62,209 research outputs found

    Efeitos dos nanomateriais no microbioma do solo: aplicação de nano-agroquímicos e biosólidos

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    The frequent application of agrochemicals and/or biosolids in agriculture may lead to an increased concentration and persistence of nanomaterials (NMs) in agricultural soils. Some of these NMs are characterized by their antimicrobial properties, affecting the microbial communities in soil, which are essential in maintaining ecosystem‚Äôs function and balance. A negative impact of these NMs on soil quality, fertility and biogeochemical processes could result in economic losses to the agricultural sector. Thus, the main aim of this thesis was to evaluate the effect of NMs on the soil microbiome and demonstrate the potential of several microbiological endpoints for the risk assessment of these NMs. For this, several NMs were tested, under different exposure scenarios, with copper-based formulations: the commercial nanopesticide Kocide¬ģ3000, copper oxide nanoparticles (nCuO) and copper hydroxide nanoparticles [nCu(OH)2]; and a silver sulfide nanoparticle (Ag2S NPs), simulating aging of AgNPs. In these experiments, the presence and/or absence of edaphic elements (invertebrates and plants), essential to the maintenance of soil functioning, was considered. Crosswise, the soil microbiome was evaluated at the structural, compositional (Denaturing Gradient Gel Electrophoresis and massive parallel sequencing), and functional levels (soil enzymatic activity, community-level physiological profiling and abundance of bacterial groups using culture-dependent methods and/or qPCR technique). Particularly for copper-based NMs, a long exposure to the commercial nanopesticide (90 days) in microcosms, using recommended concentrations for vineyard areas, influenced the structure/richness of the soil bacterial and fungal communities and the regulation of the carbon cycle. With the inclusion of decomposer organisms (Porcellionides pruinosus), these differences were not observed, suggesting an attenuated effect of this nanopesticide on the soil microbiome. Simulating more realistic conditions, the application of different copper-based NMs in mesocosms (in the presence of plants and invertebrates), resulted in a reduced abundance of bacterial classes involved in the regulation of soil organic matter and in the nitrogen cycle (depending on the tested formulation), and enzymatic activities associated with the sulfur, carbon and nitrogen cycles, after 28 days of exposure. Also, an earlier effect of these NMs in the rhizosphere microbiome (14 days) was detected compared to the effect on the non-rhizosphere soil microbiome, suggesting a faster dissolution of these NMs resulting from the root exudates activity. Regarding silver NMs, the results suggest that the exposure to Ag2S NPs affect the soil microbiome involved in the regulation of the carbon cycle (reduced ő≤-glucosidase activity, and increased abundance of bacterial classes involved in the degradation of cellulose). The function prediction analysis revealed that silver exposure changes the functioning of the nitrification process. It was also verified the emergence of variants of genes amoA and nxrB in silver-treated soils, suggesting the replacement of bacterial groups that comprise these genes. Finally, this work highlights the relevance of including the soil microbiome as an essential endpoint in the risk assessment of NMs, using a more realistic exposure scenario, for a deeper understanding of the impact of these compounds on the terrestrial environment. This work also highlights the need for specific regulation in the risk assessment of these compounds in the environment.A aplica√ß√£o frequente de agroqu√≠micos e/ou