Oswaldo Luiz Alves

Mechanistic aspects of biosynthesis of silver nanoparticles by several Fusarium oxysporum strains

Extracellular production of metal nanoparticles by several strains of the fungus Fusarium oxysporum was carried out. It was found that aqueous silver ions when exposed to several Fusarium oxysporum strains are reduced in solution, thereby leading to the formation of silver hydrosol. The silver nanoparticles were in the range of 20–50 nm in dimensions. The reduction of the metal ions occurs by a nitrate-dependent reductase and a shuttle quinone extracellular process. The potentialities of this nanotechnological design based in fugal biosynthesis of nanoparticles for several technical applications are important, including their high potential as antibacterial material.

Nanotoxicity of Graphene and Graphene Oxide

Graphene and its derivatives are promising candidates for important biomedical applications because of their versatility. The prospective use of graphene-based materials in a biological context requires a detailed comprehension of the toxicity of these materials. Moreover, due to the expanding applications of nanotechnology, human and environmental exposures to graphene-based nanomaterials are likely to increase in the future. Because of the potential risk factors associated with the manufacture and use of graphene-related materials, the number of nanotoxicological studies of these compounds has been increasing rapidly in the past decade. These studies have researched the effects of the nanostructural/biological interactions on different organizational levels of the living system, from biomolecules to animals. This review discusses recent results based on in vitro and in vivo cytotoxicity and genotoxicity studies of graphene-related materials and critically examines the methodologies employed to evaluate their toxicities. The environmental impact from the manipulation and application of graphene materials is also reported and discussed. Finally, this review presents mechanistic aspects of graphene toxicity in biological systems. More detailed studies aiming to investigate the toxicity of graphene-based materials and to properly associate the biological phenomenon with their chemical, structural, and morphological variations that result from several synthetic and processing possibilities are needed. Knowledge about graphene-based materials could ensure the safe application of this versatile material. Consequently, the focus of this review is to provide a source of inspiration for new nanotoxicological approaches for graphene-based materials.

Potential use of silver nanoparticles on pathogenic bacteria, their toxicity and possible mechanisms of action

As propriedades da prata sao conhecidas ha muitos anos. Recentemente, as nanoparticulas de prata tem chamado a atencao por sua atividade antimicrobiana que oferece a possibilidade de uso com propositos medicos e de higiene. Estas nanoparticulas de prata em diferentes formulacoes, com diferentes formas e tamanhos, exibem atividades antimicrobianas diferentes. Entretanto, os mecanismos da atividade antimicrobiana de ions e de nanoparticulas, assim como sua toxicidade em tecidos humanos nao estao totalmente esclarecidos. Esta revisao avalia o uso potencial de nanoparticulas de prata no controle de patogenicos com enfase sobre sua acao contra bacterias patogenicas, sua toxicidade e possiveis mecanismos de acao. The antimicrobial properties of silver have been known for thousands of years. Recently, silver nanoparticles have gained attention because of their antimicrobial activity which offers the possibility of their use for medical and hygiene purposes. Indeed, silver nanoparticles in different formulations and with different shapes and sizes exhibit variable antimicrobial activity. However, the mechanisms of antimicrobial activity of silver ions and silver nanoparticles, and their toxicity to human tissues are not fully characterized. This review evaluates the potential use of silver nanoparticles to control pathogens with emphasis on their action against pathogenic bacteria, their toxicity and possible mechanisms of action.

Anti-adhesion and antibacterial activity of silver nanoparticles supported on graphene oxide sheets.

This work reports on the preparation, characterization and antibacterial activity of a nanocomposite formed from graphene oxide (GO) sheets decorated with silver nanoparticles (GO-Ag). The GO-Ag nanocomposite was prepared in the presence of AgNO3 and sodium citrate. The physicochemical characterization was performed by UV-vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy (TEM). The average size of the silver nanoparticles anchored on the GO surface was 7.5 nm. Oxidation debris fragments (a byproduct adsorbed on the GO surface) were found to be crucial for the nucleation and growth of the silver nanoparticles. The antibacterial activity of the GO and GO-Ag nanocomposite against the microorganism Pseudomonas aeruginosa was investigated using the standard counting plate methodology. The GO dispersion showed no antibacterial activity against P. aeruginosa over the concentration range investigated. On the other hand, the GO-Ag nanocomposite displayed high biocidal activity with a minimum inhibitory concentration ranging from 2.5 to 5.0 μg/mL. The anti-biofilm activity toward P. aeruginosa adhered on stainless steel surfaces was also investigated. The results showed a 100% inhibition rate of the adhered cells after exposure to the GO-Ag nanocomposite for one hour. To the best of our knowledge, this work provides the first direct evidence that GO-Ag nanocomposites can inhibit the growth of microbial adhered cells, thus preventing the process of biofilm formation. These promising results support the idea that GO-Ag nanocomposites may be applied as antibacterial coatings material to prevent the development of biofilms in food packaging and medical devices.

BiVO4 thin film preparation by metalorganic decomposition

This paper describes the first obtention of BiVO4 thin films. These films were prepared with the Metalorganic Decomposition technique, starting from bismuth 2-ethyl-hexanoate and vanadium (IV) (oxy)acetylacetonate precursors. These compounds were dissolved in freshly distilled acetylacetone, dip-coated on common borosilicate glass substrates and pyrolysed at 400°C. Film thickness ranged from 50 to 100 nm, depending on the number of deposition steps. Films are transparent, allowing the first obtention of UV–vis absorption spectra acquisition in transmission mode. Raman microprobe spectra confirmed the obtention of BiVO4 deposited as an homogeneous film. Scanning electron micrographs showed a continuous and porous surface.

