In situ synthesis of water dispersible bovine serum albumin capped gold and silver nanoparticles and their cytocompatibility studies

A simple and convenient one step room temperature method is described for the synthesis of bovine serum albumin (BSA) capped gold and silver nanoparticles. BSA reduces silver ions to silver nanoparticles but does not directly reduce gold ions to gold nanoparticles at room temperature and varying pH conditions. However, when silver and gold ions are simultaneously added to BSA, silver ions get reduced to metallic silver first and these in turn reduce gold ions to gold nanoparticles through a galvanic exchange reaction. The so synthesized silver and gold nanoparticles are easily water dispersible and can withstand addition of salt even at high concentrations. It is shown that the capped protein retains its secondary structure and the helicity to a large extent on the nanoparticles surface and that the protein capping makes the nanoparticles cytocompatible.     

Paramagnetic behaviour of silver nanoparticles generated by decomposition of silver oxalate

Silver oxalate Ag₂C₂O₄, was already proposed for soldering applications, due to the formation when it is decomposed by a heat treatment, of highly sinterable silver nanoparticles. When slowly decomposed at low temperature (125 °C), the oxalate leads however to silver nanoparticles isolated from each other. As soon as these nanoparticles are formed, the magnetic susceptibility at room temperature increases from −3.14 10⁻⁷ emu.Oe⁻¹.g⁻¹ (silver oxalate) up to −1.92 10⁻⁷ emu.Oe⁻¹.g⁻¹ (metallic silver). At the end of the oxalate decomposition, the conventional diamagnetic behaviour of bulk silver, is observed from room temperature to 80 K. A diamagnetic-paramagnetic transition is however revealed below 80 K leading at 2 K, to silver nanoparticles with a positive magnetic susceptibility. This original behaviour, compared to the one of bulk silver, can be ascribed to the nanometric size of the metallic particles.     

Preparation of polyimide/BaTiO3/Ag nanocomposite films via in situ technique and study of their dielectric behavior

Triphase polyimide nanocomposite films were fabricated using barium titanate （BaTiO3） with high dielectric constant and silver （Ag） with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly（amic acid） was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver（I） was added into the BaTiO3 containing poly（amic acid） solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver （I） to metallic silver with concomitant imidization of poly（amic acid） to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.     

Moderating effect of ammonia on particle growth and stability of quasi-monodisperse silver nanoparticles synthesized by the Turkevich method

A new method to stabilize silver nanoparticles by the addition of ammonia is proposed. Colloidal dispersions of silver nanoparticles were synthesized by the Turkevich method using sodium citrate to reduce silver nitrate at high pH and at 90 °C. After approximately 12 min, a diluted ammonia solution was added to the reaction flask to form soluble diamine silver (I) complexes that played an important growth moderating role, making it possible to stabilize metallic silver nanoparticles with sizes as small as 1.6 nm after 17 min of reaction. Colloidal dispersions were characterized by UV-visible absorption spectroscopy, X-ray diffraction, and transmission electronic microscopy.     

Silver-protein (core-shell) nanoparticle production using spent mushroom substrate

A simple route for the synthesis of silver-protein (core-shell) nanoparticles using spent mushroom substrate (SMS) has been demonstrated in this work. SMS exhibits an organic surface that reduces silver ions and stabilizes the silver nanoparticles by a secreted protein. The silver nitrate solution incubated with SMS changed to a yellow color from 24 h onward, indicating the formation of silver nanoparticles. The purified solution yielded the maximum absorbance at 436 nm due to surface plasmon resonance of the silver nanoparticles. X-ray analysis of the freeze-dried powder of silver nanoparticles confirmed the formation of metallic silver. Transmission electron microscopic analysis of the samples showed a uniform distribution of nanoparticles, having an average size of 30.5 +/- 4.0 nm, and its corresponding electron diffraction pattern confirmed the face-centered cubic (fcc) crystalline structure of metallic silver. The characteristic fluorescence of the protein shell at 435 nm was observed for the silver nanoparticles in solution, when excited at 280 nm, while Fourier transform infrared (FTIR) spectroscopy confirmed the presence of a protein shell. The silver nanoparticles were found to be stable in solution for more than 6 months. It is observed that the reducing agents from the safflower stalks caused the reduction of silver ions while protein secreted by the fungus stabilized the silver nanoparticles. These silver nanoparticles showed excellent antibacterial activity against two representative bacteria, Staphylococcus aureus (Gram positive) and Klebsiella pneumoniae (Gram negative), in spite of the presence of an organic layer as a shell. Apart from ecofriendliness and easy availability, "SMS" as a biomanufacturing unit will give us an added advantage in ease of handling when compared to other classes of microorganisms.     