de bios√≥lidos na agricultura poder√° levar a um aumento acentuado da concentra√ß√£o, bem como a poss√≠vel persist√™ncia de nanomateriais (NMs) em solos agr√≠colas. Alguns destes NMs s√£o caracterizados pelas suas propriedades antimicrobianas, podendo afetar as comunidades microbianas do solo, essenciais na manuten√ß√£o da fun√ß√£o e equil√≠brio do ecossistema. Um impacto negativo na qualidade, na fertilidade e nos processos biogeoqu√≠micos do solo, poder√° resultar em perdas econ√≥micas no sector agr√≠cola. Assim, o objetivo principal desta tese consistiu em avaliar o efeito de NMs no microbioma do solo, e demonstrar a potencialidade dos par√Ęmetros microbiol√≥gicos na avalia√ß√£o do risco ambiental destes NMs. Para isso, foram testados, sob diferentes cen√°rios de exposi√ß√£o, v√°rios NMs com formula√ß√Ķes √† base de cobre: o nanopesticida comercial Kocide¬ģ3000, nanopart√≠culas de √≥xido de cobre (nCuO) e nanopart√≠culas de hidr√≥xido de cobre [nCu(OH)2], e √† base de prata, com nanopart√≠culas de prata sulfatada (Ag2S NPs). Nestes cen√°rios, a presen√ßa e/ou aus√™ncia de elementos ed√°ficos (invertebrados e plantas) essenciais √† manuten√ß√£o do funcionamento do solo, foram consideradas. Transversalmente, o microbioma do solo foi avaliado ao n√≠vel estrutural e composicional (Eletroforese em Gel de Gradiente Desnaturante e sequencia√ß√£o massiva paralela) e funcional (atividade enzim√°tica do solo, perfil fisiol√≥gico da comunidade e abund√Ęncia de grupos bacterianos por m√©todos cultiv√°veis e/ou qPCR). Particularmente para os NMs √† base de cobre, uma exposi√ß√£o longa do nanopesticida comercial (90 dias), em microcosmos e com concentra√ß√Ķes recomendadas para √°reas vit√≠colas, influenciou a estrutura/riqueza da comunidade bacteriana e f√ļngica do solo e a regula√ß√£o do ciclo de carbono. Com a inclus√£o de organismos decompositores (Porcellionides pruinosus) neste ensaio, estas diferen√ßas n√£o foram observadas, sugerindo uma atenua√ß√£o do efeito deste nanopesticida no microbioma do solo. Aquando da simula√ß√£o de condi√ß√Ķes mais realistas, a aplica√ß√£o de diferentes NMs √† base de cobre em mesocosmos (na presen√ßa de invertebrados e plantas), resultou na redu√ß√£o da abund√Ęncia de classes bacterianas envolvidas na regula√ß√£o da mat√©ria org√Ęnica do solo (dependendo da formula√ß√£o testada), e atividades enzim√°ticas associadas aos ciclos de enxofre, carbono e azoto, ap√≥s 28 dias de exposi√ß√£o. Foi tamb√©m detetado um efeito mais r√°pido destes NMs no microbioma da rizosfera (14 dias) quando comparado com o efeito no microbioma do solo n√£o rizosf√©rico, sugerindo uma dissolu√ß√£o mais r√°pida destes NMs devido √† a√ß√£o dos exsudados radiculares. Relativamente aos NMs de prata, os resultados sugerem que a exposi√ß√£o da prata sulfatada afeta o microbioma do solo principalmente ao n√≠vel da regula√ß√£o do ciclo do carbono (redu√ß√£o da atividade da ő≤-glucosidase, e o aumento da abund√Ęncia de classes bacterianas envolvidas na degrada√ß√£o da celulose). Ap√≥s an√°lise de previs√£o de fun√ß√£o, a exposi√ß√£o a prata alterou o funcionamento do processo de nitrifica√ß√£o. Verificou-se tamb√©m o aparecimento de variantes dos genes amoA e nxrB nos solos contaminados, sugerindo assim a substitui√ß√£o de grupos bacterianos que apresentam estes genes. Por fim, este trabalho evidencia a relev√Ęncia da inclus√£o do microbioma do solo como um par√Ęmetro essencial na avalia√ß√£o de risco dos NMs, sob cen√°rios de exposi√ß√£o mais realistas, para uma compreens√£o mais profunda do impacto destes compostos no ambiente terrestre. Evidencia tamb√©m a necessidade da implementa√ß√£o de legisla√ß√£o espec√≠fica para a avalia√ß√£o de risco ambiental destes compostos.Programa Doutoral em Biologia e Ecologia das Altera√ß√Ķes Globai

