Preparation of silver nanoparticles with antimicrobial activities and the researches of their biocompatibilities

Silver nanoparticles were prepared by chemical reduction method using chitosan as stabilizer and ascorbic acid as reducing agent in this work. The silver/chitosan nanocomposites were characterized in terms of their particle sizes and morphology by using UV spectrophotometer, nano-grainsize analyzer, and transmission electron microscopy. Antibacterial activities of these nanocomposites were carried out for Staphylococcus aureus and Escherichia coli. The silver nanoparticles exhibited significantly inhibition capacity towards these bacteria. Detailed studies on the biocompatibility of the silver/chitosan nanocomposites were investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cell adhesion test. The results indicated that these silver/chitosan nanocomposites were benefit for the proliferation and adhesion of L-929 cells, and the biocompatibilities between the nanocomposites and the cells would become better with the culturing days. We anticipated that these silver/chitosan nanocomposites could be a promising candidate as coating material in biomedical engineering and food packing fields wherein antibacterial properties and biocompatibilities are crucial.     

Bio-synthesis of gold and silver nanoparticles from Candida guilliermondii and their antimicrobial effect against pathogenic bacteria

In the present study we investigated the extra cellular synthesis of gold and silver nanoparticles by using the yeast Candida guilliermondii. The formation of noble metal nanoparticles was monitored by the UV-Visible spectroscopy. As prepared gold and silver nanoparticles showed distinct surface plasmon peaks at 530 nm and 425 nm respectively. Phase and morphology of the as synthesized materials were investigated by X-ray diffraction and electron microscopy techniques respectively. XRD patterns confirmed the formation of gold and silver nanoparticles with face centered cubic structures. Bio-TEM images showed the formation of near spherical, well dispersed gold and silver nanoparticles in the size range of 50-70 nm and 10-20 nm respectively. The biosynthesized nanoparticles were tested for their antimicrobial activity against five pathogenic bacterial strains. The highest efficiency for both gold and silver nanoparticles was observed against Staphylococcus aureus. A comparative study was also done to find the effect of chemically synthesized noble metal nanoparticles against the above test strains. Chemically synthesized particles had no antimicrobial activity against any of the pathogenic strains. The results obtained suggest that biosynthesized gold and silver nanoparticles can be used as effective antimicrobial agents against some of the potential harmful pathogenic microorganisms.     

Layer-by-layer deposition of green synthesised silver nanoparticles on polyester air filters and its antimicrobial activity

Silver nanoparticles stabilised with anionic polymeric polyelectrolytes were successfully synthesised by high-energy UV reduction. Three types of polyelectrolytes were used including poly(methacrylic acid) (PMA), poly(acrylic acid) (PAA) and poly(4-styrenesulphonic acid-co-maleic acid) (CoPSS). The formation of the prepared solutions exhibited surface plasmon resonance at the wavelength of 475, 730 and 408 nm by using PMA, PAA and CoPSS as the stabilising agents. UV–visible spectrophotometer, transmission electron microscope (TEM) and zeta potential analyser were employed to characterise the formation of the prepared solutions. The silver nanoparticles stabilised with anionic polyelectrolytes were immobilised on polyester air filters using a layer-by-layer technique. This is the sequential dipping of polyester air filters in a dilute solution of cationic poly(diallyldimethylammonium chloride) and anionic polymeric polyelectrolytes capped silver. The surface topography of the polyester air filters were measured by field emission scanning electron microscope. Results showed that silver nanoparticles had the highest surface coverage on the polyester air filters probably because it is a good bonding candidate and insures strong film growth. The multilayers polyester air filters coated silver nanoparticles were tested against the gram positive pathogen Staphylococcus aureus. The deposition of silver nanoparticles onto the polyester air filters resulted in 92.18%, 84.32% and 71.19% of bacteria removal using PMA, PAA and CoPSS as the stabilising agent.     

Synthesis of Starch-Stabilized Silver Nanoparticles and Their Antimicrobial Activity

In this study, silver nanoparticles were prepared using silver nitrate as the metal precursor, starch as protecting agent, and sodium borohydride (NaBH₄) as a reducing agent by the chemical reduction method. The formation of the silver nanoparticles was monitored using ultraviolet-visible absorption spectroscopy, cyclic voltammetry, and particle size analyzer and characterized by transmission electron microscopy (TEM) and x-ray diffraction (XRD). Synthesis of nanoparticles were carried out by varying different parameters, such as reaction temperature, concentration of reducing agent, concentration of silver ion in feed solution, type and concentration of the stabilizing agent, and stirrer speed expressed in terms of particle size and size distribution. Dispersion destabilization of colloidal nanoparticles was detected by Turbiscan. It was observed that size of the starch stabilized silver nanoparticles were lower than 10 nm. The microbial activity of synthesized silver nanoparticles was examined by modified Kirby-Bauer disk diffusion method. Silver nanoparticles were tested for their antibacterial activity against Gram negative bacteria such as Escherichia coli, Pseudomonas aeruginosa, and Gram positive bacteria such as Staphylococcus aureus and Staphylococcus epidermidis. High bacterial activity was observed at very low concentrations of silver (below 1.39 μg/ml). The antifungal activity of silver nanoparticles has been assayed against Candida albicans.     

