Current cancer therapies are highly cytotoxic and their delivery to exclusively the affected site is poorly controlled, resulting in unavoidable and often severe side effects. In an effort to overcome such issues, magnetic nanoparticles have been recently gaining relevance in the areas of biomedical applications and therapeutics, opening pathways to alternative methods. This led to the concept of magnetic particle hyperthermia in which magnetic nano beads are heated by a high power magnetic field. The increase in temperature kills the cancer cells, which are more susceptible to heat in comparison to healthy cells. In this dissertation, the possibility to kill cancer cells with magnetic nanowires is evaluated. The idea is to exploit a magnetomechanical effect, where nanowires cause cancer cell death through vibrating in a low power magnetic field. Specifically, the magnetic nanowires effects to cells in culture and their ability to induce cancer cell death, when combined with an alternating magnetic field, was investigated. Nickel and iron nanowires of 35 nm diameter and 1 to 5 μm long were synthesized by electrodeposition into nanoporous alumina templates, which were prepared using a two-step anodization process on highly pure aluminum substrates. For the cytotoxicity studies, the nanowires were added to cancer cells in culture, varying the incubation time and the concentration. The cell-nanowire interaction was thoroughly studied at the cellular level (mitochondrial metabolic activity, cell membrane integrity and, apoptosis/necrosis assay), and optical level (transmission electron and confocal microscopy). Furthermore, to investigate their therapeutic potential, an alternating magnetic field was applied varying its intensity and frequency. After the magnetic field application, cells health was measured at the mitochondrial activity level. Cytotoxicity results shed light onto the cellular tolerance to the nanowires, which helped in establishing the appropriate nanowire concentrations to use the nanowires + alternating magnetic field combination as a cancer treatment. Different levels of cancer cell death were achieved by changing the incubation time of the nanowires with the cells and the alternating magnetic field parameters. Cell viability was significantly affected in terms of mitochondrial activity and cell membrane integrity after applying the treatment (nanowires + alternating magnetic field) using a low-frequency alternating magnetic. Theoretical calculations considering the magnetic and viscous torques showed that the nanowires vibrate as a consequence of the applied magnetic field. This, alongside the fact that no temperature increase was measured during the treatment, makes the magnetomechanical effect the most probable action mechanism in the applied treatment that is inducing cell death. Inducing cancer cell death via magnetomechanical action using magnetic nanowires resulted in killing up to 60% of cancer cells with only 10 minutes of treatment. The required magnetic field for treatment is in a low power regime, which is safe, does not cause any discomfort to the patients, and can be generated with compact and cheap instruments.

Systems of magnetic nanowires are considered strong candidates in many technological applications as microwave filters, sensors or devices for data storage. Because of their strong potential as candidates in such applications they became lately the object of many studies. However, due to the very complicated nature of the interwire interactions, their magnetic behavior is very difficult to be interpreted. The main parameter controlling the response of magnetic nanowires assemblies is the aspect ratio of the nanowires that is defined as the ratio of the length to the wire's diameter. In our study we choose to modify the aspect ratio by keeping a constant length of nanowires and modifying the wire's diameter while keeping the same interwire distance. The samples were studied at room temperature, using vibrating sample magnetometer and X-band ferromagnetic resonance experiments. The results are explained taking into account the effects of the magnetostatic interactions and shape anisotropy.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-08-06T12:19:22Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) udson cabral.pdf: 2045459 bytes, checksum: 0c5126468995368f097978ee97cb41f5 (MD5) / Made available in DSpace on 2014-08-06T12:19:22Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) udson cabral.pdf: 2045459 bytes, checksum: 0c5126468995368f097978ee97cb41f5 (MD5) Previous issue date: 2010 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / We investigate core-shell nanowires of diluted magnetic semiconductors (DMS) with remote n-type modulation doping. The incorporation of Mn2 ions acting as spin 5/2 impurities in the core region of the wire gives rise to a strong s-d exchange coupling between electrons in the wire and those of the d levels of the Mn2 ions. Applying an external magnetic eld along the axis of the wire, within the mean eld approximation, the s-d exchange generates a spin-dependent core potential. A gate voltage is applied radially to wire, to obtain some control over the density of the wire. Electronic strucutre of the wire was calculated within the e?ective mass approximation, in both