Title: Preparation and characterization of bi-phasic magnetic nanoparticles Author: Bc. Adam Alemayehu Department: Department of Innorganic Chemistry Supervisors: doc. RNDr. Daniel Nižňanský, Ph.D. RNDr. Václav Tyrpekl, Ph.D. Consultant: M.Sc. Dominika Zákutná Abstract The work is focusing on the magnetic properties of ferrimagnetic spinel ferrites before and after the introduction of a shell on a core particle with different magnetic properties. The core nanoparticles were prepared by hydrothermal decomposition of oleate precursors. The introduction of shell was carried out by hydrothermal treatment of the already prepared core particles. The phase composition, spinel structure and the sizes of the prepared samples were investigated by powder X-ray diffraction and by transmission electron microscopy. Formation of the shell on top of the core particle was determined indirectly, using Mössbauer spectroscopy at room temperature. The interparticle interactions and the particle shape was studied by small angle X-ray scattering. The magnetic properties of the prepared samples were measured on a SQUID magnetometer. Key words: magnetic nanoparticles, core, shell, spinel structure, powder X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, TEM

Um dos radionuclídeos que se destaca mundialmente é o molibdênio-99. O 99Mo é o gerador do radioisótopo mais amplamente usado para a preparação de radiofármacos para fins de diagnóstico em medicina nuclear, o tecnécio-99m. Neste estudo, as nanopartículas de magnetita foram sintetizadas por precipitação de íons Fe2+ em meio alcalino e tratadas por irradiação de microondas e foram aplicadas na separação do 99Mo por adsorção. O material foi caracterizado por FTIR, MEV, DRX, DSC, TGA e EDS. Os estudos de adsorção foram realizados utilizando a técnica em batelada e em colunas de leito fixo. Verificou-se a influência das espécies de Al e os radioisótopos Te, I e Ru na adsorção de 99Mo. Os efeitos do pH, tempo de contato, temperatura, concentração e dose do adsorvente foram investigados. Modelos de isotermas de adsorção Langmuir e Freundlich foram usados para obter informações sobre o processo de adsorção e os modelos cinéticos de pseudo-primeira ordem, pseudo-segunda ordem e difusão intrapartículas foram estudados para avaliar a cinética de adsorção. Soluções de dessorventes para a recuperação do 99Mo foram investigadas. A nova via de síntese de nanomagnetita proposta mostrou-se simples e rápida, fazendo uso de um único reagente. As nanopartículas de magnetita apresentaram forma esférica de aproximadamente de 20 nm e polidispersão heterogênea. As caracterizações por DRX, DSC e TGA confirmaram a predominância da fase magnetita nas amostras. A adsorção de 99Mo nas nanopartículas de magnetita foi próxima de 100% no intervalo de pH entre 1 e 11, durante 30 min de tempo de contato e 15 mg de dose do adsorvente. O modelo de isoterma de adsorção de Langmuir apresentou melhor acordo para a remoção 99Mo pelas nanopartículas de magnetita, e a cinética de adsorção foi melhor descrita pelo modelo de pseudo-segunda ordem. A caracterização por EDS indicou ausência de contaminação. A recuperação do 99Mo da nanomagnetita com solução de NaOH foi superior a 95% e os elementos Ru, Te, Al e I não interferiram na propriedade adsortiva da nanomagnetita. Estes resultados mostraram que nanopartículas de magnetita são bons adsorventes para o Mo e, por conseguinte, tem grande potencial para aplicação no processo de separação e purificação do 99Mo de fissão. / One of radionuclides that stand out globally is the Molybdenum-99. The 99Mo is the radionuclide generator most widely used radioisotope for the preparation of radiopharmaceuticals for diagnostic purposes in nuclear medicine, Technetium-99m. In this study, magnetite nanoparticles were synthesized by precipitation of Fe2+ ions in an alkaline medium and treated by microwave irradiation and were studied for 99Mo adsorption and recovery The synthesized material was characterized by FTIR, SEM, XRD, DSC, TGA and EDS. Adsorption studies were carried out using the batch technique and fixed bed columns. The influence of the Al and the radioisotopes of Te, I and Ru species on 99Mo adsorption of was verified. Effects of pH, contact time, temperature, concentration and adsorbent dosage were investigated. Adsorption isotherm models of Langmuir and Freundlich were used to obtain information on the adsorption process and the kinetic models of pseudo first-order, pseudo-second order and intraparticle diffusion were studied to evaluate the adsorption. Desorbent solutions for 99Mo recovery were investigated. The new route for nanomagnetite synthesis was found to be simple and fast using of just one reagent. The magnetite nanoparticles showed spherical shape with about 20 nm in diameter and heterogeneous polydispersion. The characterizations by XRD, DSC and TGA confirmed the predominance of magnetite phase. The adsorption of 99Mo was close to 100% by the magnetite nanoparticles in the pH range from 1 to 11 for 30 min of contact time and 15 mg of adsorbent dosage. Langmuir adsorption isotherm model showed better agreement for the 99Mo adsorption by nanomagnetite nanoparticles, and the adsorption kinetics was better described by the pseudo second order model. The nanoparticle characterization by EDS indicated no contamination. The recovery of 99Mo with NaOH 2 mol L-1 from the magnetite nanoparticles was higher than 95% and the elements Ru, Te, Al and I did not interfere in the adsorption property of magnetite nanoparticles. These results showed that magnetite nanoparticles were good adsorbent for 99Mo and therefore have great potential for application in the process of separation and purification of fission 99Mo.