    On the behaviour of metal and dielectric nanoparticles

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    RESUMEN: Durante las dos √ļltimas d√©cadas, la nanoplasm√≥nica ha experimentado un gran progreso, tanto desde el punto de vista te√≥rico como experimental. Part√≠culas nanom√©tricas son capaces de confinar e intensificar campos electromagn√©ticos cuando son iluminadas. Este fen√≥meno se conoce como resonancia plasm√≥nica superficial localizada, y se produce por la oscilaci√≥n coherente de los electrones libres del metal. Nanopart√≠culas diel√©ctricas con alto √≠ndice de refracci√≥n tambi√©n son capaces de localizar e intensificar campos electromagn√©ticos. Sin embargo, mediante un fen√≥meno diferente conocido como whispering gallery mode. √©ste consiste en modos resonantes dentro de la part√≠cula los cuales crean corrientes de desplazamiento. En este trabajo se estudiar√° el comportamiento electromagn√©tico de nanopart√≠culas met√°licas y diel√©ctricas de alto √≠ndice de refracci√≥n hechas de diferentes materiales com√ļnmente usados en plasm√≥nica. Mediante este an√°lisis se pretende identificar materiales √ļtiles para aplicaciones en el visible (VIS), ultravioleta (UV) o infrarrojo cercano (NIR). Los materiales analizados con mayor detalle han sido el oro, el aluminio, el silicio y el di√≥xido de titanio.ABSTRACT: During the last two decades, nanoplasmonics has experimented a great progress, from both theoretical and experimental points of view. Nanometric particles are able to confine and intensify electromagnetic fields when they are illuminated. This phenomenon is known as localized surface plasmon resonance, and it is produced by the coherent oscillation of the free electrons in the metal. Dielectric nanoparticles with high refractive index are also able to confine and intensify electromagnetic fields. However, through a di‚ÜĶerent phenomenon known as whispering gallery mode. This phenomenon consist on resonant modes inside the nanoparticle which create displacement currents. In this work, the electromagnetic behavior of metallic and dielectric nanoparticles of high refractive index made of di‚ÜĶerent materials commonly used in plasmonics will be studied. This analysis aims to identify useful materials for applications in the visible (VIS), ultraviolet (UV) or near infrared (NIR). The materials analyzed in greater detail have been gold, aluminum, silicon and titanium dioxide.Grado en F√≠sic

    Development of reverse docking protocols for virtual screening in nanomedicine

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    One of the first computational chemistry tools that have been used in pharmaceutical research is molecular docking, which infers the interaction between two molecules, usually a small active compound and a receptor, on the basis of their 3D structures. During my three years of PhD studies I worked mainly on re-purposing molecular docking tools to investigate the interactions between a single molecule of interest and a collection of proteins of pharmacological interest. Since this process is essentially the inverse of what is usually done in pharmaceutical research, the technique is called reverse screening. Reverse screening can help in the identification of new therapeutical targets, in predicting toxicological effects and unwanted interactions or in the design of new therapeutic platforms based on the conjugation between a synthetic compound and a protein carrier. In this work, reverse screening has been applied to porphine and phthalocyanine, two chemically related photosensitizers employed in photodynamic therapy, and Gd@C82, the most promising endohedral gadofullerene for theranostic applications. For each of these two types of molecule, a reverse docking protocols has been designed and has allowed the discovery of new potential pharmaceutical targets and carrier systems that can help overcome the physico-chemical limitations to their widespread usage in nanomedicine. Finally, the application of reverse screening protocols to study the interactions between small nanoparticles (d < 5 nm) and 2D materials against bio-molecules was explored. Although theoretically possible, the sheer number of atoms that must be considered and the nanoparticle size result in a plethora of problems since docking tools have been designed with small active molecules in mind. Nevertheless, a new protocol has been devised to perform reverse screening of gold, silver and silica nanoparticles and 2D materials and it has been successfully tested on a small number of proteins

    Probing small organic molecules at the angstrom-scale in the scanning transmission electron microscope

