Spherical Silver Research Articles

Síntesis de nanopartículas de plata reducidas con desecho producido por el insecto Ulomoides dermestoides

The scale of nanotechnology goes from 0.2 nm to approximately 100 nm and is used in many different disciplines. U.dermestoides is a beetle belonging to the family Tenebrionidae,commonly known as darkling beetles, it has phytophagous habits. In its waste have been identified the following organic compounds: Saponins, coumarins, steroids, phenols, alkaloids, proteins and amino acids. The synthesis of silver nanoparticles was done using colloidal solution from the reduction of silver nitrate at different concentrations, using U. dermestoides waste from three different diets: Rye and Apple; oats, bread and Apple and finally bread and Apple. Series of qualitative tests were done to determinate the presence of phenols, alkaloids carbohydrates, proteins and amino acids. UV-vis spectrophotometry was used in a range from 200 to 800 nm. The results show that between 400-450 nm there is a surface plasmon resonance peak, indicating the formation of silver nanoparticles. By scanning electron microscopy (SEM) the presence of spherical silver nanoparticles was observed and by transmission electron microscopy (TEM) was confirmed the presence and shape of nanoparticles.

Exploring the potential of environment friendly silver nanoparticles for DNA interaction: Physicochemical approach

Nanosilver, being the most prominent nanoproduct has diverse bio-medical applications and hence the effects associated with their exposure need to be investigated in detail. The interaction of metal nanoparticles with DNA has become a matter of interest, as their effect on structural integrity, synthesis and replication could be explored through it. Present work aims at the facile synthesis and characterization of spherical silver nanoparticles (AgNPs) using Epipremnum aureum leaves extract. Nanoparticles were characterized using UV–Visible spectroscopy, Transmission Electron Microscopy (TEM), High Resolution X-ray Diffraction (HR-XRD) and Dynamic Light Scattering (DLS) studies. The interaction of AgNPs with Calf thymus DNA (CT-DNA) was investigated using different spectroscopic techniques like UV–Visible spectroscopy, UV-thermal melting, Circular Dichroism and fluorescence spectroscopic studies. Fluorescence results suggest van der Waals and H-bonding interactions, which are predominantly responsible for the interaction of AgNPs with CT-DNA. Circular dichroism and thermal melting studies are pointing towards the groove binding of AgNPs to CT-DNA. DNA duplex destabilization was confirmed by the decreased thermal melting temperature of CT-DNA on addition of AgNPs. Present study might open up new vistas for the study of unusual kind of DNA binders, which can destabilize DNA and may further be used for various biomedical applications.

Correlation between the rate of silver nanoparticle oxidation and their biological activity: the role of the capping agent

The correlation between the chemical nature of capping agents used to prepare colloidal silver dispersions and kinetic characteristics of the process of oxidation of the dispersed phase (spherical silver nanoparticles, 2–50 nm in diameter) by hydrogen peroxide was studied for the first time. The well-pronounced correlation between the oxidative dissolution rate and the biological activity of silver dispersions was revealed with respect to the inhibition of the growth of the Saccharomyces cerevisiae yeast. The biological activity of nanosilver dispersions was found to be primarily controlled by the rate of generation of silver ions while the chemical nature of the capping agent defined the rate of generation of silver ions, thus showing an effective way to control the biological action of medications based on silver nanoparticles by varying the nature of the capping agent.

Enhanced superradiance of quantum sources near nanoscaled media

We develop a rigorous theory for nanophotonic cooperative spontaneous emission of an ensemble of quantum emitters near matter, which also incorporates absorption. Such theory is highly requested since one should expect that in the field of nanophotonics the close-by emitters will emit cooperatively simultaneously with strong interaction with the exotic metamaterial complex dielectric function. The closed-form model developed here considers the buildup both of interemitter correlation over time through emitter transitions via the mutual field and of geometry-induced spatial correlation. The presence of matter alters the local density of states (LDOS), resulting in modified decay rate and emission intensity for the entire ensemble relative to values of spontaneous emission in free space. The superradiant total emission is separable into a quantum-mechanical time-dependent part and a classical space-dependent part, both being functions of the LDOS. Two distinct radiative emitter--far-field coupling mechanisms, which together account for the superradiant emission, are obtained---the coupling of every individual emitter with the far field and the coupling of emitter pairs to the far field. The calculations for superradiating emitters near silver and near-zero epsilon (NZE) materials were performed with the following results: the silver sphere augments the superradiant far-field intensity and rate by up to 400 and 1000%, respectively, while the NZE sphere enhances the far-field intensity and rate of the superradiance by approximately 1400 and 400%, respectively.