approximations Hartree and spin density functional theory. We calculated the conductance of wire using the Landauer-B?uttiker formulation in the linear response regime, which generally results in a total conductance with well-de ned plateaus in GT = 2; 6; 10G0 (G0 = e2=h is the quanta of conductance), which occurred because in the system investigated the rst level is twofold degenerated (spin degenerescence) and the others are fourfold degenerated (spin degenerescence and orbital angular momentum). In the absence of a magnetic eld we observe that when we take into account the e?ects of exchange and correlation, the states with eigenvalues of Lz nonzero will be polarized while those with l = 0 isn't polarized. This unpolarized level with eigenvalue of Lz null suggests that, perhaps, the 0.7 anomaly (the emergence of two plateau at G = 0:7G0 and the other in G = G0) quantum wires on existing geometry of split-gate is related to the geometry of the wire. The results for total energy show that there are a competition between the ferromagnetic and paramagnetic states. / Investigamos nano fios de semicondutores magnéticos dilu??dos (DMSs - Diluted Magnetic Semiconductors) do tipo caroço-casca com dopagem remota tipo-n. A incorporação dos íons de Mn+2, que atuam como impurezas de spin 5/2 no caroço do fi o, faz surgir um forte acoplamento de trocas dentre os eletrons do fio e aqueles dos níveis d do íon Mn+2. Com a aplicação de um campo magnético externo ao longo do eixo do fi o, na aproximação de campo médio, a interação de troca s-d gera um potencial dependente do spin na região do caroço do fi o. Um potencial de gate é aplicado radialmente ao nanofi o, para obtermos um certo controle sobre a densidade eletrônica do fi o. Calculamos a estrutura eletrônica do nanofi o de DMSs usando o modelo da massa efetiva, tanto na aproximação de Hartree quanto na teoria do funcional da densidade dependente de spin (SDFT - Spin Density Functional Theory). Calculamos a condutância do nano fio usando a formulação de Landauer-B?uttiker no regime de resposta linear, o que de modo geral, resultou numa condutância total com platôs bem de finidos em GT = 2; 6; 10G0 (G0 = e2=h ?e o quanta de condutância), o que ocorreu porque no sistema investigado a primeira subbanda ?e duplamente degenerada (degenerescência de spin) e as outras duas são quadruplamente degenerada (degenerescência de spin e de momento angular orbital). Na ausência de um campo magnético observamos que ao levarmos em conta os efeitos de troca e correlação, os estados que possuem autovalor de Lz diferente de zero se polarizam enquanto que os que possuem l = 0 não se polarizam. Essa não-polarização do nível com autovalor de Lz nulo sugere que, talvez, a anomalia 0,7 (o surgimento de dois platôs um em G = 0; 7G0 e outro em G = G0) existente em os quânticos com geometria de split-gate esteja relacionada com a geometria do o. Os resultados obtidos para a energia total mostram que há uma competição entre os estados ferromagnético e paramagnéticos.

Mesenchymal stem cells (MSCs) are the most widely used source for bone tissue engineering due to their capability of multipotent differentiation. The use of nanotechnology in biomedical applications and therapy has increased in recent years provides an elegant alternative in comparison to current tissue engineering methods. Magnetic nanowires have a high potential in the medical field, as they are biocompatible, are simple to fabricate, possess low cytotoxic effects and can be operated wirelessly via magnetic fields. A nanowire substrate (NW) can provide a surface with tunable elastic properties. Therefore, magnetic nanowires have many promising applications such as in cell therapy, cell separation, cancer treatment, and as a scaffold for cell culture. This thesis explores the effects of alternating magnetic field (AMF) as a biophysical stimulator of osteogenic differentiation of MSCs by culturing the stem cells on a magnetic iron (Fe) NW. To this end, Fe nanowires were fabricated through electrodeposition and interactions between the NW and cells were analysed by electron microscopy. An AMF was applied to the NW in order to induce a vibration. MSCs were exposed to different magnetic field intensities, 250 mT and 50 mT, for different application times, 12 hours on followed by 12 hours off for two days and 24 hours on followed by 12 hours off. Differentiation was determined through the assessment of osteogenic markers at the mRNA level by RT-PCR and at the protein level by flow cytometry and fluorescence microscopy. Different effects were observed on MSCs grown on Fe NWs following exposure to different magnetic field intensities and duration applications. MSC differentiation towards the osteogenic lineage increased with increased field intensities. The most enhanced osteogenic differentiation of MSCs was observed at 250 mT AMF for 12 hours, as evidenced by elevated osteogenic markers at mRNA level compared to that of an AMF free control. Based on these results, we proposed that culturing MSCs on magnetic nanomaterials has the potential to control and promote osteogenesis under magnetic field and without the addition of external differentiation factors. These findings provide a new tool for stem cell research as an effective technology for bone tissue engineering and regenerative medicine.

