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Polyethylene glycol-6000 (PEG-6000) and trisodium citrate dihydrate (TSC) form an aqueous two-phase system (ATPS). This ATPS has been explored for synthesis and separation of silver nanoparticles (AgNPs). However, synthesis of stable nanoparticles using high TSC concentration corresponding to generic ATPS composition is not possible as high ionic strength of TSC causes aggregation and precipitation of silver nuclei. In the current study, this problem was overcome by synthesizing AgNPs at low concentrations of TSC. A two-step process was used for simultaneous synthesis and separation of AgNPs. Once stable nanoparticles were synthesised at low TSC concentration, the solution was taken to biphasic ATPS composition by mixing higher concentrations of TSC and PEG-6000 solutions to ensure particle entrapment. A silver to TSC (Ag+:TSC) molar ratio ≥ 67 × 10–3 that corresponds to lower TSC concentrations resulted in the formation of stable silver nanoparticles. The synthesis was carried out in batch and continuous modes. Spherical particles of average size 9.1 ± 3.4 nm were obtained in batch mode while in the continuous mode, the size was 10.6 ± 2.5 nm. Addition of polyvinylpyrrolidone (PVP) helped in sterically stabilizing the particles. Spontaneous formation and stabilization of AgNPs were observed within 15 min of reaction time as opposed to several hours reported in literature. The adopted synthesis route thus, is an effective green process to synthesise stable nanoparticles of silver which can be used in biological applications. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNP) can help prevent infection of virus and bacteria. The size and morphology of AgNP can be crucial to function, with smaller nanoparticles (< 20 nm) able to penetrate the cell wall. This is significant as oxidative stress and genotoxicity are associated with some sizes and coatings of AgNP, contraindicating the use of AgNP to reduce infection. We present evidence that a microfluidic chip can synthesize larger sizes and distributions of AgNP from the nano-to-micro size range. We show results from a microfluidic mixing chip that can produce a wide range of nano-to-micro size (~ 24–400 nm) AgNP. Synthesis is based on a modified Turkevich method, using a single-step AgNP synthesis on the microfluidic chip using two chemical components, trisodium citrate (NaCit) and AgNO3. To make AgNP more accessible, we describe the microfluidic chip and conditions capable of synthesis. We also describe how modification of flow rate and chemical reagent concentration change particle diameter during production. In our experiments, we found that AgNP production created a visible adsorption line in the microfluidic device, possibly owing to AgNP surface interaction at the polydimethylsiloxane (PDMS) interface. We characterize these particles with dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Based on optical light microscopy, we hypothesize that AgNP formation primarily occurs at the interface between the two chemical reagent streams. We also conclude that AgNP size increases could be due to interaction with the PDMS surface, which is known to be porous. Future work will help to understand how surface interaction may influence the formation of larger particles. [ABSTRACT FROM AUTHOR]

Current work presents a detailed study on the synthesis of silver nanoparticles (70 ± 5 nm) functionalized with 4-mercaptobenzoic acid and their interaction with divalent ions (Cu2+, Fe2+, Co2+, Ni2+, Pb2+, Mn2+, Zn2+, Sn2+). The study reveals the morphological changes in the nanoparticles due to interaction with Cu2+, resulting in the formation of larger nanoparticle aggregates. The UV-Vis spectra of the pristine and aggregated nanoparticles are also discussed, providing insights into the changes in their optical properties. These nanoparticles are used to detect divalent ions using surface-enhanced Raman spectroscopy with a detection limit of 2.5 × 10–7 M for Cu2+ and also show a linear response within the 10–3 to 10–7 M concentration range. High selectivity for Cu2+, Fe2+, Co2+, Mn2+, and Pb2+ was also detected. The findings of this study could have significant implications in the field of nanomaterials and environmental chemistry, particularly in the detection and removal of heavy metal ions. [ABSTRACT FROM AUTHOR]

