High Concentrations Of Ag Research Articles

Route of exposure has a major impact on uptake of silver nanoparticles in Atlantic salmon (Salmo salar).

The potential impact of silver nanoparticles (Ag NPs) on aquatic organisms is to a large extent determined by their bioavailability through different routes of exposure. In the present study juvenile Atlantic salmon (Salmo salar) were exposed to different sources of radiolabeled Ag (radiolabeled 110m Ag NPs and 110m AgNO3 ). After 48 h of waterborne exposure to 3 μg/L citrate stabilized 110m Ag NPs or 110m AgNO3 , or a dietary exposure to 0.6 mg Ag/kg fish (given as citrate stabilized or uncoated 110m Ag NPs, or 110m AgNO3 ), Ag had been taken up in fish regardless of route of exposure or source of Ag (Ag NPs or AgNO3 ). Waterborne exposure led to high Ag concentrations on the gills, and dietary exposure led to high concentrations in the gastrointestinal tract. Silver distribution to the target organs was similar for both dietary and waterborne exposure, with the liver as the main target organ. The accumulation level of Ag was 2 to 3 times higher for AgNO3 than for Ag NPs when exposure was through water, whereas no significant differences were seen after dietary exposure. The transfer (Bq/g liver/g food or water) from exposure through water was 4 orders of magnitude higher than from feed using the smallest, citrate-stabilized Ag NPs (4 nm). The smallest NPs had a 5 times higher bioavailability in food compared with the larger and uncoated Ag NPs (20 nm). Despite the relatively low transfer of Ag from diet to fish, the short lifetime of Ag NPs in water and their transfer to sediment, feed, or sediment-dwelling food sources such as larvae and worms could make diet a significant long-term exposure route. Environ Toxicol Chem 2018;37:2895-2903. © 2018 SETAC.

Construction of Self-defensive Antibacterial and Osteogenic AgNPs/Gentamicin Coatings with Chitosan as Nanovalves for Controlled release

To solve the Ti implants-associated infection and poor osseointegration problems, we have constructed the AgNPs/gentamicin (Gen)-loaded silk fibroin (SF) coating with acceptable antibacterial and osteogenic aptitude. Nevertheless, due to uncontrollably sustained drug release, this bactericidal coating encountered some tricky problems, such as local high Ag concentration, short life-span and potential cytotoxicity. In this work, a chitosan (CS) barrier layer was constructed to prebuilt the SF-based film by two means, dip-coating (DCS) and spin-coating (SCS). Intriguingly, the CS barrier layer constructed by spin-coating highly improved the hydrophilic and protein-absorbed performances. As verified in the release profile, both coatings showed a prolonged and pH-dependent pattern of Ag+ with an accelerated release in acidic condition. Also, the multilayer coating with a SCS barrier layer showed an apparent bacteria-trigged antibacterial and biofilm-inhibited performances, whereas the improvements of antibacterial abilities of DCS coating were limited. The mechanisms could be explained that the pH decrease induced by the attachment and proliferation of bacteria triggered collapse of CS barrier layer, accelerating the release of bactericides. Moreover, benefitted from pH-dependent release behavior of Ag and bioactive SCS layer, functional coatings highly enhanced the initial adhesion, migration and proliferation of preosteoblast MC3T3-E1 cells, and subsequently accelerated osteoblast differentiation (alkaline phosphatase production). A relevant aspect of this work was to demonstrate the essential effect of reasonable construction of self-defensive barrier layer in achieving the balance between the high-efficiency bacterial killing and osteogenic activity, and highlighted its excellent potential in clinical applications.

