Photocatalysis is an advanced oxidation process for the purification and remediation of contaminated waters and wastewaters, and is advantageous over conventional treatment technologies due to its ability to degrade emerging and recalcitrant pollutants. In addition, photocatalytic disinfection is less chemical-intensive than other methods such as chlorination, and can inactivate even highly resistant microorganisms with good efficacy. Process sustainability and cost-effectiveness may be improved by utilizing solar irradiation as the source of necessary photons for photocatalyst excitation. However, solar-induced activity of the traditionally-used titania is poor due to its inefficient visible light absorption, and recombination of photo-excited species is problematic. Additionally, mass transfer limitations and difficulties separating the catalyst from the post-treatment slurry hinder conversions and efficiencies obtainable in practice. In this research, various strategies were explored to address these issues using novel visible light active photocatalysts. Two classes of carbon-enhanced photocatalytic materials were studied: activated carbon adsorbent photocatalyst composites, and carbon-doped TiO2. Adsorbent photocatalyst composites based on activated carbon and plasmonic silver/silver chloride structures were synthesized, characterized, and experimentally investigated for their photocatalytic activity towards the degradation of model organic pollutants (methyl orange dye, phenol) and the inactivation of a model microorganism (Escherichia coli K-12) under visible light. The adsorptive behaviour of the composites towards methyl orange dye was also studied and described according to appropriate models. Photocatalytic bacterial inactivation induced by the prepared composites was investigated, and the inactivation mechanisms and roles of incorporated antimicrobial silver on disinfection were probed and discussed. These composites were extended towards magnetic removal strategies for post-use separation through the incorporation of magnetic nanoparticles to prepare Ag/AgCl-magnetic activated carbon composites, and the effect of nanoparticles addition on the properties and photoactivities of the resulting materials was explored. Another silver/silver halide adsorbent photocatalyst composite based on activated carbon and Ag/AgBr exhibiting visible light absorption due to both localized surface plasmon resonance and optical band gap absorption was synthesized and its photocatalytic activity towards organics degradation and microbial inactivation was studied. Carbon-doped mixed-phase titania was also prepared and experimentally investigated.

A terahertz photoconductive source structure with nano-grating electrodes is proposed. The resonance modes of the one-dimensional nano-grating and their affect the optical power absorption are studied. In addition, an approach for optimal design of the grating to maximize the photocurrent for different proposed DC biases, is presented. The dependence of the photocurrent on physical parameters of photomixer are analyzed. A fast analysis method for a new terahertz waveguide for photo-mixing is proposed. The wave-guiding mixer structure is a modified parallel plate waveguide (PPWG) in which the top plate is replaced by a periodic array of sub-wavelength nano-slits. The substrate of the PPWG is made of a fast photoconductive material in which laser photomixing/absorption occurs. The characteristic equation of the modified PPWG when used as a THz waveguide is derived analytically, and its guided modes are studied in details over THz range of frequencies. The accuracy of the analytical results are verified by comparison with full-wave numerical simulations. The criteria for choosing the suitable mode for photomixing application are also discussed. Finally, based on dyadic Green’s function representation, a systematic approach is provided for calculating the amplitude of the guided modes that are excited by an arbitrary photocurrent.

The first section of this thesis concerns the study of interactions between the intense local plasmonic field generated by nanostructure and a well known photosynthetic protein system, bacteriorhodopsin (bR). bR is a membrane protein responsible for proton transport. Among the many intermediates formed upon photoexcitations, two of the most relevant have been studied. The intermediates under studies were I460 and M412, and their decay dynamics were measured in presence of the plasmonic field generated by the excitation of their surface electrons using visible photons. Both intermediates decay lifetime were affected when the plasmonic field was turned on, and it was verify that thermal effect were not the source of the change in dynamic. The second part concerns the investigation of third-order nonlinearity of a series of extended conjugated squaraine dyes in the telecommunication spectral region. Their nonlinearity is measured via Degenerate Four Wave Mixing and Z-scan as function of the dyes increasing conjugation length and number of squarylium groups. The dyes produced large real and imaginary values for the third order nonlinearity in the 1300-1500 nm range which makes them attractive for optical limiting type of applications.