Essa tese teve por objetivo desenvolver nanopartículas conjugadas, magnetofluorescentes, de alta performance, com base na associação de semicondutores nanocristalinos do tipo II-VI, do inglês quantum dots, com nanopartículas de óxido de ferro não-estequiométricas, em regime superparamagnético, para aplicações em ensaios não destrutivos. Foram testadas três tipos de nanopartículas de óxido de ferro para atuarem como potenciais plataformas magnéticas de ancoramento. Esses materiais foram caracterizados por diversas técnicas e, dentre elas, uma nova metodologia de pesagem externa desenvolvida para a avaliação da magnetização de saturação e para o estudo de processos magnetoforéticos. Os semicondutores nanocristalinos do tipo II-VI foram sintetizados, em meio aquoso, por uma nova metodologia, com controle cinético em tempo real que se mostrou ser uma ferramenta poderosa na investigação dos processos sintéticos. Os conjugados magnetofluorescentes foram desenvolvidos a partir da combinação adequada entre as nanopartículas de óxido de ferro e os quantum dots, utilizando brometo de hexadeciltrimetilamônio, CTAB, como espaçador químico. O material assim obtido foi caracterizado por microscopia eletrônica de transmissão de alta resolução, por espectrofluorometria, por espectroscopia eletrônica e por medidas de magnetização de amostra vibrante. Suas características ópticas e magnéticas foram exploradas com sucesso em testes iniciais de corpos de prova, na identificação de fendas estruturais por meio de ensaios magneto-luminescentes de caráter não destrutivos. / This Ph.D dissertation focused on the development of high performance magneto-fluorescent-conjugated nanoparticles, combining tunable II-VI quantum dots and surface modified-non-stoichiometric iron oxide nanoparticles, aiming application in non-destructive assays. Three types of iron oxide nanoparticles were synthesized as magnetic anchoring platforms. These materials were characterized by means of several techniques, and a new methodology of external weighting with analytical balances was developed to evaluate the saturation magnetization of the samples and to investigate the magnetophoretic process. The water-soluble quantum dots were obtained by means of kinetically controlled synthesis, which were monitored in real-time, providing a powerful technique in the investigation of synthetic pathways. The magneto-fluorescentconjugated nanoparticles were assembled by the appropriate combination of the constituents with surfactant species, acting as spacers in order to minimize the Förster Resonance Energy Transfer mechanisms (FRET). Such new probes were characterized by high resolution transmission electron microscopy, fluorescence and electronic spectroscopy, and by vibrating sample magnetometer, and were successfully tested in the in non-destructive assays for the detection of fractures in metallic structures.