Surface Typochemistry of Native Gold

Using the methods of electron spectroscopy of the surface and SEM–EDS, it is shown that native gold of the deposit related to the epithermal Au–Ag ore formation contains oxidized gold with an oxidation degree of Au (I) or higher on the surface. A thin layer (~15 nm) with high concentrations of Ag and S and an underlying SiO2-bearing layer with a thickness of ~30–60 nm play a protective role providing preservation of Ag and Au sulfides in the surface parts of the Au–Ag grains under the oxidizing conditions. S-rich marginal parts of native gold particles may be represented by solid solutions Ag2–xAu x S or (with a lack of S) by agglomerates of Ag n Au m S clusters. The formation of surface zoning in the nanoscale on the surface of native Au is abundant in nature and may be applied in prospecting.

Geochemical Peculiarities of Galena and Sphalerite from Polymetallic Deposits of the Dal’negorskii Ore Region (Primorsky Krai, Russia)

New data on the composition of the major minerals from the skarn and vein polymetallic deposits of the Dal’negorskii ore region are reported. Analysis of galena and sphalerite was carried out by the X-ray fluorescent energy-dispersive method of synchrotron radiation for the first time. It is shown that the minor elements in major minerals of different deposits are typomorphic. Among these elements are Fe, Cu, Ni, Cd, Ag, Sn, and Sb, as well as In in sphalerite and Te in galena. The high concentrations of Ag, Cu, Te, Cd, and In in the extracted minerals indicate the complex character of mineralization. The compositional patterns of ore minerals characterize the sequence of mineral formation from the skarn to vein ores, and the sequence of deposits from the mesothermal to epithermal conditions. This provides geochemical evidence for the stage model of the formation of mineralization in the Dal’negorskii ore region.

Characterization and antibacterial properties of nanosilver-applied polyethylene and polypropylene composite films for food packaging applications

Abstract Nanocomposite films were developed using masterbatches of two polymers, namely low-density polyethylene (LDPE) and polypropylene (PP) containing silver (Ag) nanoparticles, by melt compounding and melt extruding. The films became increasingly yellow as the Ag content increased. Morphological evaluation showed the effective incorporation of Ag in the polymers. The Ag/LDPE nanocomposite film showed a comparable strength to that of commercial LDPE, although stiffness increased at high Ag (240 mg/kg) concentration. The Ag/PP nanocomposite film showed enhanced mechanical properties compared to commercial PP, although high Ag content (290 mg/kg) also resulted in weakening. Both nanocomposite films were effective against E. coli and S. aureus at concentrations of 36 and 30 mg/kg Ag nanoparticles for Ag/LDPE and Ag/PP films, respectively, resulting in a > 99.9% decrease in the number of viable bacteria. The antibacterial effect was more marked on S. aureus. The results obtained indicate that the nanocomposite films produced show great potential for developing antibacterial food packaging.

Effect of dopants on the TL response of the new LiF:Mg,Cu,Ag material

The new TL LiF:Mg,Cu,Ag material was prepared and investigated in this study. The TL intensity of LiF:Mg,Cu,Ag is strongly dependent on the concentration of dopants and the preparation procedure. Any small change in these factors can cause alterations in TL response. In this study, the influence of Cu and Ag concentrations on the response of the LiF:Mg,Cu,Ag sample was investigated and showed that the height of the low, main and high temperature peaks changes with Ag concentration. Their intensities increased with increasing Ag concentration to a maximum value and decreased with higher Ag concentration. It was also found that Cu concentration less than 0.05 mol% influences the maximum peak height and TL intensity. The optimum Cu and Ag concentrations were found to be 0.05 and 0.1 mol% at 1005 °C QT, respectively. The role of dopants in LiF:Mg,Cu,Ag material was also investigated. The results showed that presence of three dopants is important for having material with sensitivity higher than LiF:Mg,Ti. The Mg dopant plays a crucial role in the formation of the trapping center and the position of the main dosimetric peak.

