Preparation of high surface area silver powder via Tollens process under sonication

High surface area silver powder was prepared through Tollens process. The process involves reduction of Tollens reagent under sonication at room temperature. By gradually adding Tollens reagent into the mixture of glucose solution and sodium hydroxide solution, the silver powder forms immediately without silver mirror formation at container wall. The powders prepared through this process were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size distribution and surface area. The powders were cubic crystalline silver with bimodal distribution and primary particle size of < 1 μm and surface area of 1.8 m²/g. The yield of silver powder was higher than 99%.     

Synthesis of silver nanoparticles from a Desmodium adscendens extract and its antibacterial evaluation on wound dressing material

The one‐pot synthesis of silver nanoparticles (AgNPs) using the medium‐polar extract of Desmodium adscendens (Sw.) DC. is presented here as an alternative synthesis of metal NPs. Characterisation of the formed NPs showed polydispersed AgNPs ranging from 15 to 100 nm where the concentration of metal ions was found to play a role in the size and shape of the prepared NPs. It could be established that the flavonoids, saponins, and alkaloids present in the extract acted as both reducing and stabilising agents during the formation of the capped metal NPs. This means of NP synthesis was also employed during the in situ immobilisation of AgNPs on gauze and plaster. An evaluation of the antibacterial activity of the medium‐polar D. adscendens extract, AgNPs suspended in solution, and the immobilised AgNPs against Staphylococcus aureus (ATCC 25923), Bacillus cereus (ATCC 11778), and Escherichia coli (ATCC 25922) showed high efficacy against the latter in particular. This suggests that gauze, dilute silver nitrate solutions, and D. adscendens extract could be used successfully in the simple in situ preparation of effective antibacterial wound dressings.Inspec keywords: wounds, silver, nanoparticles, nanomedicine, biomedical materials, antibacterial activityOther keywords: size 15 nm to 100 nm, antibacterial wound dressings, in situ preparation, dilute silver nitrate solutions, alkaloids, saponins, flavonoids, metal ions, wound dressing material, antibacterial evaluation, Desmodium adscendens extract, silver nanoparticle synthesis     

Chemical reduction method for preparation of silver nanoparticles on a silver chloride substrate for application in surface-enhanced infrared optical sensors

A new method for the preparation of silver nanoparticles (AgNPs) on silver chloride discs was developed to integrate the unique properties of plasmonic nanoparticles into infrared optical sensing technologies. AgNP layers exhibiting strong infrared surface enhancement were prepared by reacting silver chloride discs in a solution containing hydrazine, which acts as a reducing agent. The silver ions in the outer layer of the disc could be reduced under proper conditions and the reduced silver coagulated to form suitable AgNPs for surface-enhanced infrared absorption (SEIRA) measurements. To examine the influences of the reaction solution composition and also to optimize preparation of SEIRA substrates, factors such as pH value, reaction time, and concentration of reducing agent were examined. Results indicated that both the concentrations of hydrazine and hydroxide strongly influenced the SEIRA signals. The strongest signals were observed when AgNPs on a AgCl substrate were prepared by using a reducing solution of 20 mM NaOH with 0.75 mM hydrazine. Using the optimized substrates, intense SEIRA spectra were observed with an enhancement factor around two orders of magnitude compared to measurements made using conventional sampling techniques.     

Facile synthesis of silver immobilized-poly(methyl methacrylate)/polyethyleneimine core–shell particle composites

