Navegando por Palavras-chave "Silver nanoparticles"
Agora exibindo 1 - 17 de 17
Resultados por página
Opções de Ordenação
- ItemSomente MetadadadosAntimicrobial activity of biogenic silver nanoparticles, and silver chloride nanoparticles: an overview and comments(Springer, 2016) Duran, Nelson; Nakazato, Gerson; Seabra, Amedea B. [UNIFESP]The antimicrobial impact of biogenic-synthesized silver-based nanoparticles has been the focus of increasing interest. As the antimicrobial activity of nanoparticles is highly dependent on their size and surface, the complete and adequate characterization of the nanoparticle is important. This review discusses the characterization and antimicrobial activity of biogenic synthesized silver nanoparticles and silver chloride nanoparticles. By revising the literature, there is confusion in the characterization of these two silver-based nanoparticles, which consequently affects the conclusion regarding to their antimicrobial activities. This review critically analyzes recent publications on the synthesis of biogenic silver nanoparticles and silver chloride nanoparticles by attempting to correlate the characterization of the nanoparticles with their antimicrobial activity. It was difficult to correlate the size of biogenic nanoparticles with their antimicrobial activity, since different techniques are employed for the characterization. Biogenic synthesized silver-based nanoparticles are not completely characterized, particularly the nature of capped proteins covering the nanomaterials. Moreover, the antimicrobial activity of theses nanoparticles is assayed by using different protocols and strains, which difficult the comparison among the published papers. It is important to select some bacteria as standards, by following international foundations ( Pharmaceutical Microbiology Manual) and use the minimal inhibitory concentration by broth microdilution assays from Clinical and Laboratory Standards Institute, which is the most common assay used in antibiotic ones. Therefore, we conclude that to have relevant results on antimicrobial effects of biogenic silver-based nanoparticles, it is necessary to have a complete and adequate characterization of these nanostructures, followed by standard methodology in microbiology protocols.
- ItemEmbargoAvaliação da funcionalidade do processo de tratamento de água para a remoção de nanopartículas de prata provenientes da ação antrópica(Universidade Federal de São Paulo, 2024-10-24) Santos, Lúcia Fernanda dos [UNIFESP]; Nascimento, Angerson Nogueira do [UNIFESP]; Ferreira, Paula Silvia Haddad [UNIFESP]; http://lattes.cnpq.br/8472122310617187; http://lattes.cnpq.br/6172517093430235; http://lattes.cnpq.br/1936782194249535Nanociências e Nanotecnologias (N&N) permitiram à humanidade um salto evolutivo, devido aos benefícios trazidos pelo número crescente de nanomateriais em diversas áreas, como na medicina, na cosmética, na engenharia e na têxtil. As nanopartículas de prata (AgNPs) são as mais estudadas atualmente e correspondem a mais de 50% dos nanomateriais produzidos. Mas, assim como diversas atividades antrópicas, a produção de nanomateriais com AgNPs também trazem preocupações, como estudos apontando intoxicações pelo seu uso, a presença de AgNPs em ambientes marítimos, o acúmulo em peixes, além da sua presença em ambientes de água potável. O processo de produção dos nanomateriais e o seu descarte pelo consumidor final podem gerar contaminação ambiental e humana. Nesse sentido, o presente trabalho teve como objetivo avaliar a funcionalidade do processo de tratamento de água para a sua remoção, bem como sua ecotoxicidade. A primeira etapa da pesquisa focou nas sínteses química e verde de AgNPs, utilizando como agentes redutores o borohidreto e o extrato de Camellia sinensis, respectivamente. Em ambas as sínteses, observou-se que, na presença do citrato de sódio, houve maior estabilidade das AgNPs. A segunda etapa focou na simulação do tratamento de água da Companhia de Saneamento Básico do Estado de São Paulo (SABESP), através do ensaio com o Jar test, onde avaliou-se que as AgNPs sofrem oxidação durante o processo. E, na terceira etapa, realizou-se os ensaios de ecotoxicidade, com o uso de Daphnia magna e Allium cepa. Para o ensaio de toxicidade aguda, foram adicionadas Daphnia magna em soluções com diferentes concentrações de AgNPs, Ag+ e em água tratada no Jar Test, além do controle negativo. Os resultados mostraram a taxa de mortalidade para a espécie, tanto em contato com AgNPs, como com os íons Ag+ e com a água tratada no Jar Test. No ensaio com as sementes, foram separados o grupo de sementes tratadas com AgNPs, o grupo controle positivo (tratado com íons Ag+) e o controle negativo (tratado com água ultrapura). Os resultados indicaram a bioestimulação das sementes, tanto em contato com AgNPs, como com os íons Ag+.
