Microwave-assisted rapid synthesis of anisotropic Ag nanoparticles by solid state transformation

Anisotropic silver nanoparticles (NPs) have been synthesized rapidly using microwave irradiation by the decomposition of silver oxalate in a glycol medium using polyvinyl pyrolidone (PVP) as the capping agent. The obtained Ag nanoparticles have been characterized by UV-visible spectroscopy, powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies. Anisotropic Ag nanoparticles of average size around 30?nm have been observed in the case of microwave irradiation for 75?s whereas spherical particles of a size around 5-6?nm are formed for 60?s of irradiation. The texture coefficient and particle size calculated from XRD patterns of anisotropic nanoparticles reveal the preferential orientation of (111) facets in the Ag sample. Ethylene glycol is found to be a more suitable medium than diethylene glycol. A plausible mechanism has been proposed for the formation of anisotropic Ag nanoparticles from silver oxalate.     

Rapid biologically one-step synthesis of stable bioactive silver nanoparticles using Osage orange (Maclura pomifera) leaf extract and their antimicrobial activities

Synthesis of nanoparticles by using natural products as reducing and stabilizing agents have been widely used in various fields especially medicine, primarily because of its lower cost, simplicity, and less toxic byproducts. In the present work, silver nanoparticles (Ag NPs) were rapidly synthesized from silver nitrate in a green one-step synthesis by the aqueous extracts of Osage orange (Maclura pomifera) leaf as a reducing and stabilizing agent simultaneously. The effects of pH, extract quantity, and silver salt concentration were investigated to determine the optimum conditions of green synthesis of Ag NPs. The synthesized Ag NPs were characterized by different techniques including UV–Visible (UV–Vis) absorption spectroscopy, X-ray diffraction (XRD), Fourier transform Infrared (FT-IR) Spectroscopy, and Transmission Electron Microscopy (TEM). The Ag NPs showed surface plasmon resonance centered at 415?nm. The XRD pattern and TEM analysis revealed spherical, stable, and uniform Ag NPs with the average particle size of about 12?nm. The FT-IR spectroscopy showed that mainly hydroxyl functional groups, as both the reducing and stabilizing agent are responsible for silver nanoparticles synthesis. The antimicrobial activity of the synthesized Ag NPs showed a significant microbicidal effect on all clinical isolates especially, Gram-negative bacteria and fungi. These results suggest that such stable and uniform Ag NPs can be synthesized rapidly and simply for clinical as well as pharmaceutical applications.     

Characterization of silver nanoparticles synthesized on titanium dioxide fine particles

Silver nanoparticles with a narrow size distribution were synthesized over the surface of two different commercial TiO(2) particles using a simple aqueous reduction method. The reducing agent used was NaBH(4); different molar ratios TiO(2):Ag were also used. The nanocomposites thus prepared were characterized using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), dynamic light scattering (DLS) and UV-visible (UV-vis) absorption spectroscopy; the antibacterial activity was assessed using the standard microdilution method, determining the minimum inhibitory concentration (MIC) according to the National Committee for Clinical Laboratory Standards. From the microscopy studies (TEM and STEM) we observed that the silver nanoparticles are homogeneously distributed over the surface of TiO(2) particles and that the TiO(2):Ag molar ratio plays an important role. We used three different TiO(2)Ag molar ratios and the size of the silver nanoparticles is 10, 20 and 80?nm, respectively. It was found that the antibacterial activity of the nanocomposites increases considerably comparing with separated silver nanoparticles and TiO(2) particles.     

Numerical calculation of plasmonic field absorption enhancement in CdSe-quantum dot sensitized ZnO nanorods by Ag nanoparticle periodic arrays

Plasmonic field absorption enhancement (PFAE) of Ag nanoparticles (Ag NPs) periodic arrays in CdSe-quantum dot (QD) sensitized ZnO nanorods was numerically investigated by the three-dimensional finite difference time domain (FDTD). The Ag NPs with spherical morphology were found to have an optimum PFAE compared to other Ag NP morphologies such as cubic and pyramidal. The results also showed that PFAE intensity in CdSe-QD-sensitized ZnO nanorods is increased with the reduction of Ag NP diameter until 10 nm and decreases thereafter. Moreover, the optimum density of spherical Ag NPs for optimum PFAE was observed as 20%. PFAE in CdSe-QD-sensitized ZnO nanorods is improved with increasing space between ZnO nanorods until 180 nm and reduces thereafter. Finally, the results showed that PFAE of Ag NPs for the high distance between ZnO nanorods is dependent on radiation angle; while for the low distance between ZnO nanorods it is free of radiation angle.     

