Surface-functionalization of spherical silver nanoparticles with macrocyclic polyammonium cations and their potential for sensing phosphates

The synthesis of aqueous dispersion of spherical, underivatized silver nanoparticles (Ag-NPs) stabilized by macrocyclic polyammonium chlorides (MCPAC), [28]ane-(NH₂ ⁺)₆O₂·6Cl⁻ (28-MCPAC) and [32]ane-(NH₂ ⁺)₈·8Cl⁻ (32-MCPAC), which are evidently anion receptors, is reported. As-synthesized Ag-NPs are characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The 28/32-MCPAC-stabilized Ag-NPs show the surface plasmon band around 400 nm. The TEM-images show that the particles are spherical and well-dispersed. By tuning the 28/32-MCPAC:Ag-OAc (silver acetate) ratio, nanoparticles with different core diameters ranging from 13 to 8 nm for 28-MCPAC and from 10 to 6 nm for 32-MCPAC can be obtained. The advantage of using MCPAC as stabilizers is that they make the particles functionalized for sensing anions. Thus, the potential of the as-synthesized Ag-NPs for sensing phosphates: H₂PO₄ ⁻ (monobasic phosphate, MBP), HPO₄ ²⁻ (dibasic phosphate, DBP) and PO₄ ³⁻ (tribasic phosphate, TBP) is investigated spectroscopically. Interaction of phosphate ions with macrocyclic polyammonium cations makes the Ag-NPs bare, leading agglomeration. The phosphate-assisted agglomeration of 32-MCPAC-Ag-NPs follow the order TBP > DBP ≫ MBP. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and characterization of silver nanoparticles: effect on phytopathogen <Emphasis Type="Italic">Colletotrichum gloesporioides</Emphasis>

Colloidal silver nanoparticles were synthesized by reducing silver nitrate solutions with glucose, in the presence of gelatin as capping agent. The obtained nanoparticles were characterized by means of UV–Vis spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The response surface methodology (RSM) was also used to determine the influence of the variables on the size of the nanoparticles. The antifungal activity of the silver nanoparticles was evaluated on the phytopathogen Colletotrichum gloesporioides, which causes anthracnose in a wide range of fruits. The UV–Vis spectra indicated the formation of silver nanoparticles preferably spherical and of relatively small size (<20 nm). The above-mentioned was confirmed by TEM, observing a size distribution of 5–24 nm. According to RSM the synthesis variables influenced on the size of the silver nanoparticles. By means of FTIR spectroscopy it was determined that gelatin, through their amide and hydroxyl groups, interacts with nanoparticles preventing their agglomeration. The growth of C. gloesporioides in the presence of silver nanoparticles was significantly delayed in a dose dependent manner.     

Fusarium solani: a novel biological agent for the extracellular synthesis of silver nanoparticles

We report extracellular biosynthesis of silver nanoparticles by Fusarium solani (USM-3799), a phytopathogen causing disease in onion, when challenged with 1 mM silver nitrate (AgNO₃). The formation of nanoparticles was characterized by visual observation followed by UV–Vis spectrophotometric analysis, which showed a peak at about 420 nm, which is very specific for silver nanoparticles. Further analysis carried out by Fourier Transform Infrared Spectroscopy (FTIR), provides evidence for the presence of proteins as capping agent, which helps in increasing the stability of the synthesized silver nanoparticles. Transmission Electron Microscopy (TEM) investigations confirmed that silver nanoparticles were formed. The synthesized silver nanoparticles were found to be polydispersed, spherical in the range of 5–35 nm with average diameter of 16.23 nm. Extracellular synthesis of nanoparticles could be highly advantageous from the point of view of synthesis in large quantities and easy downstream processing.     