Effect of biologically synthesised silver nanoparticles on Staphylococcus aureus biofilm quenching and prevention of biofilm formation

The development of green experimental processes for the synthesis of nanoparticles is a need in the field of nanotechnology. In the present study, the authors reported rapid synthesis of silver nanoparticles using fresh leaves extract of Cymbopogan citratus (lemongrass) with increased stability. The synthesised silver nanoparticles were found to be stable for several months. UV-visible spectrophotometric analysis was carried out to assess the synthesis of silver nanoparticles. The synthesised silver nanoparticles were further characterised by using nanoparticle tracking analyser (NTA), transmission electron microscope (TEM) and energy-dispersive x-ray spectra (EDX). The NTA results showed that the mean size was found to be 32?nm. Silver nanoparticles with controlled size and shape were observed under TEM micrograph. The EDX of the nanoparticles confirmed the presence of elemental silver. These silver nanoparticles showed enhanced quorum quenching activity against Staphylococcus aureus biofilm and prevention of biofilm formation which can be seen under inverted microscope (40X). In the near future, silver nanoparticles synthesised using green methods may be used in the treatment of infections caused by a highly antibiotic resistant biofilm.     

Silver nanoparticle synthesis: novel route for laser triggering of polyelectrolyte capsules

We have demonstrated the synthesis of light-sensitive polyelectrolyte capsules (PECs) by utilizing a novel polyol reduction method and investigated its applicability as photosensitive drug delivery vehicle. The nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on silica particles followed by in-situ synthesis of silver nanoparticles (NPs). Capsules without silver NPs were permeable to low molecular weight (M(w), 479 g/mol) rhodamine but impermeable to higher molecular weight fluorescence labeled dextran (FITC-dextran). However, capsules synthesized with silver NPs showed porous morphology and were permeable to higher molecular weight (M(w) 70 kDa) FITC-dextran also. These capsules were loaded with FITC-dextran using thermal encapsulation method by exploiting temperature induced shrinking of the capsules. During heat treatment the porous morphology of the capsules transformed into smooth pore free structure which prevents the movement of dextran into bulk during the loading process. When these loaded capsules are exposed to laser pulses, the capsule wall ruptured, resulting in the release of the loaded drug/dye. The rupture of the capsules was dependent on particle size, laser pulse energy and exposure time. The release was linear with time when pulse energy of 400 μJ was used and burst release was observed when pulse energy increased to 600 μJ.     

Aqueous synthesis of silver nanoparticle embedded cationic polymer nanofibers and their antibacterial activity

This paper describes the one-pot, aqueous synthesis of cationic polymer nanofibers with embedded silver nanoparticles. Poly[2-(tert-butylaminoethyl) methacrylate] (PTBAM) was used as a cationic polymer substrate to reinforce the antimicrobial activity of the embedded silver nanoparticles. Electron microscope analyses revealed that the as-synthesized nanofibers had diameters of approximately 40 nm and lengths up to about 10 μm. Additionally, silver nanoparticles of approximately 8 nm in diameter were finely embedded into the prepared nanofibers. The embedded silver nanoparticles had a lower tendency to agglomerate than colloidal silver nanoparticles of comparable size. In addition, the nanofibers with embedded silver nanoparticles exhibited excellent antibacterial performance against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Interestingly, the prepared nanofibers exhibited enhanced bactericidal performance compared with the silver-embedded poly(methyl methacrylate) (PMMA) nanofibers, presumably because of the antibacterial properties of the PTBAM substrate.     

Fabrication of antibacterial monodispersed Ag-SiO2 core-shell nanoparticles with high concentration

Monodispersed Ag-SiO₂ core-shell nanoparticles with a high concentration of 400 mg/L were successfully fabricated by using tetraethoxysilane as silica precursor and reducing silver nitrate with ascorbic acid in the presence of cetyltrimethylammonium bromide as stabilizing agent. The nanoparticles had a spherical silver core in a size range from 14-26 nm in diameter and an amorphous silica shell of 15-28 nm thickness, respectively. The antibacterial effects of Ag-SiO₂ core-shell particles against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were tested by the usual twofold serial dilution method for minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). The results indicated that the core-shell nanoparticles owned excellent antibacterial effects.     