Nanomatériaux de silice peuvent être facilement fabriqués, façonné et fonctionnalisés comme plates-formes pour le greffage des nanoparticules pour des applications biomédicales et optiques. Ici, nous utilisons une méthodologie basée sur un modèle de préparer une collection variée de hélicoïdale nanoparticules d'or (PNB) superstructures ayant impartialité contrôlable et mesures structurelles en utilisant PNB que les blocs de construction, et les nanohelices de silice que le modèle. Le matériaux présentent synthétisé bien définir Agencement chiral de PNB suivant l'hélicité de nanohelices de silice, montrant des signaux plasmoniques de dichorism circulaire (CD). D'autres observations ont prouvé ce plasmon CD vient de l'arrangement chiral de PNB et cet effet est très taille, l'échelle et dépend du pH. Nous nous attendons à ce que cette stratégie d'assemblage va découvrir une meilleure vue sur les métamatériaux et de susciter la vue vers "bottom-up" des approches en nanosciences. / Silica nanomaterials can be easily fabricated, fashioned and functionalized as platforms for grafting of nanoparticles for biomedical and optical applications. Herein, we utilize a template-based methodology to prepare a diverse collection of helical gold nanoparticle (GNPs) superstructures having controllable handedness and structural metrics by using GNPs as the building blocks, and the silica nanohelices as the template. The synthesized materials exhibit well-defined chiral arrangement of GNPs following the helicity of silica nanohelices, showing plasmonic circular dichorism (CD) signals. Further observations proved this plasmon CD comes from the chiral arrangement of GNPs and this effect is highly size, scale and pH dependent. We expect that this assembly strategy will discover a better view towards metamaterials and spark the view towards “bottom-up” approaches in nanoscience.

Magister Scientiae - MSc / With an increase in the amount of harmful carbon emissions in the atmosphere as well as a decrease in the availability of fossil fuels, there is a relatively high demand for alternate energy devices. Solar cells have become an alternative option in aid of leading the way for clean energy; however these devices are relatively expensive and have an efficiency that is relatively low in comparison to that of fossil fuelled energy. As a result the cost of the solar cell needs to be reduced by reducing the amount of silicon used in order to compete with fossil fuelled devices; however this decrease would lead to a decrease in efficiency. In recent years silver nanoparticles have been extensively researched as a result of its extraordinary optical, electrical, catalytic, magnetic and antibacterial properties. As a result of these properties, the nanoparticles may be applied to many research areas such as photovoltaics, catalysis and medical fields. The optical properties of silver nanoparticles may thus be exploited in order to increase absorption and in turn the efficiency of the solar cell devices. This study focuses on the optimization of the polyol synthesis to possibly obtain uniformly dispersed silver nanoparticles. The silver nanoparticles would then be incorporated onto amorphous silicon thin films, deposited by hot wire chemical vapour deposition, by spraying a suspension of the silver nanoparticles onto the thin films. The silver nanoparticles were viii characterized by Ultra Violet Visible Spectroscopy (UV-VIS), High Resolution Transmission Electron Microscopy, X-ray Diffraction, and Thermogravimetric Analysis. The thin films with the incorporated silver nanoparticles were characterized by UV-VIS, and High Resolution Scanning Electron Microscopy. It was shown that silver nanoparticles with various morphologies were produced by the polyol synthesis and may be used to enhance light trapping of thin film photovoltaic devices.