Green synthesis of silver nanoparticle by <Emphasis Type="Italic">Penicillium purpurogenum</Emphasis> NPMF: the process and optimization

An eco-friendly microbial method for synthesis of silver colloid solution with antimicrobial activity is developed using a fungal strain of Penicillium purpurogenum NPMF. It is observed that increase in concentration of AgNO₃ increases the formation of silver nanoparticle. At 5 mM concentration highly populated polydispersed nanoparticles form. Furthermore, change in pH of the reaction mixture leads to change in shape and size of silver nanoparticles. At lower pH two peaks are observed in the absorption spectra showing polydispersity of nanoparticles. However, highly monodispersed spherical nanoparticles of 8–10 nm size form with 1 mM AgNO₃ concentration at pH 8. Antimicrobial activity of nanoparticles is demonstrated against pathogenic gram negative bacteria like Escherichia coli and Pseudomonas aeruginosa, and gram positive bacteria like Staphylococcus aureus. The antimicrobial activity of silver nanoparticles obtained at different initial pH show strong dependence on the surface area and shape of the nanoparticles.     

Highly bacterial resistant silver nanoparticles: synthesis and antibacterial activities

In this article, we describe a simple one-pot rapid synthesis route to produce uniform silver nanoparticles by thermal reduction of AgNO₃ using oleylamine as reducing and capping agent. To enhance the dispersal ability of as-synthesized hydrophobic silver nanoparticles in water, while maintaining their unique properties, a facile phase transfer mechanism has been developed using biocompatible block co-polymer pluronic F-127. Formation of silver nanoparticles is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopy. Hydrodynamic size and its distribution are obtained from dynamic light scattering (DLS). Hydrodynamic size and size distribution of as-synthesized and phase transferred silver nanoparticles are 8.2 ± 1.5 nm (σ = 18.3%) and 31.1 ± 4.5 nm (σ = 14.5%), respectively. Antimicrobial activities of hydrophilic silver nanoparticles is tested against two Gram positive (Bacillus megaterium and Staphylococcus aureus), and three Gram negative (Escherichia coli, Proteus vulgaris and Shigella sonnei) bacteria. Minimum inhibitory concentration (MIC) values obtained in the present study for the tested microorganisms are found much better than those reported for commercially available antibacterial agents.     

Mycogenic synthesis of silver nanoparticles by the Japanese environmental isolate <Emphasis Type="Italic">Aspergillus tamarii</Emphasis>

In this study, an environmental friendly process for the synthesis of silver nanoparticles (AgNPs) using a fungus Aspergillus tamarii has been investigated. The process of silver ion reduction by the fungal extracellular filtrate was spontaneous which lead to the development of an easy process for synthesis of silver nanoparticles. The AgNPs formed were characterized using UV–Visible spectrum, FTIR, and SEM. The results revealed that silver ions reduction by the fungal extracellular filtrate started at 420 nm after 0.5 h of incubation time. The FTIR peaks were observed at 1393, 1820, 2727, and 3545 cm⁻¹. The SEM result showed the distribution of spherical AgNPs ranging from 25 to 50 nm.     

Core–shell nanostructures and nanocomposites of Ag@TiO2: effect of capping agent and shell thickness on the optical properties

Two different shell-forming reagents viz. titanium isopropoxide and titanium hydroxyacylate, have been employed to obtain core–shell nanostructures of Ag@TiO₂. However, nanocomposites were formed when the shell-forming agent, titanium isopropoxide, was added before breaking the micelles. Titanium hydroxyacylate has been used for the first time as a shell-forming agent which resulted in uniform core–shell structures of Ag@TiO₂ with core diameter ranging from 10 to 40 nm and a shell thickness of 10–50 nm. The low rate of hydrolysis of titanium hydroxyacylate than titanium isopropoxide (used in other methods) appears to be responsible for the uniform shell thickness. The presence of capping agent (2-mercaptoethanol) disrupts the formation of a uniform shell structure of Ag@TiO₂. HRTEM, IR, and XPS studies of Ag@TiO₂ synthesized using capping agent show the formation of Ag₂S coated with an amorphous layer of TiO₂. A red shift of 25 and 10 nm was observed in the surface plasmon band of silver for Ag@TiO₂ core–shell structures (compared with that of silver nanoparticles) synthesized using titanium hydroxyacylate and titanium isopropoxide, respectively. The presence of capping agent (2-mercaptoethanol) masks the surface plasmon peak. Photoluminescence studies show an increase in the emission intensity for the core–shell structures when compared to that of TiO₂ nanoparticles.     