A lot of innovative methods to synthesize various kinds of nanoparticles having specific shape and size are being explored for targeting immense applications through nanotechnology. In this work, simple, eco-friendly and cost-effective method has been adopted for the synthesis of silver (Ag), gold (Au) and palladium (Pd) nanoparticles using tannic acid. The morphology and size of nanoparticles were determined by TEM study, which revealed that nanoparticles are spherical in shape and exhibit an average diameter of about 6.66 nm, 12.24 nm and 19.65 nm for tannic acid mediated silver, gold and palladium nanoparticles (TA-AgNPs, TA-AuNPs and TA-PdNPs), respectively. The application of these nanoparticles was then explored as catalyst for the degradation of methylene blue and congo red dyes. The presence of these dyes was found to be detrimental for the aquatic life, as these dyes can seep into the ecosystem from the industrial waste. The catalytic activity of nanoparticles was compared by determining rate constant values. For, both the dyes, the value of rate constant followed the order- kAg ˃ kPd ˃ kAu. The dye degradation potential of TA-AgNPs was higher than TA-Au and TA-PdNPs. This difference in catalytic activity was attributed to lower work function value of AgNPs as compared to AuNPs and PdNPs. Present study provides an environmentally benign pathway for synthesizing metallic nanoparticles and their utilization as catalyst for degradation of harmful dyes. Such kinetic studies of comparative catalytic analysis may be useful in selection of nanoparticles, which may be best suited for a specific purpose. [ABSTRACT FROM AUTHOR]

This paper reports the effects of the silver nanoparticle (Ag-NP) deposition on the optical properties of silicon nanowire (SiNW) layer. Vertically, SiNW arrays were prepared in HF/AgNO3 aqueous solution using metal-assisted chemical etching of p-type silicon. The insertion of Ag particles in SiNWs was performed by electroless deposition method by varying the concentration of the silver nitrate solution. Scanning electron microscopy (SEM) micrographs show arrays of parallel nanowires as well as the presence of Ag-NPs on SiNWs layer. Fourier transform infrared (FTIR) and Raman spectroscopies reveal the existence of new vibration bands that are related to silver particles and their interactions with SiNW surface. By Raman spectroscopy, we also observed the manifestation of SERS effect for SiNWs/Ag composites. The optical properties of the elaborated samples were investigated by photoluminescence spectroscopy (PL). The integrated PL intensity of SiNWs was increased fourteen times by the deposition of silver nanoparticles on their surfaces for a silver nitrate concentration of 0.05 M which is essentially due to localized surface plasmon resonance. The PL spectrum of SiNWs/Ag exhibits intense emission band at 2.36–2.39 eV which is related to the interband and intraband transitions between the electronic states of Ag nanoparticles. Energy band diagram showing the emission mechanism in Ag/SiNWs composites was proposed. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effectiveness of silver nanoparticles–chitosan composites (AgNPs) with different morphologies and particle size distributions against resistant bacteria and biofilm formation. Four different samples were prepared by a two-step procedure using sodium borohydride and ascorbic acid as reducing agents and characterized by UV–Vis absorption spectra, scanning transmission electron microscopy. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the AgNPs were determined according to the Clinical and Laboratory Standards Institute (CLSI) against clinical isolates multidrug-resistant and strains of the American Type Culture Collection (ATCC). An assay was performed to determine the MICs during 20 successive bacteria exposures to AgNPs to investigate whether AgNPs induce tolerance in bacteria. The antibiofilm activities of AgNPs were also evaluated by determining the minimum biofilm inhibitory concentration (MBIC). The spherical AgNPs present diameters ranging from 9.3 to 62.4 nm, and some samples also have rod-, oval-, and triangle-shaped nanoparticles. The MIC and MBC values ranged from 0.8 to 25 μg/mL and 3.1 to 50 μg/mL, respectively. Smaller and spherical AgNPs exhibited the highest activity, but all the AgNPs developed in this study exhibit bactericidal activity. There was no significant MIC increase after 20 passages to the AgNPs. Regarding the antibiofilm activity, MBICs ranged from 12.5 to 50 μg/mL. Again, smaller and spherical nanoparticles presented the best results with phenotypic inhibition of production of slime or exopolysaccharide (EPS) matrix. Thus, it was concluded that AgNPs have a promising potential against resistant bacteria and bacteria that grow on biofilms without inducing tolerance. [ABSTRACT FROM AUTHOR]