abstract: A proposed visible spectrum nanoscale imaging method requires material with permittivity values much larger than those available in real world materials to shrink the visible wavelength to attain the desired resolution. It has been proposed that the extraordinarily slow propagation experienced by light guided along plasmon resonant structures is a viable approach to obtaining these short wavelengths. To assess the feasibility of such a system, an effective medium model of a chain of Noble metal plasmonic nanospheres is developed, leading to a straightforward calculation of the waveguiding properties. Evaluation of other models for such structures that have appeared in the literature, including an eigenvalue problem nearest neighbor approximation, a multi- neighbor approximation with retardation, and a method-of-moments method for a finite chain, show conflicting expectations of such a structure. In particular, recent publications suggest the possibility of regions of invalidity for eigenvalue problem solutions that are considered far below the onset of guidance, and for solutions that assume the loss is low enough to justify perturbation approximations. Even the published method-of-moments approach suffers from an unjustified assumption in the original interpretation, leading to overly optimistic estimations of the attenuation of the plasmon guided wave. In this work it is shown that the method of moments approach solution was dominated by the radiation from the source dipole, and not the waveguiding behavior claimed. If this dipolar radiation is removed the remaining fields ought to contain the desired guided wave information. Using a Prony's-method-based algorithm the dispersion properties of the chain of spheres are assessed at two frequencies, and shown to be dramatically different from the optimistic expectations in much of the literature. A reliable alternative to these models is to replace the chain of spheres with an effective medium model, thus mapping the chain problem into the well-known problem of the dielectric rod. The solution of the Green function problem for excitation of the symmetric longitudinal mode (TM01) is performed by numerical integration. Using this method the frequency ranges over which the rod guides and the associated attenuation are clearly seen. The effective medium model readily allows for variation of the sphere size and separation, and can be taken to the limit where instead of a chain of spheres we have a solid Noble metal rod. This latter case turns out to be the optimal for minimizing the attenuation of the guided wave. Future work is proposed to simulate the chain of photonic nanospheres and the nanowire using finite-difference time-domain to verify observed guided behavior in the Green's function method devised in this thesis and to simulate the proposed nanosensing devices. / Dissertation/Thesis / M.S. Electrical Engineering 2013

Os metais nobres são admirados desde as culturas mais antigas por sua capacidade de refletir a luz. Com os desenvolvimentos na área da nanotecnologia se pode entender um pouco mais sobre a interação entre a luz e estes metais. Devido a esta interação foi criada a Plasmônica e a partir dela começaram os estudos acerca dos plasmons de superfície (SP). Estes estudos vêm gerando inúmeros desenvolvimentos nas pesquisas de gravação magneto-ótica, microscopia, detectores moleculares biológicos entre outras. Como os SPs são ondas evanescentes, eles precisam ser observados em campo próximo. Com o intuito de observar e compreender a propagação destes SPs foi utilizado um microscópio ótico de varredura em campo próximo (SNOM). Para isto, o SNOM foi adaptado para operar em modo de transmissão. A sonda do SNOM serviu de coletora de luz para que a partir de imagens óticas em amostras de Ag e Au pudéssemos caracterizar a propagação destes SPs na superfície do material e também a sua dependência com a distância de detecção. Os resultados mostraram que a propagação do SP é maior que 70m e a intensidade do SP na superfície do metal depende fortemente da rugosidade da amostra e de possíveis defeitos. Foi possível ainda estimar a que distância a partir da superfície da amostra, em que o SP decai para 1/e. Este resultado está de acordo com o esperado teoricamente, que prevê para a distância de propagação do SP, o valor de 420nm. Através do SP ainda foi possível analisar defeitos existentes na amostra. E pelas imagens topográficas do SNOM também foi possível observar os grãos de Ag e Au da amostra. Em posse destes resultados pudemos concluir que o SNOM é uma ótima ferramenta para a análise dos plasmons de superfície. / The noble metals are largely admired since ancient cultures because of its capability to reflect light. With the development of nanotechnology it is possible now to understand the interaction between these metals and light. Due to this strong interaction, the Plasmonic area was created and the studies on Surface Plasmons(SP) started. These studies are responsible for important new developments in magneto-optical recording, new optical microscopy apparatus, molecular biological sensors, among others. As SPs are evanescent waves, they need to be observed in near-field optics. For the observation and study of the propagation of these SPs a scanning near-field optical microscope (SNOM) was used. The SNOMs probe was used in collection mode so that we could characterize the propagation of SPs in the material surface and the dependence with the distance of detection in air, for thin films of Ag and Au. The results showed that the propagation of the SP inside the metallic film is beyon 70m. And the SPs intensity in the metal surface is strongly dependent on the roughness of the sample. It was also possible to estimate the distance from the samples surface the SP decay to 1/e. Our measurements agree to the theoretical calculation of 420nm for this distance. The SP made it possible to analyze existing defects on the sample. Furthermore, with the SNOM topographical images it was also possible to observe the grains of the policrystalline Ag and Au samples. From these results we could conclude that the SNOM is a very useful tool for the analysis of surface plasmons in thin films.