Evaluation of the toxicities of silver and silver sulfide nanoparticles against Gram‐positive and Gram‐negative bacteria

In this study, the endogenous lipid signalling molecules, N ‐myristoylethanolamine, were explored as a capping agent to synthesise stable silver nanoparticles (AgNPs) and Ag sulphide NPs (Ag₂ S NPs). Sulphidation of the AgNPs abolishes the surface plasmon resonance (SPR) maximum of AgNPs at 415 nm with concomitant changes in the SPR, indicating the formation of Ag₂ S NPs. Transmission electron microscopy revealed that the AgNPs and Ag₂ S NPs are spherical in shape with a size of 5–30 and 8–30 nm, respectively. AgNPs and Ag₂ S NPs exhibit antimicrobial activity against Gram‐positive and Gram‐negative bacteria. The minimum inhibitory concentrations (MIC) of 25 and 50 μM for AgNPs and Ag₂ S NPs, respectively, were determined from resazurin microtitre plate assay. At or above MIC, both AgNPs and Ag₂ S NPs decrease the cell viability through the mechanism of membrane damage and generation of excess reactive oxygen species.Inspec keywords: cellular biophysics, biomembranes, transmission electron microscopy, nanomedicine, microorganisms, molecular biophysics, antibacterial activity, nanofabrication, silver, biomedical materials, surface plasmon resonance, nanoparticles, materials preparation, silver compounds, lipid bilayersOther keywords: Gram‐negative bacteria, Gram‐positive bacteria, endogenous lipid signalling molecules, N‐myristoylethanolamine, capping agent, silver nanoparticles, Ag sulphide NPs, sulphidation, surface plasmon resonance, concomitant changes, transmission electron microscopy, minimum inhibitory concentrations, resazurin microtitre plate assay, cell viability, membrane damage, reactive oxygen species, Ag toxicities, Ag, Ag₂ S     

In-situ preparation of binary-phase silver nanoparticles at a high Ag+ concentration

Stable and monodisperse silver nanoparticles (NPs) have been synthesized using high metal salt concentration (up to 0.735 M) through a simple but novel technique. It is based on one-step procedure that uses glycerol for reducing Ag+ in the presence of o-phenylenediamine (o-PDA) resulting the nanoparticles are in two forms (one water-soluble, the other a precipitated). The water-soluble phase contains NPs that have a bimodal size distribution (2-3 and 5-6 nm); the other comprises precipitated NPs, having a unimodal size distribution (2-3 nm). The water-soluble NPs are covalently bonded to the aromatic amine molecules to form isolated units, while the precipitated nanoparticles are embedded in the networks formed by cross-linking between COOH groups of hydroxypyruvic acid (oxidized form of glycerol) and NH2 groups of o-PDA molecules. We used transmission electron microscopy (TEM), UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) to characterize the silver products obtained.     

Reinforcement of Ag nanoparticle paste with nanowires for low temperature pressureless bonding

Low temperature interconnection processes for lead-free packaging and flexible electronics are currently of great interest. Several studies have focused on bonding using silver nanoparticles (Ag NPs) or copper nanoparticles (Cu NPs). However, pressure assistance is generally necessary for bonding with nanomaterial pastes, which limits its industrial applications. Here, a unique method for bonding of copper wires using Ag NP and nanowire binary pastes is examined, in which joining is accomplished from 60 to 200?°C and yet without the application of pressure. Bonding is facilitated by solid state sintering of Ag nanomaterials and metallic bonding between Cu and Ag interfaces. The effects of different additions of Ag nanowires in bonded joints are studied, in which addition of 20?vol% Ag nanowires improves bonding strength after low temperature sintering by 50–80?% compared with Ag nanoparticle paste. A mechanical reinforcement effect due to introduction of Ag nanowires has been confirmed by observation of the fracture path propagation, where necking, breakage and pullout of nanowires occur on loading. This low temperature pressureless bonding technology has the potential for wide use for interconnection in lead-free microcircuits and flexible electronic packaging.     

