O óxido nítrico além de poluidor ambiental, também desempenha diversas funções no organismo, por exemplo, trata-se de uma molécula sinalizadora em diversos processos metabólicos. Por causa disso, a detecção de NO é uma importante ferramenta para a medicina. Assim, existe um significante interesse tanto da indústria como da medicina no desenvolvimento de novos materiais que possam detectar oxido nítrico Os Nanotubos de Carbono de Paredes Múltiplas, intensivamente explorados desde sua descoberta em 1991, são considerados promissores em diversas aplicações devido a sua estrutura única e a possibilidade de realizar modificações as quais influenciam suas propriedades físicas e químicas. Já o ouro, conhecido por sua baixa atividade catalíca quando utilizado na forma cristalina, começou a ter seu poder catalítico explorado a partir de 1985, quando descobriu-se que, se utilizado na forma de pequenas partículas, este comporta-se mais como átomos individuais e torna-se mais catalítico que o ouro cristalino. Assim, o objetivo deste trabalho foi promover a funcionalização dos nanotubos de carbono, o que pode ser confirmado por MEV, FTIR e RAMAN, e, a partir dos grupos funcionais gerados, ancorar nanoparticulas de ouro em suas paredes, a fim de otimizar as propriedades catalíticas do material. O material gerado foi caracterizado morfologicamente e estruturalmente por MEV-FEG, EDX, Raio-X, RAMAN e UV-vis. Já a caracterização eletroquímica foi feita por voltametria cíclica frente ao K4[Fe(CN)6], com o qual foi possível mostrar um aumento na densidade de corrente de pico, o deslocamento do potencial de pico para valores menos positivos e também a diminuição do sobrepotencial, quando comparados o sensor Náfion®/AuNP/MWCNT/GC com o Náfion®/GC, Náfion®/MWCNT/GC e Náfion®/Ouro. O eletrodo proposto foi utilizado na determinação de Óxido Nítrico, em tampão PBS pH 4,4, utilizando a técnica de voltametria de pulso diferencial. A metodologia proposta apresentou um limite de detecção de 2,4x10-10 mol L-1 e um limite de quantificação de 7,9x10-10 mol L-1. Assim, este trabalho mostrou a potencialidade de utilização do eletrodo Náfion®/AuNP/MWCNT/GC como sensor eletroquímico para detecção e quantificação de óxido nítrico. / Nitric oxide (NO) is an environmental polluter, which also plays several roles in the body, for example, as a signaling molecule for many metabolic processes. Because this, detecting NO is an important tool in medicine. As a result, there was significant interest in both industry and medicine in developing new materials that can detect NO. Multiwall carbon nanotubes, that have been intensively explored since its discovery in 1991, are considered promising in many applications due to its unique structure and because it can be easily modified in order to tuning their physical and chemical properties. But the interest in using gold as the catalytic material appeared only in 1985, when was discovered that small particles form of gold behaves as individual atoms and it are more catalytic that crystalline gold. In this way, the objectives of this study were promoted the functionalization of carbon nanotubes - which could be confirmed by SEM, FTIR, Raman - and, with the functional groups generated, anchoring gold nanoparticles in their walls, in order to improve the catalytic properties of such material. The developed material was morphologically and structurally characterized by FEG-SEM, EDX, X-ray, Raman and UV-vis. As well, the electrochemical characterization was performed by cyclic voltammetry in K4[Fe(CN)6] solution. When Nafion®/AuNP/MWCNT/GC sensor was compared with Náfion®/GC, Náfion®/MWCNT/GC and Náfion®/Gold, its show an increase in current density peak, the peak potential displacement to less positive values and also decreased potential difference between the cathodic and anodic peak. The proposed electrode was used in the determination of nitric oxide in PBS buffer pH 4.4, which showed a detection limit of 2,4x10-10 mol L-1 and a quantification limit of 7,9x10-10 mol L-1 using the differential pulse voltammetry. Thus, this study demonstrated the potential use of Nafion®/AuNP/MWCNT/GC electrode as an electrochemical sensor in the nitric oxide detection and quantification.

