Synthesis and antibacterial activity of silver nanoparticles with different sizes

Silver nanoparticles with different sizes (7, 29, and 89 nm mean values) were synthesized using gallic acid in an aqueous chemical reduction method. The nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and ultraviolet–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 microscopies studies (TEM) we observed that silver nanoparticles have spherical (7 and 29 nm) and pseudospherical shape (89 nm) with a narrow size distribution. The sizes of the silver nanoparticles were controlled by varying some experimental conditions. It was found that the antibacterial activity of the nanoparticles varies when their size diminishes.     

Rapid extra-/intracellular biosynthesis of gold nanoparticles by the fungus <Emphasis Type="Italic">Penicillium</Emphasis> sp.

In this work, the fungus Penicillium was used for rapid extra-/intracellular biosynthesis of gold nanoparticles. AuCl₄ ⁻ ions reacted with the cell filtrate of Penicillium sp. resulting in extracellular biosynthesis of gold nanoparticles within 1 min. Intracellular biosynthesis of gold nanoparticles was obtained by incubating AuCl₄ ⁻ solution with fungal biomass for 8 h. The gold nanoparticles were characterized by means of visual observation, UV–Vis absorption spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The extracellular nanoparticles exhibited maximum absorbance at 545 nm in UV–Vis spectroscopy. The XRD spectrum showed Bragg reflections corresponding to the gold nanocrystals. TEM exhibited the formed spherical gold nanoparticles in the size range from 30 to 50 nm with an average size of 45 nm. SEM and TEM revealed that the intracellular gold nanoparticles were well dispersed on the cell wall and within the cell, and they are mostly spherical in shape with an average diameter of 50 nm. The presence of gold was confirmed by EDX analysis.     

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.     

Synthesis,characterization and role of zero-valent iron nanoparticle in removal of hexavalent chromium from chromium-spiked soil

Chromium is an important industrial metal used in various products/processes. Remediation of Cr contaminated sites present both technological and economic challenges, as conventional methods are often too expensive and difficult to operate. In the present investigation, Zero-valent iron (Fe⁰) nanoparticles were synthesized, characterized, and were tested for removal of Cr(VI) from the soil spiked with Cr(VI). Fe⁰ nanoparticles were synthesized by the reduction of ferric chloride with sodium borohydride and were characterized by UV–Vis (Ultra violet–Visible) and FTIR (Fourier transform infrared) spectroscopy. The UV–Vis spectrum of Fe⁰ nanoparticles suspended in 0.8% Carboxymethyl cellulose showed its absorption maxima at 235 nm. The presence of one band at 3,421 cm⁻¹ ascribed to OH stretching vibration and the second at 1,641 cm⁻¹ to OH bending vibration of surface-adsorbed water indicates the formation of ferrioxyhydroxide (FeOOH) layer on Fe⁰ nanoparticles. The mean crystalline dimension of Fe⁰ nanoparticles calculated by XRD (X-ray diffraction) using Scherer equation was 15.9 nm. Average size of Fe⁰ nanoparticles calculated from TEM (Transmission electron microscopy) images was found around 26 nm. Dynamic Light Scattering (DLS) also showed approximately the same size. Batch experiments were performed using various concentration of Fe⁰ nanoparticles for reduction of soil spiked with 100 mg kg⁻¹ Cr(VI). The reduction potential of Fe⁰ nanoparticles at a concentration of 0.27 g L⁻¹ was found to be 100% in 3 h. Reaction kinetics revealed a pseudo-first order kinetics. Factors like pH, contact time, stabilizer, and humic acid facilitates the reduction of Cr(VI).     

Control of the aggregation behavior of silver nanoparticles in polyurethane matrix

By using N,N-dimethylformamide (DMF) as a solvent and reducing agent, and polyurethane (PU) as a structure-directing agent, flexible silver nanochains are formed under mild conditions with mean diameter of 15.97 and 35.6 nm, respectively. Some linear chain-like aggregates of silver nanoparticles with mean diameter of 6.69 nm are also formed by controlling the experimental condition. In parallel experiment, silver nanospheres with mean diameters of 5.76 nm, instead of nanochains are generated when antioxidants are added. After 3 days of aging, some nano clusters are transformed into triangular or hexagonal nanoplates. This aggregation behavior was characterized by UV–Vis spectroscopy, TEM, and powder X-ray diffraction. The aggregation mechanism of silver nanoparticles in the PU and ATPU was discussed. Our results provide potential application for new generation of nanodevice.     