Facile-chelating amine-assisted synthesis of β-In<Subscript>2</Subscript>S<Subscript>3</Subscript> nanostructures from a new single-source precursor derived from <Emphasis Type="Italic">S</Emphasis>-methyl dithiocarbazate

Flake-built 3D β-In₂S₃ nanostructures were synthesized by thermolysis of S-methyl dithiocarbazate–indium(III) complex precursor in hexamethylenediamine (HMDA). XRD patterns showed that the cubic phase of 3D β-In₂S₃ remained unchanged but the crystallinity was increased after annealing at 400 °C for 20 min. The products were also characterized by SEM, TEM, and EDS. Based on the experimental results, we propose that the growth of 3D nanostructures is controlled by the stability of the intermediate chelate complex made by indium(III) and solvent. The optical properties of the 3D β-In₂S₃ nanostructures were also investigated by UV–Vis and PL spectroscopy, which indicated strong quantum confinement effect.     

Synthesis of dendritic silver nanostructures by means of ultrasonic irradiation

In this paper, a simple and effective route for the synthesis of silver dendritic nanostructures by means of ultrasonic irradiation has been developed. Well-defined silver dendritic nanostructures were obtained by sonicating the aqueous solution of 0.04 mol/L silver nitrate with 4.0 mol/L isopropanol as reducing agent and 0.01 mol/L PEG400 as disperser for 2 h. The effects of the irradiation time, the concentration of Ag⁺ and the molar ratio of PEG to AgNO₃ on the morphology of silver nanostructures were discussed. The structures of the obtained samples were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray powder diffraction (XRD), and the chemical composition of the dendrites was examined by energy-dispersive X-ray spectrum (EDS).     

Microwave-assisted rapid extracellular synthesis of stable bio-functionalized silver nanoparticles from guava (<Emphasis Type="Italic">Psidium guajava</Emphasis>) leaf extract

Our research interest centers on microwave-assisted rapid extracellular synthesis of bio-functionalized silver nanoparticles of 26 ± 5 nm from guava (Psidium guajava) leaf extract with control over dimension and composition. The reaction occurs very rapidly as the formation of spherical nanoparticles almost completed within 90 s. The probable pathway of the biosynthesis is suggested. Appearance, crystalline nature, size and shape of nanoparticles are understood by UV–vis (UV–vis spectroscopy), FTIR (fourier transform infrared spectroscopy), XRD (X-ray diffraction), FESEM (field emission scanning electron microscopy) and TEM (transmission electron microscopy) techniques. Microwave-assisted route is selected for the synthesis of silver nanoparticles to carry out the reaction fast, suppress the enzymatic action and to keep the process environmentally clean and green.     

Influence of several factors on the growth of selenium nanowires induced by silver nanoparticles

This paper presents a study on the crystallization and growth mechanism of selenium nanowires induced by silver nanoparticles at ambient conditions with special reference to the effects of factors such as the shapes and size of silver nanoparticles, the induced reaction time, and the molar ratio of Ag⁰ to SeO₃²⁻ ions. The synthesis approach is conducted with no need of any stabilizers, and with no sonochemical process and/or templates. It is found that whether silver spherical particles or colloids can lead to the formation of nanowires with average diameter of 25 nm and lengths up to a few micrometers, and silver nanoplates lead to the formation of flat Se nanostructures. In particular, Au, Cu, Pt, and Pd particles cannot induce the growth of selenium nanowires in aqueous solution at room temperature. The results indicate that silver particles play a critical role in determining the growth of selenium nanowires. The lattice match between hexagonal-Se and orthorhombic- or trigonal-Ag₂Se particles is the major driving force in the growth of such nanostructures. The findings would be useful for design and construction of heterogeneous nanostructures with similar lattice parameter(s).     

Silvernanotherapy on the viral borne disease of silkworm <Emphasis Type="Italic">Bombyx mori</Emphasis> L.

