Abstract  The present invention relates to the preparation of nanoparticles of silver (Ag) and silver alloyed with other elements such as platinum (Pt), gold (Au), aluminum (Al), cadmium (Cd), and sulfur (S) in surfactant solutions. The surfactant molecules have the intrinsic property to absorb into the interface, which are formed between two different phases. Thus, the surfactant molecules would adsorb into the surface of nuclei in solution. The adsorbed surfactant molecules from the solution prevent the coalescence of particles and control the rate of particle growth. By choosing the proper kind and/or concentration of surfactants, the size of particles formed in solution can be controlled in nm scale.

Abstract  The biological synthesis of nanoparticles has gained considerable attention in view of their excellent biocompatibility and low toxicity. We isolated and purified rhamnolipids from Pseudomonas aeruginosa strain BS-161R and these purified rhamnolipids were used to synthesize silver nanoparticles. The purified rhamnolipids were further characterized and the structure was elucidated based on one- and two-dimensional (1)H and (13)C NMR, FT-IR, and HR-MS spectral data. Purified rhamnolipids in a pseudoternary system of n-heptane and water system along with n-butanol as a cosurfactant were added to the aqueous solutions of silver nitrate and sodium borohydride to form reverse micelles. When these micelles were mixed, they resulted in the rapid formation of silver nanoparticles. The synthesized nanoparticles were characterized by UV-Visible spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The nanoparticles formed had a sharp adsorption peak at 410 nm which is characteristic of surface plasmon resonance of the silver nanoparticles. The nanoparticles were monodispersed with an average particle size of 15.1 nm (sigma = +/-5.82 nm) and spherical in shape. The EDS analysis revealed the presence of elemental silver signal in the synthesized nanoparticles. The silver nanoparticles formed exhibited good antibiotic activity against both Gram-positive and Gram-negative pathogens and Candida albicans, suggesting their broad spectrum antimicrobial activity.

Abstract  Background: Most recently, renewed interest has arisen in manufactured silver nanomaterials because of their unusually enhanced physicochemical properties and biological activities compared to the bulk parent materials. A wide range of applications has emerged in consumer products ranging from disinfecting medical devices and home appliances to water treatment. Because the hypothesized mechanisms that govern the fate and transport of bulk materials may not directly apply to materials at the nanoscale, there are great concerns in the regulatory and research communities about potential environmental impacts associated with the use of silver nanoparticles. In particular, the unlimited combinations of properties emerging from the syntheses and applications of silver nanoparticles are presenting an urgent need to document the predominant salt precursors, reducing agents and stabilizing agents utilized in the synthesis processes of silver nanoparticles to guide the massive efforts required for environmental risk assessment and management. Objectives: The primary objective of this study is to present an evidence-based environmental perspective of silver nanoparticle properties in syntheses and applications. The following specific aims are designed to achieve the study objective: Aim 1 — to document the salt precursors and agents utilized in synthesizing silver nanoparticles; Aim 2 — to determine the characteristics of silver nanoparticles currently in use in the scientific literature when integrated in polymer matrices to form nanocomposites and combined with other metal nanoparticles to form bimetallic nanoparticles; Aim 3 — to provide a summary of the morphology of silver nanoparticles; and (4) Aim 4 — to provide an environmental perspective of the evidence presented in Aims 1 to 3. Methods: A comprehensive electronic search of scientific databases was conducted in support of the study objectives. Specific inclusion criteria were applied to gather the most pertinent research articles. Data and information extraction relied on the type of synthesis methods, that is, synthesized silver nanoparticles in general and specific applications, nanocomposites, and bimetallic techniques. The following items were gathered for: type of silver salt, solvent, reducing agent, stabilizing agent, size, and type of application/nanocomposite/bimetallic, and template (for nanocomposites). The description of evidence was presented in tabular format. The critical appraisal was analyzed in graphical format and discussed. Results: An analysis of the scientific literature suggests that most synthesis processes produce spherical silver nanoparticles with less than 20 nm diameter. Silver nanoparticles are often synthesized via reduction of AgNO3, dissolution in water, and utilization of reductants also acting as capping or stabilizing agents for the control of particle size to ensure a relatively stable suspension. Two of the most commonly used reductants and stabilizing agents are NaBH4 and citrate which yield particles with a negative surface charge over the environmental pH range (3–10). The environmental perspectives of these parameters are discussed. Concluding remarks: It is expected that the antibacterial property of bulk silver is carried over and perhaps enhanced, to silver nanoparticles. Therefore, when one examines the environmental issues associated with the manufacture and use of silver nanoparticle-based products, the antibacterial effects should always be taken into account particularly at the different stages of the product lifecycle. Currently, there are two arguments in the scientific literature about the mechanisms of antimicrobial properties of silver nanoparticles as they relate to colloidal silver particles and inonic silver. Methodologies of risk assessment and control have to account for both arguments.

