Silver Species Research Articles

Influence of silver nanoparticles on the enhancement and transcriptional changes of glucosinolates and phenolic compounds in genetically transformed root cultures of Brassica rapa ssp. rapa.

Glucosinolates (GSLs) and phenolic compounds (PCs) are biologically active and involved in the defense reaction of plants; these compounds have a beneficial effect on human health. In this study, we described the influence of biologically synthesized silver nanoparticles (Ag NPs) to enhance the phytochemicals (GSLs and PCs), their transcription levels, and their biological activities in genetically transformed root cultures (hairy root cultures) of Brassica rapa. The concentrations of silver and reactive oxygen species (malondialdehyde and hydrogen peroxide) were highly elevated in the Ag NP-elicited hairy roots (HRs). Glucosinolates (glucoallysin, glucobrassicanapin, sinigrin, progoitrin, gluconapin, 4-methoxyglucobrassicin, 4-hydroxyglucobrassicin, glucobrassicin, neoglucobrassicin, and gluconasturtiin) and their transcripts (MYB34, MYB51, MYB28, and MYB29) were significantly enhanced in the Ag NP-elicited HRs. Moreover, the phenolic compounds (flavonols, hydroxybenzoic, and hydroxycinnamic acids) were significantly enriched in the Ag NP-elicited HRs. Total phenolic and flavonoid concentrations and their transcripts (PAL, CHI, and FLS) were higher in the Ag NP-elicited HRs than in the non-elicited HRs. Additionally, biological (antioxidant, antimicrobial, and anticancer) activities were significantly higher in the Ag NP-elicited HRs than in the non-elicited HRs. The Ag NP-elicited HR cultures offered an efficient and promising in vitro method to increase the production of health-promoting bioactive compounds, which may be useful in nutraceutical and pharmaceutical industries.

Novel Covalent Triazine Framework for High-Performance CO2 Capture and Alkyne Carboxylation Reaction.

Carbon dioxide capture and conversion have attracted extreme enthusiasm from the scientific community owing to global warming and environmental problems. However, conversion of CO2 under atmospheric pressure is of great challenge because of the inertness of CO2. Herein, we present a novel covalent triazine framework (CTF-DCE) prepared via ZnCl2-catalyzed ionothermal trimerization reaction of di(4-cyanophenyl)ethyne, which displays a high Brunauer-Emmett-Teller surface area of 1355 m2 g-1 and an excellent CO2 capture capacity of 191 mg/g at 273 K/1 bar. More importantly, silver species can be successfully fixed on the CTF matrix to produce a stable CTF-DCE-Ag heterogeneous catalyst for outstanding catalysis in the terminal alkyne carboxylation reactions under atmospheric pressure. CTF-DCE-Ag exhibited over sixfold higher turnover numbers than Ag@MIL-101. The recyclability test of the CTF-DCE-Ag catalyst demonstrated a great potential application in various environmental and energy-related applications.

Thermally stable Ag/Al2O3 confined catalysts with high diffusion-induced oxidation activity

Developing catalysts with high cost-efficiency, good oxidation activities and strong thermal resistance is an ongoing task. Herein, we present the design and synthesis of confined catalysts with Ag protected by alumina. Thermal treatment at 800 °C for 10 h caused neither silver loss nor deactivation of this catalyst. Instead, nano-particles of Ag formed because of the heat/O2-derived ripening. These highly dispersed silver species and the catalyst’s mesoporous structure worked in tandem to achieve good catalytic performance for oxidation reactions, which made the aged sample a good candidate as CO elimination and gasoline particulate filter catalysts.

Antimicrobial potency of differently coated 10 and 50 nm silver nanoparticles against clinically relevant bacteria Escherichia coli and Staphylococcus aureus.

