Synthesis and Catalytic Evaluation of Silver Nanoparticles Synthesized with <Emphasis Type="Italic">Aloysia triphylla</Emphasis> Leaf Extract

In this investigation, we report the biosynthesis of the silver nanoparticles using Aloysia triphylla leaves extract. The as-prepared silver nanoparticles were characterized by ultraviolet–visible (Uv–vis) spectroscopy, X-ray diffractometry, scanning electron microscopy and transmission electron microscopy The infrared spectroscopy (FTIR) and Raman spectroscopy techniques were also used to evaluate the chemical groups of the plant extract involved in the silver ions bioreduction. The results indicate that as the plant extract/precursor salt ratio increases, the size of the nanoparticles decreases. Also, as the reaction temperature increases, the reduction rate increased too, resulting in the formation of smaller nanoparticles-size ranges. Uv–vis spectroscopy illustrates absorption peaks in the range of wavelengths of 430–445 nm corresponding to surface plasmon resonance band of silver nanoparticles. The X-ray diffraction (XRD) confirmed the presence of silver solids with fcc structure type. The FTIR analysis showed that the bands corresponding to phenolic compounds and the amide group were involved in the synthesis and stabilization of silver nanoparticles, respectively. The Raman studies showed bands at 1380 and 1610 cm^?1, which correspond to the aromatic and amide compounds, confirming the FTIR results. The Uv–vis results indicate the capacity of silver nanoparticles to reduce the methylene blue.     

Synthesis and properties of silver and gold nanocomposites in poly-1-vinyl-1,2,4-triazole matrix

Novel multifunctional hybrid nanocomposites with silver and gold nanoparticles stabilized by original polymer matrix based on poly-1-vinyl-1,2,4-triazole were synthesized and studied using UV and IR spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The obtained nanocomposites comprise silver or gold nanoparticles of spherical and elliptical shape with size 3–20 nm and 1–10 nm, respectively.     

Surface-enhanced Raman scattering on nanoshells with tunable surface plasmon resonance

Fabrication, characterization, and optical enhancement applications of bimetallic AgAu nanoparticles and nanoshells are reported. Nanoparticles with tunable surface plasmon resonances are synthesized at room temperature and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and photon correlation spectroscopy. The collective electron oscillation of the nanoparticles shows a controllable tunability in the 400-990 nm spectral range, in agreement with plasmon absorption calculated using Mie theory, providing an optimum substrate for surface plasmon-assisted enhanced spectroscopy. Surface-enhanced Raman scattering experiments show that the average enhancement factor obtained with nanoshells could be higher than those obtained with silver sols.     

Preparation of nano-silver-supported activated carbon using different ligands

In this study, we investigated the effect of water soluble ligands [i.e., sodium borohydride (NaBH₄), polyvinyl alcohol, glucose and galactose] on the preparation of nano-silver-supported activated carbon (AC). Ligand-stabilized Ag nanoparticle dispersion characteristics were also compared with those of ligand-free Ag nanoparticles. The nanoparticle distribution was investigated using a scanning electron microscope (SEM) which enabled a qualitative analysis of ligand-dependent nanoparticle adsorption onto AC. Silver nanoparticles with average sizes ranging from 7 to 20 nm were synthesized with different coatings. In particular, silver nanoparticles reduced and stabilized by NaBH₄ were found to have a dense and homogenous dispersion of sizes in the range of 100–400 nm on the AC surface. These particles also seemed to remain on the AC surface after rinsing with water. The distribution of silver nanoparticles prepared in the presence of NaBH₄/PVA was not as good as the one prepared with NaBH₄. Their aggregate size varied from 300 to 600 nm on the AC surface and particles greater than 500 nm were eliminated from the AC surface upon rinsing with water. Glucose- and galactose-stabilized silver nanoparticles did not display an extensive adsorption and their adsorption seemed to be poor. However, glucose-stabilized silver nanoparticles could still be detectable to some extent after rinsing, while galactose-stabilized ones could not. Antimicrobial studies showed that all silver-containing carbons studied in this study inhibit bacterial growth and act as bacteriostatic agents.     

