Synthesis and optical properties of silver nanoparticles and arrays.

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.     

Synthesis and physicochemical properties of silver nanoparticles stabilized by acid gelatin

Silver nanoparticles were synthesized by the reduction of silver nitrate with sodium borohydride at widely varied concentrations of the starting reagents. A physicochemical study of the synthesized nanosystems was carried out. The stabilizing ability of acid gelatin in the systems under study was considered. The stability diagram in the coordinates initial concentration of silver nitrate-concentration of gelatin was constructed.     

Synthesis, characterization and antimicrobial investigation of mechanochemically processed silver doped ZnO nanoparticles

The application of nanomaterials has gained considerable momentum in various fields in recent years due to their high reactivity, excellent surface properties and quantum effects in the nanometer range. The properties of zinc oxide (ZnO) vary with its crystallite size or particle size and often nanocrystalline ZnO is seen to exhibit superior physical and chemical properties due to their higher surface area and modified electronic structure. ZnO nanoparticles are reported to exhibit strong bacterial inhibiting activity and silver (Ag) has been extensively used for its antimicrobial properties since ages. In this study, Ag doped ZnO nanoparticles were synthesized by mechanochemical processing in a high energy ball mill and investigated for antimicrobial activity. The nanocrystalline nature of zinc oxide was established by X-ray diffraction (XRD) studies. It is seen from the XRD data obtained from the samples, that crystallite size of the zinc oxide nanoparticles is seen to decrease with increasing Ag addition. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) data also supported the nanoparticle formation during the synthesis. The doped nanoparticles were subjected to antimicrobial investigation and found that both increase in Ag content and decrease in particle size contributed significantly towards antimicrobial efficiency. It was also observed that Ag doped ZnO nanoparticles possess enhanced antimicrobial potential than that of virgin ZnO against the studied microorganisms of Escherichia coli and Staphylococcus aureus.     

Synthesis and applications of silver nanoparticles

Over the past few decades, nanoparticles of noble metals such as silver exhibited significantly distinct physical, chemical and biological properties from their bulk counterparts. Nano-size particles of less than 100 nm in diameter are currently attracting increasing attention for the wide range of new applications in various fields of industry. Such powders can exhibit properties that differ substantially from those of bulk materials, as a result of small particle dimension, high surface area, quantum confinement and other effects. Most of the unique properties of nanoparticles require not only the particles to be of nano-sized, but also the particles be dispersed without agglomeration. Discoveries in the past decade have clearly demonstrated that the electromagnetic, optical and catalytic properties of silver nanoparticles are strongly influenced by shape, size and size distribution, which are often varied by varying the synthetic methods, reducing agents and stabilizers. Accordingly, this review presents different methods of preparation silver nanoparticles and application of these nanoparticles in different fields.     

Application of anisotropic silver nanoparticles: multifunctionalization of wool fabric

Anisotropic silver nanoparticles (NPs) were successfully employed to color the wool fabrics in this study. The modified wool fabrics exhibited brilliant colors due to the localized surface plasmon resonance (LSPR) properties of silver NPs. The colors of wool fabrics altered with the morphologies of silver NPs. These modified wool fabrics were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that anisotropic silver NPs were effectively assembled on the surface of wool fibers when the solution pH and temperature was about 4 and 40°C, respectively. This assembling of silver NPs on the wool fibers was realized by the electrostatic interaction between wool fibers and silver NPs. This technique was also applied to gold NPs. The fabrics treated with anisotropic silver NPs showed high antibacterial activity against the bacteria of Escherichia coli. This study opens a new approach to color and functionalize conventional textile materials.     

Lectin sensitized anisotropic silver nanoparticles for detection of some bacteria

A method of bacteria detection by sensitized anisotropic silver nanoparticles is presented. Anisotropic silver nanoparticles with two bands of surface plasmon resonance (SPR) are prepared and sensitized with potato lectin. These nanoparticles are able to detect three bacterial species: Escherichia coli, Bacillus subtilis and Staphylococcus aureus. The interaction of these bacteria with such nanoparticles induces drastic changes in optical spectra of nanoparticles that are correlated with bacteria titer. The maximal sensitivity is observed for S. aureus (up to 1.5 × 10⁴ mL⁻¹).     