Antimicrobial coatings — obtaining and characterization

In this paper, we present inorganic–organic hybrid coatings with polymer matrix (water soluble) that contain silver nanoparticles (AgNPs). The structure and morphology of coating materials were determined by infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). Therefore, the antimicrobial activities and mechanisms of coatings for several pathogenic bacteria (Bacilius cereus and Staphylococcus aureus) were investigated. It was demonstrated that the obtained material with silver nanoparticles keep their antimicrobial effect even if they are subjected to several cycles of washing with water and detergent.     

Release of dexamethasone from PLGA nanoparticles entrapped into dextran/poly(vinyl alcohol) hydrogels

Hydrogels based on blends of poly(vinyl alcohol) (PVA) with dextran were prepared by a physical cross-linking procedure and used as matrices for the entrapment of biodegradable nanoparticles loaded with dexamethasone. The nanoparticles were prepared, by a solvent evaporation technique, using biodegradable copolymers of poly(lactic acid)–poly(glycolic acid) (PLGA). Size, morphology and surface characteristics of the nanoparticles were evaluated by scanning electron microscopy. The mechanism of drug release from the nanoparticles entrapped into the PVA-based matrices was studied and compared to that from free nanoparticles. The effect of dextran on the in vitro release profile of dexamethasone from the hydrogels was investigated. The obtained results indicate that PLGA nanoparticles are able to release dexamethasone following a diffusion-controlled mechanism. The entrapment of the nanoparticles into the hydrogels affects only slightly this mechanism of drug release. In addition, dextran/PVA hydrogels release a higher amount of drug with respect to pure PVA hydrogels and by increasing dextran content in the hydrogels, the amount of drug released increases.     

Preparation of silver nanoparticles having low melting temperature through a new synthetic process without solvent

This study presents a new synthetic method of silver nanoparticles using a novel polyoxyethylene maleate-based surfactant (PEOM). Unlike conventional process using large amount of a solvent to dissolve silver salts, large amount of silver salts (AgNO3) can be dissolved and stabilized by our surfactant without solvent. Silver salts can be dissociated within PEOM by the formation of charge complex between hydrophilic-COOH segments and Ag+NO3-, resulting in formation of self-assembled microstructures which acting as a nano-reactor and stabilizer. After reduction using NaBH4, uniform sized silver nanoparticles were formed in the hydrophilic domain of PEOM. Silver contents in the colloids were changed by 0.5 approximately 3 wt%. Distribution of silver nanoparticle sizes was investigated by using TEM and XRD. Melting temperature of silver nanoparticles was measured by differential scanning calorimetry, which depends upon the particle size of silver nanoparticles. The lowest melting temperature of 112 degrees was measured from 3.5 nm average-sized silver particles.     

In-vivo and in-vitro biocompatibility evaluations of silver nanoparticles with antimicrobial activity

In this study, the biocompatibility and antimicrobial activity of silver nanoparticles (Ag NPs) were evaluated in vitro and in vivo. The cytotoxicity of Ag NPs (average diameter: 2-5 nm) against CHO-K1 cells was determined via WST-8 assay, and their genotoxicity was examined via Salmonella typhimurium reverse mutation assay (Ames test). The acute toxicity and intracutaneous reactivity of Ag NPs were evaluated using animal models of mice and rabbits, respectively. The antibacterial effects of Ag NPs on the Gram (-) bacterial strains of Escherichia coli ATCC 8739 and Pseudomonas aeruginosa ATCC 9027 and on the Gram (+) bacterial strains of Staphylococcus aureus ATCC 6538p and Bacillus subtilius ATCC 6633 were determined by measuring the minimum inhibitory concentrations. The Ag NPs were highly cytotoxic to the L-929 cells at over 2 ppm but were non-cytotoxic at lower than 1 ppm. Moreover, the Ag NPs at 1 ppm or lower did not show genotoxicity, acute toxicity and intracutaneous reactivity. It was also found that the Ag NPs exerted effective antimicrobial activities on both the Gram (-) and (+) bacterial strains within the range from 0.06 to 0.98 ppm for 50% MIC.     