Green synthesis and characteristic of core-shell structure silver/starch nanoparticles

An eco-friendly method was put forward to synthesize Ag nanoparticles (Ag NPs) by using biodegradable starch as a stabilizing agent. The silver ion from AgNO₃ was reduced by glucose in soluble starch solution. Morphological observation and characterization of Ag NPs were performed by using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and UV–vis absorption spectroscopy. HRTEM showed that Ag NPs were covered by starch layer to form spherical core-shell Ag/starch NPs with diameter ranging from 5 to 20 nm. XRD pattern confirmed the presence of Ag NPs with face-centered cubic (fcc) structure. All these results indicated that starch played an important role in stabilizing Ag NPs.     

Forming dense arrays of gold nanoparticles in thin films of yttria stabilized zirconia by magnetron sputtering

Layers of Au nanoparticles (NPs) were formed in films of yttria stabilized zirconia (YSZ) on fusedquartz substrates by layer-by-layer magnetron deposition with subsequent annealing. The obtained structures were studied by applying high-resolution transmission electron microscopy (TEM) to transverse sections and using optical absorption spectroscopy. TEM studies revealed the formation of Au NPs with a diameter of 2?3 nm concentrated in a thin layer within the YSZ film. The optical absorption spectra of the studied samples exhibited peaks of resonance plasmon absorption in Au NPs with a maximum wavelength of ~650 nm. The dependences of geometric and structural parameters of Au NP arrays (size, density, thickness of the Au NP layer, etc.) on the formation conditions were determined, and the regimes of fabrication of dense Au NP arrays that allow for collective plasmon excitations were identified.     

Real-time monitoring of plasmonic evolution in thick Ag:SiO(2) films: nanocomposite optical tuning

An in situ optical microspectroscopy study of the surface plasmon resonance (SPR) evolution of Ag nanoparticles (NPs) embedded in thick SiO(2) films deposited on soda-lime glass has been conducted during thermal processing in air. The temperature and time dependences of the SPR were analyzed in the context of Mie extinction and crystal growth theories and were discussed along with consideration of oxidation processes and film/substrate physicochemical interactions. At relatively high temperatures, Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. At lower temperatures, an initial decrease in Ag particle size was indicated due to oxidation, followed by NP diffusion-based growth. The growth and oxidation stages appeared temperature and time dependent, allowing for the tuning of material properties. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy performed ex situ as single Ag(+) ions. The oxidative effect of the air atmosphere on Ag NPs was shown to be ultimately circumvented by the thick nanocomposite film. The phenomenon was explained on the basis of the displacement of the Ag/Ag(+) redox equilibrium toward Ag NP stability after ion migration toward the substrate being self-constrained. In addition, the current spectroscopic approach has been proposed for estimating the activation energy for silver diffusion in the SiO(2) matrix.     

