Low Amount Of Silver Research Articles

Use of a simple magnetic material for the determination and speciation of very low amounts of silver and gold

Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) can be separated of their ions by a magnetic dispersive micro-solid phase extraction procedure using non-functionalised ferrite particles. The separation and speciation are based on careful control of the acidity of the medium, without involving oxidation-reduction processes. Thus, using a small amount of ferrite particles (2 mg for a typical 10 mL sample) which is added to the sample as a suspension, Ag(I) as well as both gold species are retained in the sorbent at pH 4, while AgNPs are retained at pH 8. For the selective retention of AuNPs, ammonium diethyl dithiophosphate is added to the medium and the extraction process is repeated at pH 4. In all cases, the analytes are desorbed by treating the solid phase separated by the magnet with 0.1 mL of a thiourea solution at pH 3 and determined by electrothermal atomization atomic absorption spectrometry. For the measurement of silver, a palladium salt is used as a chemical modifier. This is not required for the determination of gold. The enrichment factor is 97 and the detection limits are 12 and 4 ng L−1 for gold and silver, respectively. The reproducibility is close to 5% for the four analytes studied. The reliability of the procedures is checked by standard additions and by the use of four standard reference materials with certified total silver content. Several water samples are analysed, and speciation results are given.

The Efficacy of a Novel Silver-Containing Bioresorbable Microfilm Matrix in At-Risk Surgical Wounds: A Clinical Case Series

For persons with diabetes, surgery is fraught with complications; of primary concern is postoperative infection. A postoperative infection rate of up to 13% has been noted in patients with diabetes undergoing elective surgical procedures compared with less than 3% in nondiabetic populations. The objective of this study was to provide preliminary evaluation of the efficacy of a novel bioresorbable microfilm matrix (20 µm thick) containing very low amounts of silver (0.16 mg/in²) in preventing surgical site infections when placed at the level of subcutaneous tissue and dermis prior to primary closure in the patient with diabetes undergoing elective surgery. Twenty-two patients with diabetes undergoing nonemergent or elective foot or ankle surgery and who met at least 1 of the following 6 criteria were included in the study: neuropathy, infection, open wound, history of recurrent infection, nonhealing wound, or peripheral vascular disease. Patients underwent amputation, removal of exostosis, midfoot bone removal, Achilles tendon repair, bunionectomy, or an elevating osteotomy with primary closure of the wound. After hemostasis was obtained and subcutaneous closure achieved, if applicable, the bioresorbable microfilm matrix was applied just deep to the incision at the level of subcutaneous tissue and dermis, and the incision primarily closed. A nonadherent cover dressing was applied over the suture line, and routine follow-up was scheduled for 3 to 5 days later. No patient exhibited signs of infection at initial follow-up, and all adherent patients achieved complete healing during the 3-month follow-up period. Eighteen patients healed at a rate typical for the respective procedure. In 2 patients, time to healing was delayed secondary to weight-bearing dehiscence. Two patients were not included in the results secondary to multiple infractions of nonadherence with the postoperative protocol. The application of microfilm matrix in surgical incisions at the level of subcutaneous tissue and dermis prior to primary closure is safe for and has the potential to prevent postoperative surgical site infections in at-risk patients with diabetes..

Surface Minimal Bactericidal Concentration: A comparative study of active glasses functionalized with different-sized silver nanoparticles

