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PubMed1986

Use of 5-(4-dimethylaminobenzylidene)rhodanine in quantitating silver grains eluted from autoradiograms of biological material.

5-(4-Dimethylaminobenzylidene)rhodamine, a silver-specific dye, was used in a colorimetric assay to quantitate the autoradiographic deposition of silver onto X-ray film after exposure to sodium dodecyl sulfate-polyacrylamide gels of radiolabeled biological material. Silver grains were eluted from autoradiograms with 5 N potassium hydroxide, dissolved in nitric acid, and neutralized with 1 M Trizma Base. The concentration of silver was measured spectrophotometrically owing to the chelation properties of the dye. After corrections for background exposure were made, the silver contents of excised bands were then determined by comparison to a standard curve generated with silver nitrate. We have used this silver assay to quantitate the relative amount of each polypeptide band comprising the polyomavirus structural protein VP2 doublet. The method reported here has proven useful when densitometry is inconvenient (i.e., short distance between bands, irregular shape of bands, very faint bands) in addition to being inexpensive and simple to perform.

Autoradiography↗
PubMed1990

Silver uptake and subsequent effects on growth and species composition in an estuarine community.

Silver within Chesapeake Bay is rapidly taken up by phytoplankton, in accordance with geochemical controls over silver speciation. Phytoplankton accumulate large cellular burdens at non-lethal concentrations, setting up the potential for transfer of silver to herbivores that graze upon the phytoplankton community. However, the American oyster, Crassostrea virginica, does not assimilate silver from phytoplankton, but rather from that dissolved in water. Oysters can accumulate high burdens of silver via this uptake pathway, without apparent effect. There is another, perhaps more significant, mechanism by which silver can impact higher trophic levels. Continuous inputs of low concentrations of silver can cause large changes in species composition and species succession in Chesapeake Bay phytoplankton communities maintained in experimental ecosystems. In addition, oyster growth was reduced significantly relative to growth of oysters of unaltered communities. Such indirect effects of low levels of toxic substances, although difficult to detect, must be considered when assessments of pollutant impacts are made.

Animals↗
PubMed2005

Contrasting effects of chloride on the toxicity of silver to two green algae, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii.

Short-term silver toxicity was determined for two freshwater algae, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii, in the presence and absence of chloride. Silver speciation in the exposure media was controlled and algal growth was measured over 6 h. For P. subcapitata, an alga with low Ag uptake fluxes, silver toxicity could be predicted on the basis of the free Ag+ concentration, in the presence or absence of significant complexation by chloride ions, as predicted by the biotic ligand model (BLM). For C. reinhardtii, an alga with high Ag uptake fluxes, silver toxicity was better predicted by the concentration of all labile dissolved Ag species than by free silver, a result that is consistent with diffusion through the unstirred layer surrounding the cell surface being the rate-limiting step in silver uptake. For both species, growth inhibition could be predicted on the basis of the Ag intracellular quota in the presence or absence of chloride, indicating that silver toxicity is a direct result of intracellular accumulation rather than cell surface interactions.

Chlorides↗
PubMed2005

Impact of heat on nanocrystalline silver dressings. Part II: Physical properties.

This work explores the effects of elevated temperature on the physical and chemical properties of nanocrystalline silver, and relates it to previously observed thermally induced changes in biological activity [Taylor PL et al. Biomaterials, in press, doi:10.1016/j.biomaterials.2005.05.040]. Microstructural evolution of nanocrystalline silver dressings, heat-treated for 24 h at temperatures from 23 to 110 degrees C, was studied in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These analyses indicated that silver nanocrystalline coatings undergo significant changes in structure when exposed to elevated temperature. XRD analysis showed a rapid increase in crystallite size above 75 degrees C along with decomposition of crystalline silver oxide (Ag2O) at the onset of crystallite growth. SEM imaging showed a loss of fine features and sintering of the structure at elevated temperatures. The XPS data indicated that silver-oxygen bonds disappeared completely, with the initial decomposition occurring between 23 and 37 degrees C, and total oxygen in the coating decreased from 16-17% to 6.5% over the temperature range of 75-110 degrees C. A comparison of these results to the data of Taylor et al. [Biomaterials, in press, doi:10.1016/j.biomaterials.2005.05.040] indicates that the unique biological properties of nanocrystalline silver are related to its nanostructure. This should guide future development of therapeutic nanocrystalline silver delivery systems.

Anti-Bacterial Agents↗
PubMed2004

Suppressive silver methods--a tool for identifying axotomy-induced neuron degeneration.

