Silver-nanoparticle-modified nanocellulose synthesized by pyroligneous acid: cytotoxicity towards HaCat cells.

In the present study, pyroligneous acid, also known as wood vinegar, has been employed as reducing and stabilizing agent in the synthesis of silver nanoparticles (AgNPs) anchored on nanocellulose (NC). The idea is to confer the latter bactericidal properties for its typical uses such as in cosmetics and food-packing. It has been demonstrated that AgNPs can be directly produced onto NC in one-pot fashion while dramatically enhancing the kinetics of AgNPs synthesis (2 h for reaction completion) in comparison to the NC-less counterpart (10 days for reaction completion). Furthermore, NC allowed for a narrower size distribution of AgNPs. NC-supported and non-supported AgNPs had sizes of 5.1 ± 1.6 nm and 16.7 ± 4.62 nm, respectively. Immortalized human keratinocytes (HaCat) cells were then employed as model to evaluate the cytotoxicity of the AgNPs-NC compound. The latter was found not to impact cell proliferation at any formulation, while decreasing the viability by only 6.8% after 72 h. This study contributes to the development of more environmentally benign routes to produce nanomaterials and to the understanding of their impact on cells.

Pyroligneous acid and antibacterial activity: criticism of a paper by Araújo et al. (2018).

AIMS: A paper by Araújo et al. (2018) claims that a variety of compounds present in pyroligneous acid (guaiacol, phenols and furfural) are responsible for the observed antimicrobial activity. We show, on the other hand, that the low pH due to acetic acid present in pyroligneous acid is the real cause of the activity. METHODS AND RESULTS: Pyroligneous acid (PA) was synthesized according to a previous method (Medeiros et al. 2019) with its inhibition activity tested on Escherichia coli and Staphylococcus aureus via the agar diffusion method. The activity of acetic acid at different concentrations was also evaluated for comparison. As expected, crude PA (pH 3.0) and acetic acid produced inhibition halos whose diameters varied according to their employed concentration. However, any PA inhibitory activity completely vanished upon neutralization (pH 7.0), a behaviour also observed for neutralized acetic acid. CONCLUSIONS: The claim that guaiacol, phenols and furfural are responsible for any inhibitory activity is unsubstantiated. The authors should have neutralized the pyroligneous acid if any activity was to be discovered. SIGNIFICANCE AND IMPACT OF STUDY: To increase awareness that interfering species may play a detrimental role on the interpretation of results. In this case, the action of acetic acid is vastly more important for the inhibitory activity than any other compound present in PA.

Processing of nanomaterials in Layer-by-Layer films: Potential applications in (bio)sensing and energy storage.

Abstract: The study and preparation of new nanostructures involving the integration of distinct nanomaterials have been important for the development of new electrochemical devices for (bio)sensing and energy storage. Such devices envisage miniaturized or flexible electronic equipment for emerging technologies, including adaptive displays, artificial skin and wearable devices. In this way, the processing of specific nanomaterials may lead to nanostructures with properties that permit the fabrication of multifunctional devices for different applications, including sensors and supercapacitors. Therefore, the use of a suitable method to manipulate nanomaterials in a same nanostructure is important for this purpose. Thus, we expect that this review provides the readers with a brief overview of the potential usage of the Layer-by-Layer technique to fabricate nanostructured films and their advantages for sensing and energy storage.

New insights into the formation mechanism of Ag, Au and AgAu nanoparticles in aqueous alkaline media: alkoxides from alcohols, aldehydes and ketones as universal reducing agents.

In this report we present new insights into the formation mechanism of Ag, Au and AgAu nanoparticles with alcohols, aldehydes and ketones in alkaline medium at room temperature. We selected methanol, ethanol, glycerol, formaldehyde, acetaldehyde and acetone to demonstrate their capability of reducing gold and silver ions under the above-mentioned conditions. We showed that the particles are also formed with potassium tert-butoxide in the absence of hydroxides. Our results strongly suggest that alkoxides, formed from any molecule containing a hydroxyl or a functional group capable of generating them in alkaline medium, are the actual and universal reducing agent of silver and gold ions, in opposition to the currently accepted mechanisms. The universality of the reaction mechanism proposed in this work may impact on the production of noble nanoparticles with simple chemicals normally found in standard laboratories.

Dendrimer-carbon nanotube layer-by-layer film as an efficient host matrix for electrogeneration of PtCo electrocatalysts.