Smart nanomaterials can selectively respond to a stimulus and consequently be activated in specific conditions, as a result of their interaction with electromagnetic radiation, biomolecules, pH change, etc. These nanomaterials can be produced through distinct routes and be used in artificial skin, drug delivery, and other biomedical applications. In this thesis, two smart nanosystems were developed, viz., i) nanocapsules formed by aniline (A) and chitosan (CS) (A-CS) containing silver nanoparticles (AgNPs), with an average size of 78 ± 19 nm, and ii) polycaprolactone (PCL) nanofibers, fabricated by the electrospinning technique containing AgNP into their bulk, with a diameter of 417 ± 14 nm. A novel system, based on the incorporation of the as-prepared nanocapsules onto the surface of PCL nanofibers containing AgNps (antibacterial mats), was also developed. The methodology employed avoids the direct contact of silver nanoparticles with the host and optimizes its release to the surrounding environment. The AgNPs release was triggered by exposing the nanocapsules to light at 405 nm. Consequently, the electronic energy vibration resulting from the interaction of the irradiation with the surface plasmon band (SPR) of AgNps, breaking the hydrogen bonds of the nanocapsules and releasing of AgNPs at a time of 150 s. To understand the perturbation of AgNps-Nanocapsules against bacteria, membrane models using Langmuir technique with the phospholipids 1,2-dipalmitoyl-sn-glycero-3-phospho-(1\'-rac-glycerol) (DPPG) and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) were employed, which are the main components of cell membrane of Escherichia coli (E. coli). The results suggest that DPPG has more influence on the incorporation of the nanoparticles on the cell membrane. The antibacterial properties of the nanofibers/nanomaterials mats towards E. coli and Staphylococcus aureus (S. aureus) were investigated using the Agar diffusion test for 8 samples. The experiments revealed that the samples based on nanofibers/nanocapsules and irradiation presented a radius of inhibition of 2.58 ± 0.28 mm for S. aureus and 1.78 ± 0.49 mm for E. coli. This nanosystem showed to be highly interesting for biomedical applications. / Nanomateriais inteligentes podem responder seletivamente a um estímulo e consequentemente ser ativados em condições específicas, como resultado da sua interação com a radiação eletromagnética, mudança do pH, campo magnético, etc. Esses materiais podem ser produzidos através de distintas rotas e utilizados em aplicações como pele artificial, liberação de fármacos, e outras aplicações biomédicas. Nessa tese, dois nanossistemas inteligentes foram desenvolvidos, a saber: i) nanocápsulas formadas por anilina (A) e quitosana (CS) (A-CS) contendo nanopartículas de prata (AgNps), com um tamanho médio de 78 ± 19 nm, e ii) nanofibras de policaprolactona (PCL), fabricadas pela técnica de eletrofiação contendo AgNps em seu interior, com diâmetro de 417 ± 14 nm. Um terceiro sistema foi desenvolvido, baseado na incorporação das nanocápsulas na superfície das nanofibras de PCL contendo AgNps (manta antibacteriana). A metodologia utilizada evita o contato direto das nanopartículas de prata com o hospedeiro e otimiza sua liberação no meio ambiente. As AgNps liberadas foram acionadas pela exposição das nanocápsulas à um fonte de luz em 405 nm. Consequentemente, a vibração da energia eletrônica resultante da interação da irradiação com a banda plasmônica de superfície (SPR) das AgNps, quebra as ligações de hidrogênio da nanocápsula e libera as AgNps no meio em um tempo de 150 s. Para entender a perturbação das AgNps-nanocapsulas contra as bactérias, modelos de membrana foram usados através