Suppressive silver methods evolved from empirical observations about 50 years ago that argyrophilia of normal nerve fibers can be suppressed by a short period of oxidation of tissue sections, whereas degenerating nerve fibers in the same preparations were still clearly visible. Based on this property, suppressive silver impregnation became the main technique for investigating pathways in the central nervous system until the early 1970s. Suppressive silver methods were also found to visualize degenerating nerve cell bodies, in addition to degenerating nerve fibers. This possibility has given these methods an important place among current tools for identifying neuronal degeneration in trauma, disease and toxicity. In this article we demonstrate and review the usefulness of suppressive silver methods in identifying neurons undergoing degeneration as a result of peripheral or central axon injury in immature animals. The documentation is based on previously published data from experiments in which silver impregnation was used to demonstrate degeneration of motoneurons following pure motor axon injury or mixed peripheral nerve injury, as well as on new results on degeneration-induced argyrophilia in the inferior olive following cerebellar lesions. We find that silver precipitates resulting from these injuries are localized either to the entire neuronal cytoplasm, to a few (typically two) intranuclear bodies, or to both sites. The findings are discussed in relation to morphological features of apoptosis, necrosis and retrograde neuronal responses. We suggest that suppressive silver methods allow visualization of different processes of neuronal degeneration, and therefore may be a useful adjunct for identifying axotomy-induced neuronal degeneration.

Animals↗
PubMed2006

Clinical and laboratory testing of a silver-impregnated lens case.

PURPOSE: Lens case contamination is a well-documented occurrence for contact lens wearers despite the efficacy of current lens disinfectants. Several microorganisms have a propensity to attach to surfaces and may become more tolerant of disinfection upon attachment. Non-compliance with disinfection regimens occasionally occurs wherein patients store their lenses in saline or in tap water. A silver-impregnated lens case was developed in an attempt to decrease case contamination. These studies examine the performance of the case both in vitro and in vivo. METHODS: In vitro, lens cases were challenged with 10(3) microorganism suspensions of bacteria. After 24h incubation at room temperature, aliquots of inocula were removed and spread plated onto appropriate growth media. Surviving colonies were counted and microorganism log drop values from initial challenge inocula were determined. Two 40-subject 1-month contralateral clinical studies were conducted with SOLO-care Aqua solution using one bowl of a silver-impregnated case and one bowl of a standard lens case for lens storage. Lens cases were collected and cultured for aerobic bacteria. RESULTS: In vitro efficacy data show significantly lower numbers of recovered microbes from silver-impregnated cases than from control cases. In both clinical studies, silver-impregnated cases had a statistically significantly lower proportion of bacterial contamination than control cases. The majority of microorganisms isolated from silver-impregnated cases were members of the normal skin flora. CONCLUSION: The performance of the silver-impregnated case in vitro and the observed lower proportion of contaminated silver-impregnated lens cases in a clinical setting demonstrate the case's ability to decrease bacterial contamination.

Colony Count, Microbial↗
PubMed2006

Silver activates mast cells through reactive oxygen species production and a thiol-sensitive store-independent Ca2+ influx.

In genetically susceptible human and/or experimental animals, heavy metals such as mercury, gold, and silver have been shown to highly induce adverse immunological reactions such as allergy and autoimmunity, in which mast cell degranulation is implicated as playing a role. We previously reported that silver activates mast cells and induces Ca2+ influx without stimulating intracellular signaling events required for activation of store-operated Ca2+ channels (SOCs). The purpose of the present study was to elucidate the possible involvement of reactive oxygen species (ROS) in the biological effects of silver. Analysis using oxidant-sensitive fluorescent probes such as dichlorodihydrofluorescein and scopoletin, as well as MCLA-amplified chemiluminescence, showed that silver induced intracellular production and/or extracellular release of ROS. Silver induced mast cell degranulation in a Ca2+ -dependent manner. Unlike IgE antigen, silver-induced Ca2+ influx was not affected by depletion of internal Ca2+ stores. Instead, the metal-induced Ca2+ influx was abolished and reversed by the cell-impermeant thiol-reducing agent dithiothreitol, indicating the regulation by oxidation of vicinal thiols on the cell surface. Consistent with this view, Ca2+ influx was blocked by the glutathione peroxidase mimetic ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) and the superoxide dismutase mimetic manganese(III) tetrakis 4-(benzoic acid)porphyrin, but not by exogenously added catalase or superoxide dismutase. These findings indicate that silver evokes the release of ROS and oxidation of thiols critical for the activation of a Ca2+ channel other than SOC. Such a novel ROS-dependent pathway might play a role in mast cell degranulation in metal-induced allergic and autoimmune reactions.