Antiviral assays of chemically and biologically synthesized silver nanoparticles were made against BmNPV (Bombyx mori Nuclear Polyhedrosis Virus). Reduction of silver ions by sodium citrate and Spirulina platensis led to the formation of spherical silver nanoparticles of 40–60 and 7–16 nm size. Single cell protein (Spirulina platensis)-synthesized silver nanoparticles showed the strongest antiviral activity. Immunological studies made on the silkworm Bombyx mori disclosed that a significant increase in the total hemocyte count and differential hemocyte count due to S. platensis-synthesized silver nanoparticles supplementation. Improvement in the defense mechanism was noticed from the strengthened peritrophic membrane of the digestive tract and the increased total protein. Overall, the results presented illustrate that single cell protein-synthesized silver nanoparticles supplementation is effective in controlling viral-borne diseases of the silkworm.     

Synthesis of silver and lithium sub-micro- and nanoparticles coated with derivatives of <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butyl thiacalix[4]arenes

The effect of solvent nature and temperature on the formation of 3D-dimensional SAM (self-assembled monolayers on nanoparticles) based on synthetically available stereoisomers of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by pyrrolidide and octylamide groups (cone, partial cone, and 1,3-alternate) with lithium and silver nanoparticles were determined by dynamic light-scattering and transmission electron microscopy. It was found that the variation of the temperature of the system and the nature of the solvent leads to the formation discrete or extended particles (CH₂Cl₂) (98–110 nm), nanostructures (CH₃CN) (120–295 nm) or three-dimensional SAM (DMF) (1–13 nm; 46–622 nm).     

UV-induced synthesis,characterization and formation mechanism of silver nanoparticles in alkalic carboxymethylated chitosan solution

The silver nanoparticles (AgNPs) were synthesized in an alkalic aqueous solution of silver nitrate (AgNO₃)/carboxymethylated chitosan (CMCTS) with ultraviolet (UV) light irradiation. CMCTS, a water-soluble and biocompatible chitosan derivative, served simultaneously as a reducing agent for silver cation and a stabilizing agent for AgNPs in this method. UV–vis spectra and transmission electron microscopy (TEM) images analyses showed that the pH of AgNO₃/CMCTS aqueous solutions, the concentrations of AgNO₃ and CMCTS can affect on the size, amount of synthesized AgNPs. Further by polarized optical microscopy it was found that the CMCTS with a high molecular weight leads to a branch-like AgNPs/CMCTS composite morphology. The diameter range of the AgNPs was 2–8 nm and they can be dispersed stably in the alkalic CMCTS solution for more than 6 months. XRD pattern indicated that the AgNPs has cubic crystal structure. The spectra of laser photolysis of AgNO₃/CMCTS aqueous solutions identified the early reduction processes of silver cations (Ag⁺) by hydrated electron formed by photoionization of CMCTS. The rate constant of corresponding reduction reaction was 5.0 × 10⁹ M⁻¹ s⁻¹.     

One-step synthesis and antibacterial property of water-soluble silver nanoparticles by CGJ bio-template

In this article, a new synthetic method of nanoparticles with fresh Chinese gooseberry juice (CGJ) as bio-template was developed. One-step synthesis of highly water-soluble silver nanoparticles at room temperature without using any harmful reducing agents and special capping agent was fulfilled with this method. In the process, the products were obtained by adding AgNO₃ to CGJ, which was used as reducing agent, capping agent, and the bio-template. The products of silver nanoparticles with diameter of 10–30 nm have strong water solubility and excellent antibiotic function. With the same concentration 0.047 μg mL⁻¹, the antibacterial effect of water-soluble silver particles by fresh CGJ was 53%, whereas only 27% for silver nanoparticles synthesized using the template method of fresh onion inner squama coat (OISC). The excellent water solubility of the products would enable them have better applications in the bio-medical field. The synthetic method would also have potential application in preparing other highly water-soluble particles, because of its simple apparatus, high yield, mild conditions, and facile operation.     