A imobilização de fotossensibilizadores (FS) em materiais nanométricos tem se mostrado uma excelente alternativa ao seu emprego na forma molecular para terapia fotodinâmica (PDT). O presente trabalho descreve uma série de estratégias sintéticas desenvolvidas para a imobilização de FS em nanoesferas de sílica contendo núcleos magnéticos, bem como o estudo das propriedades foto-químicas, foto-físicas e morfológicas dos nanomateriais obtidos. Os FS utilizados foram o azul de metileno, tionina, azure A, protoporfirina IX, hematoporfirina IX e clorofilina. As metodologias de imobilização empregadas envolveram a adição do FS durante o crescimento da camada de sílica ou a ligação do FS na superfície do nanomaterial já formado. Em alguns casos foi necessário modificar previamente o FS com organossilanos. Os núcleos magnéticos foram preparados por co-precipitação de sais de ferro(II) e ferro(III) em meio básico e o revestimento com sílica foi realizado utilizando-se tetraetilortossilicato em uma microemulsão. Os núcleos magnéticos revestidos com uma camada de sílica mantiveram o comportamento superparamagnético. Para a tionina e o azul de metileno não foi detectada geração de oxigênio singlete após a imobilização. Para o azure A, protoporfirina IX e clorofilina imobilizados, a geração de oxigênio singlete foi detectada e caracterizada por métodos químicos e físicos. O material contendo clorofilina mostrou-se bastante promissor e foi empregado em estudos preliminares com células HeLa, levando à morte celular após irradiação, o que comprova o potencial para PDT. O comportamento do fotossensibilizador imobilizado e a possível proteção extra fornecida pela camada de sílica foram estudados pela supressão de fluorescência com íons brometo e supressão da geração de oxigênio singlete com albumina de soro bovino. Hematoporfirina IX é mais afetada na forma livre do que imobilizada em nanoesferas de sílica, o que indica que o FS imobilizado é capaz de gerar oxigênio singlete e está mais protegido de interferentes. / The immobilization of photosensitizers (PS) in nanometric materials is an excellent alternative to their use in molecular forms for photodynamic therapy (PDT). The present work describes a series of synthetic strategies for the immobilization of PS on silica nanospheres containing magnetic nucleous, as well as the studies of the photochemical, photophysical and morphological properties of the obtained materials. The studied PS were methylene blue, thionin, azure A, protoporphyrin IX, hematoporphyrin IX and chlorophyllin. The immobilization methodologies involve the addition of PS during the growth of the silica shell or the attachment of PS to the material surface. Often, a previous modification of the PS with organosilanes was necessary. The magnetic cores were prepared by co-precipitation of iron(II) and iron(III) salts in basic media and the coating with silica was performed by a microemulsion using TEOS. After coating with silica, the magnetic nanomaterial maintained the superparamagnetic behavior. The generation of singlet oxygen by thionin and methylene blue was not detect after immobilization. The generation of singlet oxygen by immobilized azure A, protoporphyrin IX and chlorophyllin was detected and characterized by chemical and physical methods. The material containing chlorophyllin is promising for PDT and was applied in preliminary studies with HeLa cells, causing cell death after irradiation. The behavior of the immobilized PS and the possible extra protection given by the silica shell were investigated by fluorescence quenching with bromide ions and by suppression of singlet oxygen generation with bovine serum albumin. Hematoporphyrin IX was more affected in the free form than immobilized in silica nanospheres, which indicates that the immobilized FS still generates singlet oxygen and is more protected against interfering species

Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-05-17T18:27:28Z No. of bitstreams: 1 Tese - Elisa Magno Nunes de Oliveira.pdf: 7318970 bytes, checksum: a50f399a4afea119cd760c93cd71ff72 (MD5) / Approved for entry into archive by Sheila Dias (sheila.dias@pucrs.br) on 2018-05-23T14:59:14Z (GMT) No. of bitstreams: 1 Tese - Elisa Magno Nunes de Oliveira.pdf: 7318970 bytes, checksum: a50f399a4afea119cd760c93cd71ff72 (MD5) / Made available in DSpace on 2018-05-23T15:10:26Z (GMT). No. of bitstreams: 1 Tese - Elisa Magno Nunes de Oliveira.pdf: 7318970 bytes, checksum: a50f399a4afea119cd760c93cd71ff72 (MD5) Previous issue date: 2018-03-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The present study focuses on the development of nanoparticles with an iron oxide magnetic core, with different biocompatible coatings, and on a comparative study of their toxicities. Uncoated and dextran-, chitosan-, polyethylene glycol- and silica-coated nanoparticles were synthesized. The addition of optical markers of the benzo-thiazoles class was also accomplished. The physico-chemical properties of the nano-particles were characterized, including their magnetic, optical and contrast properties in nuclear magnetic resonance