Animals↗
PubMed2006

Interfacial assembly of a phospholipid Langmuir monolayer by electrodeposited silver colloids.

Two-dimensional nanostructured silver films were electrodeposited at the surface of a silver nitrate subphase coated by a negatively charged dimyristoylphosphatidylglycerol (DMPG) Langmuir monolayer. The modifications of the phospholipid interfacial organization generated by the growing colloidal silver film were investigated using surface pressure-time isotherms and grazing incidence X-ray diffraction experiments (GIXD). A decrease in the initial surface pressure of the DMPG monolayer is observed outside of the growing silver film, followed by a stabilization of the surface pressure when the radius of the metallic layer reaches its plateau value. This behavior is attributed to the compression of the DMPG molecules above the silver film and to the correlated relaxation and expansion of those outside the silver film area as recorded by a Wilhelmy pressure sensor. GIXD experiments further evidenced the contraction of the phospholipid monolayer above the electrochemically growing films. Indeed, the diffraction spectra show a shift in the peak position toward higher values of the in-plane component of the wave-vector transfer, indicating a closer packing of the DMPG alkyl chains. This is also in agreement with the observed loss of the chain tilt angle, suggesting that the colloidal silver film induces interfacial structuring of the DMPG monolayer.

Colloids↗
PubMed2007

Measurements of DNA damage on silver stained comets using free Internet software.

Silver stain offers the possibility to stain comets permanently, but up to now it was impossible to measure the majority of the comet parameters, because the distinction between head and tail was not recognised by software. Here, we report a silver staining protocol that allows the measurement of comet parameters using the free Internet software CASP. We validated the silver stain protocol by comparing the behaviour of the parameter '% DNA in tail' in silver and fluorescent stained comets. The range of % DNA in tail for different visual categories of damage in silver stained comets was similar to that reported with fluorescence staining. The range was for category 0 (no damage), <1%; category 1 (low damage), 1-25%; category 2 (medium damage), >25-45%; category 3 (high damage), >45-70%; category 4 (very high damage), >70%. The mean of % DNA in tail in silver stained comets was also similar to that reported with fluorescence staining. The mean was for category 0, 0.4+/-0.34%; category 1, 12+/-7%; category 2, 37+/-4%; category 3, 57+/-5% and category 4, 83+/-6%. Others comet parameters such as tail length, tail moment and Olive tail moment can be also measured. The silver staining protocol reported here opens new opportunities for those working in the assay without fluorescent microscope as the measurement of comet parameters using free Internet software and conventional microscope becomes possible.

Comet Assay↗
PubMed2003

Preparation and characterization of activated carbon fibers supported with silver metal for antibacterial behavior.

In this work, the effect of immersion in silver nitrate solution on activated carbon fibers (ACFs) was investigated in relation to adsorption behavior and antibacterial activity of ACFs supported with silver (ACF/Ag). The pore and surface properties were studied in terms of BET volumetric measurement with nitrogen adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The antibacterial activities of ACF/Ag were studied in broth dilution tests against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) from a point of view of water purification. As an experimental result, the silver content of ACF/Ag increased with increasing concentration of silver nitrate. It was found that the micropore structure slightly decreased as the silver nitrate concentration increased. Otherwise, it was revealed that the ACF/Ag possessed a strong antibacterial activity and an inhibitory effect for the growing of E. coli and S. aureus, respectively. Silver content on ACF/Ag decreased rapidly because of rough morphology of silver particles in water erosion.

Anti-Bacterial Agents↗
PubMed1990

Evaluation of a new method for silver point removal.

A new device for removing silver points was evaluated. The instrument consists of a trepan bur to expose the end of the silver point and a hollow tube which fits over the exposed tip and is bonded to it with cyanoacrylate adhesive. Twenty groups with 10 extractors and silver points in each group were tested for adhesive strength with respect to overlap between extractor and silver point, snugness of fit, and setting time of the adhesive. The adhesive strengths were evaluated using the Instron Universal Testing Machine. Adhesive strengths of 2 to 5 kg were readily achieved, and such adhesion should be adequate under typical clinical conditions for silver point removal. The amount of overlap (in the range of 1 to 3 mm) and snugness of fit were significant in relation to adhesive strengths. A setting time of 5 min was adequate for maximum bonding, except when there was loose fit between the extractor and the silver point. Clinically, the device appears to be an effective method for silver point removal.