- ItemAcesso aberto (Open Access)Dispersões altamente concentradas de nanopartículas de prata em meio aquoso: preparação, caracterização, imobilização em celulose não modificada e aplicações(Universidade Federal de São Paulo, 2023-07-31) Nunes, Rodolfo Pedro Pereira [UNIFESP]; Camilo, Fernanda Ferraz [UNIFESP]; http://lattes.cnpq.br/6334598937296642; http://lattes.cnpq.br/3948517654608176Atualmente, ainda há uma escassez na literatura de trabalhos que se concentrem na obtenção de dispersões com altas concentrações de nanopartículas de prata (AgNPs). Portanto, este trabalho apresenta um novo método de síntese de AgNPs por redução química para obter dispersões com concentrações de 5, 10, 25, 50 e 100 mM em meio aquoso, na presença do agente estabilizante polivinilpirrolidona (PVP). As dispersões produzidas consistem em partículas esféricas com diâmetros inferiores a 100 nm, baixa polidispersividade e estabilidade razoável ao longo do tempo. Com o objetivo de aumentar a estabilidade das AgNPs, elas foram imobilizadas em filmes de celulose em duas etapas. Na primeira etapa, a celulose microcristalina foi dissolvida em um líquido iônico chamado 1-butil-3-metilimidazólio (BMlmCl), e na segunda etapa, o filme foi formado usando um anti-solvente para a celulose. Foram obtidos cinco filmes por meio do contato dos filmes de celulose com as dispersões contendo 5, 10, 25, 50 e 100 mM de prata. As análises indicam que os filmes obtidos eram amorfos, contendo celulose do tipo 2, com superfície lisa e homogênea, e uma porcentagem de prata variando de 1% a 5%, dependendo da dispersão utilizada. A atividade catalítica dos filmes produzidos com diferentes concentrações de prata foi avaliada em relação à degradação do 4-nitrofenol. Os filmes utilizados resultaram na redução do 4-nitrofenol em 25 a 40 minutos, dependendo do filme utilizado. Embora a atividade catalítica diminua após o primeiro ciclo de uso, os filmes podem ser utilizados com atividade parcial por pelo menos cinco ciclos. A grande vantagem do uso de filmes em vez de dispersões de AgNP é que o filme pode ser facilmente removido do meio racional e possui um maior potencial de reutilização. Esses resultados contribuem para o avanço na obtenção de dispersões de AgNPs concentradas e sua aplicação catalítica. Estudos futuros podem otimizar as condições de síntese e imobilização, bem como explorar outras aplicações desses filmes de celulose com AgNPs.
- ItemAcesso aberto (Open Access)Estudo da interação entre nanopolímero conjugado e nanomaterial(Universidade Federal de São Paulo, 2023-10-20) Batista, Giovanna Silva [UNIFESP]; Philadelphi, Laura Oliveira Péres [UNIFESP]; Parolin, Giovana Artuzo; http://lattes.cnpq.br/5165382247780718; http://lattes.cnpq.br/7511492642565571; https://wwws.cnpq.br/cvlattesweb/PKG_MENU.menu?f_cod=0E27B800FE891EE12CC85CD1900E69D9#Os polímeros conjugados demonstram uma série de características que os tornam amplamente utilizados no ramo da eletrônica orgânica, principalmente relacionado as propriedades ópticas e semicondutoras para a produção de dispositivos como LEDs e células solares, como exemplo. O presente trabalho teve como objetivo a preparação e caracterização de um polímero conjugado em escala nano, e estudar o comportamento desse material quando unido à nanopartículas de prata em um compósito de nanomateriais, visando suas possíveis aplicações. O polímero poli-(9,9-dioctilfluoreno)-co-fenileno foi sintetizado via rota de Suzuki, e caracterizado por UV-vis, fluorescência e termogravimetria. O material foi obtido na escala nano através do procedimento de nanoprecipitação e as nanopartículas de prata por redução de nitrato de prata. Suas propriedades foram investigadas, principalmente quanto à estabilidade das nanopartículas e eletronicamente, usando-se técnicas de UV-vis e fluorescência, DLS e Potencial Zeta. Ambos os materiais foram estudados em dispersões aquosas e em filmes preparados através da técnica de casting com quitosana como matriz. De acordo com as análises de UV-vis e fluorescência, as soluções e filmes com os materiais apresentaram perfis semelhantes de absorção e emissão, apesar de demonstrarem maior estabilidade em estado sólido. Apesar das análises de Potencial Zeta que apresentaram altos valores de desvio ao longo do tempo, as nanopartículas apresentam boa estabilidade em solução, sendo confirmada pelo UV-vis. A diferença mais significativa ocorre entre o comportamento de emissão do polímero macro e nanopolímero, devido a diferença nas bandas no espectro. Além disso, o polímero macro também possui resistência a degradação térmica pelo menos 16% maior em relação a todos os filmes estudados. Foi realizado um trabalho de fotodegradação, no qual ambos os materiais demonstraram estabilidade quando submetidos a uma lâmpada de luz UV de 254 e 365 nm por um período de 3 e 6h.
