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Silver bromide nanoparticle/polymer composites: dual action tunable antimicrobial materials.

We present a simple method of fabricating highly potent dual action antibacterial composites consisting of a cationic polymer matrix and embedded silver bromide nanoparticles. A simple and novel technique of on-site precipitation of AgBr was used to synthesize the polymer/nanoparticle composites. The synthesized composites have potent antibacterial activity toward both gram-positive and gram-negative bacteria. The materials form good coatings on surfaces and kill both airborne and waterborne bacteria. Surfaces coated with these composites resist biofilm formation. These composites are different from other silver-containing antibacterial materials both in the ease of synthesis and in the use of a silver salt nanoparticle instead of elemental silver or complex silver compounds. We also demonstrate the ability to tune the release of biocidal Ag(+) ions from these composites by controlling the size of the embedded AgBr nanoparticles. These composites are potentially useful as antimicrobial coatings in a wide variety of biomedical and general use applications.

Anti-Bacterial Agents↗

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network.

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.

DNA↗

Surface-enhanced fluorescence of fluorescein-labeled oligonucleotides capped on silver nanoparticles.

Tiopronin monolayer-protected silver nanoparticles with different core sizes (average diameter = 2, 5, 20 nm) were prepared by using different mole ratios of silver nitrate/tiopronin. Ligands on the silver particles were partially displaced by fluorescein-labeled thiolate single-stranded oligonucleotides or their complementary unlabeled oligonucleotides through ligand exchange. The fluorophores on silver particles showed a surface-enhanced fluorescence (SEF) dependent on the size of metallic cores. The particles could be coupled through hybridizations of oligonucleotides bound on the particles. The coupled particles were aggregated due to multiple displacements of oligonucleotides on each particle, resulting in stronger SEF. The dye-labeled oligonucleotides were assembled on the silver islands on the solid substrate, and the complementary oligonucleotide-displaced particles were coupled via oligonucleotide hybridization. The couplings between particles and islands resulted in an obvious fluorescence enhancement.

Fluorescein↗

Gold and silver uptake and nanoprecipitation on calcium alginate beads.

Calcium alginate beads were investigated for their biosorption performance in the removal of gold and silver from aqueous solutions. It was found that uptake capacities were significantly affected by the solution pH, with optimum pH values of 2 and 4 for gold and silver, respectively. Kinetic and isotherm experiments were carried out at the optimum pH. The maximum uptake capacities were 290 mg/g for Au and 52 mg/g for Ag. FTIR analysis indicated that both carboxylic and hydroxylic functional groups in alginate beads are involved in the metal binding and later reduction of gold (+3) and silver (+1) to gold (0) and silver (0). SEM and X-ray diffraction confirmed the formation of gold and silver nanoparticles.

Adsorption↗

Surface-grafted viologen for precipitation of silver nanoparticles and their combined bactericidal activities.

A viologen, N-hexyl-N'-(4-vinylbenzyl)-4,4'-bipyridinium dinitrate (HVVN), was synthesized and subsequently graft-copolymerized on poly(ethylene terephthalate) (PET) films. Silver nanoparticles can be deposited on the surface of the HVVN-PET film through photoinduced reduction of the silver ions in salt solution. The size and distribution of the silver nanoparticles can be varied by changing the reaction time. The pyridinium groups of the HVVN graft-copolymerized on the surface of the substrate possess bactericidal effects on Escherichia coli, and this antibacterial effect can be very significantly enhanced by the incorporation of silver nanoparticles on the HVVN-PET film. The dual functionalities of HVVN and silver remain stable after prolonged immersion in phosphate buffer solution and after aging in a weathering chamber.

Anti-Bacterial Agents↗

Effects of gold nanoparticle and electrode surface properties on electrocatalytic silver deposition for electrochemical DNA hybridization detection.

