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Síntese e caracterização de nanopartículas núcleo-casca de poliestireno e polimetacrilato de metila obtidas por polimerização em emulsão sem emulsificante e fotoiniciada.; Synthesis and characterization of core-shell nanoparticles of polystyrene and poly(methyl metacrylate) obtained by emulsifier-free emulsion polymerization and photopolymerization.

Carranza Oropeza, María Verónica
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/09/2011 PT
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O objetivo do trabalho foi sintetizar e caracterizar nanopartículas de poliestireno e polimetacrilato de metila com morfologia núcleo-casca obtidas através da polimerização em emulsão sem emulsificante em dois estágios e através da fotopolimerização. Nos experimentos avaliou-se a influência de diferentes condições operacionais baseadas em fatores cinéticos sobre os dois estágios da polimerização. As condições avaliadas para o primeiro estágio de preparação de núcleos foram: a temperatura do processo, a concentração de iniciador e de monômero, e o efeito de agentes modificadores de superfície (sal, co-monômero e reticulante). Para o segundo estágio de formação da casca as condições avaliadas foram: a concentração e o regime de alimentação de monômero. Os resultados experimentais mostraram que uma relação de co-monômero e reticulante é a melhor alternativa para preparar núcleos estáveis e de diâmetros pequenos. Assim, o revestimento uniforme dos núcleos é obtido no segundo estágio e com isso a morfologia núcleo-casca em equilíbrio é alcançada. Dois sistemas experimentais (reator convencional e reator fotoquímico) foram propostos e avaliados na sua eficiência para obter partículas com este tipo de morfologia no segundo estágio (formação do revestimento). As diversas técnicas de caracterização indicaram a formação de morfologia núcleo-casca na maioria dos casos estudados para os dois sistemas propostos. Por sua vez...

Síntese e estudo da atividade eletrocatalítica de nanopartículas com estruturas do tipo Core-Shell e Hollow para a redução de O2; Synthesis and study of core-shell and nanoparticle electrocatalysts for the O2 reduction reaction

Oliveira, Francisca Elenice Rodrigues de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/03/2012 PT
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A reação de redução de oxigênio (RRO) foi estudada em eletrocatalisadores com estruturas do tipo core-shell formadas por monocamadas de Pt depositadas sobre nanopartículas a base de Au e Pd, e estruturas hollow formadas de Pt. As nanopartículas core-shell foram sintetizadas por deposição em regime de subtensão utilizando-se substratos de Au e Pd. As estruturas hollow foram preparadas a partir de nanopartículas core-shell de Pt sobre Ni ou Co, seguido por ciclagem eletroquímica em eletrólito ácido. Os eletrocatalisadores foram caracterizados utilizando-se as técnicas de Energia Dispersiva, Difração e Espectroscopia de Absorção de Raios X e Microscopia Eletrônica de Transmissão. Os testes eletroquímicos foram feitos voltametria cíclica e curvas de polarização em eletrodo rotatório. Os catalisadores do tipo core-shell mostraram uma alta atividade para a RRO, o que foi associado a mudanças nas propriedades eletrônicas e geométricas da Pt, causadas pela presença dos átomos de Au e Pd, que conduzem a uma menor força de adsorção Pt-O. Neste caso, temos um melhor balanço de reatividade para as tendências opostas de quebra e formação de ligações nos intermediários reacionais adsorvidos na superficie do eletrocatalisador. As nanopartículas de Pt hollow apresentaram maior atividade que o electrocalisador de Pt/C. Isto foi atribuído aos fenômenos de contração da rede cristalina e abaixamento do centro de banda d da Pt devido à ligação da Pt com Ni ou Co remanescente na partícula. Estas estruturas mostraram que é possível o desenvolvimento de eletrocalisadores com baixa carga de platina...