In this paper we demonstrate that layer-by-layer (LbL) films of polyamidoamine (PAMAM) dendrimers and single-walled carbon nanotubes (SWCNTs) are efficient for controlling the morphology of electrogenerated cobalt (Co) and the platinum-cobalt (PtCo) alloy. While Co grew to the micrometer scale and poorly covered the ITO substrate, with the LbL matrix it was kept in the nanoscale regime and provided full substrate coverage. Pt-decorated Co nanoparticles were then generated by applying a single potential pulse in a solution containing simultaneously Co and Pt ions. Segregation of Pt and Co deposits was observed in field emission gun (FEG) images, but the PtCo alloy was probably formed to some extent according to X-ray diffraction analysis. The PtCo-LbL hybrid exhibited superior catalytic activity toward H2O2 reduction compared to the Pt-modified LbL film, which opens new prospects for applications in biosensing and fuel cells.

Glycerol electro-oxidation over glassy-carbon-supported Au nanoparticles: direct influence of the carbon support on the electrode catalytic activity.

Glycerol is at present abundantly co-produced in the biodiesel fabrication and can be used as fuel in Direct Glycerol Fuel Cells (DGFC) for cogeneration of electricity, value-added chemicals and heat. With this motivation, in the present work, we investigated at a fundamental level the oxidation of glycerol over glassy carbon (GC) supported Au nanoparticles in alkaline medium using cyclic voltammetry. By controlling the Au deposition time, we varied the GC supported Au coverage from 0.4% to 30% maintaining a regular particle size distribution with a mean particle size of about 200 nm. An influence of the carbon support on the activity of the GC-supported Au nanoparticles was evidenced. Results from studies on the oxidation of glycerol and ethylene glycol on Au and Pt nanoparticles supported on a glassy carbon, highly ordered pyrolytic graphite and dimensionally stable anode under different pH conditions indicate that the carbon support participates actively in the oxidation of glycerol and other alcohols. We propose that active oxygenated species are gradually formed on the glassy carbon by potential cycling (up to the saturation of the carbon area) and these oxygenated species are additional oxygen suppliers for the oxidation of glycerol residues adsorbed on the Au particles, following a mechanism consisting of the synergism of two active elements: gold and carbon.

Electrogeneration of platinum nanoparticles in a matrix of dendrimer-carbon nanotubes.

Hybrid materials with enhanced properties can now be obtained by combining nanomaterials such as carbon nanotubes and metallic nanoparticles, where the main challenge is to control fabrication conditions. In this study, we demonstrate that platinum nanoparticles (PtNps) can be electrogenerated within layer-by-layer (LbL) films of polyamidoamine (PAMAM) dendrimers and single-walled carbon nanotubes (SWCNTs), which serve as stabilizing matrices. The advantages of the possible control through electrogeneration were demonstrated with a homogeneous distribution of PtNps over the entire surface of the PAMAM/SWCNT LbL films, whose electroactive sites could be mapped using magnetic force microscopy. The Pt-containing films were used as catalysts for hydrogen peroxide reduction, with a decrease in the reduction potential of 60 mV compared to a Pt film deposited onto bare ITO. By analyzing the mechanisms responsible for hydrogen peroxide reduction, we ascribed the enhanced catalytic activity to synergistic effects between platinum and carbon in the LbL films, which are promising for sensing and fuel cell applications.

Electrodeposition of catalytic and magnetic gold nanoparticles on dendrimer-carbon nanotube layer-by-layer films.

Magnetic and catalytic gold nanoparticles were electrodeposited through potential pulse on dendrimer-carbon nanotube layer-by-layer (LbL) films. A plasmon absorption band at about 550 nm revealed the presence of nanoscale gold in the film. The location of the Au nanoparticles in the film was clearly observed by selecting the magnetic force microscopy mode. To our knowledge, this is the first report on the electrochemical synthesis of magnetic Au nanoparticles. In addition to the magnetic properties, the Au nanoparticles also exhibited high catalytic activity towards ethanol and glycerol oxidation in alkaline medium.

Dual action of pyroligneous acid in the eco-friendly synthesis of bactericidal silver nanoparticles.