Silver nanoparticles in sewage treatment plant effluents: chronic effects and accumulation of silver in the freshwater amphipod Hyalella azteca

BackgroundIncreasing amounts of engineered nanoparticles (NPs) in wastewater can reach the aquatic environment by passing through the sewage treatment plant (STP). NPs can induce ecotoxicological effects due to their specific chemical properties. However, their bioavailability and toxicity are potentially influenced by transformation processes caused by substances present in the STP, e.g., humic acids or sulfides. Due to the lack of a test system allowing to test NPs under realistic environmental conditions, we coupled two existing test systems, the activated sludge simulation test (OECD TG 303A 2001) and the chronic exposure test with the freshwater amphipod Hyalella azteca (Environment Canada 2013), to gain a test scenario that allows to consider the altered behavior and fate of NPs induced by the STP process. This should improve the environmental realism of the chronic exposure test with Hyalella. In the first study, we tested the STP effluent containing AgNPs. In the second and third study, tap water and control STP effluent were spiked with AgNPs and used as test media.ResultsThe chronic exposure studies with the freshwater amphipod H. azteca showed that the investigated AgNPs lose most of their toxicity while passing through the STP. Over all studies with total Ag concentrations ranging from 0.85 to 68.70 µg/L, significant effects of the AgNPs were only observed in the survival of test animals exposed to tap water containing the highest Ag concentration (62.59 µg/L). Accumulation of silver in the body of test animals was clearly dependent on the pretreatment of the AgNPs. Silver ions (Ag+) released from AgNPs are supposed to be the major pathway leading to body burden following exposure to test media containing AgNPs.ConclusionThe coupled test system is suitable for testing substances that can reach the environment via the STP effluent. The investigated AgNPs lose most of their toxicity while passing through the STP. Accumulation of silver in the animals exposed to the different treatments was apparent, whereby silver ions (Ag+) released from AgNPs were supposed to be the major pathway leading to body burden.

Ore genesis of the Fule Pb[sbnd]Zn deposit and its relationship with the Emeishan Large Igneous Province: Evidence from mineralogy, bulk C[sbnd]O[sbnd]S and in situ S[sbnd]Pb isotopes

Magmatic activity plays an important role in mineralization, but little is understood of its role with respect to carbonate-hosted stratabound epigenetic PbZn deposits. The Fule PbZn deposit (~10 Mt of sulfide ore with mean grades of 15–20wt% Zn+Pb), is stratigraphically placed in middle Permian strata and spatially (~1m) associated with late Permian continental flood basalts of the Emeishan Large Igneous Province (ELIP). It thus provides an ideal case to investigate its genetic relationship with the ELIP. In addition, the Fule deposit is characterized by high concentrations of Ag, Cd, Ge and Ga, and contains a variety of Cu and Ni sulfide minerals. Syn-ore calcite (δ13C=+2.57–+3.01‰) and associated fluids (δ13C=+2.96–+3.40‰) have δ13C values similar to those of fresh limestone (δ13C=+1.58–+2.63‰), but the δ18O values of calcite (+16.83–+19.92‰) and associated fluids (+7.80–+10.89‰) are distinctly lower than those of limestone (δ18O=+21.85–+23.61‰). This means that C is mainly derived from limestone, whereas the O isotope signature may be related to water/rock (W/R) interaction between mantle and/or metamorphic fluids and limestone. δ34S values of sulfide minerals obtained by in situ NanoSIMS and conventional bulk techniques record a range of +9.8–+23.1‰ and +10.04–+16.43‰, respectively, reflecting the enrichment of heavy S isotopes in the ore-forming fluids and thermochemical sulfate reduction (TSR) is the principal mechanism for the formation of S2−. Cores of sulfide crystals have much higher δ34S values than their rims, indicating a probable mixture of multiple S reservoirs and/or a dynamic fractionation of S isotopes occurred during sulfide precipitation. The uniform femtosecond (fs) LA-MC-ICPMS in situ Pb isotopic data for galena plot in the field that differs from any of the three potential sources in the region. Such signatures demonstrate that metal Pb was most likely derived from a well-mixed source of basalts, sedimentary rocks and basement rocks. We propose that (a) the enrichment in Ag, Cu, Ni, Cd, Ge and Ga, and the isotope signatures of hydrothermal minerals in the Fule region are related to fluids derived from or flowed through multiple reservoirs; (b) Emeishan magmatism provided heat, elements and associated fluids, and its basalts acted as an impermeable and protective layer; and (c) fluid mixing caused TSR, and then resulted in W/R interaction and CO2 degassing, all of which played a key role in the precipitation of hydrothermal minerals.