Silver Particles with Rhombicuboctahedral Shape and Effective Isotropic Interactions with Light

Truly spherical silver nanoparticles are of great importance for fundamental studies including plasmonic applications, but the direct synthesis in aqueous media is not feasible. Using the commonly employed copper-based etching processes, isotropicplasmonic response can be achieved by etching well-defined silver nanocubes. Whilst spherical like shape is typically prevailing in such processes, we established that there is a preferential growth towards silver rhombicuboctahedra (AgRCOs), which is thethermodynamically most stable product of this synthesis. The rhombicuboctahedral morphology is further evidenced by comprehensive characterization with small-angle X-ray scattering in combination with TEM tomographyand high resolution TEM. Wealso elucidate the complete reaction mechanism based on UV-Vis kinetic studies, and the postulated mechanism can also be extended to all copper-based etching processes.

Synthesis and characterizations of Ag-decorated graphene oxide nanosheets and their cytotoxicity studies

In this paper, reduced graphene oxide nanosheets decorated with silver nanoparticles (AgNPs/rGO) were prepared by a wet chemical method. In this method, graphene oxide (GO), silver nitrate, and ammonia were used as a precursor. AgNPs/rGO composite was characterized by UV–Vis spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared transmission spectroscopy (FTIR), and transmission electron microscopy (TEM). The results show that the spherical silver nanoparticles with average size of about 6–10 nm were distributed on GO sheets. In vitro cytotoxicity of the prepared AgNPs/rGO samples was studied on neuro2A cells and found that the sample eliminates the growth of neuro2A cells up to 50% and Ag nanoparticles reduce the cytotoxicity of the GO sheets.

A Comparative Assessment of Nanotoxicity Induced by Metal (Silver, Nickel) and Metal Oxide (Cobalt, Chromium) Nanoparticles in Labeo rohita.

In the present in vivo study, we provide a comparison of toxicological consequences induced by four different types of spherical nanoparticles (NPs)—silver nanoparticles (AgNPs, 40 ± 6 nm), nickel (NiNPs, 43 ± 6 nm), cobalt oxide (Co3O4NPs, 60 ± 6 nm), and chromium oxide (Cr3O4NPs, 50 ± 5 nm)—on freshwater fish Labeo rohita. Fish were exposed to NPs (25 mg/L) for 21 days. We observed a NPs type-dependent toxicity in fish. An altered behavior showing signs of stress and a substantial reduction in total leukocyte count was noticed in all NP-treated groups. A low total erythrocyte count in all NP-treated fish except for Co3O4NPs was discerned while a low survival rate in the case of Cr3O4NP-treated fish was observed. A significant decrease in growth and hemoglobin were noticed in NiNP- and Cr3O4NP-treated fish. A considerable total protein elevation was detected in NiNP-, Co3O4NP-, and Cr3O4NP-treated groups. An upgrading in albumin level was witnessed in Co3O4NP- and Cr3O4NP-treated groups while a high level of globulin was noted in NiNP- and Co3O4NP-exposed groups. In all NP-treated groups, a depleted activity of antioxidative enzymes and pathological lesions in liver and kidney were noticed.

Simple reactor for the synthesis of silver nanoparticles with the assistance of ethanol by gas–liquid discharge plasma

Atmospheric pressure plasma technology is gaining increasing importance because it is a simple and tunable synthesis process for the production of metallic nanoparticles. In addition to the development of the power supply, improving the reactor is also one of the main strategies to enhance the utility. In this study, a simple reactor for the gas–liquid discharge plasma induced by argon gas was applied to synthesize silver nanoparticles from silver nitrate (AgNO3) in solution. An AC power supply with a peak voltage of 3.5 kV was used. The frequency and on-time were set to 50 kHz and 2.5 μs, respectively. The oscilloscope showed that the rising time was approximately 2 μs. The ethanol was used as the source for the reactive reducing agent. No more additional components existed in the solution during the discharge and neither of the electrodes was in contact with the treated solution. The temperature increased by 10 °C within 1 min without a cooling system. Carbon was the main impurity and was expected to be produced from the decomposition of the organics under the plasma. The elevated temperature decreased the organic by-products by evaporation and could also decrease the production of carbon. Transmission electron microscopy showed that the spherical silver nanoparticles with a size of approximately 10 nm were synthesized with a crystal structure and that a low concentration of ethanol prefers the production of the mono-dispersed colloid.

Ficus retusa-stabilized gold and silver nanoparticles: Controlled synthesis, spectroscopic characterization, and sensing properties.

