Óxido de grafeno e óxido de grafeno funcionalizado com nanopartículas de prata : atividade antibacteriana e aplicações em compósitos poliméricos

Orientador: Oswaldo Luiz AlvesTese (doutorado) - Universidade Estadual de Campinas, Instituto de QuímicaResumo: O óxido de grafeno (GO) é uma forma quimicamente modificada de grafeno que possui grupos funcionais contendo oxigênio (epóxi, carboxila, carbonila, e hidroxila) distribuídos sobre a base e as bordas de suas folhas. Devido à abundância dos grupamentos oxigenados, o GO tem sido usado como uma plataforma para suportar e estabilizar nanoestruturas metálicas, tais como nanopartículas de prata (NPAgs), visando aplicações biológicas. Além disso, devido à sua excelente capacidade de dispersão e elevada área superficial, o GO tem sido considerado uma carga promissora para a construção de compósitos poliméricos. Neste trabalho, relatamos a síntese do GO e dos nanocompósitos de óxido de grafeno funcionalizado com NPAgs (GO-Ag) os quais podem ser utilizados como agentes antibacterianos de amplo espectro. O GO foi sintetizado por meio do método de Hummers modificado, e o GO-Ag foi preparado através da redução in situ dos íons de prata por citrato de sódio. As folhas de GO foram funcionalizadas com NPAgs esféricas de diâmetro médio de 9,4 nm. Estes nanocompósitos exibiram excelente atividade antimicrobiana contra as principais bactérias em ambiente hospitalar, tais como Escherichia coli, Enterococcus faecalis, Acinetobacter baumannii, e Staphylococcus aureus resistente à meticilina. Os nanocompósitos GO-Ag também foram aplicados como eficazes agentes antimicrobianos a fim de evitar a proliferação bacteriana em membranas de micro e ultrafiltração. Neste sentido, membranas antimicrobianas de acetato de celulose (CA) foram fabricadas a partir da incorporação de GO e GO-Ag na matriz polimérica (CA-GOAg). Após a funcionalização, as membranas permeáveis modificadas com GO-Ag foram capazes de inativar cerca de 90% das células de E. coli em comparação com as membranas de CA não modificadas. Os resultados sugerem que a incorporação de nanocompósitos GO-Ag é uma abordagem promissora para controlar o desenvolvimento da adesão bacteriana em membranas de purificação de água. Com relação à demanda de novos materiais com elevada estabilidade e com capacidade de proteção contra radiação ultravioleta (UV), foram fabricados filmes compósitos transparentes a partir de acetato de celulose e óxido de grafeno. A caracterização físico-química revelou que as folhas de GO estão bem dispersas por toda a matriz polimérica, proporcionando filmes compósitos lisos e homogêneos. Em comparação com os filmes pristinos de CA, os filmes compósitos exibiram melhor capacidade de proteção contra radiação UV combinado com transparência óptica à luz visível, o que reforça a sua aplicação como revestimentos transparentes com proteção UV para alimentos, produtos farmacêuticos, biomédicos, e produtos eletrônicosAbstract: Graphene oxide (GO) is a chemically modified form of graphene that possesses oxygen-containing groups (epoxy, carboxyl, carbonyl, and hydroxyl) distributed on the plane and edges of the sheets. Owing to the abundance of oxygenated groups, GO has been used as a platform to support and stabilize metallic nanostructures such as silver nanoparticles (AgNPs), aiming biological applications. In addition, GO has been considered a promising material for building polymeric composites because of its excellent dispersibility and high surface area. In this work, we report the synthesis of GO and GO functionalized with AgNPs (GO-Ag) for use as a broad-spectrum antibacterial agent. GO was synthesized through the modified Hummers method, and the GO-Ag was prepared through the in situ reduction of silver ions by sodium citrate. Spherical AgNPs with average size of 9.4 nm were found well-dispersed throughout the GO sheets. This nanocomposite exhibited excellent antimicrobial activity against common nosocomial bacteria such as Escherichia coli, Enterococcus faecalis, Acinetobacter baumannii, and methicillin-resistant Staphylococcus aureus. GO-Ag nanocomposites were also applied as an effective antimicrobial agent in order to prevent the bacterial proliferation on micro and ultrafiltration membranes. Cellulose acetate (CA) membranes were then fabricated from the incorporation of GO and GO-Ag into the polymeric matrix (CA-GOAg). After functionalization, the permeable CA membranes modified with GO-Ag were able to inactivate mostly 90% of E. coli cells compared to the non-modified CA membranes. The results suggest that the incorporation of GO-Ag nanocomposites is a promising approach to control biofouling development in water purification membranes. Concerning the demand for novel ultraviolet shielding materials with high stability, transparent and UV-shielding composite films were fabricated by casting a mixture of GO with cellulose acetate (CA). The physicochemical characterization revealed that GO sheets were well-dispersed throughout the polymeric matrix, providing smooth and homogeneous composite films. By comparison with pristine CA films, the composite films displayed an improved UV-shielding capacity combined with optical transparency under visible light, which underscores their application as transparent UV-protective coatings for food, pharmaceutical, biomedical, and electronic productsDoutoradoQuimica InorganicaDoutora em Ciência

