Encapsulated Silver Nanoparticles Research Articles

Production and Characterization of Protein Encapsulated Silver Nanoparticles by Marine Isolate Streptomyces parvulus SSNP11.

Production of protein encapsulated silver nanoparticles (AgNPs) assisted by marine actinomycetes strain has been investigated. The selective isolate was identified as Streptomyces parvulus SSNP11 based on chemotaxonomic and 16S rRNA analysis. Maximum AgNPs production was observed within 24h incubation time. The produced AgNPs are spherical in shape with monodispersive and crystalline in nature. The particle size distribution ranges from 1.66 to 11.68nm with a mean size of 2.1nm. The biosynthesized AgNPs revealed stretching vibrations of primary and secondary amines along with C-H and C-N, suggesting that metabolically produced proteins are involved in size regulation of reduced AgNPs. These particles possess an average negative zeta potential value of 81.5mV with an electrophoretic mobility of 0.000628cm(2)/Vs. The biosynthesized nanoparticles revealed antimicrobial property against gram negative as well as gram positive bacterial strains.

Micelle Encapsulation of Silver Nanoparticles at Borohydride Reduction

The present work demonstrates the encapsulation of silver nanoparticles into micellar structures of the diblock copolymer (DBC) consisting chemically complementary methoxypoly (ethylene oxide) and poly(acrylic acid). The reduction of silver ions to silver nanoparticles or nanoclusters is achieved by an excess of sodium borohydride in the DBC aqueous solutions with various pH. The formation of considerably more smallest and stable Ag-nanoparticles in the DBC micellar solution at pH = 3 compare with the test of an Ag+solution without DBC micelles was revealed. The morphology of Ag-nanoparticles dispersed within DBC matrices and their average particle size were indicated by TEM images.

One‐Pot Synthesis and Catalytic Properties of Encapsulated Silver Nanoparticles in Silica Nanocontainers

The microemulsion approach constitutes a novel method for preparation of nanorattles, which are nanostructures with a preserved void between an encapsulated core and the surrounding shell of the nanocontainer. A facile one-pot synthesis and encapsulation is demonstrated for silver nanoparticles into silica nanocontainers to form Ag@SiO2 nanorattles.

Permeability of carbon shells during sulfidation of encapsulated silver nanoparticles

In this work, we have studied morphological, structural and phase changes in amorphous carbon-encapsulated silver nanoparticles (Ag@C) upon treatment by H2S gas. The carbon shells have been found to present no impassable obstacles for the silver sulfide to form. The growth of Ag2S nanocrystals occurs on the outer surface of the carbon shell, the size of the encapsulated silver nanoparticle decreasing continuously until the nanoparticle is fully consumed. An explanation of the morphological changes observed in the Ag@C nanoparticles upon treatment by H2S gas is proposed.

Amorphous carbon encapsulation of metal aerosol nanoparticles for improved collection and prevention of oxidation

A technique to encapsulate silver nanoparticles in an amorphous carbon matrix to facilitate nanoparticle collection and limit nanoparticle oxidation is presented. A carbon source added to the metal salt precursor solution decomposes to generate amorphous carbon, which forms large aggregates that are efficiently collected by filtration. The carbon matrix can be removed by oxidation with hydrogen peroxide without damaging the silver nanoparticles within it. X‐ray diffraction showed no evidence of oxidation of encapsulated particles over a two‐week period, whereas bare particles showed oxidation after 1 day. Slight oxidation was observed following carbon removal, but no further oxidation was detected over a subsequent two‐week period. Carbon encapsulation improves nanoparticle collection efficiency, relative to direct collection of unagglomerated silver nanoparticles with membrane filters. The yield of metal nanoparticles is increased by a factor 1.5 to 3 using this approach. The encapsulating carbon itself forms dendritic nanostructures that may also be of interest. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4116–4123, 2013

Photochemical and antimicrobial properties of silver nanoparticle-encapsulated chitosan functionalized with photoactive groups

Chitosan was functionalized with 4-((E)-2-(3-hydroxynaphthalen-2-yl)diazen-1-yl)benzoic acid by the coupling of the hydroxyl functional groups of chitosan with carboxylic acid group of the dye by DCC coupling method. The silver nanoparticles were prepared by sol-gel method of nanoparticle synthesis. Silver nanoparticle-encapsulated functionalized chitosan was prepared by the phase transfer method. The products were characterized by FTIR, UV-Vis, fluorescence and NMR spectroscopic methods and by SEM and TEM analysis. The photochemical properties of silver nanoparticle-encapsulated chitosan functionalized with 4-((E)-2-(3-hydroxynaphthalen-2-yl)diazen-1-yl)benzoic acid was studied in detail. The light-fastening properties of the chromophoric system was enhanced when attached to chitosan, and it can be further improved by the encapsulation of silver nanoparticles. The antibacterial analysis of silver nanoparticle-encapsulated functionalized chitosan was carried out against Staphylococcus aureus and Escherichia coli and against fungal species such as Aspergillus flavus and Aspergillus terreus. This study showed that silver nanoparticles-encapsulated functionalized chitosan can be used for antibacterial and antifungal applications.