Low antigen dose in adjuvant-based vaccination selectively induces CD4 T cells with enhanced functional avidity and protective efficacy

Abstract T cells of high functional avidity sense and respond to low levels of antigen (Ag), and their superior protective efficacy was first described using CD8 T cells cultured in vitro with low levels of Ag resulting in higher avidity and anti-tumor/viral efficacy compared to low avidity T cells cultured with high Ag concentrations. Selectively inducing high avidity by low Ag concentrations has required in vitro expansion so far, as in vivo attempts with low-dose vaccination gave no response. We show for the first time that functionally high avidity CD4, but not CD8, T cells are selectively primed in vivo by low concentrations of Ag in the strong crosspriming liposomal cationic adjuvant formulations (CAF) DDA/TDB or DDA/MMG/pIC from SSI. Increased functional avidity observed after low-dose vaccinations correlated with lower surface expression of PD-1 and higher per cell IFN-gamma production compared to low avidity CD4 T cells. We further show that IL-15, known to increase functional avidity of CTLs, is essential for high avidity of vaccine specific CD4 T cells. Importantly, high avidity CD4 T cells offered superior protection in a murine model of latent infection with Mycobacterium tuberculosis compared to low avidity T cells. Furthermore, adoptive transfers of HIV-IIIB gp140-specific CD4 T cells of high functional avidity resulting from low-dose immunizations in combination with TCR transgenic HIV-IIIB gp120 specific CTLs conferred superior protection against viral (vaccinia-HIV-IIB-gp140) challenge compared to TCR-Tg CTLs alone or in combination with low avidity CD4 T cells induced by high-dose immunization. Thus, inducing high avidity CD4 T cells by low-dose immunization is important in clearing viral and bacterial infections.

Tissue concentrations of four Taiwanese toothed cetaceans indicating the silver and cadmium pollution in the western Pacific Ocean

Muscle, lung, kidney and liver tissues of 45 bycatch and stranded cetaceans, including 14 Grampus griseus (Gg), 7 Kogia simus (Ks), 10 Lagenodelphis hosei (Lh), and 14 Stenella attenuata (Sa), were collected in the waters off Taiwan from 1994 to 1995, and from 2001 to 2012. Baseline concentrations (in μgg−1 dry weight) of the cetaceans were lung (<0.05)=muscle (<0.05)<kidney (0.08±0.04)<liver (0.43±0.28) for Ag, and muscle (0.03±0.03)=lung (0.22±0.19)<liver (3.82±3.50)<kidney (16.22±18.81) for Cd. Unhealthy and critically dangerous Ag and Cd tissue concentrations in the toothed cetaceans are suggested. Marked high concentrations of Ag and Cd found in Gg and Lh are highly related to their squid-eating and deep diving habits. The highest ever recorded concentrations of liver-Ag and kidney-Cd were found in two Lh. These Taiwanese cetaceans indicate marked Ag and Cd pollution in the recent two decades in the western Pacific Ocean.

Influence of the Ag concentration on the medium-range order in a CuZrAlAg bulk metallic glass

Fluctuation electron microscopy of bulk metallic glasses of CuZrAl(Ag) demonstrates that medium-range order is sensitive to minor compositional changes. By analyzing nanodiffraction patterns medium-range order is detected with crystal-like motifs based on the B2 CuZr structure and its distorted structures resembling the martensitic ones. This result demonstrates some structural homology between the metallic glass and its high temperature crystalline phase. The amount of medium-range order seems slightly affected with increasing Ag concentration (0, 2, 5 at.%) but the structural motifs of the medium-range ordered clusters become more diverse at the highest Ag concentration. The decrease of dominant clusters is consistent with the destabilization of the B2 structure measured by calorimetry and accounts for the increased glass-forming ability.