Adhesiveness↗
PubMed1998

Cerium oxide as a silver decolorizer in dental porcelains.

OBJECTIVES: Silver-base alloys are known to produce an esthetically unpleasant yellow-green tint in the dental porcelain when making PFM restorations. Cerium oxide is used in dental porcelains to simulate the natural fluorescence found in human dental enamel, and has also been used in the glass industry as a decolorizer. The purpose of this study was to determine the effect of CeO2 additions on the resistance of dental porcelain to staining from silver contamination. METHODS: Five batches of porcelain were prepared according to Weinstein et al. (1962) with 0.00, 0.05, 0.10, 0.15 and 0.20 wt% additions of CeO2. To determine the resistance of these porcelains to silver staining, 0.10 wt% additions of the silver oxides were triturated into the prepared CeO2 porcelains prior to sample fabrication. This procedure provided a more quantitative method of staining than firing directly on silver alloys. Silver oxide was added in two valence states as Ag2O and AgO to test for any possible effects on staining. Samples were pressed into a 17 mm diameter mold, and fired to 960 degrees C under vacuum. Three additional samples were prepared from the non-cerium porcelain frit to produce a non-stained control group. Color measurements were made with a spectrophotometer on the ten experimental groups and the control group. The CIE L*a*b* color difference, delta E*, was calculated between the control and the experimental groups. RESULTS: There was a significant decrease in the silver staining of dental porcelains when CeO2 additions of 0.10 wt% or greater were used. SIGNIFICANCE: Cerium oxide additions in the range of 0.10 to 0.20 wt% caused a three-fold reduction in the staining of dental porcelain samples which had been doped with 0.10 wt% of AgO or Ag2O.

Analysis of Variance↗
PubMed1998

Efficacy of silver-coated medical devices.

Silver coating of medical devices is believed to prevent device-associated infection. Several in-vitro and in-vivo studies, as well as clinical observations on silver-nylon, silver-intramedullary pins, silver oxide Foley catheters and silver-coated vascular prostheses have been performed during the past 30 years. Nevertheless, randomized clinical studies showing efficacy of such coated medical devices in high-risk patient populations are rare, have dealt with very small numbers of patients or are controversial. Physico-chemical, pharmacological and microbiological data explaining the antimicrobial efficacy of silver in prophylaxis of implants are presented here, as well as the scientific background for the established clinical benefits of silver-preparations in burns.

Blood Vessel Prosthesis↗
PubMed1997

Efficacy of thermal treatment and copper-silver ionization for controlling Legionella pneumophila in high-volume hot water plumbing systems in hospitals.

BACKGROUND: Thermal treatment and copper-silver ionization are often used for controlling Legionella pneumophila in high-volume hospital plumbing systems, although the comparative efficacies of these measures in high-volume systems are unknown. METHODS: Thermal treatment of a hot water circuit was accomplished by flushing hot water (> 60 degrees C) through distal fixtures for 10 minutes. Copper-silver ionization was conducted in three circuits by installing units into return lines immediately upstream from hot water tanks. Recovery rates of L. pneumophila were monitored by culturing swab samples from faucets. Concentrations of copper and silver in water samples were determined by atomic absorption spectrophotometry. RESULTS: Four heat-flush treatments failed to provide long-term control of L. pneumophila. In contrast, ionization treatment reduced the rate of recovery of L. pneumophila from 108 faucets from 72% to 2% within 1 month and maintained effective control for at least 22 months. Only three samples (1.9%) of hot water from faucets exceeded Environmental Protection Agency standards for silver, and none exceeded the standards for copper. Of 24 samples obtained from hot water tanks, 42% and 50% exceeded the silver and copper standards, respectively. CONCLUSIONS: Copper-silver ionization effectively controls L. pneumophila in high-volume plumbing systems and is superior to thermal treatment; however, high concentrations of copper and silver can accumulate at the bottom of hot water tanks.

Copper↗
PubMed1998

In vitro efficacy of a hydrophilic central venous catheter loaded with silver to prevent microbial colonization.