A interface formada por materiais biológicos e materiais sintéticos tem grande importância em aplicações biomédicas, tais como o desenvolvimento de biomateriais para implantes médicos, que tem como processo essencial a deposição de proteínas na superfície dos biomateriais, e ainda não é bem compreendido no nível molecular. Algumas proteínas sofrem mudanças conformacionais após a adsorção na interface sólido-líquido, afetando suas funções ou propriedades, e algumas técnicas podem medir mudanças conformacionais em interfaces sólido. É possível estudar a fluorescência intrínseca de proteínas: a posição do máximo na faixa espectral da fluorescência, a eficiência quântica e o tempo de vida de fluorescência são indicadores de mudanças no ambiente local de grupos de moléculas de proteína fluorescente. Por outro lado, Nanopartículas de ouro têm atraído muita atenção pela sua afinidade com materiais biológicos e suas propriedades ópticas. Nesta tese, estudamos a viabilidade de substratos de vidro, quartzo, mica e ITO (óxido de índio e estanho) modificado com quitosana, phtalocyanines (Ni, Fe e Ni) e poli(alilanina hidroclorada) (PAH) na adsorção de BSA em forma dos filmes produzidos pela técnica camada por camada. O sistema foi estudado por UV-Vis e espectroscopia de fluorescência estática e resolvida no tempo. A caracterização morfológica dos filmes foi realizada por microscopia de força atômica e microscopia óptica. Os resultados mostram que os filmes de BSA / HAP cresceram com eficiência quatro vezes maior do que os filmes feitos de quitosana, que o quartzo tem a melhor janela de trabalho de UV-vis e há uma relação entre o pH da BSA e o tempo vida de fluorescência do filme resultante. As nanopartículas de ouro foram produzidas pela redução química e estabilizada por quatro diferentes métodos. O crescimento das nanopartículas foi monitorado por UV-vis spectroscopy. A carga de superfície das nanopartículas e da BSA foi estimado em vários valores de pH por medidas de potencial zeta. Os resultados indicaram que as nanopartículas têm cargas negativas na faixa de pH estudada. Soluções de BSA foram preparadas em diferentes valores de pH, e levadas para interagir com as nanopartículas de ouro. Os dados de supressão de fluorescência da BSA mostraram uma maior afinidade da BSA com nanopartículas estabilizadas com sacarose, com pH próximo do ponto isoelétrico (IP) estimado para BSA. / The interface formed by biological materials and synthetic materials has great importance in biomedical applications such as the development of biomaterials for medical implants, which has as an essential process of protein adsorption on the surface of biomaterials, and is not yet well understood in the molecular level. Some proteins undergo conformational changes after adsorption at solid-liquid interfaces, affecting their functions or properties, and few techniques can measure conformational changes in solid interfaces. It is possible to study the intrinsic fluorescence of proteins: the position of the maximum in the spectral range of fluorescence, the quantum efficiency and lifetime of fluorescence are indicators of change in the local environment of fluorescent groups of protein molecules. On the other hand, gold nanopartículas have attracted much attention for its affinity with biological materials and their optical properties. In this thesis we study the feasibility of glass substrates, quartz, mica and ITO (Indium tin oxide) modified with chitosan, phtalocyanines (Ni, Fe and Ni) and poly (allylamine hydrochloride) (PAH) on the adsorption of BSA in the form of films produced by the layer by layer technique. The system was studied by UV-Vis and static and time-resolved fluorescence spectroscopy. Morphological characterization of the films was performed by atomic force microscopy and optical microscopy. The results indicate that the films of BSA/PAH grew with efficiency four times greater than the films made of chitosan, that the quartz has the best working window for UV-vis and there is a relationship between the pH of the BSA and lifetime of fluorescence of the resulting film. Gold nanoparticles were produced by chemical reduction and stabilized by four different methods. The growth of nanoparticles was monitored by UV-vis spectroscopy. The surface charge of nanoparticles and the BSA was estimated at various pH values by zeta potential measurements. The results indicated that the nanoparticles have negative charges in the pH range studied. BSA solutions were prepared at various pH values, were taken to interact with gold nanoparticles. Fluorescence quenching data of BSA showed a greater affinity of the BSA with nanoparticles stabilized with sucrose, at pH near the isoelectric point (IEP) estimated for BSA.