Synthesis and optical properties of poly(N-isopropylacrylamide) nanogel containing silver nanoparticles

Composite nanoparticles representing silver nanoparticle-containing polymer gels have been synthesized. The synthesis comprises two main stages. Initially, monodisperse hydrogel particles with a controlled diameter of approximately 500 nm are obtained by N-isopropylacrylamide polymerization. Then, silver ions are reduced on the surface of the polymer network. Variations in the concentration ratio between reductants and silver nitrate make it possible to produce silver nanoparticles with sizes in a range of 10–30 nm and different packing densities on the gel particle surface. The resultant nanocomposites have been studied by transmission electron microscopy, spectrophotometry, and dynamic light scattering. Depending on the size and packing density of the silver nanoparticles on the polymer particle surface, the plasmon resonance of the nanocomposites varies in a range of 420–750 nm, which determines variations in the color of the colloid from yellow, orange, and red to blue and blue-green. After the inclusion of silver nanoparticles, nanogels of poly(N-isopropylacrylamide) retain their capability for thermosensitive phase transition with a lower critical mixing temperature of 31°C.     

Synthesis of silver nanoparticles in NMMO and their in situ doping into cellulose fibers

We present a method for synthesis of silver nanoparticles in N-methylmorpholine N-oxide (NMMO) and the associated mechanism, as well as their use for in situ volume modification of cellulose fibers. The synthesized particles had diameter of about 4 nm, and their colloid solution was stable for 1 year. The nanoparticles were stabilized using polyethylenimine, which apart from preventing nanoparticle agglomeration, also accelerated Ag⁺ ion reduction and prevented NMMO degradation. A mechanism for the nanoparticle synthesis is suggested based on the electrochemical potentials of all ions in solution, with perhydroxyl ions resulting from NMMO reducing the silver ions. We also created nanocomposites from fibers and silver nanoparticles, in which the latter showed very good dispersion in the fiber volume. Such spun fibers showed improved mechanical parameters in comparison with unmodified fibers.     

Fabrication of zinc/silver binary nanoparticles,their enhanced microbial and adsorbing properties

Monometallic ZnO nanoparticles were prepared by hydrolysis of zinc acetate with ammonium hydroxide solution. Bimetallic zinc-silver nanoparticles (ZnO-AgNPs) were prepared using metal displacement galvanic cell reaction in presence of cetyltrimethylammonium bromide (CTAB). The optical and photo-physical properties of both NPs were determined. Surface plasmon resonance (SPR) intensity of ZnO-AgNPs depends on the ratio of metal salt precursors and other experimental conditions. The optical band gap (2.98 eV), agglomeration number (26819.92), and molar concentration (1.14 × 10⁻⁴ mol/liter) of ZnO-AgNPs were determined. Langmuir adsorption monolayer, Freundlich, intraparticles diffusion and multilayer adsorption isotherms used for the determination of maximum adsorption efficiency and adsorption isotherm parameters to the removal of safranin dye from an aqueous solution. The kinetics of safranin removal has also been discussed with pseudo-first order, pseudo-second order, intraparticle diffusion and multilayer kinetic models. The antibacterial and antifungal activities of ZnO, Ag and ZnO-AgNPs were determined against human pathogens using growth kinetic and disk diffusion methods. The concentrations of ZnO-AgNPs have significant effect on the bacterial growth kinetics. The death rate constants increase with increasing the NPs concentrations. It has been found that the ZnO-AgNPs hold higher microbial activities than that of monometallic counterpart, ZnO and AgNPs. Mechanism of bacterial growth and death was discussed.     

Synthesis and adsorption and luminescence properties of hydrophobic silver nanoparticles in the presence of pyrene

A procedure was developed for the synthesis of hydrophobic silver nanoparticles with an average size of 4 nm in two-phase water-organic emulsions. The physical properties of the obtained silver organosol were studied by molecular spectroscopy and electron microscopy. It was found that the synthesized silver nanoparticles had a specific surface of 60–110 m²/g. It was shown that chemically modified silver nanoparticles can be used as an adsorbent for preconcentrating polycyclic aromatic hydrocarbons (using pyrene as an example) from dilute n-hexane solutions followed by luminescence determination at room temperature.     

Synthesis of silver nanoparticles with polystyrylcarboxylate ligands

Silver nanoparticles stabilized by polystyrylmonocaboxylate ligands with varied chain lengths are synthesized via the low-temperature reduction of silver polystyrylmonocaboxylate with triethylamine. Silver nanoparticles have small dimensions, narrow size distributions, high stability, and ability to redisperse in nonpolar solvents. The kinetic features of the reaction are studied via high-performance liquid chromatography; UV, visible and IR spectroscopy; and transmission electron microscopy. It is shown that the reduction of silver occurs in the cores of reverse micelle species organized by diphilic macromolecules of silver polystyrylmonocarboxylates.     