imaging (relaxivities). In the particular case of nanopar-ticles functionalized with 6-OH-BTA-1 molecules, the affinity to the beta-amyloid pep-tide was also investigated. A second step was to evaluate the toxicological effects of these nanoparticles in vitro (using in VERO cells), and in vivo with zebrafish as an animal model. The size of the nanoparticles with the coatings ranged from 13 to 30 nm. Their crystalline structure was consistent with the ferrite spinel. The nanoparticles, independent of the coating, did not present residual magnetization and hysteresis, in-dicating superparamagnetic behaviour. For most nanoparticles, the r2 transverse re-laxivity values ranged from 76-64 mM-1.s-1, exceptfor uncoated and chitosan-coated nanoparticles, which present higher values, possibly due to the aggregation. The val-ues of r1 were similar for all nanoparticles (12.6 to 18 mM-1.s-1), with the exception of silica-coated nanoparticles (r1=2.1 mM-1.s-1). The r2/r1 ratios were between 4 and 17, typical of commercially available negative contrast-agents. The nanoparticles function-alized with benzothiazoles showed fluorescence with a Stokes shift of the emission peak of ~ 197 nm. The interaction of the beta-amyloid peptide with the 6-OH-BTA-1 molecule analyzed by fluorescence suppression is characterized by a static mecha-nism and Stern-Volmer constants of 1.53x104 mM-1 for the monomeric form, 1.40x104 mM -1 for oligomers) and 1.33x104 mM -1 for amyloid plaques.The in vitro toxicity assays indicated acceptable values of cell viability for iron concentration up to 2 mmol.L-1. The nanoparticles with the carboxysilane and polyethylene glycol showed higher biocom-patibility and silica-coated nanoparticles had the highest cytotoxicity. The in vivo as-says did not show significant changes in survival and hatchability rates, except for doses greater than 2 mmol.L-1 in the case of the chitosan-coated nanoparticles. The percentages of animals with anatomical alterations were similar between the treated and control groups. In the locomotion and exploration tests, only chitosan- and silica-coated nanoparticles induced significant changes. / O presente trabalho aborda o desenvolvimento de nanopart?culas compostas por um n?cleo magn?tico de ?xido de ferro com diferentes revestimentos biocompat?-veis e estudo comparativo de suas toxicidades. Foram sintetizadas nanopart?culas de ?xido de ferro sem revestimento e com revestimentos de dextrana, quitosana, polieti-lenoglicol e s?lica, e com a adi??o de marcadores ?pticos da classe dos benzotiaz?is. As propriedades f?sico-qu?micas das nanopart?culas foram caracterizadas, incluindo as suas propriedades magn?ticas, ?pticas e de contraste em imagens por resson?ncia magn?tica nuclear (relaxividades), bem como a afinidade ao pept?deo beta-amiloide, no caso particular de funcionaliza??o com a mol?cula 6-OH-BTA-1. Em uma segunda etapa, foram avaliados os efeitos toxicol?gicos dessas nanopart?culas em ensaios bi-ol?gicos in vitro em c?lulas VERO, e in vivo tendo como animal modelo o peixe zebra. O tamanho das nanopart?culas com revestimentos variou entre 13 a 30 nm, e estrutura cristalina coerente com o espin?lio de ferrita. As nanopart?culas n?o apresentaram magnetiza??o residual e histerese, indicando superparamagnetismo, independente do revestimento. Para a maioria das nanopart?culas, os valores de relaxividade transver-sal r2 variaram de 76-64 mM-1.s-1, com exce??o das nanopart?culas sem revestimento e de quitosana, os quais foram mais elevados, possivelmente devido ao efeito de agrega??o. Os valores de r1 foram semelhantes para todas as nanopart?culas (12,6 a 18 mM-1.s-1), com exce??o das nanopart?culas de s?lica (r1 = 2,1 mM-1.s-1). As raz?es r2/r1 foram entre 4 e 17, valores t?picos de agentes de contraste negativos comercial-mente dispon?veis. As nanopart?culas funcionalizadas com os benzotiaz?is mantive-ram sua fluoresc?ncia com deslocamentos de Stokes na ordem de 197 nm para o pico de emiss?o. As an?lises da intera??o do pept?deo beta-amiloide com a mol?cula 6-OH-BTA-1, mostraram valores de constante de Stern-Volmer para supress?o de fluo-resc?ncia de 1,53x104 mM-1 (mon?mero), 1,40x104 mM-1 (olig?mero) e 1,33x104 mM-1 (placa), indicando quenching por um mecanismo est?tico. O pept?deo na forma mo-nom?rica demonstrou maior facilidade de acesso ?s mol?culas de 6-OH-BTA-1. Os resultados dos ensaios in vitro indicaram valores aceit?veis de viabilidade celular para concentra??o de ferro inferior a 2 mmol.L-1. As nanopart?culas com o carboxisilano e polietilenoglicol demostraram maior biocompatibilidade e as nanopart?culas de s?lica tiveram a maior citotoxicidade. Os resultados dos ensaios in vivo n?o mostraram alte-ra??es significativas na taxa de sobreviv?ncia e de eclos?o do corium, exceto para as doses maiores que 2 mmol.L-1 das nanopart?culas revestidas com quitosana. Os per-centuais de animais com altera??es anat?micas foram similares entre os grupos tra-tados e de controle. Nos ensaios de locomo??o e explora??o, apenas as nanopart?cu-las de quitosana e de s?lica induziram altera??es adversas significativas.