Abstract  Silver nanoparticles fabricated in Hepes buffer exhibit potent cytoprotective and post-infected anti-HIV-1 activities toward Hut/CCR5 cells.

Abstract  Several negatively charged dyes were investigated for their possible adsorption on the surface of silver and gold colloidal particles. Those dyes that were found to adsorb on the particles were then checked for surface enhancement of Raman scattering. Highly efficient surface-enhanced Raman scattering (SERS) was observed from a carbocyanine dye in both sols. Excitation-dependence studies as well as adsorption studies confirm the SERS nature of the Raman spectra obtained. The dye is probably aggregated on adsorption and is probably attached through the naphthalene side moiety to the surface. Less efficient SERS was also observed for copper phthalocyanine. © 1982 American Chemical Society.

Abstract  Stable colloidal solutions of free silver nanoparticles (AgNPs) have been synthesized without reducing and stabilizing agents in pure acetonitrile and N,N-dimethylformamide by laser ablation of the bulk metal. Synthesis in tetrahydrofuran and dimethyl sulfoxide gave nanoparticles surrounded by a carbon shell or included in a carbon matrix. Mie theory for free and core@shell spheres accounts for the UV-vis spectra of the nanoparticles and allows their structural characterization. Transmission electron microscopy confirms the structure of the synthesized AgNPs. It is shown that free nanoparticles can be immediately functionalized, without further treatments, in the organic solvent used for the synthesis with molecules which are soluble in the same solvent.

Abstract  Mono- and bimetallic colloidal particles have gained increasing attention in science and application throughout the last several years. In this contribution, we present a synopsis of the wet chemical syntheses of these materials and survey potential applications in catalysis and materials science. Methods for the characterization of these particles and their surfaces are not reviewed here.

Abstract  We describe a modified polyol process for the synthesis of silver nanocrystals with uniform sizes ranging from several nanometers to ∼20 nm. The use of polyacrylic acid, in place of polyvinylpyrrolidone in the conventional polyol process, significantly limits the growth of silver nanocrystals, prevents the interparticle aggregation and fusion, and leads to a uniform population of samples with high water solubility. The size of nanocrystals can be conveniently tuned by controlling the reaction time, the concentration and chain length of the polymeric surfactants, and the reaction temperature. Uniform silver nanocrystals within sizes below 20 nm are preferred candidates over larger particles for applications where high density of optical absorption is required, for example, for photothermal conversion in cancer therapy.

Abstract  Silver nanoparticles were produced by laser ablation of a metal silver plate in aqueous solutions of surfactants, CnH2n+1SO4Na (n = 8, 10, 12, 16). The nanoparticles thus produced were characterized by electron microscopy and UV−visible absorption spectroscopy. The abundances of the nanoparticles before and after centrifugation were measured as a function of the surfactant concentration. The concentration dependence of the abundance implies that the surfactant coverage and the charge state on the nanoparticle surface are closely related to the stability of the nanoparticles in the solutions. The nanoparticles tend to be aggregated when the coverage is less than unity, while they are very stable when the surface is covered with a double layer of the surfactant molecules.