The increased use of silver nanoparticles (AgNPs) is expected to result in negative environmental impact, particularly on aquatic ecosystems. The effect of AgNPs to aquatic plants has received little attention. Azolla filiculoides is an interesting aquatic fern with phytoremediation capacities. Therefore, the objective of this research was to evaluate the interaction of AgNPs with A. filiculoides, observing NPs internalization, accumulation, and effects on growth and root structure with high-resolution imaging and analytical techniques. The AgNPs bio-synthesized with Camellia sinensis extracts showed regular shape (quasi-spherical) and size (26.74 ± 0.52 nm). A. filiculoides plants were grown in Yoshida nutrient solution (pH 5) and exposed to AgNPs (0.0, 0.1, 1.0, 5.0, 10.0, 100.0 mg L−1), under a completely random experimental design. The Spearman's correlation indicated a high negative relation between the AgNPs concentration, and dry biomass (DB), associated with a higher duplication rate (DR). AgNP internalization and distribution were studied with high-resolution scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) combined with backscattered electron (BSE) images on surfaces and thin (70 nm) sections of roots and fronds. Our results support the hypothesis that AgNPs deposit on roots and fronds subphases and dissociate into Ag+ that enter the root and accumulate in the endodermis, where they form AgNPs. Structural damages on the rhizodermis and vascular cylinder at high concentrations (100.0 mg AgNPs L−1) suggest the impairment of the main functions of roots, reducing either Ag+ or AgNP uptake and translocation, affecting plant growth and silver accumulation in the fern. [ABSTRACT FROM AUTHOR]

Recent years have seen significant increases in the use of silver nanoparticles (AgNPs) in areas such as medicine and agriculture. AgNPs released into environment can be accumulated by plants, potentially affecting environmental and human health. In addition, the accumulation of silver in plant tissues can negatively affect plant vascular tissues and membrane transporters that are responsible for the transport of water and essential nutrients. In this study, Lycopersicon esculentum plants were exposed to 10, 20, or 30 mg/L of silver in bulk (Ag0), nanoparticle (AgNPs), or ionic (AgNO3) form for 7 days in Hoagland media. Tissues were then harvested and subjected to elemental, molecular, and microscopic evaluation. The highest and lowest concentration of silver was detected in roots of plants exposed to 10–30 mg/L AgNO3 (432–471 μg/g dw) or AgNPs (40–47 μg/g dw), respectively. Particulate silver was detected in plants exposed to 20 nm AgNPs. The highest (52,700–58,400 particles/g) and lowest (6200–13,700 particles/g) concentrations of particles were detected in roots and leaves, respectively. The membrane transporters H+-ATPase, potassium transporter, and sulfate transporter were upregulated by 23.50%, 52.09%, and 7.6% upon exposure to all forms of silver as compared to the control group. Exposure to all forms of silver resulted in larger xylem cells (70 ± 1.1 μm in AgNP-exposed plants) than the control group (46 μm ± 0.6). Collectively, the data suggest that exposure to AgNPs resulted in the translocation and accumulation of both ionic and particulate forms of silver in tomato plants, affected the structure of vascular tissues, and significantly impacted the expression of membrane transporters. These changes subsequently affect the electrochemical potential of plant cells, the balance of water and nutrient dynamics, and plant growth; all of which have implications for sustainable agriculture and ultimately human health. These results also improve our understanding of the fate and effects of nanomaterials in food crops. [ABSTRACT FROM AUTHOR]