Silver nanoparticles (nanoAg) are effective antimicrobials and promising alternatives to traditional antibiotics. This study aimed at evaluating potency of different nanoAg against healthcare infections associated bacteria: Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. A library of differently coated nanoAg of two different sizes (10 and 50 nm) were prepared using coating agents poly-L-Lysine (PLL), cetyltrimethyl-ammonium bromide (CTAB), citrate (CIT), polyvinyl-pyrrolidone (PVP), polysorbate 80 (Tween 80), and dioctyl-sodium sulfosuccinate (AOT). Stability evaluation by means of agglomeration and dissolution behaviour was performed for all nanoAg under conditions relevant for this study. Antibacterial properties of nanoAg were addressed by determining their minimal bactericidal concentrations (MBC) in deionised (DI) water to minimise the influence of silver speciation on its bioavailability. In parallel, AgNO3 was analysed as an ionic control. Studied nanoAg were efficient antimicrobials being remarkably more potent towards E. coli than to S. aureus (4 h MBC values for different nanoAg ranged from 0.08 to 5.0 mg Ag/L and 1.0-10 mg Ag/L, respectively). The toxicity of all nanoAg to S. aureus (but not to E. coli) increased with exposure time (4 h vs 24 h). 10 nm sized nanoAg released more Ag-ions and were more toxic than 50 nm nanoAg. Coating-dependent toxicity was more prominent for 50 nm nanoAg coated with Tween 80 or CTAB rendering the least toxic nanoAg. Obtained results showed that the antimicrobial effects of nanoAg were driven by shed Ag-ions, depended on target bacteria, exposure time and were the interplay of NP size, solubility and surface coating.

Impact of chlorination on silver elution from ceramic water filters

Applying silver nanoparticles (nAg) or silver nitrate (AgNO3) to ceramic water filters improves microbiological efficacy, reduces biofilm formation, and protects stored water from recontamination. A challenge in ceramic filter production is adding sufficient silver to achieve these goals without exceeding the maximum recommended silver concentration in drinking water. Silver release is affected by silver type, application method, and influent water chemistry. Despite a lack of data, there is an assumption that chlorinated water should not be used as influent water because it may increase silver elution. Thus, the objective of this work was to systematically evaluate the impact of chlorinated water (0–4 mg/L free chlorine residual, FCR) on silver release from ceramic filter disks painted with casein-coated nAg, painted with AgNO3, or containing fired-in nAg over a range of ionic strength (IS = 0–10 mM as NaNO3) in the presence or absence of natural organic matter (NOM). Influent deionized water containing chlorine increased silver release 2–5-fold compared to controls. However, this effect of chlorine was mitigated at higher IS (≥1 mM) or in the presence of NOM (3 mg C/L). For filter disks painted with nAg or AgNO3, silver release increased with increasing IS (with or without chlorine), and effluent concentrations remained above the World Health Organization (WHO) guideline of 0.1 mg/L even after 30 h (80 pore volumes, PVs) of flow with a background solution of 10 mM NaNO3. Silver speciation (nAg vs. Ag+) was monitored in effluent samples from painted or fired-in nAg filter disks. Results indicated that in general, greater than 90% of the eluted silver was due to Ag+ dissolution rather than nAg release. Additionally, a filter disk prepared with fired-in nAg exhibited a lower % released in the nanoparticle form (nAg = 5% of total Ag in effluent) compared to painted on nAg (nAg = 14% of total Ag in effluent). The findings of this study suggest that chlorinated influent water has minimal impact on silver elution from ceramic filters under simulated natural water conditions, and thus, the recommendation to avoid the use of chlorinated water with ceramic filters is not necessary under most conditions.

Ag/SiOx nanocomposite powders synthesized from colloids obtained by pulsed laser ablation

Ag/SiOx nanopowders were obtained from Ag and Si/SiO2 colloids synthesized via pulsed laser ablation in water. The resulting composite powder was annealed at different temperatures in the region of 100–900 °C. The composition and structure of the obtained materials were studied. The interaction between silica and silver species taking place during composite formation was investigated. A stabilization of Ag nanoparticles in mixed colloids due to their interaction with soluble silicon oxide compounds was found. It was also revealed that the contact between silver and Si/SiO2 particles resulted in the decrease of the temperature at which the formation of additional oxygen-deficient centres occurs in the silica structure. New types of defects, namely 3-membered cycles and non-bridging oxygen groups, appeared as a result of Ag and Si/SiO2 surface interaction at 700 °C. Thus, silver nanoparticles facilitated the formation of defects in the structure of SiO2.