Stabilization of gold nanoparticle films on glass by thermal embedding

The poor adhesion of gold nanoparticles (NPs) to glass has been a known obstacle to studies and applications of NP-based systems, such as glass/Au-NP optical devices. Here we present a simple scheme for obtaining stable localized surface plasmon resonance (LSPR) transducers based on Au NP films immobilized on silanized glass and annealed. The procedure includes high-temperature annealing of the Au NP film, leading to partial embedding in the glass substrate and stabilization of the morphology and optical properties. The method is demonstrated using citrate-stabilized Au NPs, 20 and 63 nm mean diameter, immobilized electrostatically on glass microscope cover slides precoated with an aminosilane monolayer. Partial thermal embedding of the Au NPs in the glass occurs at temperatures in the vicinity of the glass transition temperature of the substrate. Upon annealing in air the Au NPs gradually settle into the glass and become encircled by a glass rim. In situ transmission UV-vis spectroscopy carried out during the annealing in a specially designed optical oven shows three regions: The most pronounced change of the surface plasmon (SP) band shape occurs in the first ca. 15 min of annealing; this is followed by a blue-shift of the SP band maximum (up to ca. 5 h), after which a steady red-shift of the SP band is observed (up to ca. 70 h, when the experiment was terminated). The development of the SP extinction spectrum was correlated to changes in the system structure, including thermal modification of the NP film morphology and embedding in the glass. The partially embedded Au NP films pass successfully the adhesive-tape test, while their morphology and optical response are stable toward immersion in solvents, drying, and thiol self-assembly. The enhanced adhesion is attributed to the metal NP embedding and rim formation. The stabilized NP films display a refractive index sensitivity (RIS) of 34-48 nm/RIU and 0.1-0.4 abs.u./RIU in SP band shift and extinction change, respectively. The RIS can be improved significantly by electroless deposition of Au on the embedded NPs, while the system stability is maintained. The method presented provides a simple route to obtaining stable Au NP film transducers.     

Bio-mechanochemical synthesis of silver nanoparticles with antibacterial activity

By using a bio-mechanochemical approach combining mechanochemistry (ball milling) and green synthesis for the first time, silver nanoparticles (Ag NPs) with antibacterial activity were successfully synthesized. Concretely, eggshell membrane (ESM) or Origanum vulgare L. plant (ORE) and silver nitrate were used as environmentally friendly reducing agent and Ag precursor, respectively. The whole synthesis took 30?min in the former and 45?min in the latter case. The photon cross-correlation measurements have shown finer character of the product in the case of milling with Origanum. UV–Vis measurements have shown the formation of spherical NPs in both samples. TEM study has revealed that both samples are composites of nanosized silver nanoparticles homogenously dispersed within the organic matrices. It has shown that the size and size distribution of the silver nanoparticles is smaller and more uniform in the case of eggshell membrane matrix implying lower silver mobility within this matrix. The antibacterial activity was higher for the silver nanoparticles synthesized with co-milling with Origanum plant than in the case of milling with eggshell membrane.     

Biogenic silver embedded magnesium oxide nanoparticles induce the cytotoxicity in human prostate cancer cells

This work reports the synthesis, characterization, and cytotoxicity of biogenic magnesium oxide nanoparticles (MgONPs) and nanosilver embedded magnesium oxide nanoparticles (Ag-MgONPs). The formation of nanoparticles (NPs) was confirmed by the indications of color changes and precipitations. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) pattern studies showed the agglomeration colloids, porous, spherical, needle-shaped and crystal nature of MgONPs, whereas, the Ag-MgONPs was hexagonal, and spherical structured nanocrystals. Energy-dispersive X-ray fluorescence spectrometry (EDS) study indicated the existence of Ag, Mg, and O in NPs complex. The particle size analysis (PSA) revealed the mean size of 15.09?nm for Ag-MgONPs and 13.68?nm for MgONPs. Fourier transform infrared spectroscopy (FTIR) showed the peaks corresponding to amide, carboxylic acids, aromatics, alkene and esters from mycelial cell-free extract (MCFE). The absorbed and lattices oxygen of MgO was probably assigned in the formation of Ag-MgONPs as indicated by X-ray photoelectron spectroscopy (XPS). Cytotoxicity assay showed the Ag-MgONPs was stronger in inducing the prostate cancer (PC-3) cell death than the MgONPs. This work concluded that Ag-MgONPs could be potential therapeutics for cancer therapy.     

Green synthesis of stable silver nanoparticles by the main reduction component of green tea (Camellia sinensis L.)