Bare Ag nanoparticles (∼10 nm) and Ag nanoparticles (1-20 nm) on the surfaces of larger TiO nanoparticles were prepared by laser ablation of microparticle aerosols (LAMA). The behaviors of the nanoparticles during high temperature annealing were then studied with ex situ and in situ transmission electron microscopy. For the ex situ heating experiments, Ag and Ag-on-TiO NPs were collected onto gold TEM grids and subjected to annealing treatments at 500 °C in argon, vacuum, and air. At this temperature, bare Ag NPs on carbon TEM supports coarsened rapidly in both air and argon atmospheres. In contrast, Ag-on-TiO NPs that were heated to 500 °C in flowing argon or in a vacuum did not coarsen significantly and were remarkably stable. Ag-on-TiO NPs that were heated to 500 °C in air, however, behaved quite differently. The TiO crystallized upon heating and a significant loss of Ag were observed from the surfaces of the TiO, likely due to sublimation. These results demonstrate that the surface defect structure and chemistry of the oxide support strongly influence the thermal stability of Ag NPs produced by LAMA. [ABSTRACT FROM AUTHOR]

The potential of engineered nanomaterials to induce genotoxic effects is an important aspect of hazard identification. In this study, cytotoxicity and mutagenicity as a function of metabolic activation of three silver nanoparticle (AgNP) preparations differing in surface coating were determined in Chinese hamster ovary (CHO) subclone K1 cells. Three silver nanoparticle preparations ( x <30 nm) stabilized with polyoxyethylene glycerol trioleate and polyoxyethylene sorbitan monolaurate (AgPure™), citrate (Citrate-Ag), and polyvinylpyrrolidone (PVP-Ag) were used for the experiments. The cytotoxic effect of AgNPs was assessed with the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazoliumbromide) test using different concentrations of nanoparticles, while the mutagenicity was evaluated using the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutation assay. The cytotoxicity of all three AgNPs was lower in a cell culture medium containing 10% fetal calf serum (FCS) than in medium without FCS. The HPRT test without metabolic activation system S9 revealed that compared to the other AgNP formulations, citrate-coated Ag showed a lower genotoxic effect. However, addition of S9 increased the mutation frequency of all AgNPs and especially influenced the genotoxicity of Citrate-Ag. The results showed that exogenous metabolic activation of nanosilver is crucial even if interactions of the metabolic activation system, nanosilver, and cells are not really understood up to now. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag-NP) are the most used nanomaterial in consumer products due to the intrinsic antimicrobial capacity of silver. However, Ag-NP may be also harmful to algae, aquatic species, mammalian cells, and higher plants because both Ag and nanoparticles are responsible of cell damages. The oxidative dissolution of Ag-NP would proceed to completion under oxic conditions, but the rate and extent of the dissolution depend on several factors. This work correlates the effect of the capping agent (albumin and citrate) with the stability of Ag-NP towards agglomeration in simulated body fluid (SBF) and oxidation in the presence of ROS species (HO). Capping provides colloidal stability only through electrostatic means, whereas albumin acts as bulky ligands giving steric and electrostatic repulsion, inhibiting the agglomeration in SBF. However, citrate capping protects Ag-NP from dissolution to a major extent than albumin does because of its reducing power. Moreover, citrate in solution minimizes the oxidation of albumin-coated Ag-NP even after long incubation times. HO-induced dissolution proceeds to completion with Ag-NP incubated in SBF, while incubation in citrate leads to an incomplete oxidation. In short, albumin is an excellent capping agent to minimize Ag-NP agglomeration whereas citrate provides a mild-reductive medium that prevents dissolution in biological relevant media as well as in the presence of ROS species. These results provide insight into how the surface properties and media composition affect the release of Ag from Ag-NP, related to the cell toxicity and relevant to the storage and lifetime of silver-containing nanomaterials. [ABSTRACT FROM AUTHOR]