Facile synthesis of PbTe nanoparticles and thin films in alkaline aqueous solution at room temperature

A novel, simple, and cost-effective route to PbTe nanoparticles and films is reported in this paper. The PbTe nanoparticles and films are fabricated by a chemical bath method, at room temperature and ambient pressure, using conventional chemicals as starting materials. The average grain size of the nanoparticles collected at the bottom of the bath is ∼25 nm. The film deposited on glass substrate is dense, smooth, and uniform with silver gray metallic luster. The film exhibits p-type conduction and has a moderate Seebeck coefficient value (∼147 μV K⁻¹) and low electrical conductivity (∼0.017 S cm⁻¹). The formation mechanism of the PbTe nanoparticles and films is proposed.     

Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth

We report on the use of Neem (Azadirachta indica) leaf broth in the extracellular synthesis of pure metallic silver and gold nanoparticles and bimetallic Au/Ag nanoparticles. On treatment of aqueous solutions of silver nitrate and chloroauric acid with Neem leaf extract, the rapid formation of stable silver and gold nanoparticles at high concentrations is observed to occur. The silver and gold nanoparticles are polydisperse, with a large percentage of gold particles exhibiting an interesting flat, platelike morphology. Competitive reduction of Au3+ and Ag+ ions present simultaneously in solution during exposure to Neem leaf extract leads to the synthesis of bimetallic Au core-Ag shell nanoparticles in solution. Transmission electron microscopy revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core-shell structure. The rates of reduction of the metal ions by Neem leaf extract are much faster than those observed by us in our earlier studies using microorganisms such as fungi, highlighting the possibility that nanoparticle biological synthesis methodologies will achieve rates of synthesis comparable to those of chemical methods.     

Preparation of conducting silver paste with Ag nanoparticles prepared by e-beam irradiation

Conducting silver paste was prepared by using Ag nanoparticles which were synthesized by e-beam irradiation method (from KAERI); its conductivity was comparatively determined with Ag nanoparticles which were prepared by thermolysis method (commercial). The silver nanoparticles with the diameter of approximately 150 nm size prepared by e-beam irradiation were mixed with glass frit and sintered for 1 h at 500 °C. It is presumably concluded that the wt% of silver nanoparticle, size distribution and homogenous dispersibility of Ag nanoparticles in the pastes are the critical factors for the high conductivity of the paste. Among the various wt% of silver nanoparticle in the conducting silver pastes, silver paste with 90 wt% of silver nanoparticle has the highest conductivity as 1.6×10⁴ S cm^?1. This conductivity value is 1.6 times higher than the Ag pastes which were prepared with silver nanoparticles obtained by thermolysis method.     

Thermal decomposition process of silver behenate

The thermal decomposition processes of silver behenate have been studied by infrared spectroscopy (IR), X-ray diffraction (XRD), combined thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS), transmission electron microscopy (TEM) and UV-vis spectroscopy. The TG-DTA and the higher temperature IR and XRD measurements indicated that complicated structural changes took place while heating silver behenate, but there were two distinct thermal transitions. During the first transition at 138 °C, the alkyl chains of silver behenate were transformed from an ordered into a disordered state. During the second transition at about 231 °C, a structural change took place for silver behenate, which was the decomposition of silver behenate. The major products of the thermal decomposition of silver behenate were metallic silver and behenic acid. Upon heating up to 500 °C, the final product of the thermal decomposition was metallic silver. The combined TG-MS analysis showed that the gas products of the thermal decomposition of silver behenate were carbon dioxide, water, hydrogen, acetylene and some small molecule alkenes. TEM and UV-vis spectroscopy were used to investigate the process of the formation and growth of metallic silver nanoparticles.     

Effect of temperature on ring-shaped-deposit formated at evaporation of droplets of silver-nanoparticle dispersions

The effect of temperature is studied on the geometric parameters and conductivity of ring-shaped deposits formed at evaporation of droplets of dispersions of silver nanoparticles on hydrophilic (glass) and hydrophobic (copper) substrates. It has been shown that increasing temperature leads to substantial changes in the deposit profile. Therewith, the effects of temperature on droplet evaporation on glass and copper substrates are different. It has been found that the lateral conductivity of a ring-shaped deposit formed on a glass substrate increases stepwise similarly to a percolation transition at a droplet-evaporation temperature of 58°C. It has been suggested that the reason for the temperature effect is related to a change in the ratio between the rates of physicochemical processes occurring at different stages of droplet evaporation.     