Anodic film growth and silver enrichment during anodizing of an Mg-0.6 at.% Ag alloy in fluoride-containing organic electrolytes

Binary Mg-Ag alloys are of interest as antibacterial biodegradable materials. In the present work, the behaviour of silver during galvanostatic anodizing of a sputtering-deposited Mg-0.6 at.% Ag alloy in a fluoride/glycerol electrolyte containing 5 or 60 vol.% water was investigated. Similar alloy compositions have been shown to have potential as biomaterials in in-vitro tests. The resultant barrier-type anodic films were examined using scanning and transmission electron microscopies, glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The films were shown to be nanocrystalline and to contain oxide and fluoride species, with O:F atomic ratios dependent on the amount of water in the electrolyte. Silver species were incorporated into the films, accompanied by loss of silver species to the electrolyte. Notably, silver was enriched in a ≤6 nm thick alloy layer, to concentration of at least 12 at.%.

New insights into the formation of silver-based nanoparticles under natural and semi-natural conditions

For the first time, the natural formation of silver-based nanoparticles (Ag-b-NPs) was studied in field investigations of two pre-alpine lakes in Germany that contain geogenic silver traces in the sub-ng L−1 range. Light-sensitive microorganisms most likely accumulate and transport these silver traces from deeper water layers to the surface. At the surface of the eutrophic lake, approximately 40% of total silver (5.7 ng L−1) consisted of Ag-b-NPs, whereas in the oligotrophic lake with similar enrichment of silver species, no Ag-b-NPs were detected. Additional lab experiments with nature-related Ag(I) concentrations in the lower-ng L−1 range and natural organic matter with total organic carbon values of ≤5 mg L−1 revealed that, contrary to common interpretation in the literature, Ag-b-NPs are also or even preferably formed in the dark. Particle size increases gradually with increasing reaction time, showing that Ostwald ripening occurs even at such low particle concentrations. When sulfide ions are present, smaller Ag-b-NPs with a narrower size distribution are formed.

In vitro Comparison of the Antimicrobial Efficiency of Commercially Available Silver-Wound Dressings Correlated with the Evaluation of Silver Release by Inductively Coupled Plasma–Mass Spectrometry

ABSTRACTSilver antimicrobial dressings have been extensively used as therapeutic strategies in wound management. The present study sought to asses and to compare the antimicrobial efficacy of commercially available modern silver-wound dressings. The antimicrobial activity of the silver dressings has been evaluated by the disk diffusion method, including five common wound pathogens. The silver-release profile has been determined using inductively coupled plasma–mass spectrometry. The results demonstrated different degrees of efficacy against the tested pathogens. Silver is released at different rates, within a very large range, depending on delivery medium test, but we could not establish a correlation between the silver content/silver-release profile and the antimicrobial activity of the evaluated dressings. Different factors such as the structural properties of support materials or the type of silver species contained may influence the effectiveness of silver dressings. The obtained results suggest that silver-based dressings act by a combination of antimicrobial activity and fluid handling properties and their overall characteristics should be taken into consideration.