Shear zone-controlled post-magmatic ore formation in the Huangshandong Ni–Cu sulfide deposit, NW China

The Huangshandong Ni–Cu sulfide deposit, located in the Kangguer–Jing’erquan ductile shear zone, belongs to the Jueluotage island arc belt in Eastern Tianshan of the Central Asian Orogenic Belt. The Huangshandong mafic–ultramafic pluton, which has a fusiform shape, is believed to have intruded strongly foliated Late Carboniferous volcanic rocks during the development of the regional ductile shear zone. Some orebodies in the deposit show intense ductile deformation. Among them, the No. 17 orebody is entirely controlled and hosted by the ductile shear zone. Host rocks and ores from this orebody show intense deformation and alteration, and could be called ore mylonites. Furthermore, numerous anastomosing veinlets can be observed in copper-rich carbonate-sulfide veins in the ductile shear zone. Geological field investigation and ore petrography studies indicate that sulfide ores at Huangshandong are composed of three types: undeformed magmatic ores, deformed magmatic ores, and hydrothermal overprinted ores. Magmatic ores with net fabrics remain unaltered and undeformed, and sulfide minerals in them show only brittle fractures. Silicate and sulfide minerals in deformed magmatic ores are characterized by intense deformation fabrics. Examples for such fabrics are kink bands, wavy extinction of uralite, domino structure of phlogopite, and elongated grains of pyrrhotite and pentlandite. Hydrothermal overprinted ores are characterized by strong deformation, flattened grains, and recrystallization of pyrrhotite; moreover, annealing of pyrrhotite is frequently observed. Pyrrhotite, pentlandite, and chalcopyrite in hydrothermal overprinted ores have high Ni and Co concentrations in pyrrhotite, a higher Ni concentration in pentlandite, and high Ag and Cd concentrations, respectively. We attribute Ni and Co in fluid-overprinted ores mainly to the alteration of olivine, and the dissolution of primary chalcopyrite is the likely source of copper in chalcopyrite-rich hydrothermal overprinted ores. During the intruding and cooling of the Huangshandong pluton, intense regional ductile shearing caused the ductile deformation of sulfide ores in the deposit, and subsequently, ore mylonites were formed. Gangue minerals in the deformed orebodies were crushed to fine-grained minerals and altered to serpentine, chlorite, and uralite. During these processes, fluid and ore elements were released and reacted with deformed rocks and ores, forming anastomosing veinlets on hydrothermal overprinted ores.

Multiscale Computational Design of Core/Shell Nanoparticles for Oxygen Reduction Reaction

We propose a multiscale computational framework to design core/shell nanoparticles (NPs) for oxygen reduction reaction (ORR). Essential to the framework are linear scaling relations between oxygen adsorption energy and surface strain, which can be determined for NP facets and edges from first-principles and multiscale QM/MM calculations, respectively. Based on the linear scaling relations and a microkinetic model, we can estimate ORR rates as a function of surface strain on core/shell NPs. Employing the multiscale framework, we have systematically examined the ORR activity on Pd-based core/shell NPs as a function of their shape, size, shell thickness, and alloy composition of the core. Three NP shapes—icosahedron, octahedron, and truncated octahedron—are explored, and the truncated octahedron is found to be the most active and the icosahedron is the least active. NixPd1–x@Pd NPs with high Ni concentrations and thin shells could exhibit higher ORR rates than the pure Pt(111) surface and/or Pt NPs. AgxPd1–x@Pd in the truncated octahedron shape and high Ag concentrations are predicted to be even more active than NixPd1–x@Pd NPs under the same conditions. The highly active AgxPd1–x@Pd and NixPd1–x@Pd NPs are thermodynamically stable.