Effect of the primary particle morphology on the micromechanical properties of nanostructured alumina agglomerates

Depending on the application of nanoparticles, certain characteristics of the product quality such as size, morphology, abrasion resistance, specific surface, dispersibility and tendency to agglomeration are important. These characteristics are a function of the physicochemical properties, i.e. the micromechanical properties of the nanostructured material. The micromechanical properties of these nanostructured agglomerates such as the maximum indentation force, the plastic and elastic deformation energy and the strength give information on the product properties, e.g. the efficiency of a dispersion process of the agglomerates, and can be measured by nanoindentation. In this study a Berkovich indenter tip was used for the characterisation of model aggregates out of sol–gel produced silica and precipitated alumina agglomerates with different primary particle morphologies (dimension of 15–40 nm). In general, the effect of the primary particle morphology and the presence or absence of solid bonds can be characterised by the measurement of the micromechanical properties via nanoindentation. The micromechanical behaviour of aggregates containing solid bonds is strongly affected by the elastic–plastic deformation behaviour of the solid bonds and the breakage of solid bonds. Moreover, varying the primary particle morphology for similar particle material and approximately isotropic agglomerate behaviour the particle–particle interactions within the agglomerates can be described by the elementar breaking stress according to the formula of Rumpf.     

A hybrid electrochemical–thermal method for the preparation of large ZnO nanoparticles

A simple and efficient two-step hybrid electrochemical–thermal route was developed for the synthesis of large quantity of ZnO nanoparticles using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The bath concentration and current density were varied from 30 to 120 mmol and 0.05 to 1.5 A/dm². The electrochemically generated precursor was calcined for an hour at different range of temperature from 140 to 600 °C. The calcined samples were characterized by XRD, SEM/EDX, TEM, TG-DTA, FT-IR, and UV–Vis spectral methods. Rietveld refinement of X-ray data indicates that the calcined compound exhibits hexagonal (Wurtzite) structure with space group of P63mc (No. 186). The crystallite sizes were in the range of 22–75 nm based on Debye–Scherrer equation. The TEM results reveal that the particle sizes were in the order of 30–40 nm. The blue shift was noticed in UV–Vis absorption spectra, the band gaps were found to be 5.40–5.11 eV. Scanning electron micrographs suggest that all the samples were randomly oriented granular morphology.     

Fabrication of magnetic gold nanorod particles for immunomagnetic separation and SERS application

The preparation and application of rod-shaped core–shell structured Fe₃O₄–Au nanoparticles for immunomagnetic separation and sensing were described for the first time with this study. To synthesize magnetic gold nanorod particles, the seed-mediated synthetic method was carried out and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–Vis), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). Magnetic properties of the nanoparticles were also examined. Characterization of the magnetic gold nanorod particles has proven that the resulting nanoparticles were composed of Fe₃O₄ core and the gold shell. The rod-shaped gold-coated iron nanoparticles have an average diameter of 16 ± 2 nm and an average length of about 50 ± 5 nm (corresponding aspect ratio of 3). The saturation magnetization value for the magnetic gold nanorod particles was found to be 37 emu/g at 300 K. Rapid and room temperature reaction synthesis of magnetic gold nanorod particles and subsequent surface modification with E. coli antibodies provide immunomagnetic separation and SERS application. The analytical performance of the SERS-based homogenous sandwich immunoassay system with respect to linear range, detection limit, and response time is also presented.     

Synthesis of gelatin-capped gold nanoparticles with variable gelatin concentration

Gelatin-stabilized gold nanoparticles (AuNPs-gelatin) with controlled particle size were synthesized with simple variation of concentration of gelatin by reducing in situ tetrachloroauric acid with sodium citrate. The nanoparticles showed excellent colloidal stability. Transmission electron microscopy (TEM) revealed the formation of well-dispersed gold nanoparticles (AuNPs) with different sizes. The methodology produces particles 10–15 nm in size depending on the concentration of gelatin used. The measured AuNPs are 10, 11, 12, 13, 14, and 15 nm for AuNPs-gelatin 1, 0.5, 0.25, 0.1 and 0.05%, and pure AuNPs, respectively. The AuNPs-gelatin exhibit size-dependent localized surface plasmon resonance behavior as measured by UV–visible spectroscopy. UV–vis spectroscopy and TEM results suggest that higher concentration of gelatin favor smaller particle size and vice versa. FTIR spectroscopy analysis of AuNPs-gelatin revealed the amino bands and carboxyl peak of gelatin. The crystalline nature of AuNPs was investigated by X-ray diffraction.     

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.     