<p>In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.</p>

Self-assembly has emerged as a promising technique for fabrication of novel hybrid materials and nanostructures. The work presented in this thesis has been focused on developing nanoscale materials based on synthetic de novo designed polypeptides. The polypeptides have been utilized for the assembly of gold nanoparticles, fibrous nanostructures, and for sensing applications. The 42-residue polypeptides are designed to fold into helix-loop-helix motifs and dimerize to form four-helix bundles. Folding is primarily driven by the formation of a hydrophobic core made up by the hydrophobic faces of the amphiphilic helices. The peptides have either a negative or positive net charge at neutral pH, depending on the relative abundance of Glu and Lys. Charge repulsion thus prevents homodimerization at pH 7 while promoting hetero-dimerization through the formation of stabilising salt bridges. A Cys incorporated in position 22, located in the loop region, allowed for directed, thiol-dependent, immobilization on planar gold surfaces and gold nanoparticles. The negatively charged (Glu-rich) peptide formed homodimers and folded in solution at pH &lt; 6 or in the presence of certain metal ions, such as Zn2+. The folding properties of this peptide were retained when immobilized directly on gold, which enabled reversible assembly of gold nanoparticles resulting in aggregates with well-defined interparticle separations. Particle aggregation was found to induce folding of the immobilized peptides but folding could also be utilized to induce aggregation of the particles by exploiting the highly specific interactions involved in both homodimerization and hetero-association. The possibility to control the assembly of polypeptide-functionalized gold nanoparticles was utilized in a colorimetric protein assay. Analyte binding to immobilized ligands prevented the formation of dense particle aggregates when subjecting the particles to conditions normally causing extensive aggregation. Analyte binding could hence easily be distinguished by the naked eye. Moreover, the peptides were utilized to assemble gold nanoparticles on planar gold and silica substrates. Fibrous nanostructures were realized by linking monomers through a disulphide-bridge. The disulphide-linked peptides were found to spontaneously assemble into long and extremely thin peptide fibres as a result of a propagating association mediated by folding into four-helix bundles. / Ingenjörer och vetenskapsmän har ofta inspirerats av naturen i sökandet efter lösningar på tekniska problem. Allt ifrån byggnadskonstruktioner, flygplansvingar, kompositmaterial till kardborrebandet har skapats med utgångspunkt från förebilder i naturen. Många av de material och konstruktioner som återfinns i naturen har åtråvärda egenskaper som är svåra att erhålla i syntetiska matrial med traditionell teknik. Även om vi i flera fall kan härma sammansättningen och formen blir resultatet inte nödvändigtvis det samma. Den största skillnaden mellan syntetiska material och material producerade av levande organismer är hur deras komponenter sinsemellan är organiserade och sammansatta. I syntetiska material är komponenterna ofta inbördes mer eller mindre slumpvis ordnade medan de i biologiska material är organiserade med en oerhörd precision som sträcker sig ända ned på molekyl- och atomnivå. Naturens byggstenar har genom evolutionens gång förfinats för att spontant kunna organisera sig och bilda komplexa material  och strukturer. Denna process, som styrs genom att många svaga krafter inom och mellan byggstenarna samverkar, kallas ofta för självorganisering och är en förutsättning för allt liv. Självorganisering har också blivit en allt viktigare metod inom nanotekniken för att konstruera material och strukturer med nanometerprecision. I den här avhandlingen beskrivs en typ av självorganiserande material där byggstenarna utgörs av nanometerstora guldpartiklar och syntetiska proteiner. De syntetiska proteinerna är designade för att efterlikna naturliga biomolekyler och antar en välbestämd tredimensionell struktur när två av dem interagerar med varandra. Denna interaktion är mycket specifik men kan styras genom att variera kemiska parametrar som surhet och jonstyrka vilket ger en möjlighet att påverka och kontrollera proteinernas struktur. Proteinerna har vidare modifierats för att spontant organisera sig till fibrer som är flera mikrometer långa men endast några nanometer tjocka. Proteinfibrer utgör en mycket viktig typ av strukturer i biologiska system och finns i alltifrån spindelväv till muskler. Syntetiska proteinfibrer är därför både ett intressant modellsystem och ett material med många potentiellt intressanta användningsområden. Genom att fästa de syntetiska proteinerna på ytan av guldnanopartiklar går interaktionerna mellan partiklarna att kontrollera på samma sätt som interaktionerna mellan proteinerna. Krafterna mellan proteinerna och interaktionerna involverade i proteinernas veckning har använts för att reversibelt aggregera och organisera nanopartiklarna. Ett antal olika byggstenar har studerats och utvecklats till något som liknar ett mycket enkelt nano-Lego, som på en given signal spontant bygger ihop sig eller trillar isär. Guldnanopartiklar är intressanta eftersom de är stabila och lätta att modifiera kemiskt men också på grund av deras optiska egenskaper som ger dem en ovanligt vacker vinröd färg. Färgen uppstår på grund av partiklarnas ringa storlek och varierar naturligt med egenskaperna hos den omgivande miljön. Detta gör det enkelt att studera hur partiklarna interagerar eftersom de byter färg när de närmar sig varandra, men gör dem också intressanta för sensortillämpningar. En enkel och robust sensor beskrivs i avhandlingen där syntetiska proteiner, speciellt utformade för att upptäcka och binda andra molekyler, har fästs på nanopartiklarna. Med partiklarnas hjälp går det att med blotta ögat detektera ett mänskligt protein i koncentrationer under ett tusendels gram per liter. En tidig diagnos av sjukdomstillstånd kan i de flesta fall avsevärt underlätta behandlingen och behovet av enkla sensorer för att bestämma närvaro och koncentration av medicinskt intressanta molekyler är därför mycket stort.