Abstract  Silver nanoparticles have been used in numerous commercial products, including textiles, to prevent bacterial growth. Meanwhile, there is increasing concern that exposure to these nanoparticles may cause potential adverse effects on humans as well as the environment. This study determined the quantity of silver released from commercially claimed nanosilver and laboratory-prepared silver coated fabrics into various formulations of artificial sweat, each made according to AATCC, ISO and EN standards. For each fabric sample, the initial amount of silver and the antibacterial properties against the model Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria on each fabric was investigated. The results showed that silver was not detected in some commercial fabrics. Furthermore, antibacterial properties of the fabrics varied, ranging from 0% to greater than 99%. After incubation of the fabrics in artificial sweat, silver was released from the different fabrics to varying extents, ranging from 0 mg/kg to about 322 mg/kg of fabric weight. The quantity of silver released from the different fabrics was likely to be dependent on the amount of silver coating, the fabric quality and the artificial sweat formulations including its pH. This study is the unprecedented report on the release of silver nanoparticles from antibacterial fabrics into artificial sweat. This information might be useful to evaluate the potential human risk associated with the use of textiles containing silver nanoparticles.

Abstract  Little or no information exists regarding droplet and aerosol production during most indoor tap water uses. For example, water-related particle production during cooking, household cleaning, and toilet use have been neglected by practically all studies. An order of magnitude characterization of the strength of the various sources/activities outlined in Section 4.4.2 is necessary. The information that exists about showering is preliminary and relies heavily on a single experiment. The submicrometer aerosol distribution in a shower environment has not been characterized. More experimental studies similar to the one by Gunderson and Witham (1988) are necessary. Use of a mannequin is recommended, as most respirable particles are probably produced during the collision of the droplets with the body of the person in the shower. A better understanding of the interactions between droplet formation, evaporation, and removal is necessary. Our understanding of the production of aerosols during humidifier use has significantly improved. Ultrasonic humidifiers and to a lesser degree impeller humidifiers can be significant aerosol sources.

Abstract  In this study we investigate the release of metallic silver nanoparticles (Ag-NP) from paints used for outdoor applications. A facade panel mounted on a model house was exposed to ambient weather conditions over a period of one year. The runoff volume of individual rain events was determined and the silver and titanium concentrations of 36 out of 65 runoff events were measured. Selected samples were prepared for electron microscopic analysis. A strong leaching of the Ag-NP was observed during the initial runoff events with a maximum concentration of 145 micro Ag/l. After a period of one year, more than 30% of the Ag-NP were released to the environment. Particles were mostly <15 nm and are released as composite colloids attached to the organic binders of the paint. Microscopic results indicate that the Ag-NP are likely transformed to considerably less toxic forms such as Ag2S.

Abstract  A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.

Abstract  This review article deals with the preparation, characterization and mechanisms of formation of uniform simple and composite metal particles of different modal diameters and shapes. In principle, such dispersions can be obtained by reduction of metal ions, in uncomplexed or complexed state, with suitable reducing agents and appropriate additives. The effect of the redox potential in a given oxidation/reduction system on the nature of the final particles is discussed in some detail. In another approach monodispersed particles of metal compounds are prepared first and then reduced to pure metals either in a liquid or a gaseous medium. In doing so, one can produce powders of a given morphology by selecting the precursor particles of the desired shape. A special case is represented by coated particles, consisting of cores and shells of different chemical composition. Depending on the materials, it is possible to reduce either one or both components by appropriate chemical reactions.

Abstract  An assessment of the extent of exposure to nanomaterials in the workplace will be helpful in improving the occupational safety of workers. It is essential that the exposure data in the workplace are concerned with risk management to evaluate and reduce worker exposure. In a manufacturing facility dealing with nanomaterials, some exposure data for gas-phase reactions are available, but much less information is available regarding liquid-phase reactions. Although the potential for inhaling nanomaterials in a liquid-phase process is less than that for gas-phase, the risks of exposure during wet-chemistry processes are not negligible. In this study, we monitored and analyzed the exposure characteristics of silver nanoparticles during a liquid-phase process in a commercial production facility. Based on the measured exposure data, the source of Ag nanoparticles emitted during the production processes was indentified and a mechanism for the growth of Ag nanoparticle released is proposed. The data reported in this study could be used to establish occupational safety guidelines in the nanotechnology workplace, especially in a liquid-phase production facility.