Biosynthesis of silver nanoparticles using <Emphasis Type="Italic">Ocimum sanctum</Emphasis> (Tulsi) leaf extract and screening its antimicrobial activity

Development of green nanotechnology is generating interest of researchers toward ecofriendly biosynthesis of nanoparticles. In this study, biosynthesis of stable silver nanoparticles was done using Tulsi (Ocimum sanctum) leaf extract. These biosynthesized nanoparticles were characterized with the help of UV–vis spectrophotometer, Atomic Absorption Spectroscopy (AAS), Dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Transmission electron microscopy (TEM). Stability of bioreduced silver nanoparticles was analyzed using UV–vis absorption spectra, and their antimicrobial activity was screened against both gram-negative and gram-positive microorganisms. It was observed that O. sanctum leaf extract can reduce silver ions into silver nanoparticles within 8 min of reaction time. Thus, this method can be used for rapid and ecofriendly biosynthesis of stable silver nanoparticles of size range 4–30 nm possessing antimicrobial activity suggesting their possible application in medical industry.     

Synthesis and characterization of Mg-doped ZnO hollow spheres

Mg-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Mg:Zn atomic ratio from 0 to 7%. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and magnesium acetate tetrahydrate were heated under refluxing at 65 °C using methanol as a solvent. X-ray diffraction analysis reveals that the Mg-doped ZnO crystallizes in a wurtzite structure with crystal size of 5–12 nm. These nanocrystals self-aggregated themselves into hollow spheres of size of 800–1100 nm. High resolution transmission electron microscopy images show that each sphere is made up of numerous nanoparticles of average diameter 5–11 nm. The XRD patterns, SEM and TEM micrographs of doping of Mg in ZnO confirmed the formation of hollow spheres indicating that the Mg²⁺ is successfully substituted into the ZnO host structure of the Zn²⁺ site. Furthermore, the UV–Vis spectra and photoluminescence (PL) spectra of the ZnO nanoparticles were also investigated. The band gap of the nanoparticles can be tuned in the range of 3.36–3.55 eV by the use of the dopants.     

Entrapment of dye molecules within submicron silver particles

We describe a method for the preparation of metal–organic composites submicron particles. Specifically, the preparation of silver particle-clusters 150–200 nm in size, doped with an organic dye Congo-red, is reported. The use of sodium citrate coupled with sodium hypophosphite facilitated the formation of these particle-clusters, which were fully characterized by TEM analysis, Zeta potential and size measurements, scanning electron microscopy, UV–Vis measurements, and thermogravimetric analysis. The latter reveals a catalytic action of the metal on the thermal oxidative decomposition of the entrapped dye. The use of these particles to obtain dense thin metallic films was demonstrated by the coating of ITO glass.     

Structural properties of silver nanoparticle agglomerates based on transmission electron microscopy: relationship to particle mobility analysis

In this work, the structural properties of silver nanoparticle agglomerates generated using condensation and evaporation method in an electric tube furnace followed by a coagulation process are analyzed using Transmission Electron Microscopy (TEM). Agglomerates with mobility diameters of 80, 120, and 150 nm are sampled using the electrostatic method and then imaged by TEM. The primary particle diameter of silver agglomerates was 13.8 nm with a standard deviation of 2.5 nm. We obtained the relationship between the projected area equivalent diameter (d _pa) and the mobility diameter (d _m), i.e., d _pa = 0.92 ± 0.03 d _m for particles from 80 to 150 nm. We obtained fractal dimensions of silver agglomerates using three different methods: (1) D _f = 1.84 ± 0.03, 1.75 ± 0.06, and 1.74 ± 0.03 for d _m = 80, 120, and 150 nm, respectively from projected TEM images using a box counting algorithm; (2) fractal dimension (D _fL) = 1.47 based on maximum projected length from projected TEM images using an empirical equation proposed by Koylu et al. (1995) Combust Flame 100:621–633; and (3) mass fractal-like dimension (D _fm) = 1.71 theoretically derived from the mobility analysis proposed by Lall and Friedlander (2006) J Aerosol Sci 37:260–271. We also compared the number of primary particles in agglomerate and found that the number of primary particles obtained from the projected surface area using an empirical equation proposed by Koylu et al. (1995) Combust Flame 100:621–633 is larger than that from using the relationship, d _pa = 0.92 ± 0.03 d _m or from using the mobility analysis.     

Precipitation of gold nanoparticles on the quartz surface modified by titanium (IV) butoxide

Gold nanoparticles have been precipitated on the surface of quartz slides covered with titanium (IV) butoxide. UV irradiation of modified quartz slides immersed into water solutions of hydrogen tetrachloroaurate of different concentrations (2.5 × 10⁻⁴–1.0 × 10⁻² M) has been used for this purpose. Properties of produced samples have been investigated by UV–Vis spectroscopy, IR spectroscopy, SEM-EDX, TGA, and AFM. According to the obtained data, produced gold particles are distributed on modified quartz surface very uniformly and the average size of gold particles is about 30–50 nm.     

