Mestrado em Física (IF)
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Navegando Mestrado em Física (IF) por Por Orientador "Bakuzis, Andris Figueiroa"
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Item Propriedades magneto-ópticas de colóides magnéticos á base de nanopartículas de magnetita recobertas com prata(Universidade Federal de Goiás, 2010-05-17) Lopes Junior, José Carlos Campello; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042In this work we investigated, theoretically and experimentally, the magneto-optical properties of a magnetic fluid consisting of core-shell nanoparticles, where the core is made of magnetite, while the shell is silver. The theoretical model used was based on Mie s theory, under the electrostatic approximation, i.e. for nanoparticles with diameters much less than the incident wavelength (lambda). A Clausius-Mosotti for a core-shell system was used to calculate the electrical susceptibility of the core-shell nanoparticle for equals to 632 nm. The susceptibility was shown to be strongly dependent on the core diameter and the shell thickness. Nevertheless, a maximum value of 7.20 (greater than isolated nanoparticles of silver, which has 0 = 4.30, or magnetite with 0 = 1.47) was obtained for a fraction f, defined as f = (Dcore/Dcore−shell)3, equal to 0.36. This result suggest that there exist an ideal fraction f for nanocomposites with enhanced optical properties. In order to compare our theoretical results with experimental data a core-shell magnetic fluid was synthesized on the Institute of Chemistry of UFG by the group of Dr. Em´ılia Celma de Oliveira Lima. The nanoparticles were suspended in water at fisiological pH and recovered by a double layer of lauric acid (dodecanoic acid). The nanoparticles were characterized by X-ray diffraction, high resolution electron transmission, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer. The Sturges method was used to obtain the nanoparticle diameter histogram. The data revealed the existence of a bimodal nanoparticle distribution. Both distributions were curve fitted using a lognormal function. The modal diameter of one of them was 9.24 ± 0.03 nm with a dispersity of 0.27 ± 0.02, while for the other one we found a modal diameter of 23.0 ± 0.2 nm with disperisty 0.2 ± 0.1. The energy dispersive X-ray spectroscopy confirmed the existence of magnetite and silver only for larger particle diameters, while the lower ones only magnetite was found. From the experimental analysis we confirmed the synthesis of a magnetic fluid containing 10% of core-shell nanoparticles. Magnetization data was used to estimate the magnetic particle volume fraction. The magneto-optical properties were obtained using a magnetotransmissivity technique, where the polarizer and analyser axis are positioned on the magnetic field direction. The sample containing 10% of core-shell nanoparticles, with a total particle volume fraction of 0.18%, had shown an extinction of light of 100% for a magnetic field of only 500 Oe, while a magnetic fluid with 100% of core nanoparticles, at a similar particle concentration (0.15%), had shown a 50% extinction of light at the same field range. The magnetotransmissivity data were curve fitted with a theoretical model containing only two parameters, one related to the electrical susceptibility and the other to the formation of self-organized nanostructures in the colloid. The mean agglomerate size (nanoparticles forming linear chains) had changed from 2.09 to 3.36 for a particle volume fraction increasing from 0.06% to 0.18%. Using the estimative of the double layer lenght of lauric acid, approximately 2 nm, and analyzing the magnetotransmissivity data for several particle concentrations, we were able to obtain the fraction f of core-shell nanoparticles of 0.17. This result, together with TEM data, allowed us to calculate the core diameter of the core-shell nanoparticle as 13 nm. Indeed such result suggest that in order to be suscessful in coating the nanoparticle with the shell element one might need monodisperse-like nanoparticle systems.Item Estudo magnético e magneto-ótico do internalização de nanopartículas magnéticas biocompatíveis de γ-F e2O3 recobertas com dextrana por células tumorais de sarcoma(Universidade Federal de Goiás, 2010) Silva, Anderson Costa da; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042In this work we investigated the internalization process of magnetite nanoparticles, surface coated with dextran, by mice tumour cells of Sarcoma 180 (S180) through the tech- niques of vibrating sample magnetometer (VSM) and static magnetic birefringence (SMB). The magnetic fluid