The feasibility of highly dispersed gold nanocatalyst supported on yttria-stabilized zirconia (YSZ) for the model reactions of C2H4 and CO oxidation is demonstrated for the first time. Gold nanoparticles are synthesized on YSZ powder by chemical reduction of the precursor salt in the mixture of ethanol, water and polyvinylpyrrolidone (PVP). Resulting metal loading of the catalysts are 1 wt.% with average particle sizes ranging from 6 to 9 nm. Results of CO and C2H4 oxidation display catalytic activity at 65 0C and 25 0C for CO and C2H4 oxidation, respectively. The catalytic properties of the catalysts are different due to their average particle size. Electrochemical Promotion of Catalysis (EPOC) of C2H4 oxidation is demonstrated. Application of constant potential difference between two electrodes in the bipolar electrochemical cell led to increase in C2H4 conversion. A proposed mechanism explains the bipolar EPOC phenomenon through formation of O2- flux across the electrochemical cell, resulting in the change of Work Function of gold nanoparticles placed in between the electrodes and is electronically isolated.

In this study, conjugated monomers containing fluorene units / 2-(9,9-dihexyl-2-(thiophen-2-yl)-9H-fluoren-7-yl)thiophene (TFT) and 5-(9,9-dihexyl-2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9H-fluoren-7-yl)-2,3dihydrothieno[3,4b ][1,4] dioxine (EFE) were synthesized on the basis of donor-acceptor-donor approach and their electrochemical polymerization were achieved via potential cycling. Optical and electrochemical properties of their corresponding polymers, poly(2-(9,9-dihexyl-2-(thiophen-2-yl)-9H-fluoren-7-yl)thiophene) PTFT, and poly(5-(9,9-dihexyl-2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9H-fluoren-7-yl)-2,3dihydrothieno[3,4b ][1,4] dioxine) PEFE, were investigated and it was found that polymer films exhibited quasi-reversible redox behavior (Epox= 1.10 V for PTFT, Epox = 0.70 V and 1.00 V for PEFE) accompanied with a reversible electrochromic behavior, yellow to dark green for PTFT, yellow to parliament blue for PEFE. Their band gap values (Eg) were found to be 2.36 eV and 2.26 eV for PTFT and PEFE, respectively. Furthermore, gold nanoparticles (AuNP) were prepared and their interaction with polymer films, PTFT and PEFE, were investigated using spectroscopic techniques. The fluorescence properties of the polymers and their composites, prepared by the interaction of AuNP with polymers, were also investigated.

The feasibility of highly dispersed gold nanocatalyst supported on yttria-stabilized zirconia (YSZ) for the model reactions of C2H4 and CO oxidation is demonstrated for the first time. Gold nanoparticles are synthesized on YSZ powder by chemical reduction of the precursor salt in the mixture of ethanol, water and polyvinylpyrrolidone (PVP). Resulting metal loading of the catalysts are 1 wt.% with average particle sizes ranging from 6 to 9 nm. Results of CO and C2H4 oxidation display catalytic activity at 65 0C and 25 0C for CO and C2H4 oxidation, respectively. The catalytic properties of the catalysts are different due to their average particle size. Electrochemical Promotion of Catalysis (EPOC) of C2H4 oxidation is demonstrated. Application of constant potential difference between two electrodes in the bipolar electrochemical cell led to increase in C2H4 conversion. A proposed mechanism explains the bipolar EPOC phenomenon through formation of O2- flux across the electrochemical cell, resulting in the change of Work Function of gold nanoparticles placed in between the electrodes and is electronically isolated.