A comparative study of amine and silver carboxylate adducts [RCOOAg-2(RNH)] (R = 1, 7, 11; R = 8, 12) as a key intermediate in NPs synthesis is carried out via differential scanning calorimetry, solid-state FT-infrared spectroscopy, C CP MAS NMR, powder X-ray diffraction and X-ray photoelectron spectroscopy, and various solution NMR spectroscopies (H and C NMR, pulsed field gradient spin-echo NMR, and ROESY). It is proposed that carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination as opposed to bridging bidentate coordination of pure silver carboxylates resulting from the formation of dimeric units. All complexes are packed as lamellar bilayer structures. Silver carboxylate/amine complexes show one first-order melting transition. The evidence presented in this study shows that phase behavior of monovalent metal carboxylates are controlled, mainly, by head group bonding. In solution, insoluble silver salt is stabilized by amine molecules which exist in dynamic equilibrium. Using (bis)amine-silver carboxylate complex as precursor, silver nanoparticles were fabricated. During high-temperature thermolysis, the (bis)amine-carboxylate adduct decomposes to produce silver nanoparticles of small size. NPs are stabilized by strongly interacting carboxylate and trace amounts of amine derived from the silver precursor interacting with carboxylic acid. A corresponding aliphatic amide obtained from silver precursor at high-temperature reaction conditions is not taking part in the stabilization. Combining NMR techniques with FTIR, it was possible to follow an original stabilization mechanism. [ABSTRACT FROM AUTHOR]

The present study reports the biosafety assessment, the exact molecular effects, and apoptosis induction of newly developed chitosan-silver hybrid nanoparticles (Cs-Ag NPs) in HepG2 cells. The investigated hybrid NPs were green synthesized using Cs/grape leaves aqueous extract (Cs/GLE) or Cs/GLE NPs as reducing and stabilizing agents. The successful formation of Cs/GLE NPs and Cs-Ag hybrid NPs has been confirmed by UV-Vis spectrophotometry, FTIR spectroscopy, XRD, and HRTEM. From the TEM analysis, the prepared Cs/GLE NPs are uniform and spherical with an average size of 150 nm, and the AgNPs (5-10 nm) were formed mainly on their surface. The UV-Vis spectra of Cs-Ag NPs showed a surface plasmon resonance (SPR) peak at about 450 nm confirming their formation. The synthesized Cs-Ag NPs were found to be crystalline as shown by XRD patterns with fcc phase oriented along the (111), (200), (220), and (311) planes. The cytotoxicity patterns, the antiproliferative activities, and the possible mechanisms of anticancer activity at molecular level of the newly developed Cs-Ag hybrid NPs were investigated. Cytotoxicity patterns of all the preparations demonstrated that the nontoxic treatment concentrations are ranged from 0.39 to 50 %, and many of the newly prepared Cs-Ag hybrid NPs showed high anticancer activities against HpG2 cells, and induced cellular apoptosis by downregulating BCL2 gene and upregulating P53. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this study, a simple technique for preparation of colloid solution of metal nanoparticles in polyethylene glycol (PEG)/HO is described. By this technique, stable colloidal metal solutions can be prepared ready for use without application of chemical reactions, stabilizers, or reducing agents. The nanoparticles are created by direct sputtering of metal into PEG. The influence of sputter conditions and the concentration of PEG/HO on the properties of nanoparticles was studied. The nanoparticles were characterized by transmission electron microscopy, atomic absorption spectrometry, dynamic light scattering, and UV-Vis spectroscopy. UV-Vis spectra of gold nanoparticle solution exhibit localized surface plasmon resonance characteristic peaks located in the region 513-560 nm (PEG/HO-1/1), 509-535 nm (PEG/HO-1/9), and for silver nanoparticles in the region from 401 to 421 nm. Silver nanoparticles have a broader size distribution compared with gold ones. An appropriate choice of concentration, mixing, and deposition conditions allows preparing the stable solution of gold or silver nanoparticles. [ABSTRACT FROM AUTHOR]

We report here a systematic study of the antibacterial behavior of silver nanoparticles coated with fatty acids (oleic: AgNP-O, linoleic: AgNP-L, and palmitic acids: AgNP-P) in water. We have found remarkable differences in their capability to penetrate bacteria cell over a broader range of particle size of ~4-96 nm compared to previously reported work, and a variable toxicity depending on the particles size. Our results indicate that silver nanoparticles stabilized with oleic acid showed clear advantages in antibacterial activity, penetration inside the bacteria cells, cytotoxicity, time effectiveness, efficiency, and stability against light. [ABSTRACT FROM AUTHOR]