Functional Ag‐Exchanged Zeolites as Biocide Agents

AbstractMaterials based on silver are used for controlling different pathogenic microorganisms. However, the influence of the silver carrier in the biocidal activity of the material has been scarcely reported. The present research is focused on studying the influence of zeolite properties on the biocidal activity of silver‐exchanged zeolites, acting as reservoirs of silver species. The biocidal action of Ag‐Faujasite (Ag‐FAU) and Ag‐Linde Type A (Ag‐LTA) zeolites, containing different silver contents, is studied against different types of bacteria and fungi. Importantly, zeolite structure is found to be a significant parameter for controlling the antibacterial activity of Ag‐exchanged zeolites. The results show that Ag‐FAU presents a higher activity than Ag‐LTA, because the topology of FAU combined with its highest Si/Al ratio favors the formation and release of silver species with important biocidal activity. Some insights on the bactericidal mechanism of Ag‐zeolites are envisaged by means of high resolution transmission electron microscopy, showing the multi‐targeted biocidal action of Ag species released from zeolites. Besides, it is shown that Ag‐zeolites are more active against bacteria than fungi. Antifungal activity is highly dependent on the fungi species and the structure of the zeolite is not as determinant as it is for the antibacterial activity.

A Nanocomposite Hydrogel with Potent and Broad-Spectrum Antibacterial Activity.

Local bacterial infection is a challenging task and still remains a serious threat to human health in clinics. Systemic administration of antibiotics has only short-term antibacterial activity and usually causes adverse effects and bacterial resistance. A bioadhesive hydrogel with broad-spectrum and on-demand antibiotic activity is highly desirable. Here, we designed a pH-responsive nanocomposite hydrogel via a Schiff base linkage between oxidized polysaccharides and cationic dendrimers encapsulated with silver nanoparticles. The antibacterial components, both the cationic dendrimers and silver species, could be released in response to the acidity generated by growing bacteria. The released cationic polymer and silver exhibited a synergistic effect in antibacterial activity, and thus, the nanocomposite hydrogel showed potent antibacterial activity against both Gram-negative ( Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria ( Staphylococcus epidermidis and Staphylococcus aureus). The gel showed superior in vivo antibacterial efficacy against S. aureus infection compared with a commercial silver hydrogel at the same silver concentration. In addition, no obvious hemolytic toxicity, cytotoxicity, and tissue and biochemical toxicity were observed for the antibacterial hydrogel after incubation with cells or implantation. This study provides a facile and promising strategy to develop smart hydrogels to treat local bacterial infections.

Humic acid attenuation of silver nanoparticle toxicity by ion complexation and the formation of a Ag3+ coating

The use of silver nanoparticles (AgNPs) result in an inevitable contact with aquatic environments. Here we study the behavior of AgNPs and the developmental toxicity in zebrafish embryos exposed to these nanoparticles (0–10 mg/L) with and without the presence of HA (20 mg/L), using zebrafish facility water (ZFW) and zebrafish growing media (ZGM). The presence of cations and HA gave rise to a decrease in Ag ion release and ζ-potential, an increase in the hydrodynamic diameter and oxidation of the AgNP surface. The results show that the presence of HA and cations in the media, as well as the silver speciation, i.e., the unusual presence of Ag3+, decreases the toxicity of AgNPs (LC50AgNPs: 1.19 mg/L; LC50AgNPs + HA: 3.56 mg/L), as well as silver bioavailability and toxicity in zebrafish embryos. Developmental alterations and the LC50 (1.19 mg/L) of AgNPs in ZFW were more relevant (p ≤ 0.05) than for AgNPs in ZGM (LC50 ˃ 10 mg/L). It was demonstrated that the bioaccumulation and toxicity of AgNPs depends on several factors including AgNPs concentration, nanoparticle aggregation, dissolved silver ions, speciation of silver ions, the amount of salt in the environment, the presence of humic substances and others, and different combinations of all of these factors.

Formation and Properties of Poly(Ionic Liquid)-Carbene Nanogels Containing Individually Stabilized Silver Species.

Imidazolium-based ionic liquids have the ability to undergo a variety of chemical reactions through an N-heterocyclic carbene (NHC) intermediate, which has expanded the chemical toolbox for new applications. Despite their uses and exploration, the carbene-forming properties and applications of their polymeric congeners, poly(ionic liquid)s (PILs), is still underdeveloped. Herein, we explore the NHC-forming properties of a theophylline-derived PIL for nanogel synthesis. Using silver oxide as both the carbene-forming reagent and cross-linker, nanogels containing individually stabilized ions can be created with different sizes and morphology, including large "galaxy-like" superstructures. Using high-resolution TEM techniques, we directly observed the sub-nanometer structure of these constructs. These features combined exemplify the unique chemistry of poly-NHCs for single-metal-ion-stabilization nanogel design.