A facile route to synthesize silver-embedded-poly(methyl methacrylate)/polyethyleneimine (PMMA/PEI-Ag) core–shell particle composites was illustrated in this present work. PMMA/PEI core–shell particle templates were first prepared by a surfactant-free emulsion polymerization. PEI on the templates' surface was further used to complex and reduce Ag⁺ ions (from silver nitrate solution) to silver nanoparticles (AgNPs) at ambient temperature, resulting in the PMMA/PEI-Ag particle composites. The formation of AgNPs was affected by the pHs of the reaction medium. The pH of reaction medium at 6.5 was optimal for the formation of PMMA/PEI-Ag with good colloidal stability, which was confirmed by size and size distribution, FTIR spectroscopy, UV–vis spectroscopy and X-ray diffraction. Moreover, the amount of AgNO₃ solution (4.17–12.50 g) was found to affect the formation of AgNPs. Transmission electron microscopy (TEM) indicated that the AgNPs were incorporated in the PMMA/PEI core–shell matrix, and had 6–10 nm in diameter. AgNPs immobilized on PMMA/PEI core–shell particles were also investigated by energy dispersive X-ray spectroscopy analysis mode extended from scanning electron microscopy (SEM/EDS). Furthermore, the presence of AgNPs was found to influence the thermal degradation behavior of PMMA/PEI particle composites as observed through thermogravimetric analysis (TGA).     

Alginate hydrogel microbeads incorporated with Ag nanoparticles obtained by electrochemical method

An innovative method was developed for production of alginate hydrogel microbeads incorporated with silver nanoparticles (AgNPs) based on electrochemical synthesis followed by electrostatic extrusion. AgNPs were synthesized galvanostatically at different values of AgNO₃ concentration in the initial solution (0.5–3.9 mM), current density (5–50 mA cm⁻²), and implementation time (0.5–10 min). Increase in all of these parameters increased the concentration of AgNPs in alginate solution and was confirmed by TEM analysis and UV–vis spectroscopy. Cyclic voltammetry studies and Fourier transform infrared spectroscopy proved the alginate to be a good capping agent for the electrochemical synthesis of silver nanoparticles, due to coordination bonding between hydroxyl and ether groups, as well as ring oxygen atoms in uronic acid residues of alginate molecules, and Ag nanoparticles. Ag/alginate colloid solution was used for production of uniform hydrogel microbeads (with diameter of 487.75 ± 16.5 μm) by electrostatic extrusion technique. UV–vis spectroscopy confirmed retention and entrapment of AgNPs in microbeads during the production process. Alginate microbeads incorporated with AgNPs are attractive as biocompatible carriers and/or efficient donors of AgNPs as active components especially for potential biomedical applications, which was demonstrated by the antibacterial activity against Staphylococcus aureus.     

Mechanisms of antibacterial activity and stability of silver nanoparticles grown on magnetron sputtered TiO<Subscript>2</Subscript> coatings

Nanomaterials with high stability and efficient antibacterial activity are of considerable interest. The preparation of silver nanoparticles (AgNPs) on titania coatings and their effective antibacterial activity against Staphylococcus aureus ATCC 6538 were reported. Titanium dioxide (TiO₂) coatings with AgNPs were prepared on Si wafers using the reactive magnetron sputtering method. The surface topography of AgNPs/TiO₂ coatings imaged using scanning electron microscopy revealed that the size and surface density of AgNPs grown by the photoreduction of silver ions were dependent on the concentration of AgNO₃ in the primary solution and the time of TiO₂ exposure to UV illumination. Evaluation of the antimicrobial properties and surface analysis before and after the biological test of AgNPs/TiO₂ coatings indicates their high antimicrobial stability and durability. Furthermore, the interdependence between the concentration of released silver and bacterial growth inhibition was demonstrated. In addition, direct contact killing and released silver-mediated killing have been proposed as a bactericidal mechanism of action of tested coatings with AgNPs.     

Preparation and properties of siloxane polyimide films containing silver nanoparticles and microparticles as conducting adhesive films

Electrically conducting adhesive films containing silver nanosized particles (AgNPs) were prepared using siloxane polyimide resin (SPI), and their physical properties were investigated. AgNPs with diameters of ca. 6 nm were prepared using oleylamine as a stabilizer. A mixture of the AgNPs and SPI was vigorously stirred, and cast on a polyethylene terephthalate support. Films were then fabricated using a doctor blade method. The heat resistance of the SPI film containing 60 wt% AgNPs was 35 °C higher than that of the SPI film without AgNPs. In addition, epoxy composite SPIAg (Epo-SPIAg) films containing a mixture of AgNPs and micro-sized silver flakes were prepared. Inclusion of AgNPs in these films strengthened their adhesion to silicon or bismaleimide triazine resin substrates. The glass transition temperature of the Epo-SPIAg films containing AgNPs was slightly higher than that of the film containing only micro-sized silver flakes.     

