313 and HSC 3) and noncancerous cells (HaCat) can be differentiated due to the overexpression of EGFR on the surface of cancer cells. By irradiating the cells with a CW laser, selective photothermal cancer therapy is realized in visible region by using gold nanospheres and in near infrared region by using gold nanorods. The use of nanorods allow for in vivo therapy due to the fact that their absorption is in the near infrared region at which the laser light meets less interference from the tissue absorption. In addition, the catalytic effect of gold nanoparticles on the oxidization of NADH to NAD+ is investigated. The addition of gold nanoparticles is found to quench the NADH fluorescence intensities but has no effect on the fluorescence lifetime. This suggests that the fluorescence quenching is not due to coupling with the excited state, but due to changing the ground state of NADH. The intensity of the 340 nm absorption band of NADH is found to decrease while that of the 260 nm band of NAD+ is found to increase as the concentration of gold nanoparticles increase. This conversion reaction is further supported by nuclear magnetic resonance and mass spectroscopy. The linear relationship between the initial reaction rate of NADH and the concentration of gold nanoparticles strongly supports that NADH is surface catalyzed by the gold nanoparticles. The catalytic property of this important reaction might have important future applications in biological and medical fields.

This dissertation describes the use of spherical micro- and nanoparticles as building blocks for the fabrication of colloidal crystals. The polymer component used in all of the projects that are described herein is poly-N-isopropylacrylamide (pNIPAm). The polymeric identity of particles composed of this soft, hydrogel material, which is also thermoresponsive, contributes to particle self-assembly to form ordered structures. Specifically, particles that possess a core/shell topology were investigated to allow for the localization of distinct polymeric properties. Chapter 2 examines a characterization technique using fluorescence resonance energy transfer (FRET) that was explored to investigate the structure of pNIPAm particles that possess this core/shell topology. Chapters 4-6 investigate strategies to impart both stability and flexibility to the particles so that these properties could assist in particle self-assembly as well as provide a stable construct for the production of robust crystalline materials. Styrene was used as the main monomer component in a copolymer synthesis with NIPAm to achieve poly(styrene-co-N-isopropylacrylamide particles (pS-co-NIPAm) that exhibited both hard and soft properties. Simple drying procedures were used to form crystal assemblies with these particles and the application of these pS-co-NIPAm particle suspensions as processable, photonic inks is also investigated. Chapter 7 examines the ability to physically cross-link colloidal crystals composed of pS-co-NIPAm particles by simple heating methods to produce robust films. The optical properties of these crystal films could be tuned by simple rehydration of the film due to the hydrogel character of the crystal building blocks. Chapters 3 and 5 examine the synthesis and self-assembly strategies of core/shell particles using the properties of pNIPAm shell layers that have been added to different types of core particles (silver or pS-co-NIPAm) for the purposes of fabricating colloidal crystals with enhanced properties using thermal annealing procedures. Chapter 8 explores the use of silver particles as tracers for the characterization of colloidal crystals composed of thermally annealed colloidal crystals composed of pNIPAm hydrogel particles.

The magnetic separation approach has several advantages compared with conventional separation methods / it can be performed directly in crude samples containing suspended solid materials without pretreatment, and can easily isolate some biomolecules from aqueous systems in the presence of magnetic gradient fields. This thesis focused on the development of new class of magnetic separation material particularly useful for the separation of histidine-tagged proteins from the complex matrixes through the use of imidazole side chains of histidine molecules. For that reason surface modified cobalt ferrite nanoparticles which contain Ni-NTA affinity group were synthesized. Firstly, cobalt ferrite nanoparticles with a narrow size distribution were prepared in aqueous solution using the controlled coprecipitation method. In order to obtain small size of agglomerates two different dispersants, oleic acid and sodium chloride, were tried. After obtaining the best dispersant and optimum experimental conditions, ultrasonic bath was used in order to decrease the size of agglomerates. Then, they were coated with silica and this was followed by surface modification of these nanoparticles by amine in order to add functional groups on silica shell. Next, &ndash / COOH functional groups were added to silica coated cobalt ferrite magnetic nanoparticles through the NH2 groups. After that N&alpha / ,N&alpha / -Bis(carboxymethyl)-L-lysine hydrate, NTA, was attached to carboxyl side of the structure. Finally, nanoparticles were labeled with Ni (II) ions. The size of the magnetic nanoparticles and their agglomerates were determined by FE-SEM images, particle size analyzer, and zeta potential analyzer (zeta-sizer). Vibrational sample magnetometer (VSM) was used to measure the magnetic behavior of cobalt ferrite and silica coated cobalt ferrite magnetic nanoparticles. Surface modifications of magnetic nanoparticles were followed by FT-IR measurements. ICP-OES was used to find the amount of Ni (II) ion concentration that was attached to the magnetic nanoparticle.

In order to gain insights into the electronic interactions between metallic gold and self-assembled monolayers composed of π-conjugated thiols, a series of thiol-containing molecules based on a stilbene backbone were synthesized and assembled on gold surface. The resulted monolayers were characterized with a variety of surface-sensitive techniques and the electronic properties of the obtained surfaces were studied with the use of ultraviolet photoelectron spectroscopy. Work-function changes and alignment of the molecular energy levels with respect to the Fermi level of the metal were investigated and important insights regarding the electronic properties of the metal / organic interfaces were obtained. Another aspect of interactions between organic dyes and metallic gold was studied in the context of spectroscopic properties of systems incorporating gold nanoparticles with organic fluorophores covalently attached to the nanoparticle surface. Ultrafast dynamics of the excited-state deactivation of the organic fluorophores attached to the surface of gold nanoparticles were studied with the use of a fs transient absorption technique. It was found that the close proximity of a gold nanoparticle had a profound impact on the excited-state lifetime of the studied organic fluorophore. The influence of the structure of the studied systems on the excited-state deactivation dynamics of the organic fluorophores was described.