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    Small organic molecules are the foundation of chemistry, and correspondingly, unambiguous determination of their structure is essential. While scanning transmission electron microscopy (STEM) is a powerful tool for atomic-resolution structural determination, applying STEM to small organic molecules has proved challenging due to their weak electron scattering and extreme sensitivity to electron beam damage. In this thesis, we develop sample preparation, STEM imaging, and data processing techniques that enable us to directly probe the structure and arrangements of small organic molecules at the angstrom scale. We develop methods for large-scale production and deposition of samples onto ultra-low background graphene substrates, enabling the detection of the weak molecular signal. Additionally, our studies benefit from the stability provided by the graphene substrates, which increase the dose resistance of the molecules 2-6x due to their impermeability and high electrical and thermal conductivity. We then combine graphene substrates and STEM to study two technologically important small organic molecule systems: ensembles of molecules at the surface of inorganic nanoparticles and 2-dimensional (2D) molecular crystals. A longstanding challenge in nanoparticle characterization is understanding local variations in the distributions of surface molecules. We use STEM and electron energy loss spectroscopy to quantify the molecular distribution on the nanoscale, revealing up to 30% lower binding density on the ends of the particles. This anisotropy has important implications for nanoparticle synthesis and interactions, directing their growth, chemical functionalization, and colloidal assembly. Importantly, these methods enable the study of surface chemistry with site-specificity and are broadly applicable to a range of nanomaterials. An ultimate challenge in electron microscopy is to image the structure of an individual small organic molecule. We combine the protection from graphene substrates, low-dose STEM, and advanced averaging techniques to enable direct, atomic-scale imaging of 2D small organic molecule crystals. We achieve 1.3 angstrom resolution imaging a single molecule, sufficient to distinguish individual nitrogen and carbon atoms. Importantly, our methods are well-suited to analyzing nanogram quantities of material and systems for which large crystals cannot easily be grown. Our results demonstrate the potential of atomic-scale STEM as a powerful new method for structural solution of small organic molecules. Overall, this thesis demonstrates advances in sample preparation and data analysis techniques that enable nano- and atomic-scale STEM imaging of small organic molecules.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Nanostructured Systems for Electrocatalysis of Reduction Reactions for Energy Conversion Applications

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    Oxygen Reduction Reaction (ORR) requires a platinum-based catalyst to reduce the activation barrier. One of the most promising materials as alternative catalysts are carbon-based, graphene and carbon nanotubes (CNT) derivatives. ORR on a carbon-based substrate involves the less efficient two electrons process and the optimal four electrons process. New synthetic strategies to produce tunable graphene-based materials utilizing graphene oxide (GO) as a base inspired the first part of this work. Hydrogen Evolution Reaction (HER) is a slow process requiring also platinum or palladium as catalyst. In the second part of this work, we develop and use a technique for Ni nanoparticles electrodeposition using NiCl2 as precursor in the presence of ascorbate ligands. Electrodeposition of nano-nickel onto flat glassy carbon (GC) and onto nitrogen-doped reduced graphene oxide (rGO-N) substrates are studied. State of the art catalysts for CO2RR requires rare metals rhenium or rhodium. In recent years significant research has been done on non-noble metals and molecular systems to use as electro and photo-catalysts (artificial photosynthesis). As Cu-Zn alloys show good CO2RR performance, here we applied the same nanoparticle electrosynthesis technique using as precursors CuCl2 and Cl2Zn and observed successful formation of the nanoparticles and a notable activity in presence of CO2. Using rhenium complexes as catalysts is another popular approach and di-nuclear complexes have a positive cooperative effect. More recently a growing family of pre-catalysts based on the earth-abundant metal manganese, has emerged as a promising, cheaper alternative. Here we study the cooperative effects of di-nuclear manganese complexes derivatives when used as homogeneous electrocatalysts, as well as a rhenium functionalized polymer used as heterogeneous electrocatalyst