Imaging and SERS Study of the Au Nanoparticles Interaction with HPV and Carcinogenic Cervical Tissues

In this work, gold NPs were prepared by the Turkevich method, and their interaction with HPV and cancerous cervical tissues were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, confocal and multiphoton microscopy and SERS. The SEM images confirmed the presence and localization of the gold NPs inside of the two kinds of tissues. The light absorption of the gold NPs was at 520 nm. However, it was possible to obtain two-photon imaging (red emission region) of the gold NPs inside of the tissue, exciting the samples at 900 nm, observing the morphology of the tissues. The infrared absorption was probably due to the aggregation of gold NPs inside the tissues. Therefore, through the interaction of gold nanoparticles with the HPV and cancerous cervical tissues, a surface enhanced Raman spectroscopy (SERS) was obtained. As preliminary studies, having an average of 1000 Raman spectra per tissue, SERS signals showed changes between the HPV-infected and the carcinogenic tissues; these spectral signatures occurred mainly in the DNA bands, potentially offering a tool for the rapid screening of cancer.     

A Green Approach for the Synthesis of Silver Nanoparticles Using Root Extract of <Emphasis Type="Italic">Chelidonium majus:</Emphasis> Characterization and Antibacterial Evaluation

In this study, silver nanoparticles (Ag-NPs) have been synthesized using extract of Chelidonium majus root in aqueous solution at room temperature. The root extract was able to reduce Ag⁺ to Ag⁰ and stabilized the nanoparticles Different physico-chemical techniques including UV–Vis spectroscopy, transmission electron microscopy and powder X-ray diffraction (PXRD) were used for the characterization of the biosynthesized Ag-NPs obtained. The surface plasmon resonance band appeared at 431 nm is an evidence for formation of Ag-NPs. TEM imaging revealed that the synthesized Ag-NPs have an average diameter of around 15 nm and with spherical shape. Moreover the crystalline structure of synthesized nanoparticles was confirmed using XRD pattern. Furthermore antimicrobial activities of synthesized Ag-NPs were evaluated against Escherichia coli -ATCC 25922 and Pseudomonas aeruginosa ATCC 2785 bacteria strain.     

Synthesis of cellulose–metal nanoparticle composites: development and comparison of different protocols

Deposition of nanoparticles on the surface of a variety of materials is a subject of great interest due to their potential applications in electronic devices, sensing, catalysis and bio-medical sciences. In this context, we have explored and compared various methodologies to generate gold and silver nanoparticles on the surface of cellulose fibers. It was found that boiling of the cellulose fibers in alkaline solution of gold and silver salts led to the formation and immobilization of gold and silver nanoparticles. However, in case of lecithin treated and thiol-modified cellulose fibers, high temperature was not essentially required for the formation and deposition of nanoparticles on cellulose substrate. In both these cases, fairly uniform metal nanoparticles were obtained in good yields (~43 wt% gold loading in case of thiol modified cellulose fibers) at room temperature. Borohydride-reduction method resulted in relatively lower loading (~22 wt%) with a wide size distribution of gold and silver nanoparticles on cellulose fibers. All these nanoparticle–cellulose composites were thoroughly characterized using scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, UV–visible spectroscopy, and elemental analyzer. Thiol modified cellulose–gold nanoparticle composites served as active catalysts in the reduction of 4-nitrophenol into 4-aminophenol.     

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.     

Synthesis,Characterization and Improved Bactericide Activity of Ellipsoidal Nanoscopic Ascorbic Acid Matrixes Embedding Ultrafine Silver Nuclei

The preparation and study of tailored materials with few nanometers in size are crucial challenges for contemporary material science and engineering; especially, for materials with high surface tension such as silver, which exhibit enhanced chemical and biological activities. In the present article, a facile synthesis of nanoscopic ascorbic acid matrixes embedding and stabilizing uniform ultrafine silver nanoparticles is presented. The procedure consists in the reduction of Ag⁺ ions of an aqueous solution of silver nitrate at 70 °C using water solutions of ascorbic acid (vitamin C) with concentrations higher than those explored in previous investigations. The resulting samples were characterized by different analytical techniques including transmission electron microscopy, X-ray diffraction and UV–visible and infrared spectroscopies. These studies revealed that they are constituted by nanometric matrixes of vitamin C with an elongated morphology (lengths from 120 to 200 nm and widths between 30 and 70 nm), which contain unusually small silver nanoparticles with a mean diameter of 2.2 ± 0.7 nm. The tests for the bactericidal activity of this nanostructured hybrid material show improved antimicrobial activity against both Gram-positive and Gram-negative bacteria.     