Propriedades estruturais e eletrônicas das nanopartículas puras e core-shell de prata e de ouro; Structural and electronic properties of pure and core-shell nanoparticles of gold and silver

Santos, Luiz Henrique de Melo dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/06/2015 PT
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Neste trabalho estudamos as propriedades estruturais, energéticas e eletrônicas das nanopartículas puras de prata (Ag) e de ouro (Au) e estruturas do tipo core-shell com número total de átomos variando de 147 à 923, no formato cubo-octaédrico. Estudamos também a adsorção da molécula de metanotiol (SCH4) sobre os sítios de coordenação dessas nanoestruturas, analisando, entre outros aspectos, os efeitos da interação de van de Waals. Para tanto, foram feitos cálculos teóricos de primeiros princípios dentro da Teoria do Funcional da Densidade (DFT) usando a Aproximação do Gradiente Generalizado (GGA) e Pseudopotenciais Ultrassuaves (USPP). Concluímos que as maiores nanopartículas puras e core-shell apresentam uma superfície mais esférica e suas energias de formação tendem às energias das superfícies [001] e [111] e dos bulks de Ag e de Au. Uma única camada de shell de ouro ou de prata na core-shell já determina praticamente o comportamento energético e as propriedades da nanopartícula. A inclusão da interação de van de Waals nos cálculos uniformiza, de certa forma, os padrões de deslocamento atômico das superfícies das nanopartículas e o comportamento energético das core-shell, sem entretanto alterar o perfil das densidades de estado. A adsorção da molécula de metanotiol nas nanopartículas puras de Ag e de Au e suas core-shell foi analisada verificando-se que ela praticamente não perturba os estados eletrônicos das nanopartículas e que sua estrutura molecular é preservada. Nas nanopartículas maiores verifica-se um único padrão de adsorção independente do número de camadas de shell nas estruturas core-shell.; In this work we study the structural...

Iron Oxide Versus Fe55Pt45/Fe3O4: Improved Magnetic Properties of Core/Shell Nanoparticles for Biomedical Applications

Varanda, L. C.; Imaizumi, M.; Santos, F. J.; Jafelicci, M.
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Artigo de Revista Científica Formato: 4448-4451
ENG
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In this paper, synthesis of the Fe55Pt45/Fe3O4 core/shell structured nanoparticles using the modified polyol process combined with the seed-mediated growth method is reported. Iron oxide shell thickness was tuned controlling the Fe(acac)(3)/FePt seeds in the reaction medium. Annealing of the core/shell structure leads to iron-rich layer formation around the hard FePt phase in the nanoparticle core. However, the 2 nm Fe3O4 shell thickness seems to be the limit to obtain the enhanced magnetization close to the alpha-Fe and preserving an iron oxide shell after annealing at 500 degrees C for 30 min in a reducing atmosphere. The presence of both the oxide layer on nanoparticle surface and an intermediate iron-rich FePt layer after annealing promote strong decreases in the coercive field of the 2-nm-oxide shell thickness. These annealed nanoparticles were functionalized with dextran, presenting the enhanced characteristics for biomedical applications such as higher magnetization, very low coercivity, and a slightly iron oxide passivated layer, which leads an easy functionalization and decreases the nanoparticle toxicity.

Sistemas químicos nanoestruturados : nanopartículas caroço-casca em suporte poroso funcional e filmes finos alternados de óxidos semicondutores (TiO2, MoO3, WO3); Nanostructutred chemical systems : core-shell nanoparticles in functional porous support and alternate thin films of semiconductors oxide (TiO2, MoO3, WO3)

Elias de Barros Santos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/09/2011 PT
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Este trabalho de tese é referente à preparação e caracterização de sistemas nanoestruturados na forma de nanopartículas caroço-casca e filmes finos alternados dos óxidos semicondutores: TiO2, MoO3 e WO3. Para tal finalidade foram preparadas nanopartículas monocomponentes individuais dos três óxidos mencionados (PVG/TiO2, PVG/MoO3 e PVG/WO3) e nanopartículas caroço-casca bicomponentes (PVG/TiO2-MoO3, PVG/MoO3-TiO2 e PVG/TiO2-WO3), usando o vidro poroso Vycor® (PVG) como suporte. Também foram preparados filmes finos individuais e alternados de TiO2 e MoO3. Para a síntese das nanopartículas foram feitas impregnações do PVG com soluções precursoras dos compostos di-(propóxido)-di-(2-etilhexanoato) de titânio (IV) em hexano, 2-etilhexanoato de molibdênio (VI) em hexano e do composto di-[hexaquis(m-acetato)triacetato(m3-oxo)tritungstênio(III, III, IV) em água. Foi empregado o procedimento de ciclos de impregnação-decomposição sucessivos, que consiste em repetir, empregando o mesmo suporte poroso, o procedimento de impregnação do composto e sua posterior decomposição térmica. Com este método foi possível controlar o tamanho das nanopartículas, que seguido da alternância dos precursores envolvidos em cada ciclo levou a obtenção de nanopartículas compostas por bicamadas (caroço-casca). Os sistemas de nanopartículas foram caracterizados pelas técnicas de espectroscopia Raman...