In this work the quantification of antimicrobial properties of differently sized AgNPs immobilized on a surface was studied. Three different sizes of spheroidal AgNPs with a diameter of (6, 30 and 52) nm were synthetized and characterized with UV–vis, SEM, TEM and ICP-MS. The MIC (Minimal Inhibitory Concentration) and MBC (Minimal Bactericidal Concentration) against Escherichia coli were investigated. Then, the antibacterial efficacy (R) of amino-silanized glasses coated with different amounts of the three sizes of AgNPs were quantified by international standard ISO 22196 adapted protocol against E. coli, clarifying the relationship between size and antibacterial properties of immobilized AgNPs on a surface. The total amount of silver present on glasses with an R ∼ 6 for each AgNPs size was quantified with ICP-MS and this was considered the Surface MBC (SMBC), which were found to be (0.023, 0.026 and 0.034) μg/cm2 for (6, 30 and 52) nm AgNPs, respectively. Thus, this study demonstrates that active surfaces with a bactericidal effect at least ≥ 99.9999 % could be obtained using an amount of silver almost 100 times lower than the MBC found for colloidal AgNPs. The immobilization reduces the aggregation phenomena normally occuring in liquid media, maximizing the exposed specific superficial area of the AgNPs and their direct contact with bacterial cells. Starting from this glass model system, our work could broaden the way to the development of a wide range of antibacterial materials with very low amount of silver that can be safely applied in biomedical and food packaging fields.

Strong and Nonspecific Synergistic Antibacterial Efficiency of Antibiotics Combined with Silver Nanoparticles at Very Low Concentrations Showing No Cytotoxic Effect.

The resistance of bacteria towards traditional antibiotics currently constitutes one of the most important health care issues with serious negative impacts in practice. Overcoming this issue can be achieved by using antibacterial agents with multimode antibacterial action. Silver nano-particles (AgNPs) are one of the well-known antibacterial substances showing such multimode antibacterial action. Therefore, AgNPs are suitable candidates for use in combinations with traditional antibiotics in order to improve their antibacterial action. In this work, a systematic study quantifying the synergistic effects of antibiotics with different modes of action and different chemical structures in combination with AgNPs against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus was performed. Employing the microdilution method as more suitable and reliable than the disc diffusion method, strong synergistic effects were shown for all tested antibiotics combined with AgNPs at very low concentrations of both antibiotics and AgNPs. No trends were observed for synergistic effects of antibiotics with different modes of action and different chemical structures in combination with AgNPs, indicating non-specific synergistic effects. Moreover, a very low amount of silver is needed for effective antibacterial action of the antibiotics, which represents an important finding for potential medical applications due to the negligible cytotoxic effect of AgNPs towards human cells at these concentration levels.

Nondestructive analysis of Portuguese “dinheiros” using XRF: overcoming patina constraints

“Dinheiros” are the first Portuguese coins, minted with a billon alloy (majority-based copper alloyed with silver). In this work, a set of “dinheiros” from D. Fernando of Portugal was analyzed and the composition of the alloy was compared with other “dinheiros” from previous reigns. Although the coins were in good state of conservation and no active corrosion was macroscopically observable, they still presented a corrosion layer of unknown thickness that would impair the XRF quantitative determinations. In order to overcome this hindrance, the silver K/L intensity ratios were determined and compared for the analyzed samples in order to choose “clean” spots for quantitative analysis. The results show a clear decrease in the Ag content: from 7–9 % in the previous reigns to 0.2–0.3 % in the coins attributed to D. Fernando. The silver content determined is very comparable to the silver content determined in other copper or bronze artifacts analyzed, leading us to believe that this low amount of silver was not intentionally introduced to create a billon alloy but relates to impurities present in the original mineral specimen.

Lepidopteran insect susceptibility to silver nanoparticles and measurement of changes in their growth, development and physiology