Ficus retusa was used as reducing and stabilizing agent in the green synthesis of silver and gold nanoparticles with high dispersion stability and controllable size and shape. The controlling of reaction conditions i.e. contact time, extract quantity, metal concentration, and pH value enables the tuning of the particle size and size distribution of the metal nanoparticles. UV-visible spectroscopy was used to follow the spectral profile changes of the surface plasmon resonance of the metal nanoparticles due to different treatments. The surface plasmon resonance varies between 400 and 432 nm and between 522 and 554 nm for silver and gold nanoparticles, respectively, depending on the different reaction parameters. Atomic force and transmission electron microscopy results confirmed the success of preparation of spherical silver (15 nm) and gold (10-25 nm) nanoparticles with narrow size-distribution. Fourier transform infrared spectroscopy suggested the phenolic compounds play the key role in the reduction and stabilizing of metal ions. The colorimetric sensitivity of silver and gold nanoparticles to detect the presence of heavy metals in water was studied.

Eco-friendly walnut shell powder based facile fabrication of biogenic Ag-nanodisks, and their interaction with bovine serum albumin

Walnut shell biomass was used for the extraction of juglone by water as a solvent at room temperature. Upon addition of AgNO3 to a dye solution, prefect transparent pale brown color develops within the reaction time. UV–visible spectroscopy revealed the appearance of surface plasmon absorption (SRP) peak at 410 nm for spherical silver nanoparticles (AgNPs). Transmission electron microscopy suggested the formation of spherical and truncated triangular nano-plate geometry of AgNPs with average diameter 25 nm. Juglone-surfactant interactions (micellization and incorporation) have been studied spectrophotometrically by using cationic cetyltrimethylammonium bromide (CTAB). The presence of CTAB has significant impacts on size, shape and the size distribution of AgNPs. The nucleation, growth, and adsorption processes depend on the [CTAB]. It also catalyzes the Ag+ ions reduction by juglone with a rate enhancement of ca. 100-fold. Activation parameters (activation energy, enthalpy of activation and entropy of activation) were evaluated to the synthesis of silver nano-disks. Antioxidant activity of juglone was accessed by the scavenging effect on DPPH radical. Silver nanoparticles was also used as quencher to determine their interaction with bovine serum albumin (BSA). The quenching constant were found to be 1.4 × 103 M−1 L s−1 and 4.8 × 103 M−1 L s−1 for two BSA concentrations.

Potential of graphene for shape-directing agent free growth of highly oriented silver particles and their application in surface enhanced Raman scattering

Controlling the shape of metal nanoparticles is generally accomplished using shape-directing agents. Particle synthesis without shape-directing agents and shape control have attracted strong interest given the side effects of the shape-directing agents. Here, the potential of graphene in the deposition of metallic nanoparticles with different morphologies without using shape-directing agents was investigated. Doping graphene with nitrogen via plasma treatment enhanced the metal reduction. The nitrogen content was varied by changing the plasma treatment time. Nitrogen doping mainly occurred at boundary-like defects and involved pyrrolic nitrogen as the major chemical configuration. Graphene grown on copper substrate grown via chemical vapor deposition was used to deposit spherical silver nanoparticles throughout the graphene along with microparticles that were randomly distributed on the surface. Transition of microparticles of silver from dendrites to well-defined platelets morphologies was observed with nitrogen-doped graphene after 10 min of nitrogen plasma exposure. The number density of silver particles was controlled by varying the plasma treatment time. Surface-enhanced Raman scattering activity of these silver particles grown on graphene using copper substrates was assessed using a Rhodamine 6G Raman probe in the concentration range of 10 nM to 1 mM.

Interaction and transfer of charged particles from an alternating current glow discharge in liquids: Application to silver nanoparticle synthesis

In this study, we experimentally investigated the effect of charged particles generated from an alternating current glow discharge in liquids and the ability of these particles to synthesize silver nanoparticles. The measurement of the pH and electrical conductivity in liquids was performed to study the interface reactions and transfer of species from plasmas to liquids. Solutions of sodium hydroxide, de-ionized water, sodium nitrate, and silver nitrate were used in this study. We determined that the pH of de-ionized water and sodium hydroxide solutions was reduced to 4.0 during the discharge. However, the pH of nitrate salts evolved in two opposite stages, with an initial reduction within 3 min from the start of the discharge and a subsequent increase to alkaline values. The results also showed that spherical silver nanoparticles were generated in the silver nitrate solutions under the discharge. These results indicate that alternating current glow discharge generates both positive ions and free electrons when in contact with a liquid, leading to complex chemical transformations. This suggests that the proposed approach can be used for noble nanoparticle synthesis.