Highly conductive short chain carboxylic acid encapsulated silver nanoparticle based inks for direct write technology applications

In this study silver nanoparticles were synthesized with short chain (C6–C10) carboxylic acids as capping agents and prepared as conductive inks for fabricating electrically conductive patterns using direct write technologies. The structural characterization of as-synthesized nanoparticles revealed that the particles are spherical in shape with narrow size distribution (4.1 to 4.7 nm) and have face centered cubic crystal structure. Silver-particle-based inks were prepared by dispersing the particles in toluene and separating non-dispersing particles from the inks. The loading of silver particles in the solvent was increased with the increasing chain length of capping agents. As a result, inks with a wide range of nanoparticulate concentrations (∼3 to 66 wt%) were able to be prepared and most of these inks were stable for at least a month. All the inks exhibited shear thinning behavior and this shear thinning became more prominent for higher concentration inks. As the nanoparticle concentration of the inks was increased, surface tension was decreased and the contact angles of the inks with the Kapton® and glass were increased. Printing of microelectrodes, lines and films was carried out using aerosol jet printing and ultrasonic spray coating. The conductivity of printed microelectrodes was 10 to 87% of the bulk silver conductivity with the sintering temperatures as low as 130 to 250 °C depending on the ink used.

The effect of PEG encapsulated silver nanoparticles on the thermal and electrical property of sonochemically synthesized polyaniline/silver nanocomposite

An investigation of microstructure of polyaniline nanocomposite is presented. The highly stable, semiconducting polyaniline/silver nanocomposites are prepared in-situ, employing the acoustic cavitation mechanism to obtain the composite in nanophase. The materials are characterized by UV-visible spectroscopy (UV–vis), transmission electron microscopy (TEM), thermogravimetric analyzer (TGA) and fourier transform infrared spectroscopy (FTIR). The polyaniline nanocomposites have an extended conformation in N-methyl-2-pyrrolidinone (NMP), as seen from UV–vis spectra. The plasmon resonances for silver nanoplates are also seen. A high thermal stability is observed for the polyaniline/silver nanocomposites which increased with increasing silver content. The TEM studies show that the polyaniline is formed as nanofibers, with plate-like metallic silver nanoparticles (50 nm × 35 nm in dimension) embedded into them. From the electrical conductivity measurements of pure polyaniline and its nanocomposites it was found that incorporation of polyethylene glycol stabilized silver nanoparticles leads to increased intermolecular charge hopping that results in enhanced electrical conductivity of the nanocomposites. TGA and DSC results indicated greater thermal stability for the nanocomposites along with higher crystallinity. A study of spreading resistance of the materials, done using scanning spreading resistance microscope, revealed localized sites of high and low conductivity within the polyaniline. The low conducting sites were fewer in the case of nanocomposites.

Encapsulation of Silver Nanoparticles in a Polystyrene Matrix by Miniemulsion Polymerization and Its Antimicrobial Activity

Surface-modified silver nanoparticles (NAg) were encapsulated into a polystyrene (PS) matrix by in situ miniemulsion polymerization. Silver nanoparticles were modified with 3-aminopropyltrimethoxysilane (APTMS) that acts as a coupling agent and costabilizer in the polymerization reaction. The PS-Nag nanocomposites synthesized via miniemulsion polymerization were made at two different concentrations of the initiator (0.7 and 2.5 g/L in H2O); at higher concentration of the initiator the conversion and efficiency of encapsulation increases, and the average particle size decreases. The PS-NAg composites showed excellent antimicrobial performance toward bacteria such as Escherichia coli and Staphylococcus aureus.