Increased use of nanomaterials in various fields of science has lead for the need to study the impact of nanomaterial on the environment in general and on insect and plant life in particular. We studied the impact of silver nanoparticles (AgNPs) on growth and feeding responses of two lepidopteran pests of castor plant (Ricinus communis L.) namely Asian armyworm, Spodoptera litura F. and castor semilooper, Achaea janata L. Larvae were fed with PVP coated-AgNPs treated castor leaf at different concentrations and their activity was compared to that of silver nitrate (AgNO3) treated leaf diets. Larval and pupal body weights decreased along with the decrease in the concentrations of AgNPs and AgNO3 in both the test insects. Low amounts of silver were accumulated in the larval guts, but major portion of it was eliminated through the feces. Ultrastructural studies of insect gut cell using Transmission Electron Microscopy (TEM) showed accumulation of silver nanoparticles in cell organelles. Changes in the antioxidative and detoxifying enzymes of the treated larva were estimated. The effect of treatments showed differences in the activities of detoxifying enzymes, carboxylesterases (CarE), glucosidases (Glu) and glutathione S-transferases (GST) in the larval gut. Activities of superoxide dismutase, catalase, and peroxidase were also altered in the larval bodies due to the AgNPs treatments, suggesting that exposure of larvae to nanoparticles induces oxidative stress, which is countered by antioxidant enzymes. Induction of these enzymes may be an effective detoxification mechanism by which the herbivorous insect defends itself against nanoparticle treatment.

Prediction of optimized composition for enhanced mechanical and electrochemical response of Zr-C-N-Ag coatings for medical devices

The necessity of improving the performance of existing biocompatible materials promotes the investigation of new approaches to solve biocompatibility problems caused by low chemical stability and poor mechanical performance of implanted materials. Envisioning those problems and considering the current reported complications of implanted stainless steel 316L devices, this work aimed to produce new Zr-C-N-Ag coatings and to predict an optimal composition to provide the required electrochemical stability and mechanical performance to the stainless steel 316L. The coatings were deposited by dual unbalance magnetron sputtering and characterized in terms of chemical, structural, mechanical and electrochemical properties to optimize their functional properties by means of a second-order response surface methodology. The optimization process revealed that the best mechanical and electrochemical performance was reached when stoichiometric ZrC0.5N0.5 phase is the main constituent of the materials, with low amounts of silver (<8at.%) and residual oxygen, mainly explained by the electrochemical stability and mechanical performance of the Zr-C-N solid solution. The current density applied to the silver target was identified as the main parameter affecting the final properties of the films due to its direct relation to the incorporation of metallic silver in the system. However, the reactive gases, as well as the high amount of residual oxygen, were also found to be significant in the process.

Structure of the silver containing diamond like carbon films: Study by multiwavelength Raman spectroscopy and XRD

In the present study structure of silver containing diamond like carbon (DLC:Ag) films deposited by reactive magnetron sputtering was investigated by X-ray diffractometry (XRD) and multiwavelength Raman spectroscopy. In the case of the DLC:Ag films containing low amount of silver, crystalline silver oxide prevails over silver. While at higher Ag atomic concentrations formation of the silver crystallites of the different orientations was observed. Surface enhanced Raman scattering (SERS) effect was detected for high Ag content in the films. For UV excited Raman spectra sp3 bonded carbon related Raman scattering T peak at ~1060cm−1 was detected only for the films with the highest amount of silver (34.3at.%). The dependence of the Raman scattering spectra parameters such as position of the G peak, G peak full width at half maximum (FWHM(G)), D/G peak area ratio on Ag atomic concentration in DLC:Ag film as well as Raman scattering spectra excitation wavelength were studied. The dependence on Ag amount in film was more pronounced in the case of the Raman scattering spectra excited by higher wavelength laser beam, while in the case of the spectra excited by 325nm and 442nm laser beams only weak dependence (or no dependence) was observed. Overall tendency of the decrease of the dispersion of the G peak with the increase of Ag atomic concentration was found. Thus sp3/sp2 bond ratio in DLC:Ag film decreased with the increase of Ag atomic concentration in the films.