Sintese de nanoparticulas de oxidos semicondutores tipo caroço-casca em ambiente confinado; Synthesis of semiconductors oxides core-shell nanoparticles into confined ambient

Deleon Nascimento Correa
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/02/2009 PT
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Este trabalho reporta o estudo e o desenvolvimento da metodologia de síntese e de caracterização de nanopartículas isoladas e nanopartículas heteroestruturadas caroço@casca (NCC) envolvendo os óxidos semicondutores (TiO2, CeO2 e SnO2) impregnados em suporte poroso funcional (vidro poroso Vycor ¿ PVG). Empregou-se a metodologia de Ciclos de Impregnação-Decomposição (CID) alternados de compostos metalorgânicos, a partir da técnica de decomposição de precursores metalogânicos (MOD). A metodologia CID prosseguiu com a impregnação dos compostos metalorgânicos di-(propóxido)-di-(2-etilhexanoato) de titânio (IV) [Ti(OnPr)2(hex)2], 2-etilhexanoato de cério (III) [Ce(hex)2] e 2-etilhexanoato de estanho (II) [Sn(hex)2] no PVG em condições controladas. Os estudos das curvas de ganho de massa cumulativo em função de cada CID evidenciaram que para 3 CID os sistemas responderam com um ganho cumulativo de massa de 17,5% (PVG/3SnO2), 4,3% (PVG/3CeO2) e 2,5% (PVG/3TiO2) com a concentração inicial dos precursores de partida de 0,75 molL. O efeito de confinamento quântico foi descrito pelo Modelo da Aproximação da Massa Efetiva (MAME), observado experimentalmente na borda de absorção dos espectros de refletância difusa...

CdSe/TiO2 core-shell nanoparticles produced in AOT reverse micelles : applications in pollutant photodegradation using visible light

Coutinho, Paulo J. G.; Garcia, Arlindo M. Fontes; Fernandes, Marisa S. F.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 16/02/2011 ENG
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Documento submetido para revisão dos pares. A publicar em Nanoscale Research Letters. ISSN 1556-276X.; CdSe quantum dots with a prominent band-edge photoluminescence were obtained by a soft w/o AOT microemulsion templating method with an estimated size of 2.7nm. The CdSe particles were covered with a TiO2 layer using a intermediate SiO2 coupling reagent by a sol-gel process. The resulting CdSe/TiO2 core/shell nanoparticles showed appreciable photocatalytic activity at λ=405nm which can only originate from electron injection from the conduction band of CdSe to that of TiO2.; Fundação para a Ciência e a Tecnologia (FCT); Fundo Europeu de Desenvolvimento Regional (FEDER)

Strain-release mechanisms in bimetallic core-shell nanoparticles as revealed by Cs-corrected STEM

Bhattarai, Nabraj; Casillas, Gilberto; Ponce, Arturo; Jose-Yacaman, Miguel
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/03/2013 EN
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Lattice mismatch in a bimetallic core-shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core-shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shells growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

Au/Pd core-shell nanoparticles with varied hollow Au cores for enhanced formic acid oxidation

Hsu, Chiajen; Huang, Chienwen; Hao, Yaowu; Liu, Fuqiang
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 01/03/2013 EN
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A facile method has been developed to synthesize Au/Pd core-shell nanoparticles via galvanic replacement of Cu by Pd on hollow Au nanospheres. The unique nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, and electrochemical measurements. When the concentration of the Au solution was decreased, grain size of the polycrystalline hollow Au nanospheres was reduced, and the structures became highly porous. After the Pd shell formed on these Au nanospheres, the morphology and structure of the Au/Pd nanoparticles varied and hence significantly affected the catalytic properties. The Au/Pd nanoparticles synthesized with reduced Au concentrations showed higher formic acid oxidation activity (0.93 mA cm-2 at 0.3 V) than the commercial Pd black (0.85 mA cm-2 at 0.3 V), suggesting a promising candidate as fuel cell catalysts. In addition, the Au/Pd nanoparticles displayed lower CO-stripping potential, improved stability, and higher durability compared to the Pd black due to their unique core-shell structures tuned by Au core morphologies.