- ItemAcesso aberto (Open Access)Estudo do efeito microbicida da adição de nanopartículas de prata em membranas de um copolímero de poliéter e poliamida comercial (PEBAX-2533)(Universidade Federal de São Paulo, 2024-06-05) Barros, Larissa Cardoso de [UNIFESP]; Camilo, Fernanda Ferraz [UNIFESP]; Silva, Flavia Tavares da; https://bv.fapesp.br/pt/pesquisador/93340/fernanda-ferraz-camilo/; http://lattes.cnpq.br/7155923130289771Este trabalho de conclusão de curso teve como objetivo principal a preparação de membranas elastoméricas utilizando o copolímero PEBAX-2533, enriquecido com nanopartículas de prata, com potencial uso em dispositivos médicos, como cateteres e implantes. O PEBAX-2533 é conhecido por suas excelentes propriedades mecânicas e flexibilidade. Nanopartículas de prata, escolhidas por suas eficazes propriedades microbicidas, foram sintetizadas utilizando o método bottom-up, que permite controle preciso sobre o tamanho e a forma das partículas. A síntese foi realizada em 1-butanol, um solvente capaz de dissolver eficientemente tanto o PEBAX-2533 quanto as nanopartículas de prata, garantindo a compatibilidade entre os componentes e a integridade das nanopartículas incorporadas. As membranas resultantes foram caracterizadas para avaliar a distribuição, estabilidade térmica e a integração das nanopartículas de prata na matriz do PEBAX. Os resultados mostraram que as membranas mantêm estabilidade térmica até 210 °C, o que as qualifica para aplicações biomédicas que exigem esterilização a altas temperaturas. Os testes funcionais focaram na capacidade das membranas de dispersar biofilmes de Pseudomonas aeruginosa, uma bactéria notória por sua resistência a tratamentos e prevalência em infecções hospitalares. Os resultados indicaram que as membranas contendo nanopartículas de prata são capazes de conter a formação de biofilmes. Em particular, a membrana com 1% de massa de nanopartículas de prata e 10 mM de concentração mostrou os melhores resultados, dispersando efetivamente o biofilme e impedindo a proliferação bacteriana.
- ItemSomente MetadadadosGreen synthesis of silver nanoparticles with extract of Mimusops coriacea and light(Elsevier Science Bv, 2018) Lopes, C. R. B. [UNIFESP]; Courrol, Lilia Coronato [UNIFESP]Biological methods of nanoparticle synthesis using plant extracts have been suggested as promising ecofriendly alternative to chemical and physical methods. In this study, spherical silver nanoparticles (AgNP) were synthesized from the aqueous extract of Mimusops coriacea leaves at room temperature. To accelerate the reduction of Ag+ ions was used photoreduction process with Xenon lamp. A presence of resonant surface plasmon band at approximately 415 nm confirms the formation of the nanoparticles. The shape and size of the particles were determined by transmission electron microscopy images indicating sizes from 10 to 30 nm in diameter. Zeta potential indicates good stability. To identify the products for the reduction of Ag+ ions and stability of AgNP, FTIR analysis were performed. An intense reduction in chlorophyll fluorescence was observed after formation of the nanoparticles.