Synthesis of silver nanoparticles with different shapes

Today the synthesis of silver nanoparticles is very common due to their numerous applications in various fields. Silver nanoparticles have unique properties such as: optical and catalytic properties, which, depend on the size and shape of the produced nanoparticles. So, today the production of silver nanoparticles with different shapes which have various uses in different fields such as medicine, are noted by many researchers. This article, is an attempt to present an overview of the shape-controlled synthesis of silver nanoparticles using various methods.     

Synthesis of anisotropic nanoparticles by seeded emulsion polymerization

Anisotropic polystyrene nanoparticles of diameters below 0.5 microm were prepared by coating the surface of cross-linked polystyrene latex particles with a thin hydrophilic polymer layer prior to swelling the particles with styrene and then initiating second-stage free-radical polymerization. Conditions were found so that all particles had uniform asymmetry. The effect of surface chemistry on the development of particle anisotropy during seeded emulsion polymerization of sub-0.5 microm diameter particles was studied. The extent and uniformity of the anisotropy of the final particles depended strongly on the presence of the hydrophilic surface coating. Systematic variation of the degree of hydrophilicity of the surface coating provided qualitative insight into the mechanism responsible for anisotropy. Conditions were chosen so that the surface free energy favored the extrusion of a hydrophobic bulge of monomer on the hydrophilic surface of the particle during the swelling phase: the presence of a hydrophilic layer on the particle surface causes this asymmetry to be favored above uniform wetting of the particle surface by the monomer. Kinetic effects, arising from the finite time required for the seed to swell with the monomer, also play a role.     

Synthesis of gold and silver nanoparticles using purified URAK

This study aims at developing a new eco-friendly process for the synthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) using purified URAK. URAK is a fibrinolytic enzyme produced by Bacillus cereus NK1. The enzyme was purified and used for the synthesis of AuNPs and AgNPs. The enzyme produced AgNPs when incubated with 1 mM AgNO3 for 24 h and AuNPs when incubated with 1 mM HAuCl4 for 60 h. But when NaOH was added, the synthesis was rapid and occurred within 5 min for AgNPs and 12 h for AuNPs. The synthesized nanoparticles were characterized by a peak at 440 nm and 550 nm in the UV-visible spectrum. TEM analysis showed that AgNPs of the size 60 nm and AuNPs of size 20 nm were synthesized. XRD confirmed the crystalline nature of the nanoparticles and AFM showed the morphology of the nanoparticle to be spherical. FT-IR showed that protein was responsible for the synthesis of the nanoparticles. This process is highly simple, versatile and produces AgNPs and AuNPs in environmental friendly manner. Moreover, the synthesized nanoparticles were found to contain immobilized enzyme. Also, URAK was tested on RAW 264.7 macrophage cell line and was found to be non-cytotoxic until 100 μg/ml.     

ZnO and MgO nanoparticles: Synthesis and comparative study on their properties

We report the optical and structural properties of ZnO and MgO nanoparticles. The samples are obtained by a simple method using a new template of hexamethylene tetramine. The optical properties of the samples are studied by UV-visible spectroscopy. Their crystal structure and morphology are studied by XRD and scanning electron microscopy. The absorption spectra of MgO and ZnO show that the optical band gaps are 4.27 eV and 3.02 eV, respectively. In this investigation the photocatalytic degradation of indigo carmine (IC) in water is studied. The effects of some parameters such as pH, amount of catalyst, initial concentration of dye, are examined.     

Synthesis of Gossypium hirsutum‐derived silver nanoparticles and their antibacterial efficacy against plant pathogens

Malvaceae and Brassicaceae family crops are economically important; however, their production has been markedly decreased in recent years due to various plant pests. Hence, the search for novel classes of efficient biological approaches continues due to unavailability of precise pesticides. The present study was designed to synthesize, characterize and evaluate the efficacy of silver nanoparticles (AgNPs) obtained using stem extract of Gossypium hirsutum (cotton plant) against plant pathogens Xanthomonas axonopodis pv. malvacearum and Xanthomonas campestris pv. campestris. Biosynthesized AgNPs were characterized using UV–visible spectrophotometry, Dynamic Light Scattering, Scanning Electron Microscopy combined with energy‐dispersive X‐ray analysis and Fourier transform infrared spectroscopy. The synthesized AgNPs were spherical in shape with size ranging from 20 to 100 nm. The characterized AgNPs were investigated for their efficacy against bacterial plant pathogens using the paper disc method. In vitro studies with two concentrations of AgNPs (50 and 100 μg mL^?1) showed zone of inhibition 11.0 ± 1.0 and 12.3 ± 0.5 mm for X. axonopodis pv. malvacearum and 9.7 ± 0.6 and 15.33 ± 1.0 mm for X. campestris pv. campestris. Furthermore, the AgNPs exhibited strong antioxidant activity, and a phytotoxicity study on Vigna unguiculata (cowpea plant) showed no toxicity. Overall, the findings suggest that G. hirsutum stem extract could be efficiently used in the synthesis of AgNPs and showed antimicrobial activity against plant pathogens. Hence, the synthesized nanoparticles could be used to combat plant pathogens in the agriculture sector.     