天蓝黄链霉菌胞外合成纳米银的生化机制研究

以天蓝黄链霉菌（S. coelicoflavus）菌体浸出液为还原剂和包覆剂于胞外合成纳米银,对纳米银的形貌结构、晶体结构、粒度分布、元素组成及表面包覆基团进行表征分析,并通过研究主要生物活性分子在纳米银合成过程中的重要作用,探索了纳米银胞外合成的生化反应机制。表征分析结果表明,合成的纳米银颗粒主要为球形或近似球形,少量为截边三角形、四边形或六角形;平均粒径约为34.50 nm,呈中度多分散性;具有良好的结晶度和多晶结构。生化合成机制研究表明,蛋白质和还原型谷胱甘肽（GSH）在纳米银的合成过程中起主要作用;跨膜蛋白和细菌铁蛋白包覆于形成的纳米银颗粒表面,以保持其在反应体系中的高度稳定性;硝酸还原酶可能与其他生物活性组分共同催化银离子的还原过程。     

Speciation analysis of silver nanoparticles and silver ions in antibacterial products and environmental waters via cloud point extraction-based separation

The rapid growth in commercial use of silver nanoparticles (AgNPs) will inevitably increase silver exposure in the environment and the general population. As the fate and toxic effects of AgNPs is related to the Ag(+) released from AgNPs and the transformation of Ag(+) into AgNPs, it is of great importance to develop methods for speciation analysis of AgNPs and Ag(+). This study reports the use of Triton X-114-based cloud point extraction as an efficient separation approach for the speciation analysis of AgNPs and Ag(+) in antibacterial products and environmental waters. AgNPs were quantified by determining the Ag content in the Triton X-114-rich phase with inductively coupled plasma mass spectrometry (ICPMS) after microwave digestion. The concentration of total Ag(+), which consists of the AgNP adsorbed, the matrix associated, and the freely dissolved, was obtained by subtracting the AgNP content from the total silver content that was determined by ICPMS after digestion. The limits of quantification (S/N = 10) for antibacterial products were 0.4 μg/kg and 0.2 μg/kg for AgNPs and total silver, respectively. The reliable quantification limit was 3 μg/kg for total Ag(+). The presence of Ag(+) at concentrations up to 2-fold that of AgNPs caused no effects on the determination of AgNPs. In the cloud point extraction of AgNPs in antibacterial products, the spiked recoveries of AgNPs were in the range of 71.7-103% while the extraction efficiencies of Ag(+) were in the range of 1.2-10%. The possible coextracted other silver containing nanoparticles in the cloud point extraction of AgNPs were distinguished by transmission electron microscopy (TEM), scanning electron microscopy (SEM)- energy dispersive spectroscopy (EDS), and UV-vis spectrum. Real sample analysis indicated that even though the manufacturers claimed nanosilver products, AgNPs were detected only in three of the six tested antibacterial products.     

纳米银的合成及其抗菌应用研究进展

病原微生物严重威胁着人类的健康安全,纳米银作为一种新型抗菌材料,其制备与应用已成为纳米材料领域的研究热点。本文综述了纳米银的主要合成方法,包括多糖法、Tollens试剂法、辐射法、生物法和多金属氧酸盐法等,具有原料广泛、反应温和、成本低廉和环境友好等优点。基于纳米银的优异抗菌性能,总结了纳米银的抗菌机理及其抗菌应用,并展望了纳米银在抗菌涂料、抗菌包装等领域的发展前景。     

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.     