A cost-effective nanoparticle-gap-film SERS sensor using graphene nanospacer by one-step transfer-free mechanical milling

To develop operative surface-enhanced Raman spectroscopy (SERS) sensors, nanostructures with high signal enhancement and ease of production are highly desired. The SERS-active nanoparticle-gap-film (NGF) sandwich substrate using graphene as the gap nanospacer is of particular interest due to its strong local field enhancement associated with the atomically thin graphene gap. However, the complexity in fabricating such nanostructures, especially the often involved high-temperature and vacuum processes, ultimately hampers practical applications. Here, a simple and low-cost SERS-active NGF sensor is demonstrated in which a graphene-based nanospacer was prepared by a one-step transfer-free mechanical milling process under amiable conditions. Notably, the milling process can readily produce and deposit the graphene nanospacer in a single fabrication step onto the desired metal substrates. To further enhance SERS performance, shape-anisotropic triangular silver nanoprisms were introduced into the NGF system, which offered enhanced Raman gain compared to spherical silver nanoparticles. Using Rhodamine 6G as the probe, the NGF SERS sensors exhibited a high sensitivity with a low detection limit of 5 × 10−9M with an enhancement factor of 2.7 × 105. This study opens up a new route for the facile production of cost-effective graphene-based NGF substrates for various SERS sensing applications.

Exploring the Control in Antibacterial Activity of Silver Triangular Nanoplates by Surface Coating Modulation.

In the present work, the synthesis and characterization of silver triangular nanoplates (AgNTs) and their silica coating composites are reported. Engineering control on the surface coating has demonstrated the possibility to modulate the antibacterial effect. Several AgNT-coated nanomaterials, such as PVP (Polyvinylpyrrolidone) and MHA (16-mercaptohexadecanoic acid) as a stable organic coating system as well as uniform silica coating (≈5 nm) of AgNTs, have been prepared and fully characterized. The antibacterial properties of the systems reported, organic (MHA) and inorganic (amine and carboxylic terminated SiO2) coating nanocomposites, have been tested on Gram-positive and Gram-negative bacteria strains. We observed that the AgNTs' organic coating improved antimicrobial properties when compared to other spherical silver colloids found in the literature. We have also found that thick inorganic silica coating decreases the antimicrobial effect, but does not cancel it. In addition, the effect of surface charge in AgNTs@Si seems to play a crucial role toward S. aureus ATCC 25923 bacteria, obtaining MIC/MBC values compared to the AgNTs with an organic coating.

Transcriptome profile with 20 nm silver nanoparticles in yeast.

Engineered nanomaterials are commercially used in everyday products including zinc sunscreens and water-resistant fabrics and surfaces. Therefore, understanding the effects of engineered nanomaterials on the environment is crucial for the responsible use of these technologies. We investigated the effects of 20 nm spherical citrate-coated silver nanoparticles (AgNPs) on the budding yeast Saccharomyces cerevisiae. Our growth assay showed that AgNPs have an inhibitory effect on yeast growth with concentrations above 5 μg/mL. Hundreds of genes in AgNP-treated cells were differentially expressed according to our transcriptome analysis based on RNAseq, including genes implicated in rRNA processing, ribosome biogenesis, cell wall formation, cell membrane integrity and mitochondrial functions. In particular, genes whose functions are associated with processing of small and large subunits of ribosomes were upregulated, while genes for cell wall/plasma membrane/mitochondrial integrity were downregulated. Consistently, our cell wall stability assay confirmed that cells with AgNPs are more susceptible to cell wall damage than non-treated cells. Levels of four significantly altered genes with AgNPs, including FAF1, SDA1, TIR1 and DAN1, were validated by reproducible results with RT-qPCR assays. Our transcriptome profile leads us to conclude that the exposure of cells to sublethal amounts of AgNPs affects many cellular processes negatively.

Novel triangular silver nanoparticle modified membranes for enhanced antifouling performance.