Single particle microscopy and spectroscopy strategies reveal hidden relationships between the surface plasmon resonances (SPRs) and the sizes, shapes, and arrangements of gold nanoparticles (Au NPs). The SPR, the coherent oscillation of the conduction electrons, leads to intense absorption and scattering of light at frequencies satisfying the resonance condition determined by the size, shape, and spacings between NPs. Growing and assembling NPs through wet chemistry yields a diversity of geometries. Together, optical spectroscopy, scanning electron microscopy (SEM), and computational modeling of individual NPs and NP assemblies elucidate the resulting variety of SPRs. Strong coupling of the SPRs in linear assemblies provokes particular interest for tunable structures that will benefit surface enhanced spectroscopies and optical computing. The influence of the constituents and imperfections in such assemblies, which deviate from idealized model systems, must be established one assembly at a time. This thesis demonstrates previously unknown and sensitive relationships between the SPRs and these geometric parameters through systematic single particle experiments of self-assembled ring superstructures, nanorod dimers, individual nanorods populating different size regimes, and short linear chains of Au NPs through single particle spectroscopy. Dark-field scattering of self-assembled ring superstructures of 40 nm Au NPs reveals new plasmon modes that are redshifted from the single NP SPR by hundreds of nanometers, highly polarized along the axis of alignment, and indifferent to irregularities in the NP arrangement. SPRs of Au nanorod dimers, however, are dramatically altered by NP size heterogeneity, reduced symmetry, and metallic contact, consistent with previous studies of small assemblies. Broad band single particle extinction measurements of individual Au nanorods and short chains of 200-1000 nm long demonstrate the importance of the overall dimensions of an NP or an assembly of NPs. Finally, extinction measurements of these chains provide a compelling comparison to chemical polymers via the redshifting of the lowest energy SPR, tolerance to disorder, and the influence of the repeat unit. This result extends already well-defined analogies between plasmonic assemblies and chemical molecules to the ‘plasmonic polymer’. The findings presented in this thesis bring deeper and more detailed understanding to the tunable optical properties of real NP assemblies.

Plasmonic nanoparticles and their assembly have the potential to serve as a platform in practical applications such as photonics, sensing, and nano-medicine. To use plasmonic nanoparticles in these applications, it is important to understand their optical properties and find methods to control their optical response. Using polarization-sensitive dark-field spectroscopy to study self-assembled nanoparticle rings on substrates with different permittivities I show that the interaction between collective plasmon resonances and the substrate can control the spatial scattering image. Using liquid crystals as an active medium that can be controlled with an external electric field I show that the Fano resonance of an asymmetric plasmonic assembly can be actively controlled utilizing the polarization change of scattered light passing through the liquid crystal device. Furthermore, utilizing the strong electromagnetic field enhancement of coupled plasmonic “nanospikes” on the surface of gold nanoshells with a silica core, I show the use of single spiky nanoshells as surface-enhanced Raman spectroscopy substrates. Individual spiky nanoshells give surprisingly reproducible surface-enhanced Raman spectroscopy intensities with a low standard deviation compared to clusters of nanoparticles. In summary, the work presented here provides understanding of the plasmonic response for assembled nanoparticles on different substrates, illustrated a new method to actively control the optical response of plasmonic nanoparticles, and characterizes spiky nanoshells as surface-enhanced Raman scattering platform.

Gold nanoparticles, a class of plasmonic nanoparticle, have increasingly been explored as an imaging and therapeutic agent to treat cancer due to their characteristic surface plasmon resonance phenomenon and penchant for tumor accumulation. Photothermal therapy has been shown as a promising cancer treatment by delivering heat specifically to the tumor site via gold nanoparticles. In this study, we demonstrate that gold nanorod (GNR)-mediated photothermal therapy can be more effective through the understanding of cell death mechanisms. By targeting GNRs to various cellular localizations, we explored the association of GNR localization with cell death pathway response to photothermal therapy. Furthermore, we compared the 2D monolayer experiments with 3D in vitro tumor models, multicellular tumor spheroids (MCTS), to mimic the structure of in vivo tumors. With MCTS, we evaluated the cell death response with GNRs distributed only on the periphery, as seen in typical in vivo studies, and distributed evenly throughout the tumor. We demonstrated that GNR localization influences the cell death response to photothermal therapy by showing the power threshold necessary to induce significant apoptotic and necrotic increases was lower for internalized GNRs than membrane-bound GNRs. Furthermore, apoptosis was found to increase with increasing laser power until the necrotic threshold and decreased above it, as necrosis became the dominant cell death pathway response. A similar trend was revealed with the 3D MCTS; however, the overall cell death percentages were lower, most likely due to the upregulated cell repair response and varied GNR distributions due to the presence of cell-cell and cell-matrix interactions. Furthermore, the uniformly distributed GNRs induced more apoptosis and necrosis than GNRs located in the MCTS periphery. In conclusion, we quantitatively analyzed the cell death pathway response to GNR-mediated photothermal therapy to establish that it has some dependence on GNR localization and distribution to gain a more thorough understanding of this response for photothermal therapy optimization. / text