- ItemSomente MetadadadosHow the interaction of PVP-stabilized Ag nanoparticles with models of cellular membranes at the air-water interface is modulated by the monolayer composition(Academic Press Inc Elsevier Science, 2018) Cruz Gomes da Silva, Rafael Leonardo [UNIFESP]; Oliveira da Silva, Heloiza Fernanda; da Silva Gasparotto, Luiz Henrique; Caseli, Luciano [UNIFESP]The antimicrobial property of silver nanoparticles (AgNPs) is believed to be associated to their interaction with biointerfaces such as microbial cell membranes, encouraging research on the identification of membrane sites capable of AgNPs binding. Although significant progress has been made in that regard, the exact molecular mechanism of action is yet to be fully understood. In this study, AgNPs dispersed in aqueous media and stabilized with polyvinylpyrrolidone were incorporated in Langmuir monolayers of selected lipids that served as cell membrane models. Results from pressure-area isotherms, vibrational spectroscopy and Brewster angle microscopy revealed condensation of glycoside-free lipid monolayers, evidencing that the AgNPs interact mostly with the lipid hydrophilic head groups. In contrast, the monolayers of systems containing glycoside derivatives were found to expand upon AgNPs incorporation, indicating that the glycosidic compounds might facilitate the incorporation of these nanoparticles in cellular membranes. These data can be therefore correlated with the possible toxicity and microbicide effect of AgNPs in lipidic surfaces of mammalian and microbial membranes. (C) 2017 Elsevier Inc. All rights reserved.
- ItemSomente MetadadadosThe importance of evaluating the real metal concentration in nanoparticles post-synthesis for their applications: A case-study using silver nanoparticles(Elsevier Science Bv, 2016) Galazzi, Rodrigo Moretto; Santos, Elias de Barros [UNIFESP]; Caurin, Tatiana; Pessoa, Gustavo de Souza; Mazali, Italo Odone; Zezzio Arruda, Marco AureliTo determine whether the effect observed in a study is related to the nanoparticle only or to their synergic effect with the "free" metal ions, the real concentration of silver (104 +/- 8 and 100 +/- 2 mg L-1) after AgNP synthesis is obtained through ICP-MS and ICP OES in the solution after the AgNP synthesis and in different fractions after centrifugation (at 8100g for 40 min). From the resuspension of the AgNP contained in the solution (AgNP-total) after synthesis (AgNP-res), concentrations of 49 +/- 3 and 51 3 mg L-1 are found and concentrations of 50 +/- 7 and 47 +/- 2 mg L-1 in the supernatant (Ag-sup) are found using ICP-MS and ICP OES respectively. The characterization of AgNP-total, AgNP-res and Ag-sup is performed by HRTEM and UV-vis, corroborating the results in terms of Ag determination, and indicates that half of the total silver concentration is in the AgNP form and that the other half is in the "free" silver form. The results of the stability test of the NPs indicate a 7% decrease in Ag as NP three months after its synthesis. (C) 2015 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosThe importance of evaluating the real metal concentration in nanoparticles post-synthesis for their applications: A case-study using silver nanoparticles(Elsevier Science Bv, 2016) Galazzi, Rodrigo Moretto; Santos, Elias de Barros [UNIFESP]; Caurin, Tatiana; Pessoa, Gustavo de Souza; Mazali, Italo Odone; Zezzio Arruda, Marco AureliTo determine whether the effect observed in a study is related to the nanoparticle only or to their synergic effect with the "free" metal ions, the real concentration of silver (104 +/- 8 and 100 +/- 2 mg L-1) after AgNP synthesis is obtained through ICP-MS and ICP OES in the solution after the AgNP synthesis and in different fractions after centrifugation (at 8100g for 40 min). From the resuspension of the AgNP contained in the solution (AgNP-total) after synthesis (AgNP-res), concentrations of 49 +/- 3 and 51 3 mg L-1 are found and concentrations of 50 +/- 7 and 47 +/- 2 mg L-1 in the supernatant (Ag-sup) are found using ICP-MS and ICP OES respectively. The characterization of AgNP-total, AgNP-res and Ag-sup is performed by HRTEM and UV-vis, corroborating the results in terms of Ag determination, and indicates that half of the total silver concentration is in the AgNP form and that the other half is in the "free" silver form. The results of the stability test of the NPs indicate a 7% decrease in Ag as NP three months after its synthesis. (C) 2015 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosOptical properties