Synthesis of highly stable silver nanoparticles by photoreduction and their size fractionation by phase transfer method

In this report we demonstrate a green chemical approach for the synthesis of stable silver nanoparticles in aqueous medium using tyrosine as an efficient photoreducing agent. A narrow size distribution of silver nanoparticles can be achieved by this simple photoirradiation method without using any additional stabilizing agents or surfactants. Two different irradiation sources have been explored resulting in a different particle size distribution pattern in each case. Further, we show that starting from a polydisperse tyrosine synthesized silver nanoparticles sample, it is also possible to fractionate them into different size ranges. The size fractionation was achieved by a 2 stage phase transfer method employing different organic solvents. The nanoparticles synthesized were characterized using UV-vis spectroscopy, Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques.     

Synthesis of copolymer-stabilized silver nanoparticles for coating materials

Silver ions being less toxic than silver nanoparticles, a more safe material can be obtained to be used as antimicrobial coating. This can be achieved by using thiol chemistry and covalently attach the silver nanoparticles in the coating. Our aim is to produce a coating having antimicrobial properties of silver ions but with the silver nanoparticles firmly attached in the coating. Here, we present a way to produce silver nanoparticles that can be used as a component in a coating or as such to produce an antimicrobial coating. The silver nanoparticles presented here are stabilized by a copolymer (poly(butyl acrylate–methyl methacrylate)) that is soft and has well-known good film-producing properties. The reversible addition-fragmentation chain transfer radical polymerization technique used to prepare the polymers provides conveniently a thiol group for effective binding of the silver nanoparticles to the polymers and thus to the coating.     

Synthesis of colloidal silver nanoparticles for printed electronics

Colloidal silver particles were successfully prepared by wet chemical synthesis. The pure single phase of silver was confirmed by X-ray diffraction. Transmission electron microscope categorized that the diameters of particles were 100 and 20 nm, depending on the molecular weight of the PVP stabilizer. A schematic drawing model was used to predict the packing efficiency of 1:1 wt% of two mixtures. The mixture of silver solution was deposited as a thin solid film by a desktop inkjet printer. Scanning electron microscope showed that two different sizes of silver particles give higher densely packed structure than the film of single particle size. When a 0–20 V voltage was applied, the current density reached was 0.10 J/cm², suggesting that the silver film has potential to be applied as a cathode layer in organic light emitting diode (OLED) devices.     

Synthesis of carrageenan coated silver nanoparticles by an easy green method and their characterization and antimicrobial activities

The aim of the present work was to synthesize carrageenan coated silver nanoparticles (CA–AgNPs) using carrageenan as reducing and stabilizing agent. For this purpose, 10 mL of 0.35% (w/v) carrageenan solution was mixed with 10 mL AgNO₃ solution at different concentrations (1, 5 and 10 mM), and the resulting mixture was stirred at 100 °C at high speed for 2 h. The formation of CA–AgNPs was proven with the surface plasmon peaks observed at approximately 420 nm. The sizes and zeta potentials of CA–AgNPs were determined by Zeta-Sizer. Negative zeta potentials of CA–AgNPs indicated that the obtained AgNPs were stable. With scanning electron microscope (SEM) and transmission electron microscope analysis, it was seen that CA–AgNPs have spherical structure. According to the energy dispersion spectrometer analysis based on SEM images, it was observed that the samples were elementally composed of carbon, oxygen, sulfur, potassium and silver. The chemical structures of CA–AgNPs were determined by Fourier transform infrared spectroscopy, and it was proved that the carbonyl and OH groups of carrageenan were involved in formation and stabilizing of AgNPs, respectively. According to thermal gravimetric analysis, it has been observed that CA–AgNPs were thermally more stable than pure carrageenan. Antibacterial activity of CA–AgNPs against gram-positive and gram-negative bacteria was investigated with agar well diffusion and liquid test. It has been observed that CA–AgNPs synthesized with 1 mM AgNO₃ did not have an antibacterial activity on Escherichia coli and Staphylococcus aureus. Inhibition zones of varying diameters were observed in the 5 mM and 10 mM S-AgNPs groups. The synthesized CA–AgNPs (5 and 10 mM) have the capacity to be used in wound dressing materials or topical agents applied to burns and wounds due to their antibacterial effects and stability.