In recent years, there has been increasing concern regarding the fate and transport of engineered nanoparticles (NPs) in environmental systems and the potential impacts on human and environmental health due to the exponential increase in commercial and industrial use worldwide. To date, there have been relatively few field-scale studies or laboratory-based studies on environmentally relevant soils examining the chemical/physical behavior of the NPs following release into natural systems. The objective of this research is to demonstrate the behavior and transformations of iron oxide and silver NPs with different capping ligands within the unsaturated zone. Here, we show that NP transport within the vadose zone is minimal primarily due to heteroaggregation with soil surface coatings with results that >99 % of the NPs remained within 5 cm of the original source after 1 year in intermediate-scale field lysimeters. These results suggest that transport may be overestimated when compared to previous laboratory-scale studies on pristine soils and pure minerals and that future work must incorporate more environmentally relevant parameters. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) have broad spectrum antimicrobial/biocidal properties against all classes of microorganisms and possess numerous distinctive physico-chemical properties compared to bulk Ag. Hence, AgNPs are among the most widely used engineered NPs in a wide range of consumer products and are expected to enter natural ecosystems including soil via diverse pathways. However, despite: (i) soil has been considered as a critical pathway for NPs environmental fate, (ii) plants (essential base component of all ecosystems) have been strongly recommended to be included for the development of a comprehensive toxicity profile for rapidly mounting NPs in varied environmental compartments, and (iii) the occurrence of an intricate relationship between 'soil-plant systems' where any change in soil chemical/biological properties is bound to have impact on plant system, the knowledge about AgNPs in soils and investigations on AgNPs-plants interaction is still rare and in its rudimentary stage. To this end, the current paper: (a) overviews sources, status, fate, and chemistry of AgNPs in soils, AgNPs-impact on soil biota, (b) critically discusses terrestrial plant responses to AgNPs exposure, and (c) illustrates the knowledge-gaps in the current perspective. Based on the available literature critically appraised herein, a multidisciplinary integrated approach is strongly recommended for future research in the current direction aimed at unveiling the rapidly mounting AgNPs-fate, transformation, accumulation, and toxicity potential in 'soil-plant systems,' and their cumulative impact on environmental and human health. [ABSTRACT FROM AUTHOR]

In many data evaluation procedures for particle measuring devices and in filtration models, spherical particles are assumed. However, significant fractions of aerosol particles are agglomerates of small primary spheres. The morphology of particles in filtration processes may not be known a priori and if the filtration data are processed with wrong assumption, errors can be induced. In this work, we have quantified such errors for the case of open-structured agglomerates. Filtration efficiency tests with polydisperse silver nanoparticle agglomerates and their sintered spheres were performed. After the sintering process, particles with a compact structure with the shape close to a sphere are obtained, which are referred to as sintered spheres in the present study. The testing method involved generation of particulate forms, passing the particles through the testing section, and measurement of the particle number concentrations and size distributions before and after the filter. Measurements of the aerosols upstream and downstream of the filter were conducted using scanning mobility particle sizers (SMPS, TSI Inc.), which covered the rage from 10 to 480 nm. Particles were additionally characterized from the electron microscopic images and the average primary particle size was determined to be 16.8 nm. The number-size distribution curves were obtained and used for penetration calculation. The penetration was dependent on the particle size and morphology. Silver-sintered spheres were captured with a lower efficiency than agglomerates with the same mobility diameter because of the stronger interception effect for agglomerates. Data analysis of the number-size distribution for agglomerates was processed based on sphere assumption and using the model for open-structured agglomerates developed by Lall and Friedlander. The efficiencies based on total concentrations of number, surface and volume were affected when the agglomerate model was used. The effect was weakest for the total number efficiency and strongest for the total volume efficiency. Filtration efficiency curves for agglomerates were additionally plotted as a function of the volume equivalent diameter or number of primary particles per agglomerate, because the latter parameters provide more information for the agglomerate structure. [ABSTRACT FROM AUTHOR]