    High-resolution direct ink writing of soft conductive materials

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    Conductive polymers are important materials that attract increasing attention in diverse fields due to their tunability and easy preparation. The various applications range from tissue-engineering scaffold in the biomedical field to intelligent electronics and energy storage devices. The ability to create 3D complex structures using conductive polymers could render new possibilities to develop miniaturized tissue scaffold, personalized bioelectronics, or electrode materials that have more active sites. Traditional methods, such as drop casting or inkjet printing, rely primarily on printing 2D substrates. The gap between processability in two-dimensional and three-dimensional demands is required for new techniques such as 3D printing. In addition, 3D printing offers high freedom in geometry design and materials adjustment. Moreover, 3D printing is more cost and environmentally friendly compared to lithography-based techniques. However, the use of 3D printing to fabricate conductive polymers is still in its infancy of development, and the choice of printed materials is still limited. Among these 3D printable conductive inks, most inks rely on adding nanosized conductive polymer fillers (carbon materials such as carbon nanotubes, conjugated conductive polymer particles as polypyrrole, or polyaniline) in an insulating printable matrix. These inks have several limitations. The most vital limitation is nanoparticle aggregation at printing tips, which significantly hampered high-resolution printing (<100 őľm). High-resolution 3D printing of conductive polymers offers the possibility to discriminate a single cell‚Äôs behavior rather than signals from cell clusters. Higher resolution can also increase the effective surface area. In addition to printing resolution limitations, the addition of particles also has limitations in the inhomogeneous distribution of particles within the polymer matrix. The inhomogeneous distribution significantly affects the microscopic conductivity where conductivity varies from high aggregation area to low aggregation area. Despite the demand for high-resolution 3D printable inks, the limited choice of soft materials suitable for 3D printing has dramatically thwarted further application of conductive polymers in different fields. In my thesis, three types of high-resolution 3D printable inks are developed. Central to the design of high-resolution printing is the separation of the printing process from the polymerization process, so printing through nozzles as small as 1őľm is possible. The basic design idea is to mix conductive monomer (pyrrole and aniline) into a miscible ink system with ideal rheological properties for direct ink writing extrusion. After printing, the samples are treated with chemical reagents to induce in situ polymerization. The first design is based on a poly 2-hydroxyethyl methacrylate (poly HEMA) entangled network with pyrrole as the conductive monomer. The solvent used is a mixture of water and ethanol with a specifically designed ratio. This ratio allows that poly HEMA chains remain entangled while hydrophobic pyrrole is miscible with hydrophilic poly HEMA. High-resolution 3D printing is demonstrated by smooth extrusion through a one őľm nozzle. The after-polymerization printed filaments have superior biocompatibility as even to promote cell attachment and proliferation. Furthermore, the high-resolution filaments offer the possibility to fabricate an electrophysiological platform to record single neuron activities. The as-prepared platform can differentiate action potential and stimulated potential with a >4.0 signal-to-noise ratio. The second design is conductive polymer-elastomer based upon oil-in-water emulsion to overcome the limitation in the first design that requires a saturated water environment. Pyrrole monomer is homogenized with silicone (polydimethylsiloxane) and forms tightly packed micelles in water, stabilized by sodium dodecyl sulfate. The in-situ polymerization of pyrrole is triggered when oxidant ions diffuse through the continuous water phase. This emulsion-based ink has better shape retention than poly HEMA-based hydrogel ink and can work in the open air after fully treated. In addition, the ink is used to prepare multidirectional sensors that can detect compressing, bending, and stretching. The third design is a porous conductive hydrogel system that has no insulating matrix after complete treatment. The system is built upon aniline and phytic acid that can form a self-supportive porous hydrogel system. The initial printing is made possible by incorporating a thermal-sensitive poloxamer (Pluronic F127), which can be removed after the self-supportive polyaniline network forms. In contrast to a polyHEMA-based system, the polyaniline network has a high surface area and porosity while maintaining conductive. The porous nature provides shorter diffusion paths for ions and electrons to reach active sites and opens the possibility to be used as electrode materials.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Lung-on-a-chip device with in situ imaging capabilities