In this paper we report the catalytic effects of various gold nanoparticles for silver electrodeposition on indium tin oxide (ITO)-based electrodes, and successfully apply this methodology for signal amplification of the hybridization assay. The most widely used gold nanoparticle-based hybridization indicators all promote silver electrodeposition on the bare ITO electrodes, with decreasing catalytic capability in order of 10 nm gold, DNA probe-10 nm gold conjugate, streptavidin-5 nm gold, and streptavidin-10 nm gold. Of greater importance, these electrocatalytic characteristics are affected by any surface modifications of the electrode surfaces. This is illustrated by coating the ITO with an electroconducting polymer, poly(2-aminobenzoic acid)(PABA), as well as avidin molecules, which are promising immobilization platforms for DNA biosensors. The catalytic silver electrodeposition of the gold nanoparticles on the PABA-coated ITO surfaces resembles that on the bare surfaces. With avidin covalently bound to the PABA, it is interesting to note that the changes in electrocatalytic performance vary for different types of gold nanoparticles. For the streptavidin-5 nm gold, the silver electrodeposition profile is unaffected by the presence of the avidin layer, whereas for both the 10 nm Au and DNA probe-10 nm gold conjugate, the deposition profiles are suppressed. The streptavidin-5 nm gold is employed as the hybridization indicator, with avidin-modified (via PABA) ITO electrode as the immobilization platform, to enable signal amplification by the silver electrodeposition process. Under the conditions, this detection strategy offers a signal-to-noise ratio of 20. We believe that this protocol has great potential for simple, reproducible, highly selective and sensitive DNA detection on fully integrated microdevices in clinical diagnostics and environmental monitoring applications.

DNA↗

Silver ion dynamics in the Ag5Te2Cl-polymorphs revealed by solid state NMR lineshape and two- and three-time correlation spectroscopies.

The relation between structure and ion dynamics in the three polymorphs of Ag(5)Te(2)Cl has been investigated using (109)Ag, (125)Te, and (35)Cl NMR spectroscopies. Specifically, the influence of the structural phase transitions observed near 240 K (P2(1)/c<-->P2(1)/n) and near 332 K (P2(1)/n<-->I4/mcm) upon silver ion mobilities has been studied by temperature dependent (109)Ag NMR lineshapes and spin-lattice relaxation times. While the superionic high temperature phase alpha-Ag(5)Te(2)Cl is characterized by a molten cationic sublattice, fast ion dynamics in the medium-temperature phase beta-Ag(5)Te(2)Cl occurs in spatially restricted regions comprising all the crystallographically distinct silver sites. Temperature dependent magic-angle-spinning linewidths yield an activation energy of 0.38 eV, consistent with 0.44 eV measured from dc electric conductivities. For the low-temperature gamma-modification, results of two- and three-time (109)Ag correlation spectroscopies provide a detailed insight into the nature of the silver ionic hopping motion. Temperature dependent jump rates measured by two-time correlation functions yield an activation energy E(a)= 0.48 eV. (109)Ag NMR three-time correlation functions indicate that the non-exponential relaxation behavior of the silver ions can be attributed to a broad distribution of jump rates rather than correlated forward-backward jumps. Nevertheless, all the silver ions are mobile down to temperatures of about 185 K.

Cations↗

Antibacterial activity of resin composites with silver-containing materials.

Resin composites with antibacterial activity may be useful to decrease the frequency of secondary caries around restorations. The purposes of this study were to investigate the antibacterial activity of light-activated resin composites incorporating one of three silver-containing materials and to evaluate their long-term inhibitory effect against Streptococcus mutans The three types of silver-containing materials, Novaron (N), Amenitop (AM), and AIS, were incorporated into TEGDMA-UDMA-based light-activated resin composites, and the antibacterial activities, mechanical properties and release of silver ions were examined. Minimum inhibitory concentrations in suspensions of N, AM, and AIS against S. mutans were 1.1, 1.2, and 23.0 mg/ml, respectively. Resin composites incorporating 5 wt% of Novaron (N-5) and 7 wt% of Amenitop (AM-7) inhibited the growth of S. mutans after immersion in water for 3 months, whereas the resin composite incorporating 10 wt% of AIS did not. No significant difference in either compressive or flexural strength was observed between the control and N-5 composites after 1 d and 3 months storage in water. However, for AM-5 composite, there was a significant difference in both strength parameters between the two immersion periods. There was no or extremely little release of silver ions from the N-5 and AM-5 composites after 1 d or 3 months immersion in water. These results indicated that a light-activated resin composite incorporating silver-containing materials such as Novaron may be clinically useful due to its long-term inhibitory effect against S. mutans and favorable mechanical properties.

Aluminum Oxide↗

Silver nitrate: histological effects of cautery on epithelial surfaces with varying contact times.

Silver nitrate is used extensively in rhinological practice for the treatment of recurrent epistaxis. There are currently no recommendations in the literature regarding the optimum application time of this chemical for effective treatment. We assessed the histological effects of silver nitrate on mucosal tissue at varying contact times and made recommendations based on our findings. Silver nitrate was applied at predetermined contact times to tonsillar mucosa, immediately before tonsillectomy in subjects undergoing routine surgery. The cauterized areas were subsequently analysed histologically. The depth of tissue penetration by the silver nitrate was measured. The means for 5, 10 and 20 s were 0.44, 0.30 and 0.38, respectively, P = 0.3. Overall, there was no deeper penetration of the tissues with contact times over 5 s. We conclude that it is not necessary to apply silver nitrate for greater than 5 s to achieve maximal tissue penetration.