Trace element and sulfur isotopic evidence for redox changes during formation of the Wallaby Gold Deposit, Western Australia

Wallaby is a major gold deposit of the St Ives Gold field of Western Australia, with an estimated resource of 8 million ounces of gold. It has a well-established paragenesis across five vein sets that displays macroscopic evidence of changing redox through time; from hematite to magnetite. Micro-analysis of pyrite from each vein generation shows a progressive and gradual change in redox conditions. The sulfur isotope composition has a δ34S range of −7.7 to +9.8‰ using 3μm spots on the Sensitive High Resolution Iron Micro Probe-Stable Isotope (SHRIMP-SI). Negative values indicative of an oxidized sulfur signature are found in the earliest generation of pyrite (which coexists with hematite) that also contains high concentrations of As, Ni, Zn, Ag, Sb, Cu and Pb. Conversely, positive values representative of reduced sulfur are found in later generations of pyrite, with lower concentrations of As, Ni, Sb, Cu, Zn and Pb. These later pyrite crystals display higher As/Ni, As/Sb, and As/Bi, and lower Cu/Te. These geochemical trends are the result of redox controlled transport and partitioning into pyrite of minor and trace elements now within the pyrite structure. Previous studies suggested a single orogenic event formed the Wallaby Deposit. This is not supported by the present study. Trace element ratios such as As/Ni clearly delineate the high Au generations and could be used as an exploration tool. It is suggested that pyrite from the Wallaby Gold Deposit formed via desulfidation and a gradual change in redox conditions within an evolving fluid and did not result from mixing of two separate fluids as previously advocated. Utilizing pyrite to link the entire fluid history of Wallaby demonstrates the general use of pyrite as a valuable mineral tracer in gold-bearing fluid systems.

Influence of Ag contents on structure and tribological properties of TiSiN-Ag nanocomposite coatings on Ti–6Al–4V

TiSiN-Ag nanocomposite coatings with different Ag contents were deposited on Ti–6Al–4V using reactive co-sputtering in multi-arc ion plating system. Influence of Ag contents on structure and tribological properties of TiSiN-Ag nanocomposite coatings was investigated. The TiSiN-Ag coatings were found to have unique nanocomposite structures composed of nanocrystallite and amorphous nc-TiN/nc-Ag/a-Si3N4. When the silver content was 1.4at.%, the coating exhibited high hardness (36GPa), but poor wear resistance. When the silver content was increased from 5.3 to 8.7at.%, the coatings possessed homogeneous distribution and small variation in hardness. Although these coatings revealed obvious decrease in hardness, significantly reduced in the friction coefficient and possessed excellent tribological properties, besides, the coating with the Ag content of 5.3at.% showed best wear resistance in artificial seawater and the coating (7.9at.% Ag) revealed the best wear resistance in ambient air. However, with a further increased incorporation of Ag into the TiSiN-Ag coating (17.0at.%) resulted in the formation of a large volume fraction of metallic silver, which caused a decrease both in hardness and wear resistance. The coating containing highest Ag concentration (21.0at.%) exhibited low friction coefficient both in ambient air and artificial seawater, although possessing low hardness.

Synsedimentary, Diagenetic, and Metamorphic Pyrite, Pyrrhotite, and Marcasite at the Homestake BIF-Hosted Gold Deposit, South Dakota, USA: Insights on Au-As Ore Genesis from Textural and LA-ICP-MS Trace Element Studies