Synthesis and characterization of phospholipid-functionalized silver nanoparticles

Functionalizations of silver nanoparticles (AgNPs) by phospholipids (PLs) have been manifested well by means of covalent connection between AgNPs with PLs. After functionalization, the attached PLs can self-assemble into bilayer structures on the surfaces of AgNPs. TEM displays the images of pure AgNPs and functionalized AgNPs with certain thickness of the phospholipid bilayers, as a result of chemical connection existing in AgNPs-PL conjugates. UV-vis and IR spectra confirm the strong Ag-S interaction between silver and sulfur produced during the reactions. This new modification method for AgNPs offers a good opportunity to functionalize nanoparticles with biological activity.     

A comparative study of eco-friendly silver nanoparticles synthesis using Prunus domestica plum extract and sodium citrate as reducing agents

Through the current comparative study, colloidal silver nanoparticles (AgNPs) were synthesized with various morphologies and sizes using Prunus domestica (P-dom) extract and sodium citrate as green and chemical reducing agents, respectively. AgNPs were synthesized employing different concentrations of the reducing agents in an aqueous solution at various pH values (3–10) and temperatures (25–85 °C). The UV–visible absorption spectrum indicated characteristic SPR peaks of AgNPs at 380–450 nm. Fourier transform infrared spectroscopy revealed aqueous-soluble polyols (such as glycosides, phenols, and flavanols) participation in Ag ions reduction to the corresponding AgNPs at various pH values. The crystallinity of AgNPs was detected by an X-ray diffractometer. Different morphologies (polygonal, oval, and spherical) of the AgNPs with varying pH values were confirmed conducting transmission electron microscopy (TEM). Average particle sizes of 16–50 nm were determined using scanning electron microscopy, TEM, and dynamic light scattering assessments for AgNPs synthesized at various reaction conditions. This study is a demonstration for a facile, cheap, and eco-friendly stimuli-sensitive preparation of the AgNPs.     

石墨烯-银纳米粒子复合材料的制备及表征

以无毒、绿色的葡萄糖为还原剂, 在没有稳定剂、温和的液相反应条件下, 同时还原氧化石墨和银氨溶液中的银氨离子, 原位制备石墨烯-银纳米粒子复合材料. 采用X射线衍射、红外吸收光谱、拉曼光谱、扫描电镜和透射电子显微镜对所制备的石墨烯-银纳米粒子复合材料进行了表征. 结果表明: 氧化石墨和银离子在反应过程中同时被葡萄糖还原, 银纳米粒子均匀分布于石墨烯片层之间, 生成的银纳米粒子中大多数存在着孪晶界, 银纳米粒子的大小和分布受硝酸银用量的影响, 在合适的银离子浓度下, 负载在石墨烯片层上的银纳米粒子的粒径分布集中在25 nm左右; 复合材料中石墨烯的拉曼信号由于银粒子的存在增强了7倍.     

Biosynthesis of silver nanoparticles using sun-dried mulberry leaf

The biosynthesis of silver nanoparticles (AgNPs) has been successfully conducted by reduction of silver nitrate with sun-dried mulberry leaf. Such AgNPs have been characterized by UV-visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). The results showed that such dispersed, uniform and spherical AgNPs would not aggregate under high-concentration NaCl solution and have good antibacterial activity. It was suggested that the polyol components (such as polyhydroxylated alkaloids) and protein residues of mulberry leaf should be mainly responsible for the stabilization of AgNPs. Such AgNPs produced by the environmentally friendly method have the potential for use in antibacterial and medical applications.     

Role of pH in the green synthesis of silver nanoparticles

The role of pH in the green synthesis of silver nanoparticles (AgNPs) is investigated. For the reduction synthesis of AgNPs we use silver nitrate, glucose, sodium hydroxide and starch respectively to serve as precursor, reducing agent, accelerator and stabilizer. The effect of NaOH addition on the nature of AgNPs is systematically studied. Two reaction pathways are proposed to explain the formation of AgNPs, keeping in view the pH changes that occur on addition of different amounts of NaOH. The aqueous sol of AgNPs prepared at different pH values display different surface plasmon resonance (SPR) behavior. This is explained in terms of size and size distribution of AgNPs.     