Anti-Infective Agents, Local↗

Is there evidence for recommending silver-coated urinary catheters in guidelines?

We evaluated the available literature on effectiveness of silver-coated versus uncoated catheters for the prevention of urinary tract infections in catheterized patients stratified by sex, systemic antibiotic use, renal function and duration of catheterization. Controlled clinical trials, randomized clinical trials and systematic reviews/meta-analysis were identified by a search strategy in Medline (1966-August 2001) and in the Cochrane Controlled Trials Register. Keywords were urinary catheterization, silver and infection. Trials using silver-coated catheters in the treatment group and uncoated catheters in the control group, with bacteriuria as the outcome measure, were selected. The quality of the methods used of all selected publications was assessed by using a quality assessment scale for randomized clinical trials. In addition we looked critically at subject-specific aspects. Data from the original publications were used to calculate the overall relative risk of bacteriuria in patients with silver-coated versus uncoated catheters, as well as the effect in subgroups. Thirteen trials and one meta-analysis were identified. Seven reports satisfied the selection criteria with only one achieving a high-quality score. Confounding variables were not considered in any trial. Additional studies with a high standard of internal quality and careful specification of the clinical question with regard to subject-specific critical points are necessary to decide whether the use of silver-coated catheters can be recommended.

Cross Infection↗

Silver staining of myelin by means of physical development.

For staining myelin with silver a physical development technique has been devised that can render visible the thinnest fibers in various animal species, including fishes and reptiles, even in the early phase of myelination and may be applied to both frozen and embedded materials. Its principle is as follows: Myelin can form and bind colloidal silver particles in a 0.1% ammoniacal silver nitrate solution of pH 7.5. The production of metallic silver by other tissue elements is suppressed by the sections pretreated with a 2:1 mixture of pyridine and acetic anhydride for 30 min. The colloidal silver particles bound in the myelin are enlarged to microscopic dimensions by a special physical developer.

Animals↗

Silver stains demonstrating neuroendocrine cells.

During the preimmunohistochemical era, silver stains were an important part of the staining arsenal for identifying certain tissue structures and cell types in tissue sections. Some of them were useful for demonstrating endocrine cells, especially in the gastrointestinal tract. Until the late 1950s, silver stains, particularly those identifying endocrine cells, were accompanied by a number of technical difficulties resulting from uncontrolled staining factors. In the 1960s, new silver stains were developed for endocrine cell types and these stains gave reproducible results. One of the "older" silver stains and two of the "newer" ones are emphasized in this presentation, namely the Masson, the Grimelius and the Sevier-Munger techniques. The Masson stain demonstrates the enterochromaffin (EC, serotonin) cells, the Grimelius stain is a broad endocrine cell marker, and the Sevier-Munger technique demonstrates EC and EC-like cells and the C-cells of the thyroid. Especially in the preimmunohistochemical era, these staining methods often were used for histopathological diagnosis, particularly the Grimelius technique. The silver stains were developed empirically, and with few exceptions the chemical background is not known. Staining protocols are included.

Colon↗

The feasibility of measuring silver concentrations in vivo with x-ray fluorescence.

X-ray fluorescence (XRF) has been demonstrated to be an extremely useful technique for measuring trace quantities of heavy metals in various tissues in the body. This study investigates the applicability of XRF to the measurement of silver concentrations in skin. The system chosen employs an 125I source to excite the silver K x-rays, with the source, sample and detector arranged in a 90 degrees geometry. Experiments with silver-doped skin phantoms indicate that a minimum detectable concentration of 3-4 ppm is possible in 10-20 min measurement periods. Based on estimates of silver concentrations in the skin of patients suffering from argyria, the proposed system has sufficient sensitivity to warrant further investigation into its usefulness for non-invasive monitoring of exposed populations. Specifically, such a measurement may well allow for the identification of individuals at risk of subsequently exhibiting argyria, an irreversible skin pigmentation arising from silver exposure.

Argyria↗

Silver (I) cation specifically stabilizes heteroduplex with C:C mismatch base pair: toward the efficient detection of single nucleotide polymorphism (2).