A method was developed to load the surface of a central venous catheter with silver to prevent bacterial colonization. Silver confers a broad antimicrobial activity with a relatively low risk of resistance. Catheters were incubated with a silver nitrate solution in different concentrations. The solvent, incubation temperature and incubation period were varied to examine the influence on the catheter loading. With increasing incubation temperature, time and concentration of silver nitrate, higher rates of silver elution were observed by atomic absorption spectroscopy. Furthermore, by using ethanol-water as a solvent instead of pure water, the amount of silver bound to the catheter surface was enhanced. The release of silver from the catheter surface is mainly controlled by first order kinetics. Antimicrobial efficacy of the modified catheter, in comparison to unloaded catheters, was tested in a stationary and a dynamic model with different microorganisms. Adherence experiments with Candida albicans showed almost complete inhibition of growth during a period of 72 hours, including initial adherence. While initial adherence of bacteria could not be prevented, these experiments showed an excellent reduction of bacterial colonization. In a perfusion model, adhesion of E. coli could be reduced for at least seven days. Further studies are planned to examine prolonged antimicrobial effects.

Anti-Infective Agents, Local↗
PubMed2000

Silver electrodeposition catalyzed by colloidal gold on carbon paste electrode: application to biotin-streptavidin interaction monitoring.

A new electrochemical method to monitor biotin-streptavidin interaction on carbon paste electrode, based on silver electrodeposition catalyzed by colloidal gold, was investigated. Silver reduction potential changed when colloidal gold was attached to an electrode surface through the biotin-streptavidin interaction. Thus, the direct reduction of silver ions on the electrode surface could be avoided and therefore, they were only reduced to metallic silver on the colloidal gold particle surface, forming a shell around these particles. When an anodic scan was performed, this shell of silver was oxidized and an oxidation process at + 0.08 V was recorded in NH3 1.0 M. Biotinylated albumin was adsorbed on the pretreated electrode surface. This modified electrode was immersed in colloidal gold-streptavidin labeled solutions. The carbon paste electrode was then activated in adequate medium (NaOH 0.1 M and H2SO4 0.1 M) to remove proteins from the electrode surface while colloidal gold particles remained adsorbed on it. Then, a silver electrodeposition at -0.18 V for 2 min and anodic stripping voltammetry were carried out in NH3 1.0 M containing 2.0 x 10(-5) M of silver lactate. An electrode surface preparation was carried out to obtain a good reproducibility of the analytical signal (5.3%), using a new electrode for each experiment. In addition, a sequential competitive assay was carried out to determine streptavidin. A linear relationship between peak current and logarithm of streptavidin concentration from 2.25 x 10(-15) to 2.24 x 10(-12) M and a limit of detection of 2.0 x 10(15) M were obtained.

Biotin↗
PubMed2002

Electron microscopic determination of silver incorporation in collagen fibers as a model of organic-metal chiral supramolecular structure with optical anisotropic properties.

The high positive linear dichroism (LD) exhibited by silver-impregnated collagen fibers are thought to be caused by an ordered binding of silver nanoparticles to the collagen fibers. A correlation between LD, established by image analysis, and the size of silver particles as measured by electron microscopy was investigated in the same sections of silver-impregnated tendon collagen fibers. Silver particles were found to be periodically ordered along the collagen fibers, with some preference for the 67 nm collagen period and collagen a bands. The silver particle diameter for a sample of n=279 was 18.51 nm on average, with 95% of the values ranging between 17.90 and 19.14 nm. The finding that interference colors are correlated to abnormal dispersion of birefringence characteristics supports the concept that collagen fibers induce an ordered binding of silver distributed along the fibers.

Animals↗
PubMed2001

Thiosulfate enhances silver uptake by a green alga: role of anion transporters in metal uptake.

Short-term (< 1 h) silver uptake by the green alga Chlamydomonas reinhardtii was measured in the laboratory in defined inorganic media in the presence or absence of ligands (chloride and thiosulfate). In contradiction to the free-ion model of metal uptake, silver accumulation by the alga proved to be sensitive to the choice of ligand used to buffer the free silver concentration. For a low fixed free Ag+ concentration of 10 nM, silver uptake in the presence of thiosulfate (0.11 microM) was 2x greater than in the presence of chloride (4 mM). When sulfate was removed from the exposure medium (i.e., 81 microM-->0 microM), silver uptake in the presence of thiosulfate was even more markedly enhanced (more than 4x greater than in the presence of chloride). Varying the sulfate concentration in the exposure medium only affected silver uptake if thiosulfate was present. We conclude that silver-thiosulfate complexes are transported across the plasma membrane via sulfate/thiosulfate transport systems and that sulfate acts as a competitive inhibitor of this uptake mechanism.

Animals↗