and antimicrobial effects of silver nanoparticles synthesized by femtosecond laser photoreduction(Elsevier Sci Ltd, 2018) Courrol, Daniella dos Santos; Lopes, Carla Regina Borges [UNIFESP]; Cordeiro, Thiago da Silva; Franzolin, Marcia Regina; Vieira Junior, Nilson Dias; Sarnad, Ricardo Elgul; Courrol, Lilia Coronato [UNIFESP]Silver nanoparticles exhibit a powerful antimicrobial action showing a pronounced potential to be widely used against drug resistance bacteria. The present work describes the optical properties and antimicrobial effect of silver nanoparticles produced by femtosecond laser photoreduction of AgNO3 in the presence of tryptophan water solution. The advantages of this method are the absence of hazardous chemical reducing agents in the solution, and the versatile dimensional control achieved. The synthesized silver nanoparticles were characterized by absorption and fluorescence spectroscopy and their antibacterial activity were determined by monitoring the cell viability of Escherichia coli. The effects of the silver nanoparticles concentration and laser parameters (exposure time and pulse energy), on the formation of the nanoparticles, and its influence on the bacteria growth inhibition were studied. The prepared silver nanoparticles exhibited suitable antimicrobial properties. The results demonstrated that the nanoparticles concentration plays an important role in their bactericidal efficacy. The increase in the laser energy caused an increase in E. coli growth inhibition. Irradiations with energies around 300 mu j for 60 min presented high antimicrobial activity due to the presence of kynurenine, sub product of tryptophan photolysis. The first-time formation mechanism of tryptophan silver nanoparticles in high optical intensities was also discussed. (C) 2018 Elsevier Ltd. All rights reserved.
- ItemAcesso aberto (Open Access)Preparação de nanopartículas de prata e seus compósitos com polímeros condutores m moldes flexíveis e líquidos iônicos(Universidade Federal de São Paulo, 2013-11-13) Correa, Cintia Marques [UNIFESP]; Camilo, Fernanda Ferraz [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Ionic liquids (IL), liquid salts at room temperature, show self-organization due to the electrostatic interactions between their ions and the van der Waals among the alkyl chains of the cationic species, being classified as structure directing agent for nanomaterials and polymers synthesis. This works will present the preparation, studying some synthetic parameters (different molar ratio between oxidant/monomer (K) and oxidant agent concentration (C)) of silver and two conductive polymers composites, called polyaniline (PANI), and polypyrrole (PPY), using as structure directing agent two ionic liquids, 1-butyl-3-methylimidazolium (BMIM) bis(trifluoromethanesulfonyl)imide (Tf2N) and tetrafluoroborate (BF4) and silver salts soluble in the LI . With the variation of the synthetic parameters was possible to evaluate their influence on the composites properties. PANI/Ag composites were obtained successfully and all characterizations confirmed the presence of PANI in the emeraldine form and metallic silver in nanoscale. Depending on the used conditions (K and C) electrical conductivity values ranged from 55 until 830 S.cm-1, which are higher than those of pure PANI. PPY/Ag composite exhibited electrical conductivity value around 10-1 S.cm-1. Silver nanoparticles were also prepared from Ag+ reduction using tetrabutylammonium borohydride in different ionic liquids based on imidazolium cations, called 1-butyl-3-methylimidazolium (BMIM) or 1-butyl-2,3-dimethylimidazolium (BMMIM) or 1-methyl-3-octylimidazolium (OMIM) bis(trifluoromethanesulfonyl)imide (Tf2N) and tetrafluoroborate (BF4). Although, nanoparticles have been obtained in all cited ionic liquids, in ionic liquids containing Tf2N. The dispersions showed greater stability than in IL containing BF4. The presence of polyvinylpyrrolidone (PVP) was crucial to increase the stabilization of the nanoparticles and at higher polymer concentration, the higher the nanoparticles stability. The dispersions are viscous and yellow, without precipitates and containing nanoparticles with diameters around 6-12 nm. Finally, tetrabutylammonium citrate was used for the preparation of silver nanoparticles, acting as both solvent as reducing agent. This method promoted the preparation of silver nanoparticles dispersions in the absence of any stabilizing agent, highly concentrated and containing nanoparticle with diameter of 2-6 nm.