In the present study, we demonstrate that pyroligneous acid (PA), also known as wood vinegar, functions efficiently as both reducing and stabilizing agent in the synthesis of silver nanoparticles (AgNPs). The synthesis and stabilization of AgNPs take place in the following fashion: 1) in alkaline environment, oxygenated species (phenols in the present case) contained in PA reduce silver ions to metallic silver; 2) acetic acid, abundantly present in PA, adsorb onto the AgNPs conferring electrostatic stabilization. This mechanism is supported by GC-MS and RAMAN analysis, with the former revealing the compounds lacking in PA after nanoparticle synthesis and the latter demonstrating acetic acid adsorbed on the nanoparticles. The AgNPs produced via this method were quite stable up to 150 days (zeta potential = -56 mV). The AgNPs were then found to inhibit the growth of Escherichia coli and Staphylococcus aureus. Concerning PA, we showed that it displays bactericidal properties only under acidic conditions. This study contributes to the development of more environmentally benign routes to produce nanomaterials.

Retarding mechanism of Zn2+ species in geopolymer material using Raman spectroscopy and DFT calculations.

Geopolymers are the most promising alternative to Ordinary Portland Cement for oil-well cementing and well abandonment. To that end, the slurry needs a required pumping time ensured by the addition of retarders. Although zinc has been widely known to prolong the setting time of geopolymers, its mechanism of action has yet to be fully elucidated. It is herein hypothesized that zinc ions impede the first stages of silicate oligomerization (Si-O-Al), culminating in longer setting times. Pumping time measurements showed that Zn(NO3)2 delayed the setting time by 5 h in comparison to the zinc-less sample. DFT calculations revealed Si(OH)4 to react with [Zn(OH)4]2- via a barrierless transition state, evidencing a kinetic ground for the retardation effect. Additionally, Raman spectroscopy corroborated the DFT results by showing that Q3 species in the proposed mechanism are formed more rapidly in the presence of zinc ions than in its absence.

Biospectroscopy and chemometrics as an analytical tool for comparing the antibacterial mechanism of silver nanoparticles with popular antibiotics against Escherichia coli.

Despite the fact that silver nanoparticles (AgNPs) have been widely studied in medical and correlated fields, details on their mechanisms are yet to be fully understood. Herein we present the first study on the combination of infrared spectroscopy and chemometrics as an analytical tool to investigate the mechanism of action of AgNPs against Escherichia coli by comparison with popular and commercially available antibiotics. The rationale behind this study is that the selected antibiotics act on bacteria in specific and distinct manners (DNA, cell membrane, mitochondria, etc.). Hence, via multivariate analysis we were able to compare the spectra of bacteria treated with the antibiotics and AgNPs to determine the main target of the latter. Spectral comparison, exploratory analysis, clustering and classification based on infrared spectra were carried out for E. coli samples in the absence and presence (treated) of four widely known antibiotics (ampicillin, ciprofloxacin, gentamicin and sulfadiazine) as well as RA-AgNPs and ERA-AgNPs. Chemometrics models indicated an interesting similarity between infrared spectra from E. coli treated with sulfadiazine and AgNPs, in which vibrational modes associated to phosphate groups were found to be the most representative. This result suggests that both AgNPs and sulfadiazine affects DNA structural features and availability, but not necessarily through the same mechanism. This biospectroscopy-based approach opens an interesting possibility for the understanding over the mechanism of antibacterial activity of AgNPs.

Do solvation layers of ionic liquids influence electrochemical reactions?

In this discussion paper we discuss our recent results on the electrodeposition of materials and in situ STM/AFM measurements which demonstrate that ionic liquids should not be regarded as neutral solvents which all have similar properties. In particular, we focus on differences in interfacial structure (solvation layers) on metal electrodes as a function of ionic liquid species. Recent theoretical and experimental results show that conventional double layers do not form on metal electrodes in ionic liquid systems. Rather, a multilayer architecture is present, with the number of layers determined by the ionic liquid species and the properties of the surface; up to seven discrete interfacial solvent layers are present on electrode surfaces, consequently there is no simple electrochemical double layer. Both the electrodeposition of aluminium and of tantalum are strongly influenced by ionic liquids: in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]TFSA, aluminium is obtained as a nanomaterial, whereas in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]TFSA, a microcrystalline material is made. Tantalum can be deposited from [Py(1,4)]TFSA, whereas from [EMIm]TFSA only non-stoichiometric tantalum fluorides TaF(x) are obtained. It is likely that solvation layers influence these reactions.

