Andreia Fonseca de Faria

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.

Bioremediation of a polyaromatic hydrocarbon contaminated soil by native soil microbiota and bioaugmentation with isolated microbial consortia

Biodegradation of a mixture of PAHs was assessed in forest soil microcosms performed either without or with bioaugmentation using individual fungi and bacterial and a fungal consortia. Respiratory activity, metabolic intermediates and extent of PAH degradation were determined. In all microcosms the low molecular weight PAHs naphthalene, phenanthrene and anthracene, showed a rapid initial rate of removal. However, bioaugmentation did not significantly affect the biodegradation efficiency for these compounds. Significantly slower degradation rates were demonstrated for the high molecular weight PAHs pyrene, benz[a]anthracene and benz[a]pyrene. Bioaugmentation did not improve the rate or extent of PAH degradation, except in the case of Aspergillus sp. Respiratory activity was determined by CO(2) evolution and correlated roughly with the rate and timing of PAH removal. This indicated that the PAHs were being used as an energy source. The native microbiota responded rapidly to the addition of the PAHs and demonstrated the ability to degrade all of the PAHs added to the soil, indicating their ability to remediate PAH-contaminated soils.

Fabrication of transparent and ultraviolet shielding composite films based on graphene oxide and cellulose acetate.

Graphene oxide (GO) has been considered a promising filler material for building polymeric nanocomposites because of its excellent dispersibility and high surface area. In this work, we present the fabrication and characterization of transparent and ultraviolet (UV) shielding composite films based on GO and cellulose acetate (CA). GO sheets were found to be well-dispersed throughout the CA matrix, providing smooth and homogeneous composite films. Moreover, the GO sheets were completely embedded within the CA matrix and no presence of this nanomaterial was found at the surface. Nevertheless, CAGO composite films offered an improved high energy light-shielding capacity when compared to pristine CA films. Particularly for UVC irradiation, the CAGO film containing 0.50wt% GO displayed a UV-shielding capacity of 57%, combined with 79% optical transparency under visible light. These CAGO composite films can be potentially applied as transparent UV-protective coatings for packing biomedical, pharmaceutical, and food products.

Focal transient lesions of the corpus callosum in systemic lupus erythematosus.

Focal lesions limited to the splenium of the corpus callosum are rare and little is known about their etiology. We describe three patients with systemic lupus erythematosus (SLE) that presented transient lesions of the corpus callosum. We reviewed three patients with SLE whose magnetic resonance imaging (MRI) results revealed focal lesions in the splenum of corpus callosum. The medical records, including clinical, serological, and treatment features, were reviewed to determine the etiology of these lesions. Of 115 patients who had MRI for research purposes, three patients with focal nonhemorrhagic lesions of the corpus callosum were identified. All patients had active SLE at the time of MRI. One patient had other findings on MRI, including cerebral venous thrombosis. On follow-up MRI, patients had an inactive disease and the corpus callosum lesions disappeared. A transient lesion in the splenium of corpus callosum seems to be a nonspecific endpoint of different disease processes leading to vasogenic edema. The complete and rapid reversibility in all cases with disease control is emphasized and any invasive diagnostic or therapeutic approach is discouraged.

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

Background 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.

Purification and structural characterization of fengycin homologues produced by Bacillus subtilis LSFM-05 grown on raw glycerol.

Raw glycerol is a byproduct of biodiesel production that currently has low to negative value for biodiesel producers. One option for increasing the value of raw glycerol is to use it as a feedstock for microbial production. Bacillus subtilis LSFM 05 was used for the production of fengycin in a mineral medium containing raw glycerol as the sole carbon source. Fengycin was isolated by acid precipitation at pH 2 and purified by silica gel column chromatography and characterized using electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) with collision-induced dissociation (CID). The mass spectrum revealed the presence of the ions of m/z 1,435.7, 1,449.9, 1,463.8, 1,477.8, 1,491.8 and 1,505.8, which were further fragmented by ESI-MS/MS. The CID profile showed the presence of a series of ions (m/z 1,080 and 966) and (m/z 1,108 and 994) that represented the different fengycin homologues A and B, respectively. Fengycin homologues A and B are variants that differ at position 6 of the peptide moiety, having either Ala or Val residues, respectively. Mass spectrometry analyses identified four fengycin A and three fengycin B variants with fatty acid components containing 14–17 carbons. These results demonstrate that raw glycerol can be used as feedstock to produce fengycin, and additional work should focus on the optimization of process conditions to increase productivity.