- ItemAcesso aberto (Open Access)Preparação de nanopartículas de prata em meio alcoólico e utilizando moldes rígidos de silica mesoporosa(Universidade Federal de São Paulo, 2014-06-06) Oliveira, Roselaine da Silva [UNIFESP]; Camilo, Fernanda Ferraz [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)In this work the preparation and characterization of non-aqueous dispersions of silver nanoparticles (AgNP) prepared with 1-butanol, which acted as both solvent and reducing agent of Ag+ ions, obtained from silver nitrate or silver tetrafluoroborate were shown. A biocompatible block copolymer of polyether and polyamide (PEBA) was used as dispersion agent. The goal was to obtain non-aqueous dispersions of silver nanoparticle highly concentrated and stable. It is noteworthy to mention that in aqueous media, the silver nanoparticles concentration is relatively low (around 30 mg/L - 0.47 mM) and this dispersions does not show compatibility with hydrophobic surfaces such as PTFE, silicone, polyvinyl chloride (PVC) and polyethylene (PE). After finding the best experimental conditions (reactant concentration, type of silver salt, reaction time, percentage of stabilizer), it was produced a hydrophobic dispersion of silver nanoparticles, which is stable for more than 6 months, with a concentration of 5 mM, which is higher than that obtained in water. The AgNP diameters vary from 5 to 10 nm. The dispersion showed antimicrobial activity against Staphylococcus aureus and Escherichia coli even at low concentration. In addition, it was prepared and characterized silver nanoparticles immobilized into a mesoporous silica, called MCM-41 (with pores non-functionalized and functionalized surface with –SH and –SO3-), using 1-butanol as reducing agent of the silver ions, obtained from silver nitrate. 1-butanol was able to reduce the incorporated Ag+ in the silicas pores. A partial disordering of the silica has been observed mainly in the composite prepared with pure MCM-41. It was also found that there are silver nanoparticles inside the silica’s pores and the composite with –SH groups has the greater amount of silver. The catalytic activity of these composites was evaluated by the reduction of p-nitrophenol to p-aminophenol in the presence of sodium borohydride, but the MCM-41/Ag composite showed the highest catalytic activity for this test.
- ItemSomente MetadadadosSaliva and light as templates for the green synthesis of silver nanoparticles(Elsevier B.V., 2014-01-20) Matos, Ricardo Almeida de [UNIFESP]; Courrol, Lilia Coronato [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)We report a method for the synthesis of silver nanoparticles using an aqueous saliva solution and irradiation with light from a mercury metal halide lamp. Bi-deionized water was used as the solvent, and surfactants or reducing agents were substituted by saliva and light in the procedure, characterizing the process as a green synthesis. the light was used to reduce silver ions (Ag+) to metallic silver (Ag-0). the average size, size distribution, and morphology of the nanoparticles were determined by transmission electron microscopy (TEM), UV/visible absorption spectrophotometry and Fourier transform infrared spectroscopy (FTIR). Spherical nanoparticles of similar to 20 nm in size were present after the lamp illumination. This methodology represents a non-invasive approach for disease detection and possesses a good potential for diagnostics applications. (C) 2013 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosSilver nanoparticles: A new view on mechanistic aspects on antimicrobial activity(Elsevier Science Bv, 2016) Duran, Nelson; Duran, Marcela; Jesus, Marcelo Bispo de; Seabra, Amedea Barozzi [UNIFESP]; Favaro, Wagner J.; Nakazato, GersonSilver nanoparticles are well known potent antimicrobial agents. Although significant progresses have been achieved on the elucidation of antimicrobial mechanism of silver nanoparticles, the exact mechanism of action is still not completely known. This overview incorporates a retrospective of previous reviews published and recent original contributions on the progress of research on antimicrobial mechanisms of silver nanoparticles. The main topics discussed include release of silver nanoparticles and silver ions, cell membrane damage, DNA interaction, free radical generation, bacterial resistance and the relationship of resistance to silver ions versus resistance to silver nanoparticles. The focus of the overview is to summarize the current knowledge in the field of antibacterial activity of silver nanoparticles. The possibility that pathogenic microbes may develop resistance to silver nanoparticles is also discussed.