Facile synthesis of high-concentration, stable aqueous dispersions of uniform silver nanoparticles using aniline as a reductant

A facile method was developed for preparing uniform silver nanoparticles with small particle sizes of less than 10 nm at high concentrations, in which aniline was used to reduce silver nitrate (AgNO(3)) to silver nanoparticles in the presence of dodecylbenzenesulfonic acid (DBSA) as a stabilizer. Upon the addition of excess NaOH to the DBSA-aniline-AgNO(3) (DAA) system, the formation of silver nanoparticles was almost complete in just 2 min at 90 °C (in 94% yield). The average size of those resultant silver nanoparticles was 8.9 ± 1.1 nm, and the colloids were stable for more than 1 year at ambient temperature. A possible mechanism for the formation of silver nanoparticles was proposed to be related to two factors: one was the mesoscopic structures of the DAA system in which silver ions were restricted in the dispersed phases composed of DBSA and aniline; the other was Ag(2)O nanocrystallites generated in situ that could be readily reduced by aniline to small silver nanoparticles at high concentrations.     

Modelling and measuring the thermal conductivity of multi-metallic Zn/Cu nanofluid

A metallic nanofluid is a suspension of metallic nanoparticles in a base fluid. Multi-metallic nanoparticles are a combination of two or more types of metallic particles. Such multi-metallic nanoparticles were suspended in water using an ultrasonic vibrator for different total volume fractions and different ratios of metallic/metallic nanoparticles. A transient hot wire setup was built to measure the thermal conductivity of the nanofluid at different temperatures. The experimental results were in good agreement with the results in the literature. Then, the experimental results were used as input data for an adaptive neural fuzzy inference system (ANFIS) to predict the thermal conductivity of the multi-metallic nanofluid. The maximum deviation between the ANFIS results and experimental measurements was 1 %. The predicted results and the experimental data were compared with other models. The ANFIS model was found to have good ability to predict the thermal conductivity of the multi-metallic nanofluid over the range of the experimental results.     

Polyaniline/Silver Nanoparticle-Doped Multiwalled Carbon Nanotube Composites

A simple method was used to synthesize the hybrid nanocomposites consisting of the functionalized multiwalled carbon nanotube composites (MWCNTs) with the polyaniline incorporated silver nanoparticles (a-MWCNT/PANI-Ag) through an emulsion polymerization at room temperature in order to enhance the electrical conductivity of polyaniline. The electrical conductivity of the composite with the incorporated Ag nanoparticles was 5% higher than the same weight percent for the composite without Ag nanoparticles, and the thermal stability was dramatically increased from 54% for the composite (a-MWCNT/PANI) to 69% through the incorporation of the Ag nanoparticles at 830°C. Additionally, the advantages of the Ag nanoparticles, including the improved electrical and thermal properties without damage to the polyaniline structure, were confirmed using FTIR and Raman spectroscopy.     

Extracellular biosynthesis of silver nanoparticles using the fungus Aspergillus fumigatus

Development of reliable and eco-friendly process for synthesis of metallic nanoparticles is an important step in the filed of application of nanotechnology. One of the options to achieve this objective is to use natural processes such as use of biological systems. In this work we have investigated extracellular biosynthesis of silver nanoparticles using Aspergillus fumigatus. The synthesis process was quite fast and silver nanoparticles were formed within minutes of silver ion coming in contact with the cell filtrate. UV–visible spectrum of the aqueous medium containing silver ion showed a peak at 420 nm corresponding to the plasmon absorbance of silver nanoparticles. Transmission electron microscopy (TEM) micrograph showed formation of well-dispersed silver nanoparticles in the range of 5–25 nm. X-ray diffraction (XRD)-spectrum of the silver nanoparticles exhibited 2θ values corresponding to the silver nanocrystal. The process of reduction being extracellular and fast may lead to the development of an easy bioprocess for synthesis of silver nanoparticles.     

The preparation of conducting polyaniline–silver and poly(p-phenylenediamine)–silver nanocomposites in liquid and frozen reaction mixtures

The oxidation of aniline with silver nitrate in 1 mol L⁻¹ acetic acid at 20 °C yielded a composite of two conducting components, polyaniline and silver; the acceleration with 1 mol% of p-phenylenediamine is needed for efficient synthesis. The yield and molecular weight increased when aniline was copolymerized with 10 mol% p-phenylenediamine. Such product displayed metallic conductivity below 180 K and semiconductor type above this temperature. As the result, the conductivity was the same at 100 and 300 K. The oxidation of p-phenylenediamine alone with silver nitrate also produced a conducting composite having the conductivity of 1,750 S cm⁻¹ despite the assumed nonconductivity of poly(p-phenylenediamine). The present study demonstrates that all oxidations proceeded also in frozen reaction mixtures at −24 °C, i.e., in the solid state. In most cases, molecular weights of polymer component increased, the conductivity of composites with silver improved, to 2,990 S cm⁻¹ for poly(p-phenylenediamine)–silver, and remained high after deprotonation with 1 mol L⁻¹ ammonium hydroxide.