Rapid Synthesis of Silver Nanoparticles by Microwave-Polyol Method with the Assistance of Latex Copolymer

Highly stable and monodispersed silver nanoparticles with uniform morphology have been successfully prepared by microwave (MW) irradiation within a few seconds from the mixture of silver nitrate, ethanol and latex copolymer. The aqueous emulsion of latex copolymer acts as both reducing and stabilizing agent. To the best of our knowledge, it was the first time that the effect of MW irradiation time and latex concentration on the silver nanoparticle preparation and properties was analyzed. The formation of silver nanoparticles was confirmed by Ultraviolet–visible spectroscopy and transmission electron microscopy (TEM). The UV–Vis spectra are marked by the characteristic surface plasmon absorption band in the range 410–420 nm. From TEM images, silver nanoparticles were observed to be spherical with sizes ranging from 4 to 10 nm. Electron diffraction patterns on selected area, indicated that the silver nanoparticles are crystalline with face centered cubic structure.     

Immobilization of Recombinant Human Catalase on Gold and Silver Nanoparticles

Human catalase cDNA was cloned into a pEX-C-His vector. Purified recombinant catalase was immobilized on nanoparticles. Gold and silver nanoparticles were synthesized in a variety of sizes by chemical reduction; no agglomerates or aggregates were observed in any of the colloids during dynamic light scattering or scanning transmission electron microscopy analysis. After immobilization on gold nanoparticles, recombinant catalase activity was found to be lower than that of the same amount of enzyme in aqueous solution. However, after 10 days of storage at room temperature, the activity of catalase immobilized on gold nanoparticles (AuNPs) of 13 and 20 nm and coverage of 133% was 68 and 83% greater than catalase in aqueous solution, respectively. During 10 days of experiment, percentage activity of catalase immobilized on those gold nanoparticles was higher in comparison to CAT in aqueous solution. Catalase immobilized on silver nanoparticles did not lose activity as significantly as catalase immobilized on AuNPs. Those results confirm the ability to produce recombinant human enzymes in a bacterial expression system and its potential use while immobilized on silver or gold nanoparticles.     

A Green Approach for Synthesis of Gold and Silver Nanoparticles by Leishmania sp.

The application of microorganisms for the synthesis of metal nanoparticles as an eco-friendly and promising approach is ongoing. In this paper, an attempt has been made to investigate the capability of Leishmania sp. for synthesis of metal nanoparticles from aqueous silver and gold ions. The samples were analyzed by a UV?CVis spectroscopy and the results showed the absorbance peak values at 420 and 540?nm, respectively, for the surface plasmon resonance of silver and gold nanoparticles. The surface morphology of the nanoparticles in solution was visualized by atomic force microscope and scanning electron microscope images, which showed the production of metallic nanoparticles by this protozoan. Fourier transform infrared spectroscopy analyses confirmed the presence of different bands of protein as capping and stabilizing agent on the nanoparticles surfaces. The synthesized silver and gold nanoparticles were with dimensions ranging between 10 and 100?nm for silver and 50?C100?nm for gold. These results of the present study have demonstrated the efficiency of this protozoan for synthesis of nanoparticles, by offering the merits of environmentally friendly, amenability, and time saving for large-scale production.     

Magnetite nanoparticles with tunable gold or silver shell

Fe3O4 nanoparticles with size approximately 13 nm have been prepared successfully in aqueous micellar medium at approximately 80 degrees C. To make Fe3O4 nanoparticles resistant to surface poisoning a new route is developed for coating Fe3O4 nanoparticles with noble metals such as gold or silver as shell. The shell thickness of the core-shell particles becomes tunable through the adjustment of the ratio of the constituents. Thus, the route yields well-defined core-shell structures of size from 18 to 30 nm with varying proportion of Fe3O4 to the noble metal precursor salts. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FTIR, differential scanning calorimetry (DSC), Raman and temperature-dependent magnetic studies.     