- ItemSomente MetadadadosA simple and effective method to synthesize fluorescent nanoparticles using tryptophan and light and their lethal effect against bacteria(Elsevier B.V., 2014-11-01) Tomita, Rafael Jun [UNIFESP]; Matos, Ricardo Almeida de [UNIFESP]; Vallim, Marcelo Afonso [UNIFESP]; Courrol, Lilia Coronato [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)A simple, environmentally friendly and cost-effective method was used to synthesize silver nanoparticles using typtophan and light. To prepare the nanoparticles, the following components were used: deionized water, silver nitrate, light and tryptophan. the effects of the tryptophan concentration and light exposure time on the formation of tryptophan silver nanoparticles (Tnnps) were studied. the synthesized Tnnps were characterized using transmission electron microscopy (TEM), absorption and fluorescence spectroscopy and zeta potential measurements. the synthesized Tnnps were nearly spherical, with sizes of approximately 17 nm. in addition, the antibacterial activity of Tnnps was determined by monitoring the growth curves of strains of Escherichia colt, Pseudomonas aeruginosa, Staphylococcus epidermidis, Serratia marcescens, and Enterococcus faecalis using the microdilution test. the Minimum Inhibitory Concentration (MIC) for 4 of 5 tested bacteria was determined to be between 20.0 and 17.5 mu g/mL for 48 h and between 22.5 and 20.0 mu g/mL for 72 h. (C) 2014 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosSynthesis of silver nanoparticles using agar-agar water solution and femtosecond pulse laser irradiation(Elsevier B.V., 2013-04-20) Matos, Ricardo Almeida de [UNIFESP]; Cordeiro, Thiago da Silva; Samad, Ricardo Elgul; Sicchieri, Leticia Bonfante; Vieira Junior, Nilson Dias; Courrol, Lilia Coronato [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); IPEN CNEN SPWe report a method to synthetize silver nanoparticles using an agar-agar solution illuminated by light from a xenon lamp, followed by irradiation by ultrashort laser pulses. Spherical nanoparticles of similar to 100 nm were created by the xenon lamp illumination, and after the ultrashort pulses irradiation their sizes were reduced to under 10 nm. Bideionized water was used as solvent and surfactants or reducing agents were substituted by agar-agar and light, characterizing the process as a green synthesis, a completely inoffensive procedure for the environment. the xenon light was used to reduce silver ions (Ag+) into metallic silver (Ag-0), and the laser irradiation was important to decrease the nanoparticles diameter. the average particles size, size distribution, morphology, and structure were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and UV/visible absorption spectrophotometry. (C) 2013 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosThermal precipitation of silver nanoparticles and thermoluminescence in tellurite glasses(Elsevier B.V., 2011-10-01) Giehl, J. M.; Pontuschka, W. M.; Barbosa, L. C.; Chillcce, E. F.; Da Costa, Z. M.; Alves, S. [UNIFESP]; Universidade de São Paulo (USP); Universidade Estadual de Campinas (UNICAMP); Univ Fed Juiz de Fora; Universidade Federal de São Paulo (UNIFESP)Silver metal and/or oxide precipitation of nanoparticles in thermally treated Ag-doped tellurite glasses was studied by optical absorption (OA) and transmission electron microscopy (TEM). the Lorentzian adjusted silver nanoparticles plasma resonance OA band was compared to the Drude model approach. the silver nanoparticles size distribution on the surface rather than in the bulk was determined by TEM. A model for the metallic silver precipitation is proposed. the characterization of the formation of silver nanoparticles was carried out with differential thermal analysis (DTA) to determine the glass transition temperature (Tg) and of crystallization (Tc). Previously gamma-irradiated samples exhibited thermoluminescence (TL) peaks and the defect centers TeOHC. NBOHC and TeEC were identified by electron paramagnetic resonance (EPR), but no Ag(0) signal was detected. the silver nanoparticles are known to introduce desired third-order optical nonlinearities in the composites, at wavelengths close to the characteristic surface-plasmon resonance of the metal precipitates. An increase of the glass density and refractive index with increasing AgNO(3) content was observed. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.