Fabrication of core-shell nanoparticles via controlled aggregation of semi-flexible conjugated polymer and hyaluronic acid

Twomey, Megan; Na, Yoonmi; Roche, Zahilyn; Mendez, Eladio; Panday, Namuna; He, Jin; Moon, Joong Ho
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Core-shell conjugated polymer nanoparticles (CPNs) were fabricated by complexing a semi-flexible, primary amine-containing conjugated polymer (CP) with hyaluronic acid (HA). Flexibility introduced in the rigid rod conjugated backbone allows backbone reorganization to increase π-π interaction under ionic complexation, resulting in core-shell nanoparticles with a hydrophobic CP core wrapped with a HA shell. The core-shell nanoparticles exhibited no cellular toxicity and high cancer cell specificity with minimal binding to normal cells.

Structural characterization of Pt–Pd core–shell nanoparticles by Cs-corrected STEM

Esparza, R.; García-Ruiz, Amado F.; Salazar, J. J. Velázquez; Pérez, R.; José-Yacamán, M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/2012 EN
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Pt–Pd core–shell nanoparticles were synthesized using a modified polyol method. A thermal method under refluxing, carrying on the reaction up to 285 °C, has been performed to reduce metallic salts using ethylene glycol as reducer and poly(N-vinyl-2-pyrrolidone) as protective reagent of the formed bimetallic nanoparticles. According to other works, this type of structure has been studied and utilized to successfully increase the catalytic properties of monometallic nanoparticles Pt or Pd. Core–shell bimetallic nanoparticles were structurally characterized using aberration-corrected scanning transmission electron microscopy (Cs-STEM) equipped with a high-angle annular dark field detector, energy-dispersive X-ray spectrometry (EDS), and electron energy-loss spectroscopy (EELS). The high-resolution elemental line scan and mappings were carried out using a combination of STEM–EDS and STEM–EELS. The obtained results show the growth of the Pd shell on the Pt core with polyhedral morphology. The average size of the bimetallic nanoparticles was 13.5 nm and the average size of the core was 8.5 nm; consequently, the thickness of the shell was around 2.5 nm. The growth of the Pd shell on the Pt core is layer by layer, suggesting a Frank-van der Merwe growth mechanism.

Multi-photon excited luminescence of magnetic FePt core-shell nanoparticles

Seemann, K.M.; Kuhn, B.
Fonte: Optical Society of America Publicador: Optical Society of America
Tipo: Artigo de Revista Científica
Publicado em 27/06/2014 EN
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We present magnetic FePt nanoparticles with a hydrophilic, inert, and biocompatible silico-tungsten oxide shell. The particles can be functionalized, optically detected, and optically manipulated. To show the functionalization the fluorescent dye NOPS was bound to the FePt core-shell nanoparticles with propyl-triethoxy-silane linkers and fluorescence of the labeled particles were observed in ethanol (EtOH). In aqueous dispersion the NOPS fluorescence is quenched making them invisible using 1-photon excitation. However, we observe bright luminescence of labeled and even unlabeled magnetic core-shell nanoparticles with multi-photon excitation. Luminescence can be detected in the near ultraviolet and the full visible spectral range by near infrared multi-photon excitation. For optical manipulation, we were able to drag clusters of particles, and maybe also single particles, by a focused laser beam that acts as optical tweezers by inducing an electric dipole in the insulated metal nanoparticles. In a first application, we show that the luminescence of the core-shell nanoparticles is bright enough for in vivo multi-photon imaging in the mouse neocortex down to cortical layer 5.