Ag-Cu based catalysts for the selective ammonia oxidation into nitrogen and water vapour

XRD, BET, H2-TPR, UV–vis-DRS, XPS and XAFS were used to characterize a series of Ag and/or Cu – Ag (1–5%), Cu (10–15%) or Ag-Cu (1–1, 1–10, 1.5–10, 5–5% of metal) – supported on γ-Al2O3. Correlation between physicochemical properties, catalytic activity and selectivity in NH3-SCO were thoroughly investigated. Silver species mainly in the form of Ag2O on the Ag/Al2O3 catalysts led to enhanced activity together with drop in N2 selectivity with increasing silver loading up to 5%. A mixture of CuO and CuAl2O4 formed on the Cu/Al2O3 catalysts. Easily reducible highly dispersed CuOx promoted the activity of the catalysts, while bulk CuOx and CuAl2O4 decreased N2 selectivity up to 500 °C. The activity of all Cu-containing materials was inferior to Ag-containing ones. Thus, the gap between the high conversion temperature over Cu/Al2O3 and low N2 selectivity over Ag/Al2O3 was bridged by applying the Ag-Cu/Al2O3 catalysts, with the optimum loading of 1.5 and 10 wt.% for silver and copper, respectively. NH3-TPD, NH3-TPSR and in situ FTIR were used to determine the in situ selective catalytic reduction (i-SCR) mechanism over 1.5% Ag/Al2O3, 10% Cu/Al2O3 and 1.5% Ag-10% Cu/Al2O3 respectively. The i-SCR mechanism involved the partial oxidation of NH3 into NOx species, along with adsorbed NOx species interacting with adsorbed ammonia (NHx species) and being reduced to reaction products.

Changes in bimetallic silver – platinum catalysts during activation and oxidation of methanol and propene

A series of bimetallic silver-platinum catalysts based on pure-silica mesostructured cellular foam (MCF) with various Ag/Pt atomic ratios were prepared, tested in methanol oxidation and propene oxidation and characterized by UV–vis spectroscopy, X-Ray Diffraction (XRD), X-ray Absorption Spectroscopy (XAS) and Transmission Electron Microscopy (TEM). Bimetallic catalysts were not more active than monometallic ones in propene oxidation but their selectivity to acrolein was significantly higher, especially over 4AgPt/M activated in inert gas. This catalyst showed also high activity and selectivity to methyl formate in methanol oxidation. Upon activation of the catalysts in different environments and oxidation reactions, the reduction of silver oxide and segregation of bimetallic nanoparticles took place. This effect was the highest upon activation in hydrogen flow and was responsible for exposition of metallic platinum leading to high conversion of substrates (methanol or propene) and their total oxidation. Segregation of bimetallic species and increasing dispersion after activation and exposition of the activated samples to the reagents (propene, methanol, oxygen) were consequences of the mobility of silver species and their susceptibility to change the oxidation state.

Improvement in the corrosion protection and bactericidal properties of AZ91D magnesium alloy coated with a microstructured polypyrrole film

Abstract In this work hollow rectangular microtubes of polypyrrole (PPy) films were potentiostatically electrodeposited on magnesium alloy AZ91D in salicylate solution. The substrate was previously anodized under potentiostatic conditions in a molybdate solution in order to improve the adherence of polymer. Finally the duplex film was modified by the incorporation of silver species. The obtained coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopies (XPS) and the antimicrobial activity against the bacteria Escherichia coli was evaluated. The corrosion protection properties of the coatings were examined in Ringer solution by monitoring the open circuit potential, polarization techniques and electrochemical spectroscopy (EIS). The duplex coating presents an improved anticorrosive performance with respect to the PPy film. The best results concerning corrosion protection and antibacterial activity were obtained for the silver-modified composite coating.