As diversas aplicações tecnológicas de nanopartículas magnéticas (NPM) vêm intensificando o interesse por materiais com propriedades magnéticas diferenciadas, como magnetização de saturação (MS) intensificada e comportamento superparamagnético. Embora MNP metálicas de Fe, Co e bimetálicas de FeCo e FePt possuam altos valores de MS, sua baixa estabilidade química dificulta aplicações em escala nanométrica. Neste trabalho foram sintetizadas NPM de Fe, Co, FeCo e FePt com alta estabilidade química e rigoroso controle morfológico. NPM de óxido metálicos (Fe e Co) também foram obtidas. Dois métodos de síntese foram empregados. Usando método baseado em sistemas nanoheterogêneos (sistemas micelares ou de microemulsão inversa), foram sintetizadas NPM de Fe3O4 e Co metálico. Foram empregados surfactantes cátion-substituídos: dodecil sulfato de ferro(III) (FeDS) e dodecil sulfato de cobalto(II) (CoDS). Para a síntese das NPM, foram estudados e determinados a concentração micelar crítica do FeDS em 1-octanol (cmc = 0,90 mmol L-1) e o diagrama de fases pseudoternário para o sistema n-heptano/CoDS/n-butanol/H2O. NPM esferoidais de magnetita com3,4 nm de diâmetro e comportamento quase-paramagnético foram obtidas usando sistemas micelares de FeDS em 1-octanol. Já as NPM de Co obtidas via microemulsão inversa, apesar da larga distribuição de tamanho e baixa MS, são quimicamente estáveis e superparamagnéticas. O segundo método é baseado na decomposição térmica de complexos metálicos, pelo qual foram preparadas NPM esféricas de FePt e de óxidos metálicos (Fe3O4, FeXO1-X, (Co,Fe)XO1-X e CoFe2O4) com morfologia controlada e estabilidade química. O método não mostrou a mesma efetividade na síntese de NPM de FeAg e FeCo: a liga FeAg não foi obtida enquanto que NPM de FeCo com estabilidade química foram obtidas sem controle morfológico. NPM de Fe e FeCo foram preparadas a partir da redução térmica de NPM de Fe3O4 e CoFe2O4, as quais foram previamente recobertas com sílica. A sílica previne a sinterização inter-partículas, além de proporcionar caráter hidrofílico e biocompatibilidade ao material. As amostras reduzidas apresentaram aumento dos valores de MS (entre 21,3 e 163,9%), o qual é diretamente proporcional às dimensões das NPM. O recobrimento com sílica foi realizado via hidrólise de tetraetilortosilicato (TEOS) em sistema de microemulsão inversa. A espessura da camada de sílica foi controlada variando-se o tempo de reação e as concentrações de TEOS e de NPM, sendo então proposto um mecanismo do processo de recobrimento. Algumas amostras receberam um recobrimento adicional de TiO2 na fase anatase, para o qual foi empregado etilenoglicol como solvente e ligante para formação de glicolato de Ti como precursor. A espessura da camada de TiO2 (2-12 nm) é controlada variando as quantidades relativas entre NPM e o precursor de Ti. Ensaios de hipertermia magnética foram realizados para as amostras recobertas com sílica. Ensaios de hipertermia magnéticas mostram grande aumento da taxa de aquecimento das amostras após a redução térmica, mesmo para dispersões diluídas de NPM (0,6 a 4,5 mg mL-1). Taxas de aquecimento entre 0,3 e 3,0oC min-1 e SAR entre 37,2 e 96,3 W g-1. foram obtidos. A atividade fotocatalítica das amostras recobertas foram próximas à da fase anatase pura, com a vantagem de possuir um núcleo magnético que permite a recuperação do catalisador pela simples aplicação de campos magnéticos externos. Os resultados preliminares dos ensaios de hipertermia magnética e fotocatálise indicam um forte potencial dos materiais aqui relatados para