Recently the use of medicinal plants potential in the production of nanoparticles has received serious attention. Here, the main component of Camellia sinensis L. (green tea) extract was detected by spectroscopy and the optimal conditions were determined for their performance in green synthesis of silver nanoparticles at room temperature. Epigallocatechin gallate was identified as the dominant component in the extract as determined by spectroscopy, and it was established that its oxidation was a function of the solution pH. Transmission electron microscopy, dynamic light scattering, and visible absorption spectroscopy (UV‐Vis) confirmed the reduction in silver ions to silver nanoparticles (Ag NPs). Controlling over Ag NPs shape and narrow size distribution was achieved with 10 ml green tea leaf extract solution and in different reaction pH. Spherical colloidal Ag NPs with well‐defined hydrodynamic diameters (with average hydrodynamic size of 27.9–50.2 nm) were produced. Silver nitrate concentrations used in this study were lower than that of reported in similar works, and synthesis efficiency was also higher. Nanoparticles were perfectly spherical and their uniformity, compared to similar studies, was much higher. These NPs showed higher degree of stability and were aqueously stable for >10 months in dark glasses at 4°C.Inspec keywords: hydrodynamics, nanoparticles, particle size, pH, visible spectra, ultraviolet spectra, reduction (chemical), transmission electron microscopy, silver, microorganisms, nanofabrication, colloids, biomedical materials, nanomedicine, drug delivery systemsOther keywords: transmission electron microscopy, dynamic light scattering, visible absorption spectroscopy, silver ions, narrow size distribution, silver nitrate concentrations, green synthesis, medicinal plants, solution pH, green tea leaf, hydrodynamic size, silver nanoparticles, Camellia sinensis L, drug delivery, reduction component, epigallocatechin gallate, UV‐visible spectra, hydrodynamic diameters, spherical colloidal Ag NPs, temperature 4.0 degC, Ag     

Microemulsion synthesis of silver nanoparticles using biosurfactant extracted from Pseudomonas aeruginosa MKVIT3 strain and comparison of their antimicrobial and cytotoxic activities

In the present study, an efficient biosurfactant producing bacterial strain Pseudomonas aeruginosa MKVIT3 was isolated from an oil logging area in Vellore district of Tamil Nadu, India. Liquid chromatography–mass spectrometry (LC‐MS/MS) analysis was performed for the identification of different congeners present in the extracted biosurfactant. The column purified biosurfactant was used to stabilise the formation of silver nanoparticles (NP) using borohydrate reduction in reverse micelles. The silver NP were characterised using UV‐vis absorption spectroscopy, Powder‐XRD TEM analysis and zeta potential. A comparative study of the antimicrobial activity and cytotoxic efficacy was done for the extracted purified biosurfactant and the silver NP. The LC‐MS/MS analysis of the biosurfactant revealed the presence of five rhamnolipid congeners. The synthesised silver NP showed the characteristic absorption peak in UV‐vis at 440 nm. Powder‐XRD and TEM analysis revealed the average particle size of the NP as 17.89 ± 8.74 nm as well as their cubic structure. Zeta potential value of −30.9 mV suggested that the silver NPs are stable in the suspension. Comparative study of the antimicrobial activity revealed that the silver NP are more potent than the biosurfactant in inhibiting the growth of microbes. Cytotoxic activity revealed that the biosurfactant are more effective than the synthesised silver NP.Inspec keywords: microemulsions, silver, nanoparticles, nanomedicine, cellular biophysics, surfactants, microorganisms, chromatography, mass spectroscopic chemical analysis, ultraviolet spectra, visible spectra, antibacterial activityOther keywords: Ag, microemulsion synthesis, silver nanoparticles, Pseudomonas aeruginosa, MKVIT3 strain, antimicrobial activities, cytotoxic activities, biosurfactant producing bacterial strain, oil logging area, Vellore district, Tamil Nadu, India, liquid chromatography–mass spectrometry, LC‐MS/MS analysis, extracted biosurfactant, column purified biosurfactant, borohydrate reduction, reverse micelles, UV‐vis absorption spectroscopy, powder‐XRD TEM analysis, zeta potential, antimicrobial activity, cytotoxic efficacy, extracted purified biosurfactant, rhamnolipid congeners     

Photocatalytic degradation of methyl red dye by silica nanoparticles

Silica nanoparticles (SiO2 NPs) were found to be photocatalytically active for degradation of methyl red dye (MR). The SiO2 NPs and SiO2 NPs doped with silver (and or) gold nanoparticles were prepared. From the transmission electron microscopy (TEM) images the particle size and particle morphology of catalysts were monitored. Moreover, SiO2 NPs doped with silver and gold ions were used as a photocatalyst for degradation of MR. The rate of photocatalytic degradation of MR was found to be increased in the order of SiO2 NPs, SiO2 NPs coated with gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs), SiO2 NPs coated with Ag NPs, SiO2 NPs coated with Au NPs, Ag+-doped SiO2 NPs, and Au3+-doped SiO2 NPs. The kinetic and mechanism of photocatalytic reaction were studied and accorded well with experimental results.     