da técnica de Langmuir com os fosfolipídios 1,2-dipalmitoil-sn-glicero-3- fosfo-(1\'-rac-glicerol) (DPPG) and 1,2-dimiristoil-sn-glicero-3-fosfoetanolamina (DMPE), que são os principais componentes da membrana celular de Escherichia coli (E. coli). Os resultados sugerem que DPPG tem mais influência na incorporação das nanopartículas na membrana celular. As propriedades antibacterianas das mantas de nanofibras/nanomateriais contra E. coli e Staphylococus aureus (S. aureus) foram investigadas usando o teste de difusão Agar em 8 grupos, o qual revelou que o grupo contendo a nanofibra/nanocapsula e irradiação apresentou um raio de inibição de 2.58 ± 0.28 mm para S. aureus e 1.78 ± 0.49 mm para E. coli. Este nanossistema mostrou ser altamente interessante para aplicações biomédicas.

Multifunctional plasmonic nanoparticles have shown extraordinary potential for near infrared photothermal and triggered-therapeutic release treatments of solid tumors. However, the accumulation rate of the nanoparticles in the target tissue, which depends on their capacity to escape the immune system, and the ability to efficiently and accurately track these particles in vivo are still limited. To address these challenges, we have created two different systems. The first one is a multifunctional nanocarrier in which PEG-coated gold nanorods were grouped into natural cell membrane vesicles from lung cancer cell membranes (A549) and loaded with β-lap (CM-β-lap-PEG-AuNRs). Our goal was to develop specific multifunctional systems for cancer treatment by using the antigens and the unique properties of the cancer cell membrane combined with photothermal properties of AuNRs and anticancer activity of β-lap. The results confirmed the assembly of PEG-AuNRs inside the vesicles and the irradiation with NIR laser led to disruption of the vesicles and release of the PEG-AuNRs and β-Lap. In vitro studies revealed an enhanced and synergic cytotoxicity against A549 cancer cells, which can be attributed to the specific cytotoxicity of β-Lap combined with heat generated by laser irradiation of the AuNRs. No cytotoxicity was observed in absence of laser irradiation. In the second system, MRI-active Au nanomatryoshkas were developed. These are Au core-silica layer-Au shell nanoparticles, where Gd(III) ions are encapsulated within the silica layer between the inner core and outer Au layer of the nanoparticle (Gd-NM). This theranostic nanoparticle retains its strong near infrared optical absorption properties, essential for in vivo photothermal cancer therapy, while simultaneously providing increased T1 contrast in MR imaging by concentrating Gd(III) within the nanoparticle. Measurements of Gd-NM revealed a substantially enhanced T1 relaxivity (r1 ~ 17 mM-1 s-1) even at 4.7 T, surpassing conventional Gd(III)-DOTA chelating agents (r1 ~ 4 mM-1 s-1) currently in clinical use. The observed relaxivities are consistent with Solomon-Bloembergen-Morgan (SBM) theory, describing the longer-range interactions between the Gd(III) and protons outside the nanoparticle. These novel multifunctional systems open the door for the development of more efficient nanoplatforms for diagnosis and treatment of cancer. / Nanopartículas plasmônicas multifuncionais têm revelado elevado potencial para fototermia na região (NIR) do infravermelho e liberação controlada de fármacos para o tratamento de tumores sólidos. No entanto, a taxa de acumulação das nanoparticulas no tecido alvo, que depende da capacidade delas de escapar do sistema imunológico, e a habilidade de rastrear de maneira efetiva essas partículas in vivo ainda são limitadas. Para superar essas barreiras, dois sistemas diferentes foram desenvolvidos. O primeiro corresponde a um