Corrosion of low-antimony lead–cadmium alloys in conditions of long-term polarization

Nowadays, lead-acid battery grids are manufactured mostly from low-antimony and lead–calcium alloys. A variable corrosion resistance of battery grids is caused by either battery operation conditions, purity of used alloy components, an alloy makeup, and the castings quality. Such compositions as usual lead–antimony alloy, low-antimony lead–arsenious alloy and lead–calcium alloy with moderate content of tin today may be regarded as the most studied ones. A significant share of published works has been devoted to low-antimony lead–tin alloys. In the present article, results of corrosion tests of the samples made with application of cadmium as the second component of low-antimony alloy, has been represented. Several samples were extra-alloyed by selenium and silver. Samples of lead–calcium and usual antimony alloys as well as pure lead samples were being tested simultaneously. Upon termination of polarization, weight of anodic films referred to a unit of the sample surface has been determined. Thus, the film covering lead–antimony alloy sample has the maximal weight, whereas the oxidation products on the pure lead surface have the lowest one. Among low-antimony alloys, the highest corrosion resistance has been found out with the samples alloyed by a low amount of silver. The microstructure of the castings surface has been analysed. Process of corrosion has been considered in connection with size of grains.

Composition, Enthalpy, and Vaporization Temperature Calculation of Ag?SiO2 Plasmas with Air in the Temperature Range from 1000 to 6000�K and for Pressure Included between 1 and 50 bars

With the Gibbs free energy minimization method, the molar fraction of chemical species are determined in temperature range included between 1000 and 6000 K for several proportions of air, silver and silica and for pressures included between 1 and 50 bars. The enthalpy and the vaporization temperature of liquid silver and liquid silica are studied. The key role of pressure on composition, enthalpy and the vaporization temperature is shown. The electrical neutrality is study, and the importance of ionized gaseous silver at low temperature is shown even for low amount of silver. The increase of electro‐negative ions (Ag− and O−) with pressure is shown. The vapor pressures fitting coefficients of Ag and SiO2 are given.

Bioaccumulation and toxicity of silver compounds: A review

AbstractA eview of the literature revealed that bioaccumulation of silver in soil is rather low, even if the soil is amended with silver‐containing sewage sludge. Plants grown on tailings of silver mines were found to have silver primarily in the root systems. In marine and freshwater systems, the highest reported bioconcentration factors (BCFs) were observed in algae (&gt;105), probably because of adsorption of the dissolved silver (&lt;0.45 μm fraction) to the cell surface. In herbivorous organisms (e.g., zooplankton and bivalves), the BCF was lower by about two orders of magnitude. Low amounts of silver were assimilated from food with no substantial biomagnification. In carnivores (e.g., fish), the BCF was also lower by one order of magnitude with no indication of biomagnification. Toxicity of silver occurs mainly in the aqueous phase and depends on the concentration of active, free Ag+ions. Accordingly, many processes and water characteristics reduce silver toxicity by stopping the formation of free Ag+, binding Ag+, or preventing binding of Ag+to the reactive surfaces of organisms. The solubility of a silver compound, and the presence of complexing agents (e.g., thiosulfate or chloride), dissolved organic carbon, and competing ions are important. In soil, sewage sludge, and sediments, in which silver sulfide predominates, the toxicity of silver, even at high total concentrations, is very low. The highly soluble silver thiosulfate complex has low toxicity, which can be attributed to the silver complexed by thiosulfate. Silver nitrate is one of the most toxic silver compounds. The toxic potential of silver chloride complexes in seawater is and will be an important issue for investigation. Aquatic chronic tests, long‐term tests, and tests including sensitive life stages show lower toxicity thresholds (˜1 μg Ag+/L). The organisms viewed as most sensitive to silver are small aquatic invertebrates, particularly embryonic and larval stages.

Ultramicrodetection of proteins in polyacrylamide gels

Here we report the development of a highly sensitive procedure to detect proteins within separation matrices which should facilitate the characterization of rare proteins. The procedure is based on photochemical reactions where very low amounts of silver are deposited around proteins and in a series of steps are converted to silver sulfide. When this conversion is carried out in the presence of [ 35S]thiourea the resulting radioactive silver sulfide allows detection down to femtogram quantities of protein. In this work we applied the above principle to proteins separated on sodium dodecyl sulfate-polyacrylamide gels, thus not influencing physical and chemical parameters which are important for separation. This procedure should find application in any technique where detection of very low or limited amounts of proteins are required.