Presence Of Silver Ions Research Articles

Alteration of DNAzyme Activity by Silver Ion

Abstract The thermal stability of the parallel motif triple helix DNA containing CG.CH+ base triplets is improved by silver ions. The N3 protons of cytosines on the third strand are replaced by the ions to form CG.CAg+, which are stable regardless of the pH values. The activity of the DNAzyme that binds its substrate DNA through triple helix formation was examined in the presence of silver ions. The DNAzyme activity was retained even at neutral pH with the assistance of silver ions.

Influence of Ag doping on structural and optical properties of ZnO thin films synthesized by the sol–gel technique

Thin films of Ag–ZnO samples deposited on glass substrates with a different percentage of Ag content (1, 2, and 3 at%) were synthesized, at room temperature, by a dip-coating sol-gel method. The obtained samples are hexagonal wurtzite structure. The average grain size of deposits is about 5 nm. Up to 3 at%, c-axis lattice parameter shifts toward a higher value, which indicates that silver atoms replace Zn atoms in the crystal lattice. As shown by the DRX spectra, growth rate in the (101) direction is favored by the presence of silver ions in the ZnO. The layers present a homogeneous crystallites distribution, as we can remark it on SEM micrographs and exhibit a very low roughness according to AFM images. The entire samples exhibit a transmission value greater than 80 %, in the visible region, while the maximum is obtained for those doped at 2 at%. Energy band varies between 3.15 eV and 3.25 eV. The wider gap obtained is that of the ZnO layer doped with 2 at%. It is worth noting a strong UV emission observed on PL spectrum, performed at very low temperature (liquid nitrogen temperature), for silver doped ZnO compared to that of pure ZnO.

Synthesis and characterization of a new dinuclear platinum(II) alkynyl complex with a ferrocene bridge and its interaction with silver ion

A new dinuclear alkynyl platinum(II) complex with a ferrocene (Fc) bridge (Pt(II)–Fc–Pt(II)), referred as Sensor 1(1), was synthesized and characterized. The photophysical, luminescent and cation-binding properties were studied by UV–Vis spectrophotometric, fluorometric, 1H NMR titration methods, and the ESI-MS. Sensor 1 showed a significant luminescent quenching in the presence of silver ions (Ag+).

Highly specific sensing of silver based on aggregation of G-quadruplex-capped gold nanoparticles

A novel, simple, and rapid colorimetric strategy is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by the unfolding of G-quadruplex (G4) in the presence of silver ions (Ag+). AuNPs to which compact G4 structures were attached had higher stability toward salt-induced aggregation of AuNPs than those on which random coil single-stranded DNA (ssDNA) structures were anchored. In the Ag+-free system, AuNPs remained mono-dispersed. In contrast, upon addition of Ag+, the G4 structure unfolded, inducing aggregation of the AuNPs. The linear range of the as-established colorimetric assay for Ag+ was from 2.0 × 10−8 M to 2.0 × 10−6 M, with a detection limit of approximately 7 nM. Additionally, the colorimetric sensor showed good selectivity toward Ag+. The proposed method offers a new assay for metal ion-mediated aggregation-based colorimetric sensing and may pave a new way for heavy metal ions detection.

Biocidal properties of TiO2 powder modified with Ag nanoparticles.

Silver nanoparticles (NPs) were synthesized sonochemically by the reduction of silver ions with ethylene glycol and simultaneously deposited on different forms of TiO2 powders (commercial Degussa P-25, synthetic anatase and mesoporous titania). The Ag-TiO2 nanocomposites were characterized by X-ray electron diffraction (XRD), transmission electron microscopy (TEM), energy-dispersed X-ray analysis (EDX), UV absorption spectroscopy (UV), Z-potential measurements and electron paramagnetic resonance (EPR). The results demonstrated homogeneous distribution of silver nanoparticles ∼3 nm in size, strongly attached to the surface of titania. The antimicrobial properties of Ag-TiO2 were tested against a number of Gram-positive and Gram-negative bacteria. A high bactericidal effect was found in the absence of UV light. The reduction in bacterial viability was between 3 and 4.2 logs. Based on the experimental data it was concluded that enhanced antimicrobial activity of the Ag-TiO2 originated from both the oxidative stress generated by silver nanoparticles and the presence of silver ions on the surface of the silver-titania composite.