sample, stable in physiological conditions, was prepared by the coprecip- itation method. The growth of nanoparticles occurred in conjunction with the nanoparticle surface coating process by dextran. The crystal structure was confirmed by X-ray diffraction. The nanoparticles were characterized by high resolution transmission electronic microscopy. The Sturges method was used to obtain the polydispersity in diameter, which was fitted by a lognormal size distribution obtaining a modal diameter of 5.5 ± 0.1 nm and dispersity of 0.18 ± 0.02.The mice tumour cell sarcoma 180 was obtained using protocol established by the American Type Culture Collection (ATCC, Rockville, MD, USA). Studies of cytotoxicity, using the MTT method, were obtained for a nanoparticle volumetric fraction of φ = 0.00065 after one and five hours of exposure of cells S180 to the nanoparticles. In particular, we found a cellular viability of 87 ± 11 % after one hour of exposure proving that there was no appreciable cell death in the time interval in which the measurements of MAV and BME were performed. Magnetization measurements were performed to obtain the volume fraction of nanoparticles. Tests regarding the effect of centrifugation of nanoparticles suspended in cell culture medium RPMI 1640 showed a extremely low sedimentation of magnetic nanoparticles. A procedure, using a acceleration of 260×g for 10 minutes, was used to separate cells containing internalized nanoparticles from nanoparticles suspended in RPMI 1640. Measurements of magnetization of S180 cells containing nanoparticles were performed in a wide range of exposure time (100 iv minutes). Between 10 and 70 minutes the amount of nanoparticles in mass unit increased from 52 ± 20 pg/cell to 110 ± 15 pg/cell. Indeed magnetometry data indicate that the process of internalization had achieved saturation between 30 to 40 minutes. Magneto-optical technique of SMB was also used to investigate the process of inter- nalization of nanoparticles. Firstly, SMB measurements were performed in control samples consisting of magnetic nanoparticles suspended in RPMI 1640. We investigated the effects of nanoparticle concentration and aging time (related to the dynamics of nanoparticle agglom- eration). In particular, the average size of the agglomerate (Q), associated with the number of nanoparticles forming a linear chain, remained basically constant, Q = 4.8 ± 0.2 for a full- time of 70 minutes. Magnetic birefringence saturation data also remained stable in this time interval. Additionally, analysis of the measurements of SMB were also used to estimate the thickness of the coating layer (dextran), from which we found 1.70 ± 0.02 nm. Unlike VSM data, SMB measurements were obtained on samples containing both S180 cells and magnetic nanoparticles inside the RPMI medium 1640. Data were obtained in a wide range of time (120 min.). Initially it was observed that the SMB signal decreases in a time range and then increases again (between 30-40 min.). The fit of the experimental data indicate that the mag- netic birefringence saturation (∆ns) decreases in the first 30 minutes and then increases again smoothly, while the average size of the cluster has the opposite behavior, i.e. increases in the first 30 minutes and then decreases. In particular, for a exposure time, t(exp), of 10 min. the average size of the agglomerate (magnetic birefringence saturation) changed from 4.18 ± 0.04 (∆n(s) = 3.41 ± 0.02 ×1018 cm−3 min. As the birefringence saturation is proportional to the number of nanoparticles contribut- ing to the magneto-optical signal one can conclude that the decrease in the magneto-optical signal was due to the process of internalization of magnetic nanoparticles by cells S180. On the other hand, the analysis of the aging time dependence of the mean size of the agglomerate also suggests that the process of internalization occurs primarily with anisometric nanoparticles or nanostructures forming small agglomerates. Finally, after reaching saturation of the process ) to 5.22 ± 0.08 (∆ns = 2.75 ± 0.02 ×1018 cm−3 ) at texp = 30 v of nanoparticle internalization we found a formation of small agglomerates in the RPMI 1640 medium, which is responsible for the increased intensity of the magneto-optical signal, as well as the decrease of the mean size of the agglomerate for times longer than 30 minutes.Item Avaliação dos efeitos das hipertermias magnética e fototérmica na síntese de heteroestruturas à base de nanopartículas de MnFe2O4 e Au(Universidade Federal de Goiás, 2015-12-14) Sousa Júnior, Ailton Antônio de; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Lima, Emília Celma de