Effect of Gold Nanoparticle on 5-Fluorouracil-Induced Experimental Oral Mucositis in Hamsters.

BACKGROUND: Oral mucositis (OM) is a severe inflammation of the oral mucosal cells associated with chemotherapy and/or radiotherapy-induced toxicity, resulting in epithelial ulcers and higher risk of death from sepsis. The aim of the present study was to evaluate the nanoparticle (AuNp) effect on OM induced in hamsters. MATERIALS AND METHODS: 5-fluorouracil (5FU) was used on the first and second day of the experimental model in Golden sirian hamsters, and on the fourth day, mechanical trauma was applied to induce OM. The animals were divided into groups, i.e., polyvinylpyrrolidone (PVP), mechanical trauma (MT), 5FU, and groups treated with gold nanoparticles (AuNps) (62.5, 125, and 250 µg/kg). On the 10th day, animals were euthanized for macroscopic, histopathological, immunohistochemical, western blot, quantitative polymerase chain reaction (qRT-PCR), and AuNp quantification. RESULTS: AuNp (250 µg/kg) reduced TNF-α, IL-1ß, COX-2, NF-κB, TGF-ß, and SMAD 2/3; increased glutathione levels; decreased the expression of Kelch ECH-associated protein 1 (KEAP1); and induced heme oxygenase 1 (HMOX-1) and NAD (P) H quinone oxidoreductase 1 (NQO1) genes. CONCLUSIONS: AuNp (250 µg/kg) prevented 5-FU-induced OM in hamsters and improved the parameters of inflammation and oxidative stress.

Rutin-modified silver nanoparticles as a chromogenic probe for the selective detection of Fe3+ in aqueous medium.

The development of nanoprobes for selective detection of metal ions in solution has attracted great attention due to their impact on living organisms. As a contribution to this field, this paper reports the synthesis of silver nanoparticles modified with rutin in the presence of ascorbic acid and their successful use as a chromogenic probe for the selective detection of Fe3+ in aqueous solution. Limits of detection and quantification were found to be 17 nmol L-1 and 56 nmol L-1, respectively. The sensing ability is proposed to proceed via an iron-induced nanoparticle growth/aggregation mechanism. A practical approach using image analysis for quantification of Fe3+ is also described.

Environmentally compatible bioconjugated gold nanoparticles as efficient contrast agents for inflammation-induced cancer imaging.

For many cancers, early detection is the key to improve survival and reduce the morbidity, which is associated with radical resections due to late diagnosis. Here, we describe the efficiency of primary antibody-conjugated gold nanoparticles (AuNPs) to specifically target chronic inflammatory processes, specially M2 macrophages, in tissue sections of ulcerative colitis (UC) and steatohepatitis in rats which may lead to colorectal cancer and liver carcinoma, respectively. In this study, we demonstrate that AuNPs synthesized by a simple, inexpensive, and environmentally compatible method can be easily conjugated with the antibodies anti-COX-2, anti-MIF, and Alexa Fluor® 488 (ALEXA) to perform immunofluorescence staining in inflamed tissues. Moreover, we showed that primary antibody-conjugated gold nanoparticles (AuNPs) can be used to target M2 macrophages by flow cytometry. We designed three immunofluorescence staining protocols of tissue section with AuNPs for 30 min and overnight incubation, as well as one flow cytometry protocol of M2 macrophage labeling with AuNPs for 30 min. Immunofluorescence and flow cytometry results suggest that conjugation was achieved by direct adsorption of antibodies on the AuNPs surface. When compared to the standard ALEXA protocol in immunofluorescence (IF) and flow cytometry (FC), our 30-min incubation protocol using AuNPs instead of ALEXA decreased from approximately 23 h to 5 h for IF and from 4 h to 1 h for FC, proving to be less laborious, which makes the method eligible for inflammation-induced cancer diagnostic.

How the interaction of PVP-stabilized Ag nanoparticles with models of cellular membranes at the air-water interface is modulated by the monolayer composition.

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.

Lipopolysaccharides and peptidoglycans modulating the interaction of Au naparticles with cell membranes models at the air-water interface.