Effect of thermal treatments on sputtered silver nanocluster/silica composite coatings on soda-lime glasses: ionic exchange and antibacterial activity

Silver nanocluster/silica composite coatings were deposited on both soda-lime and silica glasses by radio frequency (RF) co-sputtering. The effect of thermal treatments on the microstructure in the range of 150–450 °C were examined by UV–visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Time of Flight-Elastic Recoil Detection Analysis. Sodium/silver ionic exchange was evidenced for coatings sputtered on soda-lime substrates after heating at 450 °C; presence of silver ions and/or silver nanoclusters, nanocluster size and their position inside the sputtered layers will be discussed for as-deposited and heated coatings on both substrates. The antibacterial activity of all coatings was determined against Staphylococcus aureus and Candida albicans by disk diffusion method and colonies forming units count; in agreement with microstructural results, the antibacterial activity present on all coatings was slightly reduced after heating at 450 °C. All coatings have been submitted to humidity plus UV ageing and sterilization by autoclave, gamma ray and ethylene oxide gas. Tape resistance (ASTM D3359-97) tests have been done on each coating before and after ageing and sterilizations, revealing a good adhesion on soda-lime substrates, except for those aged in humidity plus UV and sterilized by autoclave. Scratch tests and nanoindentation tests have been done on each coating, as-deposited and after heating at 450 °C. The coating hardness was improved by heating only when coatings were deposited on silica. The heating of coatings deposited on soda-lime substrates gave opposite effect on their hardness.

On the different growth conditions affecting silver antimicrobial efficacy on Listeria monocytogenes and Salmonella enterica

Silver is known to inhibit microorganisms and therefore it is an ideal candidate for its incorporation in a wide variety of materials for food applications. However, there is still a need for understanding how silver prolonged exposure to bacterial contamination affects the bioavailability of the active silver species. In the present study, growth curves of Listeria monocytogenes and Salmonella enterica were performed for 3–5days in Tryptic Soy Broth (TSB) and M9 minimal medium (M9) in the presence of silver ions and silver solutions previously in contact with the growth media. The cultivability of the bacteria under these conditions was correlated with the viability of the bacterial populations as measured by flow cytometry analysis (FC) using a LIVE/DEAD BacLight kit. It was found that, after a period where viable counts were not detected, bacterial populations recovered and were able to proliferate in most cases. The resuscitation of the cultures was explained by both the existence of a resilient fraction of bacteria in a compromised state and the parallel inactivation of the silver species. This inactivation was found to be highly influenced by time dependant chemical reactions taking place in the environment of exposure, producing differences of at least 3 fold between results for nutrient rich environments and results for limiting environments. This study points out the need for understanding these chemical interactions and bacterial mechanisms of adaptation and may have relevance in the design of silver-based antimicrobial systems for food-related applications.

The possible mechanisms involved in nanoparticles biosynthesis

Several aspects of silver nanoparticle (NP) biosynthesis using Fusarium oxysporum under different conditions, that have not been previously considered, were explored. NP synthesis with different nitrate concentrations and silver sulfate instead of silver nitrate was investigated. The ability of F. oxysporum to synthesize NP under oxygen-limited conditions was also evaluated. In the presence of a nitrate reductase inhibitor, different mechanism rather than the reduction of metal ions by a nitrate-dependent reductase, was revealed. SDS-PAGE analysis indicated that a protein with 14kDa molecular weight could be involved in a specific response of the fungus in the presence of silver ions.

Electron Hopping Through Single-to-Few-Layer Graphene Oxide Films. Side-Selective Photocatalytic Deposition of Metal Nanoparticles.

Single- to few-layer graphene oxide (GO) sheets have been successfully anchored onto TiO2 films using electrophoretic deposition. Upon UV illumination of TiO2-GO films, photogenerated electrons from TiO2 are captured by GO. These electrons are initially used in GO's reduction, while additional electron transfer results in storage across its sp(2) network. In the presence of silver ions, deposition of silver nanoparticles (NPs) is accomplished on the GO surface opposite the TiO2, thus confirming the ability of GO to transport electrons through its plane. Illumination-controlled reduction of silver ions allows for simple selection of particle size and loading, making these semiconductor-graphene-metal (SGM) films ideal for custom catalysis and sensor applications. Initial testing of SGM films as surface-enhanced resonance Raman (SERRS) sensors produced significant target molecule signal enhancements, enabling detection of nanomolar concentrations.

Starfruit-Shaped Gold Nanorods and Nanowires: Synthesis and SERS Characterization

Recently, branched and star-shaped gold nanoparticles have received significant attention for their unique optical and electronic properties, but most examples of such nanoparticles have a zero-dimensional shape with varying numbers of branches coming from a quasi-spherical core. This report details the first examples of higher-order penta-branched gold particles including rod-, wire-, and platelike particles which contain a uniquely periodic starfruitlike morphology. These nanoparticles are synthesized in the presence of silver ions by a seed-mediated approach based on utilizing highly purified pentahedrally twinned gold nanorods and nanowires as seed particles. The extent of the growth can be varied, leading to shifts in the plasmon resonances of the particles. In addition, the application of the starfruit rods for surface-enhanced Raman spectroscopy (SERS) is demonstrated.