The use of nanowires, nano and micro needles in biomedical applications has markedly increased in the past years, mainly due to attractive properties such as biocompatibility and simple fabrication. Specifically, these structures have shown promise in applications including cell separation, tumor cell capture, intracellular delivery, cell therapy, cancer treatment and as cell growth scaffolds. The work proposed here aims to study two platforms for different applications: a vertical magnetic nanowire array for mesenchymal stem cell differentiation and a micro needle platform for intracellular delivery. First, a thorough evaluation of the cytotoxicity of nanowires was done in order to understand how a biological system interacts with high aspect ratio structures. Nanowires were fabricated through pulsed electrodeposition and characterized by electron microscopy, vibrating sample magnetometry and energy dispersive X-ray spectroscopy. Studies of biocompatibility, cell death, cell membrane integrity, nanowire internalization and intracellular dissolution were all performed in order to characterize the cell response. Results showed a variable biocompatibility depending on nanowire concentration and incubation time, with cell death resulting from an apoptotic pathway arising after internalization. A vertical array of nanowires was then used as a scaffold for the differentiation of human mesenchymal stem cells. Using fluorescence and electron microscopy, the interactions between the dense array of nanowires and the cells were analyzed, as well as the biocompatibility of the array and its effects on cell differentiation. A magnetic field was additionally applied on the substrate to observe a possible differentiation. Stem cells grown on this scaffold showed a cytoskeleton and focal adhesion reorganization, and later expressed the osteogenic marker osteopontin. The application of a magnetic field counteracted this outcome. Lastly, a micro needle platform was fabricated through lithography and electrodeposition, characterized using the previously mentioned techniques and then evaluated as a vector for intracellular delivery. Fluorescence and electron microscopy imaging were first performed to assess the biocompatibility, cell spreading and the interface of the cells and the needles. Intracellular delivery of a fluorescent dye was achieved via inductive heating of the needles, with the results showing a dependency of delivery and cell survivability on the exposure time.

Estudamos o comportamento estático e os mecanismos de inversão da magnetização de arranjos auto-organizados de nanofios de Ni e Co com alta anisotropia de forma. Os arranjos são obtidos a partir da anodização em dois passos de lâminas de Al e subseqüente eletrodeposição do metal magnético. Sua caracterização estrutural é realizada por microscopia eletrônica de varredura, microscopia de força atômica e magnética e difração de raios X. Seu comportamento magnético é estudado a partir da medida de curvas de inversão de primeira ordem (FORCs) a temperatura ambiente, via magnetometria SQUID ou de amostra vibrante. A análise FORC consiste na construção de uma mapa da resposta magnética do material a partir dos dados experimentais e pode ser interpretado a partir da analogia direta com o modelo de histerese de Preisach. Apresentamos resultados da influência dos diâmetros dos nanofios e do ângulo do campo externo aplicado em relação ao eixo de anisotropia sobre as principais características dos diagramas FORC. Estudamos também a dinâmica de spins em superfícies de O-Fe/W(001) através de espectroscopia por perda de energia de elétrons spin-polarizados (SPEELS). As amostras consistem em 30 monocamadas atômicas de Fe crescidas sobre um monocristal de W(001), via epitaxia por feixe molecular a temperatura ambiente. Subseqüentemente, a amostra é exposta a 5 langmuirs de O2 e sofre um suave annealing a 500 K. A estrutura e a pureza da amostra são analisadas por difração de elétrons de baixas energias e espectroscopia de elétrons Auger. A caracterização magnética é realizada por magnetometria por efeito Kerr magneto-óptico, resultando num filme com alta magnetização remanente no plano. Os espectros de SPEELS revelam uma rica profusão de picos inelásticos tipo spin-flip e nãospin-flip, que exibem clara dispersão ao longo de toda a zona de Brillouin de superfície. Os resultados são atribuídos a modos de superfície de fônons e mágnons (ondas de spin), de acordo com resultados da literatura e com modelos teóricos atuais. / We study the static behavior and the mechanisms of magnetization reversal of arrays of self-organized Ni and Co nanowires with high shape anisotropy. The arrays are obtained by two-step anodization of Al foils and subsequent electrodeposition of the magnetic metal.Their structural characterization is obtained by scanning electron microscopy, atomic and magnetic force microscopy and X-ray diffraction. Their magnetic behavior is studied from the measurement of first order reversal curves (FORCs) at room temperature, via