nanocarreador multifunctional, onde nanobastões de ouro funcionalizados com PEG foram agrupados dentro de vesículas de membranas de células naturais originarias de células cancerígenas de pulmão (A549) conjugadas com β-Lap (CM-β-lap-PEG-AuNRs). Nosso principal objetivo foi desenvolver um sistema multifuncional especifico para tratamento de câncer utilizando os antígenos e propriedades únicas da membrana das células cancerígenas combinados com as propriedades fototérmicas dos AuNRs e a atividade anticancerígena da β-Lap. Os resultados confirmaram o agrupamento dos PEG-AuNRs dentro das CM e irradiação com o laser no NIR levou ao rompimento das vesículas e liberação dos AuNRs e β-Lap. Estudos in vitro revelaram uma elevada e sinérgica citotoxicidade contra células A549, que pode ser atribuída a combinação da especifica toxicidade da β-Lap com o calor gerado pelos AuNRs por meio da irradiação com laser. Nenhuma citotoxicidade significativa foi observada na ausência de irradiação com laser. No segundo sistema, nanomatryoshkas de Au ativas em MRI foram desenvolvidas. Elas consistem em um núcleo de Au, uma camada intersticial de sílica, onde os íons de Gd(III) são encapsulados, e uma camada externa de Au (Gd-NM). Esta nanopartícula teranóstica mantém as propriedades de elevada absorção óptica no NIR, enquanto simultaneamente fornece um elevado contraste T1 em imagem por ressonância magnética por meio da concentração dos íons de Gd(III) dentro da nanoparticula. Medidas de Gd-NM revelaram uma relaxividade elevada (r1 ~ 17 mM-1 s-1 ) a 4,7 T, superando os convencionais agentes quelantes de Gd(III)-DOTA (r1 ~ 4 mM-1 s-1) utilizados clinicamente. As relaxividades observadas são consistentes com a teoria Solomon-Bloembergen-Morgan (SBM), descrevendo as interações de longo alcance entre Gd(III) e prótons de H fora da partícula. Os novos sistemas multifuncionais desenvolvidos abrem oportunidades para o desenvolvimento de nanoplataformas mais eficientes para o diagnóstico e tratamento de câncer.

Dans cette thèse, la définition du SERS en tant que biocapteur a été testée et une nouvelle approche a été développée. Ainsi, concernant la quantification, il est montré que le SERS peut-être un outil très efficace. Concernant la sélectivité, la qualité spectrale a été améliorée. Une excellente limite de détection associée à l’approche statistique et dynamique permet une très bonne sensibilité (inférieure au nanomolaire). Cette approche permet également une grande reproductibilité du capteur dans le temps. Ainsi, alors que le SERS ne réponds pas forcément bien aux caractéristiques d’un capteur dans son approche classique, dans notre cas le couplage entre un substrat de nanoparticules d’or non fonctionnalisées associé à un système microfluidique, le tout monté sur un microscope confocal pour des études temporelles dynamiques analysées statistiquement a contribué à définir le SERS comme un biocapteur efficace. / In this thesis, the definition of SERS as a biosensor has been tested and a new approach developed for. Also, in terms of quantification, it has been shown that SERS can be an efficient tool. Concerning the selectivity, the spectral quality was improved. A low limit of detection associated to the statistical and dynamic approach allows a very good sensitivity (under the nanomolar). This approach also enables a high reproducibility in time of the sensor. Thus, as low as SERS does not well answer to the sensor capabilities in a classical approach, in our case the coupling between a non-functionalized GNPs substrate coupled with a microfluidic chip, all mounted on a confocal microscope for temporal dynamic studies statistically analyzed has contributed to define SERS as an efficient biosensor.