Silver nanoparticles with gelatin nanoshells: photochemical facile green synthesis and their antimicrobial activity

In the current study, a facile green synthesis of silver-gelatin core–shell nanostructures (spherical, spherical/cubic hybrid, and cubic, DLS diameter: 4.1–6.9 nm) is reported via the wet chemical synthesis procedure. Sunlight-UV as an available reducing agent cause mild reduction of silver ions into the silver nanoparticles (Ag-NPs). Gelatin protein, as an effective capping/shaping agent, was used in the reaction to self-assemble silver nanostructures. The formation of silver nanostructures and their self-assembly pattern was confirmed by SEM, AFM, and TEM techniques. Further investigations were carried out using zeta-potential, UV–Vis, FTIR, GPC, and TGA/DTG/DTA data. The prepared Ag-NPs showed proper and acceptable antimicrobial activity against three classes of microorganisms (Escherichia coli Gram-negative bacteria, Staphylococcus aureus Gram-positive bacteria, and Candida albicans fungus). The antibacterial and antifungal Ag-NPs exhibit good stability in solution and can be considered as promising candidates for a wide range of biomedical applications.     

Amine-capped gold nanoparticles: reaction steps during the synthesis and the influence of the ligand on the particle size

Alkylamine-capped gold nanoparticles were synthesised using the Leff method. In order to investigate the influence on the complexes formed during the synthesis and the final size of the protected nanoparticles the chain length of the stabilizing ligands varied. Phase transfer and amine complex formation were studied in solution with X-ray absorption spectroscopy. The phase transfer complexes retain the quadratic planar conformation whilst all alkyl amines form a linear coordinated gold(I) complex. After reduction, the particles were characterised in solution with EXFAS, UV–Vis spectroscopy, and compared to TEM measurements. The size of the particles was determined from the coordination number of the first gold shell. The position of the UV–Vis plasmon band and the distance of the first gold shell were used to qualitatively compare the effects of the ligands on the particle size. The size of the particles decreases with increasing chain length.     

One-pot synthesis of gold nanoparticles using tetradentate porphyrins

In this study, the meso-tetra (p-hydroxyphenyl) porphyrin and meso-tetra (m-hydroxyphenyl) porphyrin were coated on to gold nanoparticles (AuNPs) via thioacetate anchors which easily dissociate to form S–Au bonds. 4-tert-butyl phenyl thioacetate-AuNPs were prepared and used as a monodentate passivant to control the size of the tetradentate porphyrin-AuNPs. The porphyrin-coated AuNPs were characterized by UV–Vis, TEM, XRD, and XPS analyses. The tetradentate porphyrin-AuNPs size is within a range of 5–15 nm in diameter with exotic shapes. The plausible network formation for AuNP@p-TPP-SAc and the capping structure of the AuNP@m-TPP-SAc have been suggested.     

Mono and bimetallic nanoparticles of gold,silver and palladium-catalyzed NADH oxidation-coupled reduction of Eosin-Y

Abstract  

Mono metallic (Au, Ag, Pd) and bimetallic (Au–Ag, Ag–Pd, Au–Pd) with 1:1 mol stoichiometry, nanoparticles are synthesized using one-pot, temperature controlled chemical method using cetyltrimethylammonium bromide (CTAB) as the capping agent. The particle sizes (Au = 5.6, Ag = 5.0, Pd = 6.0, Au–Ag = 9.2, Ag–Pd = 9.6, Au–Pd = 9.4 nm) are characterized by UV–Vis, HRTEM, and XRD measurements, respectively. CTAB bindings onto mono and bimetallic nanoparticles are analyzed by FTIR spectra. The catalytic activities of mono and bimetallic nanoparticles are tested on the reaction between NADH oxidation and Eosin-Y reduction. The effects of base, pH, ionic strength, nature of mono and bimetallic catalysts are studied and the reaction conditions are optimized. Bimetallic nanoparticles exhibited better catalysis than the mono metallic nanoparticles, which may be due to the electronic effects of the core to shell metal atoms.     

Synthesis and Characterization of Ag@TiO2 Core-shell Nanoparticles and TiO2 Nanobubbles

Ag@TiO₂ core-shell structured particles of nano-size dimensions have been successfully prepared via a one-step way, which has proved quite effective in procuring stable colloids. Transmission electron microscopy (TEM) was employed to characterize the core size and the shell thickness, which typically were 20~40 nm and ~2 nm, respectively. X-ray diffraction (XRD) indicated the existence of silver. Optical absorption dependence on core size and synthetic temperature has been explored by UV–Vis absorption spectroscopy. Finally, the interesting titanium dioxide nanobubbles with silver core leached out by a unique means, were studied, which consequently proved the core-shell structure of the prepared nanoparticles, confirming the TEM observation.