Structural and morphological investigations of β-cyclodextrin-coated silver nanoparticles.

This paper describes the synthesis of silver nanoparticles using an aqueous silver nitrate solution in the presence of glucose as a reducing agent, sodium hydroxide as a reaction catalyst and β-CD as a stabilizer. The structure and the morphology associated to the stabilizing layer around the silver nanoparticles were investigated. Raman spectroscopy confirmed the nanoparticle surface modification by β-CD, demonstrating the interaction between the β-CD rim hydroxyl groups and the AgNP surface. Transmission electron microscopy images showed an average 28.0nm diameter pseudo-spherical nanoparticles. Apart from this, a novel characterization of the β-CD layer surrounding the nanoparticles was carried out by using complementary analytical electron microscopy based on electron spectroscopy imaging in the transmission microscope. Mapping images revealed the presence of carbon and oxygen, demonstrating the existence of a uniform and interacting β-CD layer covering the nanoparticles. The antibacterial activity was also investigated and the β-CD-coated silver nanoparticles showed a promising bactericidal activity against the microorganism Escherichia coli.

Cellulose acetate membrane embedded with graphene oxide-silver nanocomposites and its ability to suppress microbial proliferation

Abstract Bacterial adhesion and consequent biofilm formation are one the biggest hurdles in membrane-based technologies. Due to numerous problems associated with bacterial colonization on membrane surfaces, the development of new approaches to prevent microbial growth has been encouraged. Graphene oxide, produced by the chemical exfoliation of graphite, is a highly water-dispersible nanomaterial which has been used as a platform for the anchoring of nanoparticles and bioactive molecules. In this present study, we propose the fabrication of antimicrobial membranes through the incorporation of graphene oxide-silver nanocomposites into a cellulose acetate polymeric matrix. Transmission electron microscopy, Raman, and UV–visible diffuse reflectance spectroscopy measurements confirmed the presence of graphene oxide-silver sheets in the modified membranes. In comparison to pristine membranes, membranes containing graphene oxide-silver nanocomposites showed larger surface pores and increased pure water flux. In addition, membranes embedded with graphene oxide-silver presented strong antibacterial activity, being able to inactivate adhered bacteria at a rate of 90% compared to pristine cellulose acetate membranes. Our results strongly suggest that the incorporation of graphene oxide-silver nanocomposites to cellulose acetate is a promising strategy to produce membranes that are able to minimize bacterial attachment and growth.Graphical Abstract

Toxicity of Nanomaterials to Microorganisms: Mechanisms, Methods, and New Perspectives

In the last few years, several nanomaterials with unique physicochemical properties have been developing. Specially, nano-sized materials such as silver and zinc nanoparticles, carbon nanotubes, and graphene oxide have been attracting great attention due to their potential as novel antimicrobial agents. Worldwide, the constant and indiscriminate use of conventional antibiotics has been responsible for the development of several resistant microbial species. In this context, there is a real and increasing demand for new antimicrobial agents. Nanomaterials offer several benefits due to their small size (high aspect volume/area) that provides to nanoparticles great ability to get through physical barriers such as membranes and cellular walls. Henceforth, the aim of this present chapter is to discuss the toxicological aspects of nanomaterials to microorganisms, describing the methods to evaluate their antimicrobial activity and highlighting their implications on the microbial communities of soil and water environments. We also stress the main industrial applications of antimicrobial-engineered nanomaterials.