Recent trends in field-effect transistors-based immunosensors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Immunosensors are analytical platforms that detect specific antigen-antibody interactions and play an important role in a wide range of applications in biomedical clinical diagnosis, food safety, and monitoring contaminants in the environment. Field-effect transistors (FET) immunosensors have been developed as promising alternatives to conventional immunoassays, which require complicated processes and long-time data acquisition. The electrical signal of FET-based immunosensors is generated as a result of the antigen-antibody conjugation. FET biosensors present real-time and rapid response, require small sample volume, and exhibit higher sensitivity and selectivity. This review brings an overview on the recent literature of FET-based immunosensors, highlighting a diversity of nanomaterials modified with specific receptors as immunosensing platforms for the ultrasensitive detection of various biomolecules.Immunosensors are analytical platforms that detect specific antigen-antibody interactions and play an important role in a wide range of applications in biomedical clinical diagnosis, food safety, and monitoring contaminants in the environment. Field-effec44FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)2013/22127-2; 2016/04739-9sem informação: The authors acknowledge the financial assistance provided by The São Paulo Research Foundation (FAPESP, project #2013/22127-2 and grant #2016/04739-9) and the National Council for Scientific and Technological Development (CNPq

Graphene oxide-silver nanocomposite as a promising biocidal agent against methicillin-resistant Staphylococcus aureus

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOBackground: Methicillin-resistant Staphylococcus aureus (MRSA) has been responsible for serious hospital infections worldwide. Nanomaterials are an alternative to conventional antibiotic compounds, because bacteria are unlikely to develop microbial resistance against nanomaterials. In the past decade, graphene oxide (GO) has emerged as a material that is often used to support and stabilize silver nanoparticles (AgNPs) for the preparation of novel antibacterial nanocomposites. In this work, we report the synthesis of the graphene-oxide silver nanocomposite (GO-Ag) and its antibacterial activity against relevant microorganisms in medicine. Materials and methods: GO-Ag nanocomposite was synthesized through the reduction of silver ions (Ag+) by sodium citrate in an aqueous GO dispersion, and was extensively characterized using ultraviolet-visible absorption spectroscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy. The antibacterial activity was evaluated by microdilution assays and time-kill experiments. The morphology of bacterial cells treated with GO-Ag was investigated via transmission electron microscopy. Results: AgNPs were well distributed throughout GO sheets, with an average size of 9.4 +/- 2.8 nm. The GO-Ag nanocomposite exhibited an excellent antibacterial activity against methicillin-resistant S. aureus, Acinetobacter baumannii, Enterococcus faecalis, and Escherichia coli. All (100%) MRSA cells were inactivated after 4 hours of exposure to GO-Ag sheets. In addition, no toxicity was found for either pristine GO or bare AgNPs within the tested concentration range. Transmission electronic microscopy images offered insights into how GO-Ag nanosheets interacted with bacterial cells. Conclusion: Our results indicate that the GO-Ag nanocomposite is a promising antibacterial agent against common nosocomial bacteria, particularly antibiotic-resistant MRSA. Morphological injuries on MRSA cells revealed a likely loss of viability as a result of the direct contact between bacteria and the GO-Ag sheets.Methicillin-resistant Staphylococcus aureus (MRSA) has been responsible for serious hospital infections worldwide. Nanomaterials are an alternative to conventional antibiotic compounds, because bacteria are unlikely to develop microbial resistance against10168476861FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOsem informaçãosem informaçã

Comparative in vitro toxicity of a graphene oxide-silver nanocomposite and the pristine counterparts toward macrophages