Understanding the interactions between nanoparticles and biological surfaces is of great importance for many areas of nanomedicine and calls for detailed studies at the molecular level using simplified models of cellular membranes. In this paper, water-dispersed polyvinylpyrrolidonestabilized gold nanoparticles (AuNPs) were incorporated in floating monolayers of selected lipids at the air-water interface as cell membrane models. Surface pressure-area isotherms showed the condensation of glycoside-free lipid monolayers, suggesting their adsorption on the nanoparticle surface through the hydrophilic head groups. On the other hand, monolayers containing glycoside derivatives expanded upon AuNPs incorporation, pointing that the supramolecular structure formed should facilitate the incorporation of these nanoparticles in cellular membranes. These findings can be therefore correlated with the possible toxicity, microbicide and antitumorigenic effects of these nanoparticles in lipidic surfaces of erythrocyte and microbial membranes.

On the synergy between silver nanoparticles and doxycycline towards the inhibition of Staphylococcus aureus growth.

In a previous paper (RSC Adv., 2015, 5, 66886-66893), we showed that the combination of silver nanoparticles (NanoAg) with doxycycline (DO) culminated in an increased bactericidal activity towards E. coli. Herein we further investigated the metabolic changes that occurred on Staphylococcus aureus upon exposure to NanoAg with the help of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) coupled with multivariate data analysis. It has been discovered that the combination of DO with NanoAg produced metabolic changes in S. aureus that were not simply the overlap of the treatments with DO and NanoAg separately. Our results suggest that DO and NanoAg act synergistically to impede protein synthesis by the bacteria.

Apoptosis in human liver carcinoma caused by gold nanoparticles in combination with carvedilol is mediated via modulation of MAPK/Akt/mTOR pathway and EGFR/FAAD proteins.

In cancers, apoptosis signaling pathways and cell survival and growth pathways responsible for resistance to conventional treatments, such as Pi3K/Akt/mTOR and mitogen-activated protein kinase (MAPK) become dysregulated. Recently, alternative treatments to promote tumor cell death have become important. The present study reports on the antitumor and cytoprotective action of gold nanoparticles (GNPs) and carvedilol in combination and in isolated application. Apoptosis was analyzed by FITC/propidium iodide staining flow cytometry; caspase-3, caspase-8, Bcl-2 and MAPK/ERK activity by immunofluorescence microscopy; gene expression of proteins related to cell death as Akt, mTOR, EGFR, MDR1, survivin, FADD and Apaf, by the real-time PCR; and western blot analysis for MAPK/ERK, Akt and mTOR. Oxidative stress evaluation was performed by reduced glutathione (GSH) and malondialdehyde (MDA) levels. Intracellular GNPs targets were identified by transmission electron microscopy. After exposure to a combination of GNPs (6.25 µg/ml) and carvedilol (3 µM), death as promoted by apoptosis was detected using flow cytometry, for expression of pro-apoptotic proteins FADD, caspase-3, caspase-8 and sub-regulation of anti-apoptotic MAPK/ERK, Akt, mTOR, EGFR and MDR1 resistance. Non-tumor cell cytoprotection with GSH elevation and MDA reduction levels was detected. GNPs were identified within the cell near to the nucleus when combined with carvedilol. The combination of GNP and carvedilol promoted downregulation of anti-apoptotic and drug resistance genes, over-regulation of pro-apoptotic proteins in tumor cells, as well as cytoprotection of non-tumor cells with reduction of apoptosis and oxidative stress.

Spherical neutral gold nanoparticles improve anti-inflammatory response, oxidative stress and fibrosis in alcohol-methamphetamine-induced liver injury in rats.

This study aimed to elucidate the anti-inflammatory, anti-oxidant and antifibrotic effects of gold nanoparticles (GNPs) in rats subjected to liver injury with ethanol and Methamphetamine (METH). The liver injury was induced by gavage administrations of 30% alcoholic solution (7 g/kg) once a day during 28 days, followed by METH (10 mg/kg) on the 20th and 28th days of treatment. GNPs treatment (724.96 µg/kg) during the ethanol and METH exposure was associated with reduced steatosis, hepatic cord degeneration, fibrosis and necrosis. Furthermore, there was a reduction in biochemical markers of liver damage and oxidative stress, and pro-inflammatory cytokines IL-1ß and TNF-α, compared to ethanol + METH group alone. A decrease of FGF, SOD-1 and GPx-1 expression was also observed. GNPs down-regulated the activity of Kupffer cells and hepatic stellate cells affecting the profile of their pro-inflammatory cytokines, oxidative stress and fibrosis through modulation of signaling pathways AKT/PI3K and MAPK in ethanol + METH-induced liver injury in a rat model.