Encapsulation of silver nanoparticles into graphite grafted with hyperbranched poly(amidoamine) dendrimer and their catalytic activity towards reduction of nitro aromatics

Hyperbranched polyamidoamine (PAMAM) dendrimer have been successfully grafted on the graphite surface and silver nanoparticles (AgNPs) were readily synthesized within the graphite grafted PAMAM dendrimer templates and applied as nanocatalysts in the reduction of nitro aromatics. Three generations of PAMAM dendrimers with varying chain branches have been utilized in order to serve this purpose. The grafting of PAMAM dendrimer on graphite surface has been monitored using TGA, Raman and FT-IR spectra and the AgNPs/GR-G1.0PAMAM, AgNPs/GR-G2.0PAMAM, AgNPs/GR-G3.0PAMAM nanocatalysts were characterized using XRD, UV–visible spectra, SEM, TEM and EDX spectral analysis. The prepared catalysts were found to exhibit enhanced catalytic activity towards the reduction of 4-nitrophenol and the reaction rate constant for our third generation catalyst was estimated to be 21.7×10−3s−1, which is the highest reported heterogeneous system so far. The efficiency of the system has been further demonstrated through the reduction of halonitroarenes without dehalogenation in the halo-substituted nitro benzenes and reduction of nitro groups in the presence of imine functionalities under mild condition.

One-Step Deposition of Nano-Sized Gold onto the Carbon Surface of Encapsulated Silver Nanoparticles

In the present work, we demonstrate the modification of silver nanoparticles encapsulated in the shells of amorphous carbon by nanoparticles of noble metals using galvanic replacement reactions. We show that the treatment of these types of carbon encapsulated silver nanoparticles with HAuCl4 solution is accompanied by the deposition of the gold nanoparticles on the outer surface of the carbon capsules. This process opens extremely broad possibilities for the design and direct preparation of composite carbon-based nanomaterials of different compositions for a wide variety of practical applications.

Electrochemical Fabrication of Anodic Aluminum Oxide Films with Encapsulated Silver Nanoparticles as Plasmonic Photoconductors

Two dimensional photoconductors based on anodic aluminum oxide (AAO) films with 80 nm pore size and 100 nm inter-pore spacing encapsulated with silver nanoparticles have been electrochemically fabricated. A 405 nm laser was used to illuminate the encapsulated silver nanoparticles through a transparent AAO barrier layer to induce photocurrent proportional to the laser power and applied voltage between two electrodes. The photoconductivity is attributed to plasmonic coupling among neighboring silver nanoparticles. The AAO barrier layer provides protection to encapsulated silver nanoparticles against possible degradation by the ambient environments and makes the device useful for biomedical sensors and electro-optical applications.

Non‐Toxic Dry‐Coated Nanosilver for Plasmonic Biosensors

The plasmonic properties of noble metals facilitate their use for in-vivo bio-applications such as targeted drug delivery and cancer cell therapy. Nanosilver is best suited for such applications as it has the lowest plasmonic losses among all such materials in the UV-visible spectrum. Its toxicity, however, can destroy surrounding healthy tissues and thus, hinders its safe use. Here, that toxicity against a model biological system (Escherichia coli) is "cured" or blocked by coating nanosilver hermetically with a about 2 nm thin SiO2 layer in one-step by a scalable flame aerosol method followed by swirl injection of a silica precursor vapor (hexamethyldisiloxane) without reducing the plasmonic performance of the enclosed or encapsulated silver nanoparticles (20 - 40 nm in diameter as determined by X-ray diffraction and microscopy). This creates the opportunity to safely use powerful nanosilver for intracellular bio-applications. The label-free biosensing and surface bio-functionalization of these ready-to-use, non-toxic (benign) Ag nanoparticles is presented by measuring the adsorption of bovine serum albumin (BSA) in a model sensing experiment. Furthermore, the silica coating around nanosilver prevents its agglomeration or flocculation (as determined by thermal annealing, optical absorption spectroscopy and microscopy) and thus, enhances its biosensitivity, including bioimaging as determined by dark field illumination.

Production of carbonaceous nanostructures from a silver-carbon ambient spark

Using silver-carbon ambient sparks, hollow carbon nanospheres or multiwall carbon nanotubes were produced separately from carbon encapsulated silver nanoparticles (−1,400 K s−1) during relatively slow (−800 K s−1) or fast (−2,900 K s−1) cooling process. Different cooling processes (i.e., different exposures within high temperature) caused the formation of different carbon precipitates in the process of silver mediated graphitization: for −2,900 K s−1 and <−1,400 K s−1, respectively, obtained tubelike and sphere (encapsulated and hollow)-like carbonaceous nanostructures.