Broadband zero-backward and near-zero-forward scattering by metallo-dielectric core-shell nanoparticles

Li, Yan; Wan, Mingjie; Wu, Wenyang; Chen, Zhuo; Zhan, Peng; Wang, Zhenlin
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 18/08/2015 EN
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Efficient control of optical radiation at subwavelength scales plays important roles for various applications. Dielectric nanoparticles or dielectric shells with a large refractive index of n ~ 3–4, which are only achievable for limited semiconductors, are involved in most designs so far to control the scattering by overlapping the electric and magnetic dipolar modes of the same magnitude. Here we propose a new mechanism based on the interplay between dipolar and quadrupolar resonances of different amplitudes, both magnetic and electric, to suppress the backward scattering or the forward scattering by using metallo-dielectric core-shell nanoparticles with a dielectric shell layer having a refractive index of n = 2.0. We demonstrate that broadband zero-backward or near-zero-forward scattering can be achieved by optimizing the structural parameters. We also demonstrate that the core-shell nanoparticles with identical dielectric shells but metal cores with various sizes are able to suppress the backward or forward scattering at the same wavelength, thus revealing a large tolerance to fabrication errors induced by the size distributions in the metal cores. These features make the proposed core-shell nanoparticles beyond the dipole limit more easily realized in practical experiments.

Core-Shell Assisted Bimetallic Assembly of Pt and Ru Nanoparticles by DNA Hybridization

Lee, Jim Yang; Yang, Jun; Too, Heng-Phon; Chow, Gan-Moog; Gan, Leong M.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 19871 bytes; application/pdf
EN
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We have discovered that the current protocols to assemble Au nanoparticles based on DNA hybridization do not work well with the small metal nanoparticles (e.g. 5 nm Au, 3.6 nm Pt and 3.2 nm Ru particles). Further investigations revealed the presence of strong interaction between the oligonucleotide backbone and the surface of the small metal nanoparticles. The oligonucleotides in this case are recumbent on the particle surface and are therefore not optimally oriented for hybridization. The nonspecific adsorption of oligonucleotides on small metal nanoparticles must be overcome before DNA hybridization can be accepted as a general assembly method. Two methods have been suggested as possible solutions to this problem. One is based on the use of stabilizer molecules which compete with the oligonucleotides for adsorption on the metal nanoparticle surface. Unfortunately, the reported success of this approach in small Au nanoparticles (using K₂BSPP) and Au films (using 6-mercapto-1-hexanol) could not be extended to the assembly of Pt and Ru nanoparticles by DNA hybridization. The second approach is to simply use larger metal particles. Indeed most reports on the DNA hybridization induced assembly of Au nanoparticles have made use of relatively large particles (>10 nm)...

Incorporation of silica into baroplastic core-shell nanoparticles

Hewlett, Sheldon A
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 33 p.; 1356517 bytes; 1355580 bytes; application/pdf; application/pdf
ENG
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Core-shell baroplastics are nanophase materials that exhibit pressure-induced flow at low temperatures and high pressures. Core-shell baroplastics used in this work are comprised of a low Tg poly(butyl acrylate) (PBA) core and a high Tg polystyrene (PS) shell. These novel polymer systems can be molded into fully formed, 3-D shapes with the application of high pressure at room temperature. While the mechanical properties are equivalent to or better than those of commercial thermoplastic elastomers, more can be done to improve upon individual aspects of the mechanical properties, such as elastic modulus. This work looks at creating baroplastic nanocomposites with the goal of improving upon the mechanical properties. To accomplish this goal, two incorporation strategies for introducing silica nanoparticles were developed. The pre-emulsion strategy incorporated hydrophobized silica nanoparticles inside the core-shell nanoparticles to create core-shell-shell nanoparticles. The post-emulsion strategy incorporated charged silica nanoparticles after core-shell emulsion, with the intention of creating crystalline structures with silica and core-shell nanoparticles.; (cont.) The pre-emulsion strategy resulted in a decrease in particle size for the core-shell-shell nanoparticles...

A technical and economic evaluation of novel pH-responsive core-shell nanoparticles : delivering innovation from laboratory to market

Cho, Eun Chol, M. Eng. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 71 leaves
ENG
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Many potentially powerful therapeutic strategies for the treatment of disease require the delivery of drugs into the cytosolic or nuclear compartments of cells. Members of the Irvine laboratory have developed a novel pH-responsive core-shell nanoparticle system that can achieve efficient and non-cytotoxic drug delivery into the cytosol. Another advantage is that the shell can be easily modified to bind to different types of drug agents and incorporate ligands for specific cell targeting. Experimental analysis of the newly synthesized nanoparticles with various shell structures has demonstrated that modification of the shell does not compromise their cytosolic delivery. These nanoparticles, if successful, will improve the therapeutic potential of a wide range of drugs. However, critical issues on the research side need to be resolved, and an appropriate intellectual property strategy should be initiated in the near future. Applications to siRNA delivery and vaccines have been examined in depth, as cytosolic delivery is one of the main challenges in these fields. Partnerships with large pharmaceutical companies are critical in order to acquire key patents on siRNA/antigen. Even though the market is competitive, there is a strong demand for innovative delivery platforms; provided that the overall profile of the core-shell nanoparticles is comparable to that of emerging drug delivery systems...