Oliveira; Castro, Marcos Antônio de; Mendanha Neto, Sebastião AntônioThe purpose of this project is to synthesize and characterize heterostructures composed by manganese ferrite nanoparticles (MnFe2O4 NPs) and gold nanoparticles (Au NPs) able to: 1) respond to external alternating magnetic fields, what would enable their use in cancer diagnostic as contrast agentes for magnetic resonance imaging, as well as in cancer treatment via magnetic hyperthermia; 2) respond to eletromagnetic radiation, what would enable their use in cancer diagnostic as contrast agents for X-ray computed tomography (CT), as well as in cancer treatment via photothermal hyperthermia. We evaluate four MnFe2O4-Au heterostructures synthesis protocols. On Protocol 1, we use part of the energy of a laser beam (808 nm, 800 mW) to promote the nucleation of Au NPs at the surface of previously synthesized MnFe2O4 NPs covered by DMSA (dimercaptosuccinic acid). On Protocol 2, we use part of the energy of an alternating magnetic field (333,8 kHz, 17 mT) to promote this nucleation. We also perform an analysis of the influence of MnFe2O4 NPs covering layer, by comparing the ionic surfactants DMSA and sodium citrate. On Protocols 3 and 4, both the magnetic cores (MnFe2O4 NPs) and the metalic cores (Au NPs) are previously synthesized. Therefore, three Au NPs synthesis methods are evaluated. On Protocol 3, we promote the coupling between Au NPs and MnFe2O4-DMSA NPs using part of the energy from the same laser beam used on Protocol 1. On Protocol 4, we promote the coupling between cysteine-covered Au NPs and lysine-covered MnFe2O4 NPs via peptidic reaction between these two aminoacids. Finally, we conduct a comparative analysis between magnetic and photothermal hyperthermia, proposing a method for the determination of the optical SLP (Specific Loss Power). Moreover, we submit some of our samples to CT imaging. Protocol 1 is the best one in terms of covering the magnetic core by Au NPs. Protocol 2 allows the nucleation of Au NPs with diameters greater than the ones obtained via Protocol 1. Protocols 3 and 4 offer nanostructures with better potential with respect to their use as contrast agents in CT. However, the final yield of all four protocols is very low. Comparing magnetic and photothermal hyperthermia, we verify that the optical SLP is two to three orders of magnitude greater than the magnetic SLP under the assessed conditions, what suggests that protocols using laser beams have more energy available for the nucleation/coupling of Au NPs at the surface of MnFe2O4 NPs than those using alternating magnetic fields or simple heating on hot plate.Item Hipertermia magnética de nanopartículas à base de ferrita de manganês: efeito do recobrimento superficial de nanopartículas por moléculas de citrato(Universidade Federal de Goiás, 2012-05-31) Zufelato, Nícholas; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Silva, Sebastião William da; Pelegrini, FernandoThis work investigated the magneto-thermal properties of manganese ferrite-based nanoparticles. The nanosctructures were synthesized by the coprecipitation method. Three samples were studied, namely: non passivated (2A), passivated (2B), and passivated with citrate coating molecules (2B cit). The particles were characterized by x-ray diffraction (XRD), transmission eléctron microscopy (TEM), vibrating sample magnetometer (VSM) and electron magnetic resonance (EMR). The non-coated samples showed similar diameter and saturation magnetization values, while the citrate-coated sample showed striking diferente values. In particular, the 2B cit sample showed lower values of particle size (determined from Scherrer relation), saturation magnetization and magnetic anisotropy. Those results corroborate with a core-shell nanoparticle model. The magnetic hyperthermia studies, perfomed around 300kHz, revealed that sample 2B had a higher magneto-thermal effiency when compared with the 2B cit one. Dynamic hysteresis curves, obtained within the linear response regime, were capable to explian qualitatively the experimental data. The phenomena was related to a lower magnetic anisotropy for the 2B cit nanoparticles. In addition, the biocompatible magnetic colloid (2B cit) showed SAR values around 50 W/g of MnFe 2 O 4 at the high field limit. However, differently from results reported in the literature, based upon magnetite/maghemite nanoparticles, saturation is achieved at a lower magnetic field amplitude. This suggest that this type of material has great biomedical potential for low-field magnetic hyperthermia applications, which might be necessary in order to inhibit harmful eddy currents inside the patient’s body.