SQUID or vibrating sample magnetometry. The FORC analysis method consists in building a map of the magnetic response of the material from the experimental data and it can be interpreted from the direct analogy with the Preisach model of hysteresis. We present results of the influence of the diameter of the nanowires and the angle of the applied external field in relation to the anisotropy easy-axis on the main features of the FORC diagrams. We also study the spin dynamics of O-Fe/W(001) surfaces through spin-polarized electron energy loss spectroscopy (SPEELS). The samples consist of 30 atomic monolayers of Fe grown on a W(001) single crystal via molecular beam epitaxy at room temperature. Subsequently, the samples are exposed to 5 langmuirs of O2 and suffer a mild annealing at 500 K. The structure and purity of the samples are analyzed by low-energy electron diffraction and Auger electron spectroscopy. The magnetic characterization is performed by magneto-optical Kerr effect magnetometry, resulting in films with high remanent in-plane magnetization. SPEEL-spectra reveal a rich profusion of inelastic spin-flip and non-spin-flip peaks, which exhibit clear dispersion for wave vectors throughout the whole surface Brillouin zone. The results are attributed to surface modes of phonons and magnons (spin waves), in accordance with the literature and with current theoretical models.

Orientadores: Marcelo Knobel, Daniela Zanchet / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T12:53:07Z (GMT). No. of bitstreams: 1 Silva_ElvisLirada_M.pdf: 8983880 bytes, checksum: 9cf84b0bedd17ff35f94bf813d128441 (MD5) Previous issue date: 2006 / Resumo: Os arranjos de nanofios magnéticos tem atraído um interesse considerável da comunidade científica, motivado principalmente pela sua utilização como sistemas-modelo e na possível aplicação em mídias magnéticas de alta densidade de informação. O comportamento magnético macroscópico desses sistemas é fortemente dependente das anisotropias magnéticas efetivas (determinadas principalmente pelas contribuições das anisotropias de forma, magnetocristalina e magnetoelástica). Neste trabalho realizamos um estudo completo das propriedades magnéticas de nanofios magnéticos de Ni e Co, variando o comprimento dos nanofios e a temperatura das amostras. Os nanofios são obtidos por eletrodeposição em nanoporos de membranas de alumina preparadas por um duplo processo de anodização em substratos de alumínio. A caracterização estrutural dos nanofios foi feita por microscopia eletrônica de varredura de alta resolução e microscopia de força magnética e revela que os arranjos de nanofios estão organizados em uma rede hexagonal onde possuem diametros de aproximadamente 35 nm e a distância entre os nanofios de aproximadamente 105 nm. O comprimento dos nanofios varia de aproximadamente 560 nm até 2250 nm. Observamos uma mudança do eixo fácil de magnetização da direção paralela ao eixo dos nanofios na temperatura ambiente para direção perpendicular ao eixo dos nanofios em baixas temperaturas. Analisamos a dependência da remanência reduzida e da coercividade em relação à temperatura e verificamos que as amostras apresentam uma temperatura de cruzamento entre as remanências reduzidas com campo aplicado paralela e perpendicularmente ao eixo dos nanofios, que varia de acordo com o comprimento dos nanofios. Interpretamos nossos resultados em termos de uma competição entre a anisotropia de forma, que tende orientar a magnetização na direção paralela ao eixo dos nanofios, e uma anisotropia dependente da temperatura, que tenta alinhar a magnetizaçao na direção perpendicular ao eixo dos nanofios. O mecanismo utilizado para tentar explicar de maneira qualitativa os resultados que observamos, ao diminuirmos a temperatura da amostra, origina-se da tensão provocada pela alumina sobre os nanofios, em decorrência dos diferentes coeficientes de expansão térmica desses materiais, que induz uma anisotropia magnetoelástica perpendicular ao eixo dos nanofios / Abstract: Arrays of magnetic nanowires have attracted considerable interest, mainly motivated by their use as model systems and by possible applications in high-density magnetic information storage. The macroscopic magnetic behavior of such systems is strongly dependent on the effective magnetic anisotropy (mainly determined by shape and crystalline contributions). In this work, we carry out a systematic study of the magnetic properties on highly-ordered magnetic arrays of Co and Ni nanowires as functions of length of the nanowires and temperature. Nanowires were obtained by electrodeposition into nanopores of alumina membranes prepared by a two-step anodization process from pure aluminium. Structural studies were performed by high resolution scanning electron microscopy and magnetic force microscopy. The images revealed uniform arrays of nanowires with diameter of 35 nm, and with hexagonal symmetry arrangement with lattice constant (or inter-nanowire distance) of 105 nm. The nanowires length varies between 560 nm and 2250 nm. We