Synthesis and plasmonic properties of silver and gold nanoshells on polystyrene cores of different size and of gold–silver core–shell nanostructures

Simple methods of preparing silver and gold nanoshells on the surfaces of monodispersed polystyrene microspheres of different sizes as well as of silver nanoshells on free-standing gold nanoparticles are presented. The plasmon resonance absorption spectra of these materials are presented and compared to predictions of extended Mie scattering theory. Both silver and gold nanoshells were grown on polystyrene microspheres with diameters ranging from 188 to 543 nm. The commercially available, initially carboxylate-terminated polystyrene spheres were reacted with 2-aminoethanethiol hydrochloride (AET) to yield thiol-terminated microspheres to which gold nanoparticles were then attached. Reduction of silver nitrate or gold hydroxide onto these gold-decorated microspheres resulted in increasing coverage of silver or gold on the polystyrene core. The nanoshells were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis spectroscopy. By varying the core size of the polystyrene particles and the amount of metal (silver or gold) reduced onto them, the surface plasmon resonance of the nanoshell could be tuned across the visible and the near-infrared regions of the electromagnetic spectrum. Necklace-like chain aggregate structures of gold core–silver shell nanoparticles were formed by reducing silver nitrate onto free citrate-gold nanoparticles. The plasmon resonance absorption of these nanoparticles could also be systematically tuned across the visible spectrum.     

Effect of Poly(Vinyl Alcohol) on the Size,Shape, and Rate of Silver Nanoparticles Formation

The kinetics of cetyltrimethylammonium bromide (CTAB) stabilized silver nanoparticles have been studied spectrophotometrically at 425 nm (λ_max of silver sol) in the absence and presence of water soluble polymer (poly(vinyl alcohol); PVA). Transmission electron microscopy (TEM), ultraviolet-visible spectroscopy, and viscosity measurements were used to determine the size, shape, and the size distribution of the silver nanoparticles. The reaction follows the same behavior with respect to [CTAB], [tri-sodium citrate], and [Ag⁺] in both the media indicating the silver nonoparticles were formed through the same reaction path. The sigmoid nature of the kinetic curves suggests an autocatalytic path in the growth of nanoparticles. The reaction rate is increased by increasing [CTAB]. The presence of PVA inhibits nucleation and retards the rate of particle growth, absorbance and size of the particles. Polymer-surfactant interactions were analyzed based on the viscosity of the reaction mixture.     

A Novel Green Synthesis of Silver Nanoparticles Using Gum Karaya: Characterization,Antimicrobial and Catalytic Activity Studies

Stable silver nanoparticles have been synthesized using gum karaya acting as both reducing and stabilizing agent without using any synthetic reagent. The reaction is performed using water, which is an environmentally safe solvent. This reaction was carried out in an autoclave at a pressure of 15 psi and 120 °C temperature by varying the time. The influence of different parameters such as time, change of concentration of silver nitrate and concentration of gum karaya on the formation of silver nanoparticles has been studied. The synthesized silver nanoparticles are characterized by UV–Vis spectroscopy, FTIR, XRD and TEM. UV–Vis analysis of the sample confirmed the formation of silver nanoparticles exhibiting a sharp peak at a wavelength of 420 nm. TEM micrographs showed the formation of well-dispersed silver nanoparticles of size 2–4 nm. The antimicrobial activity of silver nanoparticles stabilized in gum karaya is tested against Escherichia coli, Micrococcus luteus and is found to be possessing inhibiting property. The silver nanoparticles stabilized in gum karaya exhibited very good catalytic activity and the kinetics of the reaction was found to be pseudo first order with respect to the 4-nitrophenol.     

Solution-based direct readout surface enhanced Raman spectroscopic (SERS) detection of ultra-low levels of thiram with dogbone shaped gold nanoparticles