The cellular responses and antibacterial activities of silver nanoparticles stabilized by different polymers

Silver nanoparticles (AgNPs) are known for their excellent antibacterial activities. The possible toxicity, however, is a major concern for their applications. Three types of AgNPs were prepared in this study by chemical processes. Each was stabilized by a polymer surfactant, which was expected to reduce the exposure of cells to AgNPs and therefore their cytotoxicity. The polymer stabilizers included poly(oxyethylene)-segmented imide (POEM), poly(styrene-co-maleic anhydride)-grafting poly(oxyalkylene) (SMA) and poly(vinyl alcohol) (PVA). The cytotoxicity of these chemically produced AgNPs to mouse skin fibroblasts (L929), human hepatocarcinoma cells (HepG2), and mouse monocyte macrophages (J774A1) was compared to that of physically produced AgNPs and gold nanoparticles (AuNPs) as well as the standard reference material RM8011 AuNPs. Results showed that SMA-AgNPs were the least cytotoxic among all materials, but cytotoxicity was still observed at higher silver concentrations (>30 ppm). Macrophages demonstrated the inflammatory response with cell size increase and viability decrease upon exposure to 10 ppm of the chemically produced AgNPs. SMA-AgNPs did not induce hemolysis at a silver concentration below 1.5 ppm. Regarding the antibacterial activity, POEM-AgNPs and SMA-AgNPs at 1 ppm silver content showed 99.9% and 99.3% growth inhibition against E. coli, while PVA-AgNPs at the same silver concentration displayed 79.1% inhibition. Overall, SMA-AgNPs demonstrated better safety in vitro and greater antibacterial effects than POEM-AgNPs and PVA-AgNPs. This study suggested that polymer stabilizers may play an important role in determining the toxicity of AgNPs.     

Dextran templating for the synthesis of metallic and metal oxide sponges

Silver or gold-containing porous frameworks have been used extensively in catalysis, electrochemistry, heat dissipation and biofiltration. These materials are often prepared by thermal reduction of metal-ion-impregnated porous insoluble supports (such as alumina and pumice), and have surface areas of about 1 m(2) g(-1), which is typically higher than that obtained for pure metal powders or foils prepared electrolytically or by infiltration and thermal decomposition of insoluble cellulose supports. Starch gels have been used in association with zeolite nanoparticles to produce porous inorganic materials with structural hierarchy, but the use of soft sacrificial templates in the synthesis of metallic sponges has not been investigated. Here we demonstrate that self-supporting macroporous frameworks of silver, gold and copper oxide, as well as composites of silver/copper oxide or silver/titania can be routinely prepared by heating metal-salt-containing pastes of the polysaccharide, dextran, to temperatures between 500 and 900 degrees C. Magnetic sponges were similarly prepared by replacing the metal salt precursor with preformed iron oxide (magnetite) nanoparticles. The use of dextran as a sacrificial template for the fabrication of metallic and metal oxide sponges should have significant benefits over existing technologies because the method is facile, inexpensive, environmentally benign, and amenable to scale-up and processing.     

Synthesis and layer-by-layer self-assembly of silver nanoparticles capped by mercaptosulfonic acid

Spherical silver nanoparticles capped by mercaptosulfonic acid with a diameter of about 8 nm were prepared by a simple chemical reaction. The resulting silver nanoparticles were characterized by UV–vis spectroscopy (UV–vis) and transmission electron microscopy (TEM). Using layer-by-layer (LBL) self-assembly technique, the multilayer films containing silver nanoparticles and polycation poly(dialyldimethylammonium chloride) (PDDA) were successfully fabricated. The fabrication process was monitored by UV–vis spectra and the morphology of the multilayer films was investigated by atomic force microscopy (AFM). The cyclic voltammogram (CV) measurements further confirmed that the silver nanoparticles had assembled into the multilayer films successfully. Surface-enhanced Raman spectroscopy (SERS) measurements showed that the multilayer films containing silver nanoparticles could serve as SERS-active substrate.     

银系抗菌剂对包装原纸性能的影响

目的 研究银系抗菌剂对包装原纸抗菌性能、白度和力学性能的影响。方法 选用乙酸银、纳米银、磺胺嘧啶银等3种不同的银系抗菌剂,采用表面涂布的方法制备出抗菌纸;选用大肠杆菌和金黄色葡萄球菌检测其抗菌性能;比较抗菌纸和空白试样的力学性能。结果 3种抗菌纸对大肠杆菌和金黄色葡萄球菌均有一定的抗菌效果,抑菌圈直径为0.35~5.46 mm,其中对金黄色葡萄球菌的抗菌效果最为明显;当抗菌液的质量分数为0~0.5%时,随着浓度的增加,乙酸银抗菌纸的抗菌性能随之增加;当抗菌液的质量分数为0~10%时,随着浓度的增加,纳米银抗菌纸的抗菌性能也逐渐增加;当抗菌液的质量分数为0.6%时,磺胺嘧啶银抗菌纸抗菌性能达到最佳;抗菌剂对包装原纸白度有一定影响,但对力学性能的影响不明显。结论 3种抗菌纸对金黄色葡萄球菌的抗菌效果比对大肠杆菌的优良,抗菌纸的抗菌性能与抗菌剂种类和浓度有关;抗菌处理对包装原纸的力学性能和表面结构影响不大,但乙酸银和纳米银抗菌剂会导致纸张白度的下降。     