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    Engineered tools can be used for biological studies that investigate the interplay between mechanical forces and cell biology. More specifically, lung-on-a-chip microfluidic platforms offer increasingly sophisticated methods to study the in vivo lung response. These platforms do so by applying hydrodynamic and mechanical forces to pulmonary lung tissue to mimic the physiological environment within the alveolar-capillary interface. In this dissertation, I outline the development of a lung-on-a-chip platform that enables ex-vivo studies under active physio-mechanical stress to vascular endothelial cells. Lung-on-a-chip platforms can be used to study lung cell biology, disease states, pre-clinical drug response, and/or the effects of environmental pollutants (e.g., nanoparticles). Chapter 2 of this thesis investigates the impact of gold nanoparticles on the metabolic activity and morphology of human pulmonary endothelial cell monolayers. Nanoparticles are moving towards use as consumer products and therapeutic agents, and are gaining prevalence as environmental toxins. This has led to increasing concern for the impact that nanoparticles have on human health, specifically the lung. To study some of these effects, a gold nanoparticle library was developed including nanoparticles with three different sizes and two surface chemistries (citrate and poly(allylamine hydrochloride)). To stabilize the nanoparticles in cell culture medium, a bovine serum albumin pretreatment protocol was developed. The development of the nanoparticle library and pretreatment protocol was performed in collaboration with the Murphy research group at the University of Illinois at Urbana-Champaign. I performed a colorimetric assay to determine the effect the nanoparticle library has on human pulmonary artery endothelial cell metabolic activity. Then, I used subcellular imaging to observe the morphological impact of acute gold nanoparticle exposure on endothelial actin networks and intercellular gaps. While gold nanoparticles only modestly affect endothelial metabolic activity, exposure of primary vascular endothelial cells to citrate- or poly(allylamine hydrochloride)-coated gold nanoparticles resulted in cortical actin remodeling and an increase in intercellular gap formation. I was also able to identify that the bovine serum albumin pretreatment helped to mitigate the negative effects of free or bound polyelectrolytes on endothelial monolayers. The fabrication approach and design reported in Chapter 3 aims to improve accessibility of organ-on-a-chip technology to the broader biomedical research community. Access to current lung-on-a-chip platforms is hampered by the need for advanced fabrication techniques to create these platforms, and the need for extensive ancillary equipment for their operation. I report the use of dual layer lithography to significantly reduce the technical expertise and equipment required to create porous, stretchable membranes. A cost effective, portable pressure regulator was developed to apply physiologically relevant cyclic stretch (to resemble breathing) across cells grown on the porous membrane. I incorporated cyclic olefin copolymer sheets into the microfluidic platform design to reduce the total device thickness to enable fluorescence imaging ‚Äėon-chip‚Äô. Furthermore, the reversible bond between the polydimethylsiloxane platform and the cyclic olefin copolymer lid allows for exposure of the cells to aerosolized particulates using a nebulizer. The lung-on-a-chip platform outlined in this dissertation takes advantage of Arduino technology for application of cyclic stretching to cells and traditional photo/soft lithography techniques to reduce equipment requirements, while allowing for imaging ‚Äėon-chip‚Äô. Chapter 4 reports the capacity to image cells in situ on the lung-on-a-chip platform. I obtained subcellular, actin images ‚Äėon-chip‚Äô of bovine aortic endothelial cells and human pulmonary aortic endothelial cells. I also validated the platform with respect to its ability to apply shear stress and cyclic stretch in vitro to confluent layers of endothelial cells, mimicking the in vivo microenvironment. Using ‚Äėon-chip‚Äô imaging, I characterized the impact of physiologically relevant shear stress and cyclic stretch on endothelial cell morphology. Specifically, in vitro morphological alignment was used as a marker for recapitulating in vivo cell behavior. The accessible lung-on-a-chip platform outlined in this dissertation can be used in a wide variety of biological studies, ranging from mechanobiology experiments to studying the impacts of environmental pollutants or pharmaceuticals on bilayers of pulmonary epithelial and endothelial cells.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    On the electromagnetic behavior of small high refractive index dielectric particles