The Paleoproterozoic Homestake deposit, northern Black Hills, South Dakota, is the largest banded iron-formation (BIF)-hosted gold deposit in the world and one of the largest single gold deposits globally (~1,300 t Au mined at an average grade of 8.4 g/t). The origin of the deposit has remained in dispute from its discovery, with views broadly falling into two groups: (1) the gold and associated elements were externally sourced and deposited in a suitable structural and/or chemical trap (e.g., iron formation), and (2) gold was indigenous to the host iron formation, from which it was remobilized into dilatant structural zones during deformation and metamorphism. In recent times, most workers have favored the former model, appealing to the broad synchroneity of Paleoproterozoic metamorphism, felsic magmatic activity, and gold event timing. LA-ICP-MS analysis of synsedimentary to early diagenetic sulfides at Homestake and surrounding area indicates that the Au in the orebodies may have originally had a significant syngenetic component. In particular, LA-ICP-MS mapping of multistage pyrites from carbonaceous shale in the upper Poorman Formation shows that Au and a suite of trace elements (Co, Ni, Cu, Zn, Se, Mo, Ag, Sb, Te, Au, Hg, Tl, Pb, and Bi), similar to those in diagenetic pyrite from around the globe, are contained in anhedral, sponge-textured cores and nodules surrounded by relatively trace element barren, Au-poor, euhedral pyrite rims. Furthermore, interelement ratios (e.g., Co/Ni, Ni/Ag) of the trace element-rich spongy and nodular pyrites are also similar to those of typical diagenetic pyrite. LA-ICP-MS imaging of pyrrhotite in the same rocks reveals multistage growth in this mineral as well, with the earlier generation having higher concentrations of Ag, Sb, Pb, Tl, and Bi than its presumed metamorphic counterpart. Imaging of marcasite in the shales of the upper Poorman Formation demonstrates this mineral’s high abundance of W and Tl relative to all generations of pyrite and pyrrhotite. Mass-balance calculations indicate that the volume of upper Poorman Formation in the mine area (approx. 12 km3) could potentially yield ~4,500 t of Au, a value greater than the total mined resource by more than a factor of three. These geochemical data and calculations suggest that a significant portion of the gold at Homestake may have been sourced from the relatively thick carbonaceous and sulfidic black shale facies in the stratigraphic footwall to the host iron formation, in a manner similar to other sediment-hosted gold districts.

Exposure of juvenile turbot (Scophthalmus maximus) to silver nanoparticles and 17α-ethinylestradiol mixtures: Implications for contaminant uptake and plasma steroid hormone levels

Combined exposure to engineered nanoparticles (ENPs) and anthropogenic contaminants can lead to changes in bioavailability, uptake and thus effects of both groups of contaminants. In this study we investigated effects of single and combined exposures of silver (Ag) nanoparticles (AgNPs) and the synthetic hormone 17α-ethinylestradiol (EE2) on tissue uptake of both contaminants in juvenile turbot (Scophthalmus maximus). Silver uptake and tissue distribution (gills, liver, kidney, stomach, muscle and bile) were analyzed following a 14-day, 2-h daily pulsed exposure to AgNPs (2 μg L−1 and 200 μg L−1), Ag+ (50 μg L−1), EE2 (50 ng L−1) and AgNP + EE2 (2 or 200 μg L−1+50 ng L−1). Effects of the exposures on plasma vitellogenin (Vtg) levels, EE2 and steroid hormone concentrations were investigated. The AgNP and AgNP + EE2 exposures resulted in similar Ag concentrations in the tissues, indicating that combined exposure did not influence Ag uptake in tissues. The highest Ag concentrations were found in gills. For the Ag+ exposed fish, the highest Ag concentrations were measured in the liver. Our results show dissolution processes of AgNPs in seawater, indicating that the tissue concentrations of Ag may partly originate from ionic release. Plasma EE2 concentrations and Vtg induction were similar in fish exposed to the single contaminants and the mixed contaminants, indicating that the presence of AgNPs did not significantly alter EE2 uptake. Similarly, concentrations of most steroid hormones were not significantly altered due to exposures to the combined contaminants versus the single compound exposures. However, high concentrations of AgNPs in combination with EE2 caused a drop of estrone (E1) (female fish) and androstenedione (AN) (male and female fish) levels in plasma below quantification limits. Our results indicate that the interactive effects between AgNPs and EE2 are limited, with only high concentrations of AgNPs triggering synergistic effects on plasma steroid hormone concentrations in juvenile turbots.