We report the use of two different sizes of dogbone shaped gold nanoparticles as colloidal substrates for surface enhanced Raman spectroscopy (SERS) based detection of ultra-low levels of thiram, a dithiocarbamate fungicide. We demonstrate the ability to use a solution based, direct readout SERS method as a quantitative tool for the detection of ultra-low levels of thiram. The two different sizes of dogbone shaped gold nanoparticles are synthesized by using the seed-mediated growth method and characterized by using UV-visible spectroscopy and transmission electron microscopy (TEM). The smaller dogbone shaped nanoparticles have an average size of 43 ± 13 nm. The larger dogbone shaped gold nanoparticles have an average size of 65 ± 15 nm. The nanoparticle concentration is 1.25 × 10(11) nanoparticles per mL for the smaller dogbone shaped gold nanoparticles and is 1.13 × 10(11) nanoparticles per mL for the larger dogbone shaped gold nanoparticles. Different concentrations of thiram are allowed to bind to the two different sizes of dogbone shaped gold nanoparticles and the SERS spectra are obtained. From the calibration curve, the limit of detection for thiram is 43.9 ± 6.2 nM when the smaller dogbone shaped gold nanoparticles are used as colloidal SERS substrates In the case of the larger dogbone shaped gold nanoparticles, the limit of detection for thiram is 11.8 ± 3.2 nM. The lower limit of detection obtained by using the larger dogbone shaped gold nanoparticles as colloidal substrates is due to the lightning rod effect, higher contributions from the electromagnetic enhancement effect, and larger number of surface sites for thiram to bind.     

Synthesis with Glutaraldehyde and Characterization of Uniformly Coated Alkaline Phosphatase-Nanoparticle Bioconjugates

Alkaline phosphatase from raw milk was immobilized on cysteine-functionalized silver nanoparticles with high efficiency. The nanoparticles were characterized by ultraviolet–visible spectroscopy, X-ray diffraction, and transmission electron microscopy. The surface functionalization was confirmed by infrared spectroscopy. The spherical nanoparticles were from 40 to 60?nm in size and used for the covalent immobilization of alkaline phosphatase on the surface with glutaraldehyde treatment. As compared to soluble enzyme, an enhanced enzymatic activity of 79.87% was obtained with a percentage immobilization of 75.41%. The immobilization process did not significantly affect the structure and size of the nanoparticles, while providing a uniform coating of the enzyme on the nanoparticle as characterized by electron microscopy. The bioconjugates were reusable for up to eight times with 85% retention of the initial enzymatic activity. The synthesis of these enzyme–nanoparticle bioconjugates with high activity and stability suggests their use in biological applications.     

Synthesis of highly stable silver nanoparticles using imidazolium-based ionic liquid

Highly stable, aqueous dispersions, and hydrophilic ionic liquid-capped silver nanoparticles with positive surface charge were synthesized by in situ reduction of AgNO₃ with NaBH₄ in the presence of an imidazolium-based ionic liquid, viz., 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim][Cl]) at room temperature. Prepared silver nanoparticles were characterized by UV–vis spectra, transmission electron microscopy (TEM), and zeta potential. UV–visible spectrum of the aqueous medium peaked at 407 nm corresponding to the plasmon absorbance of silver nanoparticles. TEM analysis revealed the spherical shape of the particles with sizes about 9 nm and low polydispersed. The surface charge of the synthesized silver nanoparticles was determined as +5.0 mV. The ionic liquid ([C₁₂mim][Cl]) capped silver nanoparticles were stable for at least 8 months.     

Ion beam sputtering deposition of silver nanoparticles and TiOx/ZnO nanocomposites for use in surface enhanced vibrational spectroscopy (SERS and SEIRAS)

Hybrids consisting of silver nanoparticles (in varying fractions) and of TiOx/ZnO were prepared via top-down ion beam sputtering (IBS) deposition on silicon substrates. The deposited nanomaterials were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. It is shown that such composites represent a viable substrate for use in both surface enhanced Raman spectroscopy (SERS) and surface enhanced infrared absorption spectroscopy (SEIRAS), as exemplarily shown for crystal violet as the model analyte. The C-H bending mode at about 1181 cm^?1 and the C-N vibration at 1361 cm^?1 observed in the SERS and SEIRAS spectra, respectively, have been used as analytical signal. The substrate consisting of TiOx NPs with 33% fraction of silver provides the strongest enhancement in SERS (up to 10,000-fold), while TiOx/AgNPs with thickness of 2 and 1 nm in ion beam sputtering, respectively, provides the best sensitivity in SEIRAS. The substrates also display photocatalytic activity as shown by the degradation of adsorbed crystal violet under ultraviolet irradiation.

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Graphical abstract Schematic of the preparation of hybrid substrates consisting of Ag and TiOx/ZnO nanoparticles via ion beam sputtering deposition. They were applied in both surface enhanced Raman and surface enhanced infrared absorption spectroscopies using crystal violet as model analyte, showing enhancements up to >10,000-fold in Raman.