observed a change in the magnetic easy axis from parallel to the axis wires at room temperature to transverse to the wire axis at low temperatures. We analysed the temperature dependence of the reduced remanence and coercive field we verified that the samples present a crossover temperature of reduced remanence with magnetic field applied both perpendicular and parallel to the nanowires axis that varies with nanowires length. We interpreted our results in terms of a competition between the shape anisotropy of the wires, which tends to align the magnetization along the wires axis and the temperature dependent magnetic anisotropy, which tends to orient the magnetization transverse to the wires axis. The mechanism which can qualitatively explain the observed results as a function of temperature is an induced anisotropy of magnetoelastic origin transversal to the nanowires axis, caused by strains and stresses, due to the different thermal expansion coefficient of nanowires and the alumina matrix, respectively / Mestrado / Materiais Magneticos e Propriedades Magneticas / Mestre em Física

Estudamos o comportamento estático e os mecanismos de inversão da magnetização de arranjos auto-organizados de nanofios de Ni e Co com alta anisotropia de forma. Os arranjos são obtidos a partir da anodização em dois passos de lâminas de Al e subseqüente eletrodeposição do metal magnético. Sua caracterização estrutural é realizada por microscopia eletrônica de varredura, microscopia de força atômica e magnética e difração de raios X. Seu comportamento magnético é estudado a partir da medida de curvas de inversão de primeira ordem (FORCs) a temperatura ambiente, via magnetometria SQUID ou de amostra vibrante. A análise FORC consiste na construção de uma mapa da resposta magnética do material a partir dos dados experimentais e pode ser interpretado a partir da analogia direta com o modelo de histerese de Preisach. Apresentamos resultados da influência dos diâmetros dos nanofios e do ângulo do campo externo aplicado em relação ao eixo de anisotropia sobre as principais características dos diagramas FORC. Estudamos também a dinâmica de spins em superfícies de O-Fe/W(001) através de espectroscopia por perda de energia de elétrons spin-polarizados (SPEELS). As amostras consistem em 30 monocamadas atômicas de Fe crescidas sobre um monocristal de W(001), via epitaxia por feixe molecular a temperatura ambiente. Subseqüentemente, a amostra é exposta a 5 langmuirs de O2 e sofre um suave annealing a 500 K. A estrutura e a pureza da amostra são analisadas por difração de elétrons de baixas energias e espectroscopia de elétrons Auger. A caracterização magnética é realizada por magnetometria por efeito Kerr magneto-óptico, resultando num filme com alta magnetização remanente no plano. Os espectros de SPEELS revelam uma rica profusão de picos inelásticos tipo spin-flip e nãospin-flip, que exibem clara dispersão ao longo de toda a zona de Brillouin de superfície. Os resultados são atribuídos a modos de superfície de fônons e mágnons (ondas de spin), de acordo com resultados da literatura e com modelos teóricos atuais. / We study the static behavior and the mechanisms of magnetization reversal of arrays of self-organized Ni and Co nanowires with high shape anisotropy. The arrays are obtained by two-step anodization of Al foils and subsequent electrodeposition of the magnetic metal.Their structural characterization is obtained by scanning electron microscopy, atomic and magnetic force microscopy and X-ray diffraction. Their magnetic behavior is studied from the measurement of first order reversal curves (FORCs) at room temperature, via SQUID or vibrating sample magnetometry. The FORC analysis method consists in building a map of the magnetic response of the material from the experimental data and it can be interpreted from the direct analogy with the Preisach model of hysteresis. We present results of the influence of the diameter of the nanowires and the angle of the applied external field in relation to the anisotropy easy-axis on the main features of the FORC diagrams. We also study the spin dynamics of O-Fe/W(001) surfaces through spin-polarized electron energy loss spectroscopy (SPEELS). The samples consist of 30 atomic monolayers of Fe grown on a W(001) single crystal via molecular beam epitaxy at room temperature. Subsequently, the samples are exposed to 5 langmuirs of O2 and suffer a mild annealing at 500 K. The structure and purity of the samples are analyzed by low-energy electron diffraction and Auger electron spectroscopy. The magnetic characterization is performed by magneto-optical Kerr effect magnetometry, resulting in films with high remanent in-plane magnetization. SPEEL-spectra reveal a rich profusion of inelastic spin-flip and non-spin-flip peaks, which exhibit clear dispersion for wave vectors throughout the whole surface Brillouin zone. The results are attributed to surface modes of phonons and magnons (spin waves), in accordance with the literature and with current theoretical models.