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Graphene oxide (GO) is a highly oxidized graphene form with oxygen functional groups on its surface. GO is an excellent platform to support and stabilize silver nanoparticles (AgNP), which gives rise to the graphene oxide-silver nanoparticle (GOAg) nanocomposite. Understanding how this nanocomposite interacts with cells is a toxicological challenge of great importance for future biomedical applications, and macrophage cells can provide information concerning the biocompatibility of these nanomaterials. The cytotoxicity of the GOAg nanocomposite, pristine GO, and pristine AgNP was compared toward two representative murine macrophages: a tumoral lineage (J774) and peritoneal macrophages collected from Balb/c mouse. The production of reactive oxygen species (ROS) by J774 macrophages was also monitored. We investigated the internalization of nanomaterials by transmission electron microscopy (TEM). The quantification of internalized silver was carried out by inductively coupled plasma mass spectrometry (ICP-MS). Nanomaterial stability in the cell media was investigated overtime by visual observation, inductively coupled plasma optical emission spectrometry (ICP OES), and dynamic light scattering (DLS). Results: The GOAg nanocomposite was more toxic than pristine GO and pristine AgNP for both macrophages, and it significantly induced more ROS production compared to pristine AgNP. TEM analysis showed that GOAg was internalized by tumoral J774 macrophages. However, macrophages internalized approximately 60 % less GOAg than did pristine AgNP. The images also showed the degradation of nanocomposite inside cells. Conclusions: Although the GOAg nanocomposite was less internalized by the macrophage cells, it was more toxic than the pristine counterparts and induced remarkable oxidative stress. Our findings strongly reveal a synergistic toxicity effect of the GOAg nanocomposite. The toxicity and fate of nanocomposites in cells are some of the major concerns in the development of novel biocompatible materials and must be carefully evaluated.Graphene oxide (GO) is a highly oxidized graphene form with oxygen functional groups on its surface. GO is an excellent platform to support and stabilize silver nanoparticles (AgNP), which gives rise to the graphene oxide-silver nanoparticle (GOAg) nanoco14CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)140560/2014-9The authors thank the National Council for Technological and Scientific Development (CNPq) for the PhD student scholarship (140560/2014-9) and the financial support. The authors also acknowledge Dr. Daniel Ruiz Abanádes for suggestions, Renata Magueta fo

Estudo e desenvolvimento de banhos contendo benzotriazol para eletrodeposição de níquel e caracterização química, física e morfologica dos filmes

In this work, nickel electrodeposition has been studied in the presence of the additives BTAH and/or EDTA onto platinum substrate from Watts plating bath, at different pH. The deposition and dissolution processes with or without additives were investigated through voltammetric techniques. The deposits obtained from these electrolytic solutions were analyzed by scanning electronic microscopy (SEM), X-ray dispersion (EDX) and X-ray diffraction (DRX). Voltammetric studies showed the presence of additives in the plating bath the deposition current densities decreased. The anodic scan suggested the formation of different nickel crystallographic faces, besides that it also suggested other processes that can occur in parallel with dissolution of deposits. The highest efficiencies of the deposition process were obtained at low jdep for all systems studied. The hydrogen evolution reaction occurs simultaneously to the nickel deposition process since the initial moments. The nickel deposition studies from alkaline solutions that contain high concentration of EDTA showed that the complex NiY2- did not discharge to metallic nickel. The deposits were formed only when EDTA was used in low concentrations (additive proportions). Analysis of the deposits by SEM showed that the best conditions to obtain these deposits were carried out at Ed = -1,0 V or jdep = 2,5 mA cm-2 from nickel solutions at pH 6,0 in the presence of 1,0 x 10-3 mol L-1 BTAH. By EDX analysis we could verify that there was O and Cl incorporation in the deposits. The deposits of nickel morphology depends on the deposition potential and consequently on chemical composition of the deposits.Universidade Federal de Minas GeraisNeste trabalho estudou-se a eletrodeposição de níquel na presença dos aditivos BTAH e/ou EDTA sobre substrato de Pt a partir de soluções do tipo Watts em diferentes valores de pH. O processo de deposição e dissolução dos depósitos de níquel na presença ou não de aditivos foi investigado por meio de técnicas voltamétricas. Os depósitos obtidos a partir destas soluções foram caracterizados por meio de microscopia eletrônica de varredura, espectroscopia de dispersão de raios-X e espectroscopia de difração de raios-X. Estudos voltamétricos mostraram que a presença dos aditivos nos banhos diminuiu a densidade de corrente do processo de deposição de níquel. A varredura anódica sugeriu a formação de diferentes fases cristalográficas de níquel, além de outros processos que podem ocorrer paralelamente à dissolução dos depósitos. Elevadas eficiências do processo de deposição foram obtidas em baixas jdep, para todos os sistemas estudados. A reação de evolução de hidrogênio acompanhou o processo de deposição de níquel desde os momentos iniciais. Os estudos de eletrodeposição de níquel a partir de soluções alcalinas contendo elevada concentração de EDTA mostraram que o complexo NiY2- não se descarrega a Ni metálico, os depósitos foram formados apenas quando o EDTA foi empregado em baixas concentrações (quantidade de aditivo). Análise dos depósitos por MEV mostraram que as melhores condições de obtenção dos mesmos foram em Ed = -1,0 V ou jdep = 2,5 mA cm-2, a partir de soluções tipo Watts em pH 6,0 na presença de BTAH 1,0 x 10-3 mol L-1. Por EDX, verificou-se que para todos os sistemas estudados houve a incorporação de O e Cl. A morfologia dos depósitos de níquel depende do potencial de deposição e conseqüentemente da composição química dos mesmos