Green synthesis and characterisation of Ag NPs using aqueous extract of Phyllanthus maderaspatensis L.

In this study we consider the synthesis of silver nanoparticles (Ag NPs) from the aqueous leaf extracts of Phyllanthus maderaspatensis, which, we demonstrate, is a highly potential herb for the biosynthesis of NPs. Ag NPs were effectively produced within 24?h and NPs were characterised using UV–visible spectrophotometry, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. Ag NPs of sizes ranging approximately between 59 and 76?nm were reported. Studies also indicated a gradual increase in the synthesis of NPs with time, thus proving the efficiency of P. maderaspatensis as an ideal catalyst in the formation of biologically synthesised phytonanoparticles.     

Controllable assembly of silver nanoparticles induced by femtosecond laser direct writing

We report controllable assembly of silver nanoparticles (Ag NPs) for patterning of silver microstructures. The assembly is induced by femtosecond laser direct writing (FsLDW). A tightly focused femtosecond laser beam is capable of trapping and driving Ag NPs to form desired micropatterns with a high resolution of ∼190 nm. Taking advantage of the ‘direct writing’ feature, three microelectrodes have been integrated with a microfluidic chip; two silver-based microdevices including a microheater and a catalytic reactor have been fabricated inside a microfluidic channel for chip functionalization. The FsLDW-induced programmable assembly of Ag NPs may open up a new way to the designable patterning of silver microstructures toward flexible fabrication and integration of functional devices.     

Controllable assembly of silver nanoparticles induced by femtosecond laser direct writing

Abstract

We report controllable assembly of silver nanoparticles (Ag NPs) for patterning of silver microstructures. The assembly is induced by femtosecond laser direct writing (FsLDW). A tightly focused femtosecond laser beam is capable of trapping and driving Ag NPs to form desired micropatterns with a high resolution of ～190 nm. Taking advantage of the ‘direct writing’ feature, three microelectrodes have been integrated with a microfluidic chip; two silver-based microdevices including a microheater and a catalytic reactor have been fabricated inside a microfluidic channel for chip functionalization. The FsLDW-induced programmable assembly of Ag NPs may open up a new way to the designable patterning of silver microstructures toward flexible fabrication and integration of functional devices.     

A facile method to prepare size-tunable silver nanoparticles and its antibacterial mechanism

The antibacterial effect of silver nanoparticles (denoted as Ag NPs) is closely related to size. This could partly explain why size controllable synthesis of Ag NPs for bactericidal application is drawing much attention. Thus, we establish a facile and mild route to prepare size-tunable Ag NPs with highly uniform morphologies and narrow size distributions. The as-prepared Ag NPs with averaged sizes of 2, 12 and 32?nm were characterized by transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV–vis), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The antimicrobial effect of the as-prepared Ag NPs with different particles size was assessed by broth dilution and disk diffusion as well as measurement of optical density (OD₆₀₀). Moreover, their antibacterial mechanism was discussed in relation to morphology observation of microorganism by scanning electron microscopy (SEM) and to concentration detection of Ag⁺ by stripping voltammetry. It was found that the parameters such as reactant molar ratio, reaction time, dropping speed, and most of all, pH of the reactant solutions, have significant influences on size-regulation of Ag NPs. The as-prepared Ag NPs exhibit excellent antibacterial properties, and their antimicrobial activities increase with decreasing particles size. Besides, two kinds of mechanisms, i.e., contact action and release of Ag⁺, are responsible for the antimicrobial effect of Ag NPs.