Encapsulation of Silver Nanoparticles into Polystyrene Microspheres

Hydrogen reduction of a saturated silver(I) oxide solution at elevated temperatures in the presence of ∼200 nm polystyrene (PS) microspheres followed by acetone treatment lead to the encapsulation of the resulting silver nanoparticles (Ag NPs) into the PS microspheres. Extinction spectra reveal an expected red-shift of the characteristic plasmon resonance frequency of Ag−PS core−shell particles due to the increase in the surrounding dielectric constant. The Ag−PS core−shell particles maintain their stability when redispersed back into water.

Using a T-junction microfluidic chip for monodisperse calcium alginate microparticles and encapsulation of nanoparticles

This article describes the simulation of flow velocity distribution and the process of formation of monodisperse calcium alginate microparticles (Ca-alg MPs) by using microfluidic T-junction geometries. Based on sheath stresses, water-in-oil (w/o) emulsions of an aqueous solution of a biopolymer (e.g. sodium alginate, Na-alg) are emulsified in an oil phase. The emulsions are collected into a bath containing calcium-ions to form the Ca-alg MPs. Experimental data show that Ca-alg MPs with diameters ranging from 70 μm to 220 μm with a variation less than 10% are precisely generated. The size of the emulsions can be tunable by adjusting the relative sheath/sample flow rate ratio. In addition, the encapsulation of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) is studied. The approach in manipulation of microparticles will provide many potential usages for pharmaceutical application. The proposed method has advantages of being readily controlled, cost-effective and easy to operate, together with its ability to produce a uniform size.

Spontaneous formation of silver nanoparticles in aminosilica

We report a rapid and spontaneous metallization process associated with sol–gel reaction of aminosilane that can be utilized to synthesise silver embedded silica nanocomposite without involving additional reducing agents. The reduction reaction induced by bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS) involves amine functional moieties, which drive the reduction reaction with presence of water. Cyclic voltammetry was used to investigate the redox potential of enTMOS and its relation to chemical environment. It was found that the oxidation potential of enTMOS depending on the amount of water (water:enTMOS (v/v) = 8:1–0:1) ranges from 0.48 to 0.68 V versus Ag/AgCl electrode in methanol. The oxidation potential of aminosilane decreases with water content and becomes more negative than that of Ag, suggesting the aminosilane acts as a silver reducing agent while serving as a matrix to encapsulate silver nanoparticles after reacting with water. This process has been utilized to produce evenly dispersed silver nanoparticles with sizes ranging from 5 to 20 nm in both liquid and solid forms of aminosilane, allowing us to prepare silver nanoparticles doped silica nanocomposite that exhibits enhanced electrochemical properties.

A convenient approach to synthesize stable silver nanoparticles and silver/polystyrene nanocomposite particles

AbstractIn this study, silver nanoparticles were prepared by the reduction of silver nitrate in SDS+ isopentanol/styrene/H2O reverse microemulsion system using sodium citrate as reducing agent. The Ag/PS nanocomposite particles were prepared by in situ emulsion polymerization of the styrene system containing silver nanoparticles that did not separate from the reaction solution. The polymerization dynamic characteristic was studied, at the same time, silver nanparticles and the encapsulation of composite particles were characterized by Fourier‐transform‐infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X‐ray diffraction (XRD) measurement, UV–vis diffuse reflectance spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The results of TEM and UV–vis absorption spectra showed that well‐dispersed silver nanoparticles have a narrow size distribution. XRD showed that Ag and Ag/PS nanocomposite particles were less than 10 and 20 nm in size, which is similar to those observed by TEM. The results of XPS spectra revealed that the microemulsion system can stabilize the silver nanoparticles from aggregation and provided supporting evidence for the polystyrene encapsulated silver nanoparticle structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.

Encapsulation of silver nanoparticles within micropores of block copolymers constructed by emulsion‐induced method

Encapsulation of silver nanoparticles within micropores of block copolymers constructed by emulsion‐induced method

Synthesis and characterization of carbon thin wires linked carbon hollow spheres encapsulating Ag nanoparticles

Monodisperse carbon hollow spheres encapsulating silver nanoparticles have been successfully synthesized by a facile approach with imidazolium ionic liquid ([C 14mim]BF 4) as the soft template. Meanwhile, a novel Ag/C nanocomposite with an interesting structure, in which the carbon hollow spheres encapsulating silver nanoparticles were assembled by fine carbon wires, exists in this experiment. The Ag/C nanocomposites was characterized by XRD, TEM (HRTEM), SEM, FTIR spectroscopy, Raman spectrometer and energy dispersive X-ray analysis (EDX). The possible formation mechanism of the nanocomposites has been proposed.