Orientador: Kleber Roberto Pirota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T03:13:48Z (GMT). No. of bitstreams: 1 Carvalho_PetersonGrandinide_M.pdf: 8255135 bytes, checksum: 51addf2df8b7383dc2ab652f85205ea2 (MD5) Previous issue date: 2013 / Resumo: Redes de nanofios (NF) magnéticos têm atraído muita atenção devido suas possíveis aplicações tecnológicas. Do ponto de vista tecnológico tais redes poderiam ser utilizadas em diversas aplicações tais como dispositivos spintrônicos, sistemas de armazenamento de memória magnética, elementos sensores de campo magnético e em diversas aplicações biológicas. Por outro lado, do ponto de vista da ciência de base é fundamental compreender o efeito da baixa dimensionalidade nas propriedades magnéticas dos materiais. Muitas das propriedades magnéticas dos NF decorrem simplesmente de sua geometria. Neles, há uma forte anisotropia magnética de forma que tende a manter os momentos magnéticos alinhados ao eixo principal dos NF. No cobalto com estrutura hexagonal compacta (hcp), os momentos magnéticos tendem a se alinhar em uma direção cristalina preferencial (eixo c), ou seja, há uma anisotropia magnetocristalina. Tal anisotropia é da mesma ordem de grandeza da anisotropia de forma de NF ideias (cujo comprimento é muito maior que o diâmetro). Nanofios de cobalto hcp são interessantes basicamente porque suas propriedades magnéticas dependerão fortemente da estrutura cristalina (tamanho do grão e orientação do cristal em relação ao eixo principal dos nanofios). Como as duas contribuições de anisotropia são da mesma ordem de grandeza, pode-se controlar a anisotropia efetiva ao longo do NF através do controle da direção cristalina. Neste trabalho foram produzidas redes de NF de Co via eletrodeposição em moldes de membrana nanoporosa de alumínio anodizado (MNPAA). Alterou-se a estrutura cristalina dos NF através do pH de eletrodeposição (1,9; 3,9 e 5,5). Os NF possuem diâmetro de 35 nm, comprimento de ~10 ?m e a distância entre eles na rede é de 110 nm . A estrutura cristalina foi estudada através de técnicas de microscopia eletrônica (de varredura e de transmissão) e por difração de raios-X. As propriedades magnéticas foram inferidas através de técnicas de magnetometria. Foram obtidas curvas de histerese em função da temperatura e do ângulo entre o campo magnético aplicado e o eixo principal dos NF. Também foram obtidas curvas de magnetização inicial com o campo aplicado paralelo e perpendicular aos NF, e após diferentes ciclos de desmagnetização. Também foram feitos alguns breves estudos sobre o efeito do tratamento térmico nas propriedades magnéticas dos NF; sobre a dieletroforese, que é uma técnica de separação dos NF removidos da MNPAA e dispersos em solução, e sobre as alterações morfológicas e grau de oxidação dos nanofios quando retirados da MNPAA. Observou-se que para pH¿s baixos o eixo c é perpendicular ao eixo principal e os grãos são pequenos. O aumento do pH tende a tornar o eixo c paralelo ao eixo principal dos nanofios, o que aumenta a anisotropia magnética efetiva da rede. O tamanho dos grãos também aumenta com o pH, tornando o meio cristalino local mais expressivo no processo de inversão da magnetização. Também se observou que, dependendo da direção do eixo c, a diminuição da temperatura pode inverter a direção fácil de anisotropia efetiva dos nanofios, devido ao aumento da anisotropia magnetocristalina / Abstract: Magnetic nanowire (NW) arrays have been attracting great attention due to their possible technological applications. Such arrays are promising candidates for different applications, such as spintronic devices, magnetic memory storage systems, magnetic field sensors and in several biological systems. On the other hand, from a basic science point of view, it is fundamental to understand the low dimensionality effect on materials magnetic properties. Many of the NW magnetic properties simply occur due to its elongated geometry. It creates a strong magnetic anisotropy which tends to maintain the magnetic moments aligned to the NW¿s main axis. In bulk cobalt with a hexagonal compact structure (hcp), the magnetic moments tend to align in a preferential