Characterization and photocatalytic activity of new photocatalysts based on Ag, F-modified ZnO nanoparticles prepared by thermal shock method

Ag-modified ZnO, F-modified ZnO and (Ag, F)-modified ZnO nanoparticles were prepared by thermal shock method in order to study the effects of doping agents on their crystal structure, morphology, optical properties, surface structure and photocatalytic activity. The catalysts were characterized by XRD, FE-SEM, TEM, FTIR, UV–Visible diffuse reflectance and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA and visible light irradiation. According to the results, the thermal shock process with AgNO3 did not modify the morphology but successfully created silver species on the surface of ZnO, which induces the visible light absorption and then increases the photocatalytic activity. The enhanced phototcatalytic performance was also observed in F-modified ZnO sample owing to the increase of surface hydroxyl groups and the formation of zinc vacancies. Among three modified ZnO samples, (Ag, F)-modified ZnO was found to be the best sample with the photocatalytic activity enhanced by the factor of 3 under both UVA and visible light, which may be attributed to the synergic effects of AgNO3 and KF used in thermal shock process.

Comparative proteomic analysis of hepatic effects induced by nanosilver, silver ions and nanoparticle coating in rats

The presence of nano-scaled particles in food and food-related products has drawn attention to the oral uptake of nanoparticles and their interactions with biological systems. In the present study, we used a toxicoproteomics approach to allow for the untargeted experimental identification and comparative analysis of cellular responses in rat liver after repeated-dose treatment with silver nanoparticles, ions, and the coating matrix used for particle stabilization.The proteomic analysis revealed treatment-related effects caused by exposure to silver in particulate and ionic form. Both silver species induced similar patterns of signaling and metabolic alterations. Silver-induced cellular alterations comprised, amongst others, proteins involved in metal homeostasis, oxidative stress response, and energy metabolism. However, we discovered that secondary nano-scaled structures were formed from ionic silver. Furthermore, also the coating matrix alone gave rise to the formation of nano-scaled particles.The present data confirm, complement, and extend previous knowledge on silver toxicity in rodent liver by providing a comprehensive proteomic data set. The observation of secondary particle formation from non-particle controls underlines the difficulties in separating particle-, ion-, and matrix coating-related effects in biological systems. Awareness of this issue will support proper evaluation of nanotoxicology-related data in the future.

Thermal and photo-thermal PROX reaction over Ag/SiO2 catalysts

The effect of plasmonic excitation of Ag/SiO2 catalysts was studied in the preferential CO oxidation in presence of H2 (PROX) at low temperature. Catalysts with 5 wt% silver loading were prepared by wet impregnation in aqueous and basic media. TEM analysis indicates the presence of Ag nanoparticles with a broad particle size distribution which can achieve both, good PROX activity at low temperature and plasmonic interaction with visible light. Photo-assisted reaction at 35 °C enhance CO and O2 conversions; however, the greater improvement was found for O2 conversion. The selectivity towards CO2 decrease when reaction took place under photo-thermal conditions. Occurrence of different silver species and particle size changed after reaction as evidenced by DRS-UV–vis and TEM.

Structural and spectroscopic properties of Eu3+ doped tellurite glass containing silver nanoparticles

The growth of large silver nanoparticles in a tellurite glass of basic composition 70TeO2, 10Nb2O5, 20ZnO and doped with Eu3+ ions was evidenced by XRD and TEM measurements. Several experimental techniques were used to elucidate the nature of silver species and their effect on the luminescence of Eu3+ ions inside differently heat-treated glass samples. The analysis of the obtained results and the use of Judd-Ofelt theory have allowed us to suggest that the enhancement of Eu3+ ions is mainly due to an increase of the excitation rate of these ions induced by the local field enhancement via surface plasmon resonance (SPR) of silver nanoparticles and radiative energy transfer from small luminescent neutral silver clusters. On the other hand, the small emission quenching after long annealing time was attributed to back energy transfer from Eu3+ ions to silver species or to local field saturation.