Chlorella sp. based biosensor for selective determination of mercury in presence of silver ions

Whole cell based biosensor is prepared by immobilizing Chlorella sp. microbes over glassy carbon electrode. The proposed biosensor is optimized for characteristics like substrate concentration, pH, response time, and durability. The electrode responds linearly in concentration range of 10−14M to 10−6M for mercury and showed its rare selectivity over silver, alkali metals, alkaline earth metals and transition metals with an expected life of 14 days.

Improving the mass transfer rate in G–L membrane contactors with ionic liquids as absorption medium. Recovery of propylene

The use of membrane contactors for the G–L separation of olefins by means of reactive absorption with ionic liquid silver complexes presents a great potential to intensify the conventional separation process based on cryogenic distillation. Nevertheless, the key issue to be addressed is the high mass transfer resistance offered by the ionic liquid that flows through the shell side of the membrane contactor. It is therefore crucial to improve the fluid dynamics of the system in order to enhance the mass transfer rate in the liquid film. This work reports the analysis of the performance of a gas–liquid transverse flow membrane contactor applied to the reactive absorption of propylene in BMImBF 4–Ag + as reaction media. First the mass transfer phenomena developed in the system in the absence of chemical reactions were assessed; several experiments were carried out at 293 K flowing pure BMImBF 4 at flow rates between 6.42 × 10 −6 m 3 s −1 and 1.19 × 10 −5 m 3 s −1 with propylene as fed gas. Under the operational conditions used in this work, the resistances across the gas film and the microporous membrane are negligible so the overall mass transfer resistance is controlled by the diffusional resistance in the liquid boundary layer. The experimental data were fitted to an empirical correlation, Sh = 1.1 · Re 0.32 Sc 0.33, that allows to calculate the mass transfer rate in the ionic liquid flowing through the shell side of the module at low Reynolds numbers. Moreover it was observed that for the BMImBF 4 flowing at 6.42 × 10 −6 m 3 s −1 and 293 K the improved fluid-dynamics of the transverse flow membrane contactor leads to an overall mass transfer coefficient 17.6 times higher than that reported previously using a parallel-flow contactor. Furthermore, a detailed mathematical model was developed in order to predict and analyze the performance of the system under different operational conditions. This model was applied to simulate the performance of the system under the presence of silver ions in the reaction medium. The reactive absorption of propylene using ionic liquids–silver complexes in the transverse flow membrane contactor has provided promising results, showing a process intensification by a factor of 17.4 in terms of mass transfer per specific area compared to a conventional stirred tank reactor system ( K overall × a(MC)/ K overall × a(CSTR)).

Gelcasting of Al 2O 3/Ag nanocomposite using water-soluble solid-salt precursor

In the present work, Al 2O 3/5 wt.% Ag nanocomposite was prepared by gelcasting process. Silver nitrate was used as the source of silver nanoparticles in the alumina matrix. Dolapix ET85 was found as the most effective dispersant agent to neutralize of unwelcome influence of silver ions on the behavior of slurry. The results indicated that the rheological properties and sedimentation behavior of the prepared slurries were significantly modified using 1.5 wt.% dolapix ET85, which also acts as a chelating agent. The FTIR investigations showed the preventative effect of dolapix on the damaging of rheological properties in the presence of silver ions. The average particle size of silver nanoparticles was measured to be about 50 nm using TEM microscopy.

Preparation and characterization of silver‐chitosan nanocomposite particles with antimicrobial activity

AbstractA nanocomposite of silver nanoparticles (AgNPs) embedded in chitosan (Cts) matrix was successfully synthesized by crosslinking technology. Colloidal AgNPs formed in situ by chemical reduction of silver ions in presence of Cts showed a good stability. Transmission electron micrographs, X‐ray diffraction patterns, and UV‐visible spectra of Ag‐Cts composite particles confirmed the formation of silver nanocrystals. Fourier transform infrared spectroscopy verified the presence of Cts as a stabilizing agent surrounded AgNPs. Thermogravimetric‐differential scanning calorimeter analysis revealed Ag‐Cts nanocomposite had a higher thermal stability than Cts. X‐ray photoelectron spectroscopy suggested that the Ag‐O bond in the nanocomposite coule lead to the tight combination between silver and Cts. Microbial experiments showed the nanocomposite had excellent and wide spectrum antibacterial properties, and were more efficient than either AgNPs or Cts alone for inactivating bacteria. Therefore, the resultant nanocomposite could be used as antimicrobial materials for medical and biological applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Three-Dimensional Morphology and Crystallography of Gold Nanorods

We determine the three-dimensional shape, to within 1 nm resolution, of single-crystal gold nanorods grown in the presence of silver ions using electron tomography and thickness profile measurements. We find that, contrary to the current literature, the octagonal side-facets are sparsely packed atomic planes all belonging to the same symmetry-equivalent family, {0 5 12}. Furthermore, the rod ends terminate in a pyramid with slightly different facets, and each pyramid is connected to the sides by four small {0 5 12} "bridging" facets.