This study marks the first ever attempt at the successful fabrication of a novel reactive membrane to combat fouling through layer-by-layer (LBL) surface modification with polyelectrolyte (PE), followed by anisotropic triangular silver nanoparticles (TSNP). The morphology and the presence of TSNP on the membrane was confirmed by HR-TEM, FE-SEM and XPS. The charge density of the novel membrane (PE-TSNP) was increased 15.6 fold, as a result of the sharp-tip morphology of the TSNP forming tip-based “hot spots” on the membrane surface and high-atom-density active facets, which also enhanced the membrane hydrophilicity by 36%. Owing to these improved features, the novel membrane displayed remarkable antibacterial and anti-adhesion properties by achieving 100% bactericidal effect against high initial bacterial concentration (107 CFU mL−1). The membrane flux was improved by 31% while retaining a high flux recovery rate of 98.2% against biofouling. The membrane also mitigated organic and bio-organic fouling by maintaining high flux recovery rates of 96% and 95% respectively. As compared with a spherical silver nanoparticle modified membrane (PE-SSNP), the PE-TSNP membrane was 25.7% more hydrophilic and achieved 10% higher bacterial killing. Moreover, the novel membrane displayed 9.5%, 11.6%, and 14% higher flux recovery rates than that of the PE-SSNP membrane against biofouling, organic and bio-organic fouling respectively. Furthermore, the novel membrane retained a long-term biocidal capability of 93% even after 4 months of successive tests. ICP-MS revealed silver ion leaching of 4 μg L−1 and the total silver loss of 14% from the PE-TSNP membrane after 14 days.

Characterization of the Scattering Properties of a Spherical Silver Nanoparticle via the Finite-Difference Time-Domain Method

Characterization of the Scattering Properties of a Spherical Silver Nanoparticle via the Finite-Difference Time-Domain Method

Heat transfer from an immersed fixed silver sphere to a gas fluidised bed of very small particles

Results of unique heat transfer measurement in beds of fine, cracking catalyst particles, fluidized by air or helium gas, are compared with predictions from a theoretical model presented in the literature, and also with an earlier established empirical correlation. Moreover, the results have been related to dense phase flow conditions around a silver heat transfer probe by a simple turbulence model. A maximum heat transfer coefficient of h = 2300 W/m2K has been measured in a bed of 14?m (average diameter) particles, fluidized by helium gas. The data collected, and the model developed, can be used for the design of heat transfer tubes in fluidized beds of fine particles as for instance in fluid catalytic cracking (FCC) of crude oil heavy residues. The FCC is one of the most important conversion processes in the petroleum refineries.

About the relevance of particle shape and graphene oxide on the behavior of direct absorption solar collectors using metal based nanofluids under different radiation intensities

Nanofluids based on spherical gold, silver, and copper nanoparticles, nonspherical silver nanoparticles, layered graphene oxides (GO), and GO/silver hybrid structures, were synthesized to analyze their effect on the thermal behavior of direct absorption solar collectors. The thermal conductivities at room temperature of all the nanofluids were similar, with values 4% higher than pure water, meaning up to three orders of magnitude differences compared to the values expected from the Maxwell model. Photothermal conversion experiments under simulated solar radiation with 1 Sun (=1 kW/m2) of intensity showed that all the spherical metal nanofluids presented up to 5 K higher temperatures and 35% increase of the efficiencies than pure water after 3000 s of irradiation. A much larger effect was seen with nonspherical silver and GO/silver hybrid particles, as these nanofluids presented around 20% higher efficiencies than pure spherical silver nanofluids. The large effect of silver morphology and the addition of GO led to further tests of these nanofluids under natural solar radiation using a parabolic dish mirror with a concentration ratio of 60. Under this high radiation, nanofluids showed up to 50 K higher temperatures and 100% increase in the efficiencies than pure water. Indeed, a boiling process after just 200 s was seen in nanofluids, while in pure water this phase change did not occur. Non-spherical silver nanofluids and GO/silver hybrid structures produced steam faster than spherical silver nanofluids. Our results confirm the relevance of the nanoparticles on the thermal conversion of nanofluids, with nonspherical silver nanofluids and GO/silver hybrid nanofluids presenting the best behaviors under low and high solar radiation.

Silver‐Nanowire‐Catalyzed Three‐Component Coupling of Carbon Dioxide, Amines and Propargylic Alcohols for the Synthesis of β‐Oxopropyl Carbamates

AbstractBoth one‐dimensional silver nanowires(AgNWs) and spherical silver nanoparticles (Ag NPs) were synthesized with good dispersity and uniformity. In the presence of 4,4′‐dimethylaminopyridine (DMAP), the Ag NWs could catalyze the three‐component coupling of carbon dioxide, secondary amines, and propargylic alcohols efficiently, furnishing a range of structurally diverse β‐oxopropyl carbamatesin good to excellent yields, whereas the Ag NPs had a lower catalytic activity under similar reaction conditions. Moreover, the Ag NWs could be recycled and reused at least up to four times without significant loss of catalytic activity.