aplicações em biomedicina e em fotocatálise. / The most diverse technological applications of magnetic nanoparticles (MNP) have intensifiedthe interest for materials with different magnetic properties such as enhanced saturationmagnetization (MS) and superparamagnetic behavior. Despite the high MS values of metalparticles of Fe, Co, FeCo and FePt, their low chemical stability hinders most applications at thenanoscale. This thesis reports the synthesis of metallic Fe and Co and bimetallic FeCo and FePtMNP with high chemical stability and strict morphological control. MNP of iron oxide and mixediron-cobalt oxide were also synthesized. Two methods were employed. The first method, basedon nanoheterogeneous systems (micellar or reverse microemulsion systems), was used toprepare magnetite and metallic Co NPM. The method applies cation-substituted surfactants:iron(III) dodecyl sulfate iron (FeDS) and cobalt(II) dodecyl sulfate (CoDS). Before the MNPsyntheses, it were studied e determined the critical micelle concentration of FeDS in 1-octanol(cmc = 0.90 mmol L-1) and the pseudo-ternary phase diagram of n-heptane/CoDS/nbutanol/H2O. Spheroidal MNP of magnetite with 3.4 nm in diameter and quasi-paramagneticbehavior were prepared in octanolic FeDS micellar systems. Despite their broad sizedistribution and low MS, metallic Co MNP were produced in reverse microemulsions withchemical stability and superparamagnetic behavior. The second synthesis method, based onthermal decomposition of metal complexes, was employed to prepare spherical FePt and metaloxides (Fe3O4, FeXO1-X, (Co, Fe)XO1-X and CoFe2O4) MNP. Strict morphological control and highchemical stability were reached. Such method does not show the same effectiveness tosynthesize FeAg and FeCo MNP: the FeAg bimetallic alloy was not obtained while FeCo MNPwith chemical stability and compositional control were prepared with no morphological control.Fe and FeCo MNP were produced by thermal reduction of silica-coated Fe3O4 and CoFe2O4 MPN. The coating, beyond to prevent inter-particle sintering, provides biocompatibility andhydrophilic character. The reduced samples showed a significant increase in MS values(between 21.3 and 163.9%), which is directly proportional to MNP size. The silica coating wasaccomplished by tetraethylorthosilicate (TEOS) hydrolysis in reverse microemulsions. Thethickness of the silica layer is controlled by varying the reaction time and concentration of TEOSand NPM. The observations during coating process allowed to propose its probable mechanism.An additional coating of TiO2 (anatase phase) was performed onto silica layer for somesamples. Anatase coating was achieved by using ethylene glycol as both solvent and ligand toproduce an intermediate complex Ti precursor. The variation of the relative amounts of NPMand the Ti precursor allows to control the thickness of the anatase layer between 2 and 12 nm. Assays of magnetic hyperthermia were performed for silica-coated samples. The heating rate of the reduced samples increases after thermal reduction, even for dilute MNP dispersions (0.6 to4.5 mg mL-1). Heating rates between 0.3 and 3.0o C min-1 and SAR in the range of 37.2 96.3 Wg-1 were obtained. The photocatalytic activities of pure anatase particles and TiO2 -coated MNPwere close, but the magnetic samples has the advantage of being recovered from reactionmedia by applying the external magnetic fields. The preliminary results of magnetichyperthermia and photocatalysis assays indicate such materials have strong potential forapplications in biomedicine and photocatalysis.