Reduction of the spoilage-related microflora in absorbent pads by silver nanotechnology during modified atmosphere packaging of beef meat.

Silver-based antibacterial hybrid materials have been developed by in situ reduction of silver nitrate (1%) adsorbed on cellulose fibers by thermal and UV treatments. Microscopy revealed that the silver nanoparticles were dispersed and regular in shape. Migrated silver ions achieved 60 ppm in beef meat exudates. The ability of the silver-loaded absorbent pads to lower microbial contamination of exuded fluids was studied during storage of beef meat in modified atmosphere packaging. Cellulose-silver hybrid materials reduced the levels of the major microbial groups (total aerobic bacteria, lactic acid bacteria, Pseudomonas spp., and Enterobacteriaceae) present in the absorbent pads by an average of 1 log CFU/g during the entire storage period. The levels of total aerobic bacteria and Pseudomonas spp. were significantly reduced in the presence of silver ions, whereas lactic acid bacteria were less sensitive and not significantly affected. Enterobacteriaceae levels remained under the detection limit when silver was present. Neither the color of the meat nor the microbial loads were markedly affected by the presence of the silver-based antimicrobial hybrid materials.

Antybakteryjne wlokna poliestrowe zawierajace jony srebra Cz. II. KINETYKA UWALNIANIA JONOW SREBRA I WYBRANE WLASCIWOSCI MODYFIKOWANYCH WLOKIEN

Studies on the rate of release of silver ions from ethylene polyterephthalate (PET) fibers, which had earlier been grafted with acrylic or metacrylic acid and then impregnated with silver nitrate, into a 0.01% aqueous solution of nitric acid has been presented. The results confirm, that the Ag+ ions are released gradually and in low concentrations into the acid solution (Fig. 1. Table 1). The changes in the tensile strength of the fibers caused by the two-stage modification process was evaluated. It was observed that grafting at optimal conditions of temperature, duration and acid concentration did not influence the tensile strength of the studied PET significantly. However, a pronounced decrease in tensile strength was caused by the presence of silver ions in the fiber structure (Tables 2 and 3). In vitro determination of the antibacterial properties of the modified fibers against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa was also performed.

Hexazamacrocycle assisted sensing of silver ion through facile synthesis of silver nanoparticles

The ease of generation of silver nanoparticles by using hexazamacrocycle ligand, L1 is utilized for the visual detection of the presence of silver ions at lower concentrations.

Highly silver ion selective fluorescence ionophore: Fluorescent properties of polythiazaalkane derivatives bearing 8-(7-hydroxy-4-methyl)coumarinyl moiety in aqueous solution and in liquid–liquid extraction systems

Two novel fluoroionophores, N-(7-hydroxy-4-methylcoumarin-8-ylmethyl)-3,9-dithia-6-azaundecane (1) and N-(7-hydroxy-4-methylcoumarin-8-ylmethyl)-3,9-dithia-6-azaundecane (2), were synthesized as fluorescence extractants for selective silver determination. The absorption and fluorescence spectra were measured in aqueous 1,4-dioxane solution (28 v/v%) in the absence and presence of silver ion, and their acid dissociation constants were determined from the pH-dependent spectral changes. In the liquid-liquid extraction of some metal ions from neutral aqueous solution into dichloromethane phase, compounds 1 and 2 exhibited excellent silver ion selectivity, and dramatic fluorescence spectral changes were observed in the dichloromethane solutions containing these compounds. The determination limit of 2 for silver ion was 2.0 x 10(-8) mol dm(-3) in the liquid-liquid extraction.

The influence of proteins on the dispersability and cell-biological activity of silver nanoparticles

Spherical silver nanoparticles with a diameter of 50 ± 20 nm and stabilized with either poly(N-vinylpyrrolidone) (PVP) or citrate were dispersed in different cell culture media: (i) pure RPMI, (ii) RPMI containing up to 10% of bovine serum albumin (BSA), and (iii) RPMI containing up to 10% of fetal calf serum (FCS). The agglomeration behavior of the nanoparticles was studied with dynamic light scattering and optical microscopy of individually tracked single particles. Whereas strong agglomeration was observed in pure RPMI and in the RPMI–BSA mixture within a few hours, the particles remained well dispersed in RPMI–FCS. In addition, the biological effect of PVP-stabilized silver nanoparticles and of silver ions on human mesenchymal stem cells (hMSCs) was studied in pure RPMI and also in RPMI–BSA and RPMI–FCS mixtures, respectively. Both proteins considerably increased the cell viability in the presence of silver ions and as well as silver nanoparticles, indicating a binding of silver by these proteins.