Comprehensive study on surfactant role on silver nanoparticles (NPs) prepared via modified Tollens process

Surfactants represent not only commonly used wetting agents but also substances that can be used as growth modifiers in the process of solid nanoparticle (NP) preparation. In this study we report influential character of different types of surfactants – i.e. ionic (SDS, CTAC) and non-ionic (Tween 80) – on fundamental characteristics of silver NPs, which were prepared by a modified Tollens process. The influential character of surfactants was evaluated throughout a reasonable improvement of the polydispersity (in the case of the tested non-ionic surfactants from 8.5% even down to 2.5%) and in the case of ionic surfactant, SDS and CTAC, also significant change of zeta potential (from −20 to −50 mV for the highest tested concentration of SDS). A slight influence of the tested surfactants was observed on the sizes of the prepared silver NPs. Therefore the obtained results from the performed surfactant-assisted syntheses revealed a possibility how to tailor silver NPs by means of their polydispersity and zeta potential according to the application demands.     

Green Synthesis of Silver Nanoparticles Using Salacia chinensis: Characterization and its Antibacterial Activity

The aim of the present research work was to synthesize silver nanoparticles (AgNPs) using Salacia chinensis plant extract and to evaluate its antibacterial activity. AgNPs were successfully synthesized and formation of AgNPs was confirmed by visual color change and UV (ultraviolet) spectroscopy. Prepared AgNPs were purified and characterized by using dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDAX), and transmission electron microscopy (TEM). UV peak at 434 nm confirmed the formation of AgNPs. DLS studies showed that AgNPs size prepared in all conditions were in the range of 100–200 nm. XRD studies revealed crystalline nature of AgNPs. EDAX studies confirmed the presence of silver in colloidal dispersion and images were recorded by using SEM and TEM. Synthesized AgNPs were found to be effective against Staphylococcus aureus and Pseudomonas aeruginosa. In conclusion, AgNPs could serve as a good alternative in treatment of bacterial infections in this era of multidrug resistance.     

纳米银-聚合物薄膜的制备及力电性能测试

聚合物基底上纳米银颗粒薄膜的制备工艺相对简单,成本较低,且该薄膜具有成为高敏感性压阻应力/应变传感材料的潜力。本文采用银镜制备法在聚酰亚胺(PI)和聚乙烯(PE)上合成了纳米银颗粒薄膜,系统研究了该薄膜制备工艺、结构特性、材料性能之间的关系。实验考察了材料“浸泡”时间及聚合物材料前处理等因素对材料表面吸附纳米颗粒含量的影响,研究了 “浸泡”时间对纳米银颗粒粒径大小、颗粒含量及分布的影响,并探讨了不同聚合物基体的颗粒特性对薄膜二维导电渗滤,压阻特性及拉伸性能的影响。研究表明,增加“浸泡”时间能够增加纳米银颗粒粒径大小,提高银颗粒的含量及分布均匀性；在相同的制备条件下,PI基底较PE基底对纳米银颗粒具有更加优异的吸附效果；在PI 和PE基底上的纳米银颗粒薄膜均表现出显著的压阻性能,且电阻对应变的敏感性随应变的增大及银颗粒含量的减少而显著提高。     

Preparation of nanosilver particles into sulfonated poly(ether ether ketone) (S-PEEK) nanostructures by electrospinning

By using the interaction between the sulfonated groups and silver ions, nanosilver particles were successfully introduced into S-PEEK nanostructures (nanospheres and nanofibers) by electrospinning. The nanoparticles were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectra (XPS), UV/vis, etc. The size of the spheres increases with the weight concentration of silver exchanged sulfonated poly(ether ether ketone) (S-PEEK-Ag) increasing. The size of the silver particles can be controlled by adjusting the sulfonated degree (number of sulfonate groups per repeating unit) of sulfonated poly(ether ether ketone) (S-PEEK) and the weight ratio of the S-PEEK solutions. This paper provides a new method for the preparation of nanometal particles into nanostructures.