     

Synthesis of Silver and Gold Nanoparticles by a Novel Electrochemical Method

Spherical silver and gold nanoparticles with narrow size distributions were conveniently synthesized in aqueous solution by a novel electrochemical method. The technological keys to the electrochemical synthesis of monodispersed metallic nanoparticles lie in the choice of an ideal stabilizer for the metallic nanoclusters and the use of a rotating platinum cathode. Poly(N‐vinylpyrrolidone) (PVP) was chosen as the stabilizer for the silver and gold clusters. PVP not only protects metallic particles from agglomeration, but also promotes metal nucleation, which tends to produce small metal particles. Using a rotating platinum cathode effectively solves the technological difficulty of rapidly transferring the (electrochemically synthesized) metallic nanoparticles from the cathode vicinity to the bulk solution, avoiding the occurrence of flocculates in the vicinity of the cathode, and ensuring the monodispersity of the particles. The particle size and particle size distribution of the silver and gold nanoparticles were improved by adding sodium dodecyl benzene sulfonate (SDBS) to the electrolyte. The electrochemically synthesized nanoparticles were characterized by TEM and UV/Vis spectroscopy.     

单分散性银纳米粒子的可控制备

以卤化银或氧化银作为前驱体,室温下以水为溶剂,在较高溶液浓度下,利用化学还原法制备了单分散性银纳米粒子,并通过改变前驱体的种类,实现了粒径可控制备。采取扫描电子显微镜（SEM）、紫外-可见光谱仪（UV-Vis）、X射线-粉末衍射仪（XRD）、X射线-光电子能谱仪（XPS）等对所制备的银纳米粒子的形貌及成分进行了表征。结果显示,所制备的银纳米粒子具有较高的单分散性,粒径在40~150 nm之间,具有面心立方多晶结构。该方法制备的银纳米粒子可用于喷墨打印RFID天线。     

The preparation of conducting polyaniline�Csilver and poly(p-phenylenediamine)�Csilver nanocomposites in liquid and frozen reaction mixtures

The oxidation of aniline with silver nitrate in 1?mol?L^?1 acetic acid at 20?°C yielded a composite of two conducting components, polyaniline and silver; the acceleration with 1?mol% of p-phenylenediamine is needed for efficient synthesis. The yield and molecular weight increased when aniline was copolymerized with 10?mol% p-phenylenediamine. Such product displayed metallic conductivity below 180?K and semiconductor type above this temperature. As the result, the conductivity was the same at 100 and 300?K. The oxidation of p-phenylenediamine alone with silver nitrate also produced a conducting composite having the conductivity of 1,750?S cm^?1 despite the assumed nonconductivity of poly(p-phenylenediamine). The present study demonstrates that all oxidations proceeded also in frozen reaction mixtures at ?24?°C, i.e., in the solid state. In most cases, molecular weights of polymer component increased, the conductivity of composites with silver improved, to 2,990?S?cm^?1 for poly(p-phenylenediamine)?Csilver, and remained high after deprotonation with 1?mol?L^?1 ammonium hydroxide.     

The effect of silver nanoparticles on the phase state of comb-shaped liquid crystalline polymers with cyanobiphenyl mesogenic groups

A new approach is proposed for the preparation of a new class of hybrid polymer systems based on comb-shaped LC polymers with cyanobiphenyl mesogenic groups and silver nanoparticles with dimensions ranging from 5 to 54 nm. A correlation between copolymer composition and dimensions of the formed nanoparticles is established. As the concentration of nanoparticles in LC copolymer is increased, the resultant glass transition temperature increases, and the temperature interval of the existence of LC phase is reduced. This behavior is related to the adsorption of cyanobiphenyl and carboxylic polymer groups on the surface of silver nanoparticles. In this case, the conductivity and dielectric permittivity of the composites are also increased.     

Silver nanoparticle formation in microemulsions acting both as template and reducing agent

A novel method of making silver nanoparticles in water-in-oil microemulsions using the surfactants as both the reducing agent and as the structure-directing agent is presented. Since no external strong reducing agent is used the kinetics of the formation is slow, which makes it possible to study the silver nanoparticle formation in situ. The microemulsions used were based on either the nonionic surfactant Brij30 (C12E4), which reduces the silver ion to metallic silver and is thereby partly oxidized, or mixtures of Brij30 and AOT (sodium bis(2-ethylhexyl) sulfosuccinate, where the latter does not reduce the silver ions. The influences of silver ion and nonionic surfactant concentrations on the formation kinetics of the nanoparticles were followed in situ using UV-vis spectroscopy, and both parameters were found to have a big influence. The microemulsion droplet's size, size distribution, and shape were examined by small-angle X-ray scattering (SAXS), and the formed silver nanoparticles were studied using both transmission electron microscopy and SAXS. The SAXS measurements showed that the presence of silver nitrate does not affect the microemulsion systems noticeably and that the droplet's size and shape are retained during the particle formation. It is shown that the size and morphology of the particles do not directly follow the shape and size of the microemulsion droplets even though there is a relation between the droplet size and the radii of the formed particles.