Propriedades magneto-ópticas de colóides magnéticos á base de nanopartículas de magnetita recobertas com prata; Magneto-optical properties of magnetic nanoparticles colloids based on magnetite and coated with silver

Lopes Junior, José Carlos Campello
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG)
Tipo: Dissertação Formato: application/pdf
POR
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In 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...

Diverse Melting Modes and Structural Collapse of Hollow Bimetallic Core-Shell Nanoparticles: A Perspective from Molecular Dynamics Simulations

Huang, Rao; Shao, Gui-Fang; Zeng, Xiang-Ming; Wen, Yu-Hua
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 14/11/2014 EN
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Introducing hollow structures into metallic nanoparticles has become a promising route to improve their catalytic performances. A fundamental understanding of thermal stability of these novel nanostructures is of significance for their syntheses and applications. In this article, molecular dynamics simulations have been employed to offer insights into the thermodynamic evolution of hollow bimetallic core-shell nanoparticles. Our investigation reveals that for hollow Pt-core/Au-shell nanoparticle, premelting originates at the exterior surface, and a typical two-stage melting behavior is exhibited, similar to the solid ones. However, since the interior surface provides facilitation for the premelting initiating at the core, the two-stage melting is also observed in hollow Au-core/Pt-shell nanoparticle, remarkably different from the solid one. Furthermore, the collapse of hollow structure is accompanied with the overall melting of the hollow Pt-core/Au-shell nanoparticle while it occurs prior to that of the hollow Au-core/Pt-shell nanoparticle and leads to the formation of a liquid-core/solid-shell structure, although both of them finally transform into a mixing alloy with Au-dominated surface. Additionally, the existence of stacking faults in the hollow Pt-core/Au-shell nanoparticle distinctly lowers its melting point. This study could be of great importance to the design and development of novel nanocatalysts with both high activity and excellent stability.

Size effect on the hysteresis characteristics of a system of interacting core/shell nanoparticles

Afremov, Leonid; Anisimov, Sergei; Iliushin, Ilia; Qiang, You
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/11/2015
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We have developed a model for the interacting ore/shell nanoparticles, which we used to analyze the dependence of the coercive field Hc, the remanent saturation magnetization Mrs and the satu- ration magnetization Ms on the interfacial exchange interaction between the core and the shell, the size of the nanoparticles and their interaction for Fe/Fe3O4 nanoparticles have been carried out. It has been shown that the hysteresis characteristics increase together with the size of nanoparticles. Hc and Mrs are changing nonmonotonic when the constant interfacial exchange interaction changes from negative to positive values. In the system of core/shell nanoparticles, magnetic interaction results in Hc and Mrs dropping, which was conformed by experiments. Usage: Secondary publications and information retrieval purposes.

One pot synthesis of PbS/Cu2S core-shell nanoparticles and their optical properties

Serrano,T.; Gómez,I.
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2014 EN
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The synthesis of PbS/Cu2S core-shell nanoparticles with emission on the visible range and with improved luminescence properties was carried out by the colloidal solution-phase growth method by using simple stabilizers such as trisodium citrate and 3-mercaptopropionic acid. The core shell arrangement for particles with different crystalline structure was achieved, in addition this is the first report related to the synthesis PbS/Cu2S core-shell system. The data obtained from absorption spectra, PL spectra, and HRTEM image provided direct proof of the formation of PbS core with size around 11 nm and Cu2S shell of 5 nm thickness. According to the UV-vis absorption and PL spectrum, the optical characteristics observed in the synthesized material correspond to a PbS/Cu2S system that has a higher confinement effect than the pure PbS nanoparticles. The QY was improved in 15 % from PbS to PbS/Cu2S nanoparticles. The estimated band (HOMO-LUMO) alignment determined by CV measurements corresponds to a type-I core shell arrangement.