Neste trabalho, estudou-se a síntese por sol-gel da ferrita de cobalto (CoFe2O4), variando-se a temperatura de tratamento térmico do xerogel. Nitrato de ferro e nitrato de cobalto foram utilizados como fonte de cátions e ácido cítrico como mineralizador. Os produtos obtidos, tratados a 750, 800 e 850°C, tiveram sua microestrutura e propriedades magnéticas investigadas no intuito de encontrar correlações entre as condições de síntese, as posições ocupadas pelos cátions dentro da estrutura espinélio do composto e as propriedades magnéticas medidas. Estudos de difratometria de raios X exibiram reflexões características da estrutura espinélio, o que sugere que o tratamento térmico não afetou significativamente a estrutura cristalina do material. Uma fração secundária de hematita também foi observada. As ferritas apresentaram área superficial específica (por BET) de aproximadamente 4 m².g-1. Imagens por MEV indicam que o material apresenta-se aglomerado. Quanto às propriedades magnéticas, um máximo de coercividade de 1405.2 Oersted foi encontrado para a amostra tratada a 800°C. Espectros Mößbauer indicaram um baixo grau de inversão nos espinélios formados, o que é incomum para a ferrita de cobalto. Subtraindo do espectro obtido por Mößbauer o excesso de ferro na forma de hematita, há um forte indicativo que a ferrita foi sintetizada de maneira sub-estequiométrica deficiente em ferro. / We herein report a study on the sol-gel synthesis of cobalt ferrite (CoFe2O4) and the effect of treatment temperature on the product outcome. Iron nitrate and cobalt nitrate were used as cation sources and citric acid as mineralizer. Products treated at 750, 800 and 850°C had their microstructure and magnetic properties assessed in order to correlate their synthesis conditions, the positions in which the cations are inserted in the spinel structure and the magnetic behavior displayed by the ferrites. X-ray diffractometry studies exhibit the characteristic reflections of spinel group materials, suggesting that the thermal treatment does not sensibly affect the crystalline structure of the material. A secondary fraction of hematite was also observed. The ferrites exhibit a specific surface area (from BET) of approximately 4 m².g-1. SEM images indicate the material forms agglomerates. As to the magnetic properties, a maximum of 1405.2 Oersted was achieved for the sample treated at 800°C. Mößbauer spectra indicate a fairly low inversion degree in the synthesized materials, which is rather unusual for cobalt ferrite. After deducting the iron fraction present in the form of hematite, there are strong indications that cobalt ferrite was synthesized as a substoichiometric iron-deficient spinel.

A imobilização de fotossensibilizadores (FS) em materiais nanométricos tem se mostrado uma excelente alternativa ao seu emprego na forma molecular para terapia fotodinâmica (PDT). O presente trabalho descreve uma série de estratégias sintéticas desenvolvidas para a imobilização de FS em nanoesferas de sílica contendo núcleos magnéticos, bem como o estudo das propriedades foto-químicas, foto-físicas e morfológicas dos nanomateriais obtidos. Os FS utilizados foram o azul de metileno, tionina, azure A, protoporfirina IX, hematoporfirina IX e clorofilina. As metodologias de imobilização empregadas envolveram a adição do FS durante o crescimento da camada de sílica ou a ligação do FS na superfície do nanomaterial já formado. Em alguns casos foi necessário modificar previamente o FS com organossilanos. Os núcleos magnéticos foram preparados por co-precipitação de sais de ferro(II) e ferro(III) em meio básico e o revestimento com sílica foi realizado utilizando-se tetraetilortossilicato em uma microemulsão. Os núcleos magnéticos revestidos com uma camada de sílica mantiveram o comportamento superparamagnético. Para a tionina e o azul de metileno não foi detectada geração de oxigênio singlete após a imobilização. Para o azure A, protoporfirina IX e clorofilina imobilizados, a geração de oxigênio singlete foi detectada e caracterizada por métodos químicos e físicos. O material contendo clorofilina mostrou-se bastante promissor e foi empregado em estudos preliminares com células HeLa, levando à morte celular após irradiação, o que comprova o potencial para PDT. O comportamento do fotossensibilizador imobilizado e a possível proteção extra fornecida pela camada de sílica foram estudados pela supressão de fluorescência com íons brometo e supressão da geração de oxigênio singlete com albumina de soro bovino. Hematoporfirina IX é mais afetada na forma livre do que imobilizada em nanoesferas de sílica, o que indica que o FS imobilizado é capaz de gerar oxigênio singlete e está mais protegido de interferentes. / The immobilization of photosensitizers (PS) in nanometric materials is an excellent alternative to their use in molecular forms for photodynamic therapy (PDT). The present work describes a series of synthetic strategies for the immobilization of PS on silica nanospheres containing magnetic nucleous, as well as the studies of the photochemical, photophysical and morphological properties of the obtained materials. The studied PS were methylene blue, thionin, azure A, protoporphyrin IX, hematoporphyrin IX and chlorophyllin. The immobilization methodologies involve the addition of PS during the growth of the silica shell or the attachment of PS to the material surface. Often, a previous modification of the PS with organosilanes was necessary. The magnetic cores were prepared by co-precipitation of iron(II) and iron(III) salts in basic media and the coating