Construction and evaluation of an optical pH sensor based on polyaniline-porous Vycor glass nanocomposite

This work describes the preparation of a polyaniline (Pani)‐porous Vycor glass (PVG) nanocomposite and its use as sensing phase in an optical fibre pH sensor. Nanocomposites of Pani‐PVG were prepared by in situ polymerisation of aniline absorbed inside the pores of a PVG (Corning 7930) with an average porous size of 8 nm. The optical sensor was constructed by fixing a PVG slide onto a distal end of bifurcated optical fibre bundle, with a cyanoacrylic resin. The sensor response was found to be reversible in the pH range from 5 to 12 and linear from pH 7.4 to 9.5. Response times of 4, 8 and >16 min were obtained for slide thickness’ of 0.5, 1 and 1.5 mm, respectively. Changes of temperature, ranging from 20 to 408C, showed minor effect on the dynamic range. Similarly, the ionic strength (0.15, 0.30 and 0.50 mol l ˇ1 ) and the nature of the ions (NaCl, KCl and NaClO4) showed minor influence on the sensor response. Leaching of Pani was not observed and the sensor lifetime was determined as being at least 5 months. These results indicate that a Pani‐PVG nanocomposite is suitable for the construction of optical pH sensors, with good analytical performance, since the glass slides can be prepared with good reproducibility and durability. # 2001 Elsevier Science B.V. All rights reserved.

Nanostructured silver vanadate as a promising antibacterial additive to water-based paints

In this article, we report the use of nanostructured silver vanadate as a promising antibacterial additive to water-based paints that has potential for applications in bathrooms, kitchens, and hospital environments. This hybrid nanomaterial was prepared by a simple and fast precipitation reaction involving silver nitrate and ammonium vanadate, dismissing the hydrothermal treatment. The preparation involved using Ag vanadate nanowires (β-AgVO(3)) with diameters ranging from 20 to 60 nm and decorated with silver (Ag) nanoparticles (NPs) with diameters ranging from 5 to 40 nm. Results of antibacterial tests show that this hybrid material has a promising antibacterial activity against several types of bacteria strains, such as methicillin-resistant Staphylococcus aureas (MRSA), Enterococcus faecalis, Escherichia coli, and Salmonella enterica Typhimurium. The evaluated material exhibits antibacterial activity 30 times larger than that of Oxacillin. In addition, this nanomaterial was tested as an antibacterial additive to water-based paints, and formulations with 1% show a 4-mm inhibition zone against a MRSA strain.

Inter-atomic distance contraction in thiol-passivated gold nanoparticles

Abstract Size-dependent inter-atomic distance contraction was investigated by Extended X-ray Absorption Fine Structure in thiol-capped gold nanoparticles. A slight nearest-neighbor distance reduction was observed as a function of particle diameter (2–4 nm range) but, for all samples, it was less than 1%. This value contrasts with the larger effect expected and found in other systems, especially for the smallest particles (2 nm) where it is twice as small. Our analysis also points out a short metal–ligand bond, suggesting a rather strong surface interaction. We interpreted these results as a passivant effect where the metal–ligand interaction partially compensates the expected lattice contraction.

Biocerâmicas: tendências e perspectivas de uma área interdisciplinar

The need for new materials to substitute injured or damaged parts of the human body has led scientists of different areas to the investigation of bioceramics since the 70s, when other materials in use started to show implantation problems. Bioceramics show some advantages like being the material that best mimics the bone tissue but also, present low mechanical strength due to its ceramic nature. This paper presents a general view about the topic.

Unveiling the structure and composition of titanium oxide nanotubes through ion exchange chemical reactions and thermal decomposition processes

Neste trabalho reportamos reacoes de troca ionica e decomposicao termica em nanotubos de oxido de titânio, obtidos pelo tratamento hidrotermico de TiO 2 e NaOH. Considerando os resultados obtidos, sugerimos uma nova composicao quimica para os nanotubos: Na 2 Ti 3 O 7 ·nH 2 O. Os resultados tambem indicam que a estrutura da parede dos nanotubos seria isoestrutural as lamelas observadas para o Na 2 Ti 3 O 7 bulk. Dependendo da natureza da lavagem (agua deionizada ou solucao acida) executada no nanotubo apos o tratamento hidrotermico a concentracao de ions Na + pode ser modificada atraves de um processo de troca ionica do Na + por H + . Tais resultados permitem sugerir a seguinte formula quimica geral para os nanotubos obtidos: Na 2-x H x Ti 3 O 7 ·nH 2 O (0≤ x ≤2), sendo x dependente das condicoes de lavagens. In this paper we report the ion exchange reactions and the thermal decomposition of titanium oxide nanotubes, obtained by hydrothermal treatment of TiO 2 and NaOH. Based on these results we propose a new composition for the as-prepared nanotubes as Na 2 Ti 3 O 7 ·nH 2 O. Our results also suggest that nanotube walls have structure similar to those observed in the layer of the bulk Na 2 Ti 3 O 7 . Depending on how the washing process is performed on the nanotubes (water or acid solutions) the Na + content can be modified via the exchange reaction of Na