Solvothermal preparation of nano-β-HgS from a precursor,bis(dibenzyldithiocarbamato)mercury(II)

A simple solvothermal method for the selective synthesis of β-HgS (meta cinnabar) nanoparticles in aqueous solutions is reported with bis(dibenzyldithiocarbamato)mercury(II) as the precursor. Crystal structure, size, morphology and composition of the products are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, high-resolution transmission electron microscopy (HRTEM), SAED and X-ray photoelectron spectroscopy (XPS). PXRD shows (111), (220), (200), (311), (222), (400), (331), (420) reflections characteristic of β-HgS. SEM micrographs display the spherical nature of the nano-β-HgS. EDX analysis showed the presence of Hg and S. HRTEM images indicate the spherical nature of the nanoparticles with their size in the range of 10–15 nm and the FFT pattern shows the crystalline nature of the spherical particles. The results are in agreement with those estimated from the XRD pattern. XPS signals observed at 162.6 and 162.8 eV are due to S2p _3/2 and S2p _1/2 electrons and the S2s was observed at 222.3 eV. The band gap of nano-β-HgS has been found to be 3.6 eV from the UV–visible spectral measurement. The blue-shifted band gap compared to the bulk HgS is a consequence of “size quantization” effect. A comprehensive characterization of the precursor by IR and single crystal X-ray crystallography shows the presence of HgS₄ coordination environment, with a distinct Hg–S bond asymmetry.     

Structural, optical and electrical properties of cubic AlN films deposited by laser molecular beam epitaxy

Cubic AlN films were successfully deposited on TiN buffered Si (100) substrates by a laser molecular beam epitaxy (LMBE) technique, and their crystal structure and optical and electrical properties were studied. The results indicate that cubic AlN films show the NaCl-type structure with a (200) preferred orientation, and the lattice parameter is determined to be 0.4027 nm. The Fourier transform infrared (FTIR) pattern of the cubic AlN film displays sharp absorption peaks at 668 cm⁻¹ and 951 cm⁻¹, corresponding to the transverse and longitudinal optical vibration modes. Ellipsometric measurements evidence a refractive index of 1.66–1.71 and an extinction coefficient of about zero for the cubic AlN film in the visible range. Capacitance–voltage (C–V) traces of the metal–insulator–semiconductor (MIS) device exhibit that the cubic AlN film has a dielectric constant of 8.1, and hysteresis in the C–V traces indicates a significant number of charge traps in the film.     

Polyol-thermal synthesis of silver nanowires for Hg<Superscript>2+</Superscript> sensing detection

This study demonstrates a facile but effective polyol-thermal reaction method for the synthesis of silver nanowires in autoclaves (160–180 °C). By this approach, the generated silver nanowires show an average diameter of ~40 nm and length up to tens of micrometers with a high yield and potential for large-scale production. To achieve shape- and size-controlled Ag nanowires, several experimental parameters were investigated and optimized, including surface controller(s), molar ratio of surfactant(s) to silver ions, temperature, and concentration of reactants. The structure and composition of silver nanowires were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. In particular, the twinned crystal structure observed in both spherical particles and nanowires was analyzed by HRTEM technique, and the possible formation and growth mechanisms were discussed. The optical property of the as-prepared product was measured by ultraviolet–visible (UV–vis) spectroscopy. The sensing detection of metal ions (e.g., Hg²⁺) using the obtained silver nanowires in aqueous media was finally investigated.     

Iron–cobalt nanocrystalline alloy supported on a cubic mesostructured silica matrix: FeCo/SBA-16 porous nanocomposites

A series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal stability. Low-angle X-ray diffraction, N₂ physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction in H₂ flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy nanoparticles with spherical shape and narrow size distribution (4–8 nm) are homogeneoulsy distributed throughout the matrix and they seem in a large extent to be allocated inside the pores.     

Simple and environmentally friendly preparation and size control of silver nanoparticles using an inhomogeneous system with silver-containing glass powder

A simple, environmentally friendly method for preparing highly size-controlled spherical silver nanoparticles was developed that involved heating a mixture of silver-containing glass powder and an aqueous solution of glucose. The stabilizing agent for silver nanoparticles was found to be caramel, which was generated from glucose when preparing the nanoparticles. The particle size was independent of the reaction time, but it increased proportionally with the square root of the glucose concentration in the range 0.25–8.0 wt% (corresponding to particle sizes of 3.48 ± 1.83 to 20.0 ± 2.76 nm). Difference of the generation mechanism of silver nanoparticles between this inhomogeneous system and a system in which Ag⁺ was homogeneously dispersed was discussed.