with silica was performed by a microemulsion using TEOS. After coating with silica, the magnetic nanomaterial maintained the superparamagnetic behavior. The generation of singlet oxygen by thionin and methylene blue was not detect after immobilization. The generation of singlet oxygen by immobilized azure A, protoporphyrin IX and chlorophyllin was detected and characterized by chemical and physical methods. The material containing chlorophyllin is promising for PDT and was applied in preliminary studies with HeLa cells, causing cell death after irradiation. The behavior of the immobilized PS and the possible extra protection given by the silica shell were investigated by fluorescence quenching with bromide ions and by suppression of singlet oxygen generation with bovine serum albumin. Hematoporphyrin IX was more affected in the free form than immobilized in silica nanospheres, which indicates that the immobilized FS still generates singlet oxygen and is more protected against interfering species

The motivation of this study is to investigate the size dependent properties of Gadolinium silicide nanoparticles and their potential applications in Biomedicine. We use two approaches in our investigation - size dependence and possible exchange interaction in a core-shell structure. Past results showed Gd5Si4 NPs exhibit significantly reduced echo time compared to superparamagnetic iron oxide nanoparticles (SPION) when measured in a 7 T magnetic resonance imaging (MRI) system. This indicates potential use of Gd5Si4 ferromagnetic nanoparticles as T2 contrast agents for MRI. Until recently most contrast agents (CA) that are used in Magnetic Resonance Imaging (MRI) studies have been paramagnetic. However, ferromagnetic CAs are potentially more sensitive as T2 CAs than T1 paramagnetic compounds due to their large magnetic moments. Furthermore, the need for better MRI images without the need of upgrading to the higher magnetic field strength can be achieved using better CA such as Gd5Si4 NP. The quality of the image contrast in MRI is improved by shortening T1 and T2 relaxation times at the site or close proximity to the CA. In this study, effect of Gd5Si4 NP of varying sizes and with different concentrations are investigated on T1, T2 and T2* (effective/observed T2) relaxations times. Further study was carried out on possible exchange interaction between Fe3O4 and Gd5Si4 to enhance the magnetic properties of the Gd5Si4 which could be later used to synthesize core-shell structures. Exchange interaction / bias is a phenomena associated with the exchange anisotropy created at the interface between the two magnetic materials. Therefore, thin films of varying thickness was deposited and studied for their magnetic properties.

Magnetite (Fe3O4) and Maghemite (&amp / #947 / -Fe2O3) are well-known iron oxide phases among magnetic nanoparticles due to their magnetic properties, chemical stability, and nontoxicity. They have gained acceptance in several fields of application of nanomaterials such as magnetic recording systems, magnetic refrigeration, magneto-optical devices, magnetic resonance imaging, magnetic separation techniques and separation and purification of biological molecules. Recently, there is a growing interest in the synthesis of magnetic iron oxide nanoparticles in a polymeric, glassy or ceramic matrix since the preparation of pure phase iron oxide composite material involves, presently, some difficulties partially arising from different oxidation states of iron which can lead to the presence of various oxides. Matrix support, in principle, modifies the properties of nanomaterials, thus opening new possibilities for the control of their performance. In addition, the chosen matrix, polymer or sol-gel, provides binding of the functional groups and also prevents grain growth and agglomeration. Therefore, extensive research is conducted on this subject. Sonochemical technique is an effective method to synthesize magnetic nanoparticles with many unique properties due to extreme reaction conditions. Besides, a microscopic mixing in the synthesis procedure is obtained because of the microjet effect which comes from the collapse of the bubbles. This effect creates relatively uniform reaction conditions. Thus, well-dispersed and stable nanoparticles are obtained by using ultrasound. In this study, &amp / #947 / -Fe2O3, maghemite nanoparticles are accommodated in an inert, inorganic, transparent and temperature resistant sol gel matrix to achieve stabilization. The nature and concentration of the salt used, evaporation conditions of the sols, the following heat treatments had been investigated and shown that they had great influence on the particle size and the final iron oxide phase in the sol-gel. The Fe2O3/SiO2 nanocomposites were characterized using X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) techniques. In addition, magnetite (Fe3O4) nanoparticles were synthesized via co-precipitation in the presence of poly(methacrylic acid) (PMAA) in aqueous solution. PMAA, which was used as the coating material, prevents magnetite nanoparticles from oxidation towards a lower saturation magnetization iron oxide phases. In order to achieve small particle size and uniform size distribution of the magnetite nanoparticles in PMAA matrix, ultrasonic irradiation was applied during co-precipitation. The polymer coated Fe3O4 nanoparticles were characterized using scanning electron microscopy (SEM), laser particle sizer, X-ray diffraction, (XRD) and vibrating sample magnetometry (VSM) techniques and zeta potential measurements.