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    RESUMEN: Se ha estudiado el comportamiento electromagn√©tico de diferentes geometr√≠as de nanopart√≠culas diel√©ctricas de alto √≠ndice de refracci√≥n con el objetivo de analizar las posibles aplicaciones de este tipo de nanoestructuras. En particular, se han considerado part√≠culas aisladas y agregados. Para los primeros, se han evidenciado las capacidades de las nanopart√≠culas tanto puras, constituidas por materiales de alto √≠ndice de refracci√≥n, como formadas por un n√ļcleo met√°lico y una corteza diel√©ctrica de alto √≠ndice de refracci√≥n como sensores. Adem√°s, tambi√©n se ha investigado el comportamiento electromagn√©tico de estas nanoestructuras en funci√≥n de su tama√Īo. Adicionalmente, nanopart√≠culas n√ļcleo met√°lico-corteza diel√©ctrica de alto √≠ndice de refracci√≥n exc√©ntricas han sido exploradas. Dependiendo del desplazamiento del n√ļcleo respecto al centro de la nanopart√≠cula, se han puesto de manifiesto diferentes aplicaciones: construir dispositivos de conmutaci√≥n √≥ptica y aumentar la eficiencia de las c√©lulas solares. Ambas pueden ser mejoradas utilizando d√≠meros de part√≠culas diel√©ctricas de alto √≠ndice de refracci√≥n m√°s peque√Īas que la longitud de onda de la radiaci√≥n excitadora. Para profundizar en la posibilidad de usar nanopart√≠culas diel√©ctricas de alto √≠ndice de refracci√≥n en aplicaciones de c√©lulas solares, se ha analizado la fracci√≥n de radiaci√≥n que es difundida hacia el sustrato fotosensible cuando agregados de nanopart√≠culas de alto √≠ndice de refracci√≥n se disponen sobre su superficie.ABSTRACT: We have studied the electromagnetic response of different geometries of High Refractive Index Dielectric (HRID) nanoparticles in order to analyze possible applications of this kind of nanostructures. In particular, isolated particles or aggregates have been considered. For the former, the great capabilities of either pure or metallo-HRID core-shell nanoparticles for sensing purposes have been evidenced. In addition, the electromagnetic behavior of those structures as a function of the nanoparticle size has been investigated. Furthermore, eccentric metallo-dielectric core-shell nanoparticles have been explored. Depending on the core displacement from the nanoparticle center, different applications have been shown: building switching devices and increasing the efficiency of solar cells. Both of them can be improved by means of dimers of HRID subwavelength particles. To go further in the possibility of using HRID nanoparticles for solar cells applications, the fraction of radiation that is scattered into the photosensitive substrate has been analyzed when aggregates of HRID nanoparticles are located on its surface

    Nanocarbon-Supported Electrocatalysts for the Alkaline Water Splitting and Fuel Cells

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    Electrocatalysts play a significant role in the processes of electrochemical energy conversion. This thesis focuses on the preparation of carbon-supported nanomaterials and their application as electrocatalysts for alkaline water electrocatalysis and fuel cell. A general synthetic route was developed, i.e., species intercalate into carbon layers of graphite forming graphite intercalation compound, followed by dispersion producing graphenide solution, which then as reduction agent reacts with different metal sources generating the final materials. The first metal precursor used was non-noble metal iron salt, which generated iron (oxide) nanoparticles finely dispersed on carbon layers in the final composite materials. Meanwhile, graphite starting materials differing in carbon layer size were utilized, which would diversify corresponding graphenide solutions, and further produce various nanomaterials. The characterization results showed that iron (oxide) nanoparticles varying in size were obtained, and the size was determined by the starting graphite material. It was found that they were electrocatalytically active for oxygen reactions. In particular, the one with small iron (oxide) nanoparticles showed excellent electrocatalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Afterwards, the metal precursor was tuned from non-noble metal salt to noble metal salt. It was confirmed that carbon-supported Rh, Pt, and RhPt (oxide) nanoparticle composite materials were also successfully obtained from the reaction between graphenide solution and corresponding noble metal precursor. The electrochemical measurements showed that the prepared noble metal-based nanomaterials were quite effective for hydrogen evolution reaction (HER) electrocatalysis, and the Rh sample could also display excellent electrocatalytic property towards OER. Moreover, by this synthetic approach carbon-supported noble metal Pt and non-noble metal nickel (Ni) composite material was also prepared. Therefore, the utilization efficiency of noble metal could be improved. The prepared NiPt sample displayed a property close to benchmark HER electrocatalyst

    Géis coloidais multi-funcionais como plataformas bioinstrutivas celulares para engenharia de tecidos