Mechanistic Study of the Synergistic Antibacterial Activity of Combined Silver Nanoparticles and Common Antibiotics.

A combination of silver nanoparticles (AgNPs) and an antibiotic can synergistically inhibit bacterial growth, especially against the drug-resistant bacteria Salmonella typhimurium. However, the mechanism for the synergistic activity is not known. This study chooses four classes of antibiotics, β-lactam (ampicillin and penicillin), quinolone (enoxacin), aminoglycoside (kanamycin and neomycin), and polykeptide (tetracycline) to explore their synergistic mechanism when combined with AgNPs against the multidrug-resistant bacterium Salmonella typhimurium DT 104. Enoxacin, kanamycin, neomycin, and tetracycline show synergistic growth inhibition against the Salmonella bacteria when combined with AgNPs, while ampicillin and penicillin do not. UV-vis and Raman spectroscopy studies reveal that all these four synergistic antibiotics can form complexes with AgNPs, while ampicillin and penicillin do not. The presence of tetracycline enhances the binding of Ag to Salmonella by 21% and Ag(+) release by 26% in comparison to that without tetracycline, while the presence of penicillin does not enhance the binding of Ag or Ag(+) release. This means that AgNPs first form a complex with tetracycline. The tetracycline-AgNPs complex interacts more strongly with the Salmonella cells and causes more Ag(+) release, thus creating a temporal high concentration of Ag(+) near the bacteria cell wall that leads to growth inhibition of the bacteria. These findings agree with the recent findings that Ag(+) release from AgNPs is the agent causing toxicity.

How Does Nanoporous Gold Dissociate Molecular Oxygen?

Nanoporous Au and other dilute AgAu alloys are highly active and selective oxidation catalysts. Their ability to dissociate O2 is to a large extent unexplained, given that unsupported Au cannot generally dissociate O2, while large ensembles of Ag atoms (>4) are generally necessary to lower the O2 dissociation barrier significantly. Here, we identify a site on the surface of dilute AgAu alloys that is stable under reaction conditions and has a low O2 dissociation barrier, in agreement with experimental measurements. Although Ag generally prefers to disperse throughout Au, the presence of adsorbed O near surface steps creates sites of high local Ag concentration, where the Ag atoms sit in the rows next to the step Au atoms. O2 adsorbs on the Au step atoms, but the transition state involves significant Ag–O interaction, resulting in a barrier lower than expected from the adsorption energies of either the initial or final state.

Biomedical Potential of Ultrafine Ag/AgCl Nanoparticles Coated on Graphene with Special Reference to Antimicrobial Performances and Burn Wound Healing.

In recent years, researchers have proven the release of silver ions (Ag(+)) from silver nanoparticles (Ag NPs) significantly affects their toxicity to bacteria and other organisms. Due to the difficulty in maintaining a steady flux of a high concentration of Ag(+), it is still challenging to develop a highly efficient, stable, and biocompatible Ag NP-based antimicrobial material. To circumvent this issue, we developed a new Ag-based bactericide through the fabrication of sunlight-driven and ultrafine silver/silver chloride anchored on reduced graphene oxide (Ag/AgCl/rGO). This stable Ag/AgCl nanophotocatalyst with negligible release of Ag(+) generated a high amount of oxidative radicals, killing the bacteria, thus achieving both high bactericidal efficiency and stability. Moreover, functionalization of the nanomaterial with poly(diallyldimethylammonium chloride) (PDDA) gives it a highly adsorptive capacity, which allows it to capture the bacteria and possibly enhances the bactericidal activity. In vivo histopathological studies showed that the Ag/AgCl/rGO nanomaterial could obviously promote the regeneration of the epidermis, which indicated the good biomedical potential of Ag/AgCl/rGO nanomaterial in burn wound healing.