纳米氧化高银的制备及抗菌性能

采用液相氧化沉淀法制备纳米氧化高银颗粒.以硝酸银为原料,氢氧化钠为沉淀剂,过硫酸钾为氧化剂,控制pH值为11,反应温度为80℃,在磁力搅拌器上反应30min,静置3h后,离心洗涤数次,70℃真空干燥3h,得到黑色纳米氧化高银颗粒.通过X射线衍射(XRD)、透射电子显微镜(TEM)对纳米氧化高银颗粒的形貌和结构进行表征;采用异养菌测试瓶法,用制备的氧化高银和粒径为30nm的纳米银对金黄色葡萄球菌进行抗菌性能测试.结果表明:制得的球形纳米颗粒粒径为10～30ntn;纳米氧化高银颗粒比纳米银具有更强的杀菌性能.     

Antibacterial activities of polyethylene glycol, tween 80 and sodium dodecyl sulphate coated silver nanoparticles in normal and multi-drug resistant bacteria

Antibacterial activity of silver nanoparticles coated with different functionalizing agents i.e., polyethylene glycol, tween 80 and sodium dodecyl sulphate were evaluated on both normal and multi-drug resistant strains of bacteria. Under the same reaction conditions, these functionalizing agents were added separately to coat silver nanoparticles. Among these, polyethylene glycol coated nanoparticles were most effective in killing all the bacterial strains which includes Escherichia coli DH5a, Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus and multi-drug resistant clinical isolates of Shigella spp. (flexneri, boydii, sohnea) and Vibrio cholerae. The minimum inhibitory concentration of polyethylene glycol coated silver nanoparticles was also less compared to the other two sets of nanoparticles. Consistence with that polyethylene glycol coated nanoparticles produced more intracellular reactive oxygen species in bacteria. Moreover, when human cell lines MCF7 and Chang Liver were incubated in presence of these nanoparticles for 18 h with same concentrations as used for bacteria, no toxicity was observed. But significant increase in cell killing was observed with longer incubation time. Thus our present investigation implicates the potential therapeutic use of silver nanoparticles as antibacterial agent particularly the polyethylene glycol coated one.     

The polymerizations of alkylsilane and bis-(γ-triethoxysilylpropyl)-tetrasulfide catalyzed by copper nanoparticles and the effects of transition metal ions on the polymerizations of alkylsilane catalyzed by silver nanoparticles

Poly(vinylpyrrolidone) (PVP)-capped copper nanoparticles synthesized by solvent-based polyol reduction were found to be effective catalysts for the polymerization of octadecylsilane and bis-(γ-triethoxysilylpropyl)-tetrasulfide. Comparing with PVP-capped silver nanoparticles, copper nanoparticles exhibited different catalytic activity, and the polymerization products also showed different morphologies. The effects of transition metal ions on the polymerization of octadecylsilane catalyzed by PVP-capped silver nanoparticles were also investigated. It was found that transition of metal ions not only had strong effects on the morphologies of the products of polymerizations, but also resulted in the disappearance of silver oxide. The products were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray powder diffraction (XRD).     

Effect of pH on the extra cellular synthesis of gold and silver nanoparticles by Saccharomyces cerevisae

In the present study, the synthesis of gold and silver nanoparticles was investigated using the culture supernatant broth of the yeast Saccharomyces cerevisae. Gold nanoparticles were formed within 24 hours of gold ion coming in contact with the culture supernatant broth. In case of silver the reduction process took 48 hours. The synthesized nanoparticles were investigated by UV-Visible spectroscopy. Distinct surface plasmon peaks were observed at 540 nm and 415 nm for gold and silver nanoparticles respectively. Bio-TEM micrographs of the synthesized nanoparticles indicated that the particles were well dispersed and near spherical in shape. The size range of the gold and silver nanoparticles was around 20-100 nm and 5-20 nm respectively. XRD patterns showed the presence of three distinct peaks corresponding to gold and silver nanoparticles respectively. A pH range of 4 to 6 and 8 to 10 favored optimum synthesis of gold and silver nanoparticles respectively. The process of reduction being extra cellular could be used in future for downstream processing in an eco friendly manner.