crystalline direction, i.e. there is a magnetocrystalline anisotropy. Such anisotropy is of the same order of magnitude than NW¿s shape anisotropy (when the length is much bigger than the diameter). Hcp cobalt nanowires are mainly interesting because their magnetic properties strongly depend on their crystalline structure (grain size and crystal orientation with respect to the NW main axis). Since the two anisotropy contributions are of the same order of magnitude, we can control the effective anisotropy along the NW by controlling the crystalline structure orientation. In this study were produced Co NW arrays through eletrodeposition in aluminum nanoporous templates. The NW crystalline structure was altered by the pH during the eletrodeposition process. The NW present a diameter of 35 nm, length of ~10 ?m and an interwire distance of 110 nm. The crystalline structure was investigated through electronic microscopy techniques (scanning and transmission) and X-ray diffraction. The magnetic properties were inferred through magnetometry techniques. Hysteresis curves were obtained as a function of temperature and of the angle between the applied magnetic field and the NW¿s main axis. Initial magnetization curves with the applied field parallel and perpendicular to the NW, and after different demagnetization cycles, were also obtained. Finally, some brief studies have also been made about the effect of heat treatment on the NW magnetic properties; about dielectrophoresis, which is a separation technique for the NW removed from the alumina template and dispersed in solution; and about the morphological changes and the NW oxidation degree when removed from the alumina template / Mestrado / Física / Mestre em Física

Cancer prevails as one of the most devastating diseases being at the top of death causes for adults despite continuous development and innovation in cancer therapy. Nanotechnology may be used to achieve therapeutic dosing, establish sustained-release drug profiles, and increase the half-life of drugs. In this context, magnetic nanowires (NWs) have shown a good biocompatibility and cellular internalization with a low cytotoxic effect. In this thesis, I induced cancer cell death by combining the chemotherapeutic effect of iron NWs functionalized with Doxorubicin (DOX) with mechanical disturbance under a low frequency alternating magnetic field. Two different agents, APTES and BSA, were separately used for coating NWs permitting further functionalization with DOX. Internalization was qualitatively and quantitatively assessed for both formulations by confocal reflection microscopy and inductively coupled plasma-mass spectrometry. From confocal reflection analysis, BSA formulations demonstrate to have a higher internalization degree and a broader distribution within the cells in comparison to APTES formulations. Both groups of functionalized NWs generated a comparable cytotoxic effect in MDA-MB-231 breast cancer cells in a DOX concentration-dependent manner, (~60% at the highest concentration tested) that was significantly different from the effect produced by the free DOX (~95% at the same concentration) and non-functionalized NWs formulations (~10% at the same NWs concentration). A synergistic cytotoxic effect is obtained when a low frequency magnetic field (1 mT, 10 Hz) is applied to cells treated with the two formulations that is again comparable (~70% at the highest concentration). Furthermore, the cytotoxic effect of both groups of coated NWs without the drug increased notoriously when the field is applied (~25% at the highest concentration tested). Here, a novel bimodal method for cancer cell destruction was developed by the conjugation of the magneto-mechanical properties of the iron NWs coupled with the chemotoxic effect of an anticancer drug. Moreover, it was demonstrated that iron nanowires possess an outstanding biocompatibility and showed high efficacy as drug delivery agents coupled to a high degree of cell internalization. Finally, the proposed method benefits from the low power fields applied during treatment. This poses much less safety risks and allows using cheaper and simpler equipment.