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    Colloidal gels represent one of the most promising classes of biomaterials for biomedical applications owing to their potential for exploring different nanoparticle combinations towards the assembly of macro-scale multi-particle platforms. In these systems, nanosized units can serve both as crosslinking nodes and as structural building blocks resulting in highly hierarchic networks. Typically, these nanostructured systems leverage intrinsic supramolecular interactions for self-assembling. The resulting constructs present highly attractive physicochemical properties, such as viscoelasticity, self-healing and shear-thinning features and may present injectability and fit-to-shape features. Despite the inherent potential of colloidal gels, their exploitation as inks for additive manufacturing, namely 3D printing, is still limited and largely unexplored. In fact, most of the current developed colloidal systems are single-network assembled via weak particle-particle supramolecular interactions (such as Van der Waals, electrostatic, etc.), not providing sufficient mechanical stability to 3D printed constructs, which often exhibit a low structural lifetime. To overcome these limitations, this master dissertation focused on the development of a 3D-printable double-network colloidal ink with refined programable, modular and inherent cell supporting features. For this, two oppositely charged unitary nanoparticle building-blocks that also exhibited light-responsiveness were initially combined via electrostatic-driven bottom-up assembly, resulting in the formulation of a colloidal ink with suitable rheological properties to be processed via extrusion 3D printing. The presence of light-responsive chemical moieties in nanoparticles enabled the production of double network (i.e., electrostatic and covalent) constructs exhibiting mechanical robustness after light induced in situ photocrosslinking. The resulting constructs were biocompatible and exhibited adhesive properties for enabling human adipose derived mesenchymal stems adhesion, promoting cell spreading and proliferation, for more than 14 days. These findings support the future use of these systems as cell bioinstructive platforms and as highly modular and processable inks for 3D printing of nanoparticle only constructs that may find numerous biomedical applications.Os g√©is coloidais representam uma das classes de biomateriais mais promissoras para aplica√ß√Ķes biom√©dicas devido √† possibilidade de explorar diferentes combina√ß√Ķes de nanopart√≠culas tendo em vista a formula√ß√£o de plataformas macrosc√≥picas multi-part√≠culadas. Nestes sistemas, as unidades nanom√©tricas podem servir tanto como pontos de reticula√ß√£o ou blocos estruturais, sendo que a sua combina√ß√£o pode resultar na forma√ß√£o redes altamente hier√°rquicas. Tipicamente, estes sistemas nano-estruturados tiram partido de intera√ß√Ķes supramoleculares intr√≠nsecas para promover a agrega√ß√£o das nanopart√≠culas. As plataformas resultantes apresentam propriedades f√≠sico-qu√≠micas altamente atrativas, como viscoelasticidade, caracter√≠sticas de auto-regenera√ß√£o e de diminui√ß√£o da sua viscosidade aquando da aplica√ß√£o de uma for√ßa, podendo tamb√©m apresentar injetabilidade e ajuste a qualquer forma. Apesar do potencial inerente aos g√©is coloidais, a sua utiliza√ß√£o como tintas para manufatura aditiva, nomeadamente impress√£o 3D, ainda √© limitada e amplamente inexplorada. De facto, a maioria dos sistemas coloidais atualmente desenvolvidos s√£o combinados numa rede √ļnica via intera√ß√Ķes supramoleculares fracas part√≠cula-part√≠cula (e.g., for√ßas de Van der Waals, eletrost√°ticas, etc.), n√£o fornecendo estabilidade mec√Ęnica suficiente √†s constru√ß√Ķes impressas em 3D, que exibem frequentemente problemas estruturais p√≥s-impress√£o. Tendo em vista melhoramentos nesta tecnologia, esta disserta√ß√£o de mestrado focou o desenvolvimento de uma tinta coloidal modular e de dupla rede que apresenta caracter√≠sticas para o suporte de c√©lulas em cultura e possibilidade de processamento via impress√£o 3D. Para tal, duas classes de nanopart√≠culas com cargas opostas e com responsividade √† luz foram inicialmente combinadas, resultando na forma√ß√£o de uma tinta coloidal com propriedades reol√≥gicas favor√°veis ao seu processamento via impress√£o 3D. A presen√ßa de grupos qu√≠micos responsivos √† luz, possibilitaram a formula√ß√£o de tintas de dupla rede (e.g., eletrost√°tica e covalente) exibindo robustez mec√Ęnica ap√≥s foto-reticula√ß√£o induzida por luz. As constru√ß√Ķes resultantes apresentaram biocompatibilidade e exibiram propriedades adesivas para c√©lulas estaminais derivadas de adip√≥citos humanos, promovendo a propaga√ß√£o prolifera√ß√£o celular por mais de 14 dias. Estas descobertas suportam o futuro uso destes sistemas como plataformas bioinstrutivas e como tintas altamente modulares e process√°veis por impress√£o 3D, podendo assim originar plataformas formadas unicamente por nanopart√≠culas, podendo assim contribuir para diversas aplica√ß√Ķes biom√©dicas.Mestrado em Biotecnologi
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