We examined the effect of silver (I) cation on the thermal stability of heteroduplex and homoduplex. Addition of silver (I) cation increased the melting temperature of heteroduplex containing C:C mismatch base pair by about 3-4 degrees C. The thermal stability of homoduplex and heteroduplexes containing other kinds of mismatch base pairs was not significantly changed by the addition of silver (I) cation. We conclude that silver (I) cation specifically stabilizes heteroduplex containing C:C mismatch base pair. Our results certainly support the idea that the addition of silver (I) cation to C:C mismatch base pair in heteroduplex could be a convenient strategy for heteroduplex analysis and may eventually lead to progress in single nucleotide polymorphism genotyping.

Base Pair Mismatch↗

Silver-containing dressings and the need for evidence.

The field of wound care has been inundated with "active" dressings--those that deliver biologically active substances to the wound site--and much attention has been given to those containing silver. Silver is a broad-spectrum agent: it is bactericidal to a large number of Gram-positive and Gram-negative microorganisms, many aerobes and anaerobes, and several antibiotic-resistant strains. More than 10 dressings containing pure silver are currently available; all claim to enhance wound healing through the antimicrobial activity of silver. But research findings on silver's antimicrobial efficacy are often inconclusive or contradictory. How, therefore, can clinicians decide which dressing is most appropriate for each patient? A grading system for reviewing the literature is presented.

Anti-Infective Agents↗

A prospective, randomized evaluation of the effect of silver impregnated subcutaneous cuffs for preventing tunneled chronic venous access catheter infections in cancer patients.

OBJECTIVE: This study was performed to evaluate the effect of a silver-impregnated cuff on the incidence of catheter-related bacteremia/fungemia or tunnel tract infection in cancer patients with chronic dual-lumen tunneled venous access catheters. SUMMARY BACKGROUND DATA: Infection is a frequent and potentially life-threatening complication of tunneled chronic cuffed silastic central venous access catheters in cancer patients. Recent experience with antimicrobial silver-impregnated cuffs placed on nontunneled percutaneously inserted central venous catheters suggests that such a cuff may render the catheter less prone to infection. METHODS: The authors prospectively randomized 200 cancer patients to receive either a dual-lumen 10 French tunneled cuffed silastic central venous access catheter or the same catheter with a second more proximal subcutaneous silver-impregnated cuff. All patients then were followed prospectively for infectious morbidity until the device was removed or the patient died. RESULTS: The hazard rate for infection/day (95% confidence limits) was 0.0022 (0.0015 to 0.0030) for standard catheters compared with 0.0027 (0.0019 to 0.0037) for catheters with silver-impregnated cuffs (p = not significant). Regression analysis of infection-free interval of both catheter types shows no difference over the lifetime of catheter as well as the over the first 48 days after insertion. CONCLUSIONS: The study indicated no effect of a silver-impregnated cuff in decreasing the incidence of catheter-related bacteremias/fungemias, tunnel infections, or the spectrum of causative microorganisms involved in cancer patients with tunneled chronic venous access catheters.

Adolescent↗

Effect of topical applications of silver sulfadiazine on the natural killer cell activity in a rat model of thermal injury.

The effect of topical application of silver sulfadiazine cream on the natural killer (NK) cell cytotoxicity was studied in a rat model of thermal injury. The rats were given a 30% total body surface area scald injury and the NK cell cytotoxicity was studied in rats at different days postinjury with or without treatment with silver sulfadiazine. The NK cell activity was observed to be significantly (P less than .0025) suppressed at day 7 postinjury in nontreated burned rats compared with control sham burned animals. Interestingly, in rats treated with silver sulfadiazine twice daily, no suppression in NK cell activity was observed. The application of base cream (without silver sulfadiazine) did not have any significant effect on the NK cell activity in burned rats. The data show that the effect of silver sulfadiazine on NK cell activity may be due to the sulfadiazine component, since the serum levels of sulfadiazine (33.7 +/- 1.9 micrograms/dL) were observed to be maximal at day 7 postinjury.

Administration, Cutaneous↗

Comparative evaluation of zinc sulfadiazine and silver sulfadiazine in burn wound infection.

One percent silver sulfadiazine has been commonly used as a topical antimicrobial agent after a burn injury. Incidence of burn wound colonization by Staphylococcus aureus in patients treated with silver sulfadiazine has spurred research for other agents. A topical preparation that contains zinc and sulfadiazine (Zad-G) was evaluated for in vitro antibacterial spectrum and in vivo efficacy. Muscle biopsy specimens of rats treated with Zad-G appear to have fewer colonies of S. aureus than groups treated with silver sulfadiazine. Topical therapy with Zad-G for patients with burns was comfortable, reduced wound infection, and was comparable to therapy with silver sulfadiazine. A topical Zad-G preparation that contains zinc sulfadiazine appears to be an effective alternative to silver sulfadiazine in the treatment of burn wounds.

Administration, Topical↗