Abstract  Monodisperse silver nanocubes with edge length of 55 +/- 5 nm were, for the first time, synthesized in water on the basis of HTAB-modified silver mirror reaction at 120 degrees C (HTAB, n-hexadecyltrimethylammonium bromide). The individual nanocube was crystallographically well defined with a single crystal bonded by six {200} facets. The nanocubes were soluble to form stable aqueous solutions and had a strong tendency to assemble into two-dimensional arrays with regular checked pattern on substrate.

Abstract  A very effective and simple way to produce silver colloids for surface-enhanced Raman scattering (SERS) is reported. Reduction of silver nitrate with hydroxylamine hydrochloride at alkaline pH and at room temperature yields highly sensitive SERS colloids within a short time. The so-produced colloids can be used for SERS spectroscopy immediately after preparation. The overall procedure is fast, simple, and characterized by a high preparation success rate. Changing the mixing order and rate of the two involved solutions, silver nitrate and hydroxylamine hydrochloride containing sodium hydroxide, one can control the size and dispersion of the produced colloids. The obtained colloids have been characterized by UV−vis spectroscopy, transmission electron microscopy, and SERS using a 1064 nm laser line on a Fourier transform and a 785 nm laser line on a dispersive Raman spectrometer. The SERS enhancement factor of the hydroxylamine-reduced silver colloids was tested using crystal violet, rhodamine 6G, methylene blue, and 9-aminoacridine. It was found that for both excitation lines sensitivities comparable to those achievable with a Lee−Meisel silver colloid were obtained thus rendering the new colloid advantageous because of its significantly simpler and faster synthesis.

Abstract  Monodisperse samples of silver nanocubes were synthesized in large quantities by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP). These cubes were single crystals and were characterized by a slightly truncated shape bounded by {100}, {110}, and {111} facets. The presence of PVP and its molar ratio (in terms of repeating unit) relative to silver nitrate both played important roles in determining the geometric shape and size of the product. The silver cubes could serve as sacrificial templates to generate single-crystalline nanoboxes of gold: hollow polyhedra bounded by six {100} and eight {111} facets. Controlling the size, shape, and structure of metal nanoparticles is technologically important because of the strong correlation between these parameters and optical, electrical, and catalytic properties.

Abstract  The potential for human exposure to engineered nanoparticles due to the use of nanotechnology-based consumer sprays (categorized as such by the Nanotechnology Consumer Products Inventory) is examined along with analogous products, which are not specified as nanotechnology-based (regular products). Photon correlation spectroscopy was used to obtain particle size distributions in the initial liquid products. Transmission electron microscopy was used to determine particle size, shape, and agglomeration of the particles. Realistic application of the spray products near the human breathing zone characterized airborne particles that are released during use of the sprays. Aerosolization of sprays with standard nebulizers was used to determine their potential for inhalation exposure. Electron microscopy detected the presence of nanoparticles in some nanotechnology-based sprays as well as in several regular products, whereas the photon correlation spectroscopy indicated the presence of particles <100 nm in all investigated products. During the use of most nanotechnology-based and regular sprays, particles ranging from 13 nm to 20 μm were released, indicating that they could he inhaled and consequently deposited in all regions of the respiratory system. The results indicate that exposures to nanoparticles as well as micrometer-sized particles can be encountered owing to the use of nanotechnology-based sprays as well as regular spray products.

Abstract  Products containing silver nanoparticles are entering the market rapidly, but little is known about the potential for inhalation exposure to nanosilver. The objectives of this work were to characterize the emissions of airborne particles from consumer products that claim to contain silver nanoparticles or ions, determine the relationship between emissions and the products' liquid characteristics, and assess the potential for inhalation exposure to silver during product use. Three products were investigated: an antiodor spray for hunters, a surface disinfectant, and a throat spray. Products emitted 0.24-56 ng of silver in aerosols per spray action. The plurality of silver was found in aerosols 1-2.5 μm in diameter for two products. Both the products' liquid characteristics and the bottles' spray mechanisms played roles in determining the size distribution of total aerosols, and the size of silver-containing aerosols emitted by the products was largely independent of the silver size distributions in the liquid phase. Silver was associated with chlorine in most samples. Results demonstrate that the normal use of silver-containing spray products carries the potential for inhalation of silver-containing aerosols. Exposure modeling suggests that up to 70 ng of silver may deposit in the respiratory tract during product use.