The synthesis of stable colloidal solutions of silver nanoparticles is a major goal in the industry to control their fate in aqueous solutions. The present work studies 10-20-nm silver nanoparticle aggregation triggered by the presence of chloride ions. The aggregation process was followed by UV-Vis-NIR spectroscopy and transmission electron microscopy. We found that the mechanism involved differs from the classic explanation of nanoparticle aggregation triggered by an increase in the ionic strength. Moreover, our results give evidence that even when nanoparticles are resistant to an increment of the total amount of ions, the formation of insoluble salts in the vicinity of the nanoparticle is enough to induce the aggregation. The presence of silver chloride around the silver nanoparticles was documented by an X-ray diffraction pattern and electrochemical methods because chloride anions are ubiquitous in real media; this alternative process jeopardized the development of many applications with silver nanoparticles that depend on the use of stable colloids. [ABSTRACT FROM AUTHOR]

In-vitro free radical scavenging activity of biosynthesized gold (Au-NPs) and silver (Ag-NPs) nanoparticles was investigated in the present study. Natural precursor Prunus armeniaca (apricot) fruit extract was used as a reducing agent for the nanoparticle synthesis. The free radical scavenging activity of the nanoparticles were observed by modified 1,1′-diphynyl-2-picrylhydrazyl, DPPH and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid), ABTS assay. The synthesized nanoparticles were characterized by UV-Visible spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy, and fourier transform infrared spectroscopy (FTIR). Appearance of optical absorption peak at 537 nm (2.20 keV) and 435 nm (3 keV) within 0.08 and 0.5 h of reaction time was confirmed the presence of metallic Au and Ag nanoclusters, respectively. Nearly spherical nanoparticles with majority of particle below 20 nm (TEM) for both Au-NPs and Ag-NPs were synthesized. XRD pattern confirmed the existence of pure nanocrystalline Au-NPs while few additional peaks in the vicinity of fcc silver-speculated crystallization of metalloproteins of fruit extract on the surface of the Ag-NPs and vice versa. FTIR spectra was supported the role of amino acids of protein/enzymes of fruit extract for synthesis and stabilization of nanoparticles. Dose-dependent scavenging activity was observed for Au-NPs and Ag-NPs in both DPPH and ABTS in-vitro assay. 50 % scavenging activity for DPPH were 11.27 and 16.18 mg and for ABTS 3.40 and 7.12 mg with Au-NPs and Ag-NPs, respectively. [ABSTRACT FROM AUTHOR]

Growth of silver nanoparticles (NPs) with a size ranging from of 6 ± 0.8-42 ± 1.6 nm was investigated systematically by the NaBH reduction of silver nitrate using citrate and poly (vinyl pyrrolidone) (PVP) as stabilizers through a facile one-pot aqueous synthesis. Because of controlling nucleation and growth processes, the NPs revealed narrow size distribution. Citrate and NaCl play important roles for the NPs with spherical morphology because of the adsorption of CHOon the {111} facet of silver particles and the etching of Cl/O. The addition of PVP resulted in the NPs small size and narrow size distribution. Spherical Ag NPs cannot be acquired by such one-pot reduction method in the absence of sodium citrate and NaCl, indicating the poor balance between the nucleation and growth processes in the reactions. On the basis of the results, reduction of the silver precursor (Ag) was promoted with sodium citrate, attributed to the higher activity of the citrate reductant. The selective adsorption role of CHO and PVP on the {111} plane, in addition to the stacking fault of {111} plane, led to silver atoms in the reaction solution deposited on {111} facet in the absence of NaCl, and then formed triangular silver nanoplates. [ABSTRACT FROM AUTHOR]

The plasmonic spectra and local field enhancement properties of the silver nanocrescent with fixed maximum thickness are theoretically studied using the discrete dipole approximation calculation. Both the particle plasmon mode and tip-cavity plasmonic coupling of the nanocrescent could be fine tuned by controlling the negative curvature of the nanocavity. The plasmonic conversion between particle plasmon of the silver tip and symmetric plasmon hybridization of the silver shell could be switched by changing the open and close state of the nanocavity. The intensity of intra-particle plasmonic coupling between tip and cavity resonance and the corresponding local field enhancement could also be tuned by the cavity radius. This study indicates that the metal surface with changing negative curvature takes great effect on the surface charge distribution of the metallic nanostructure and then controls the plasmon coupling and local field enhancement. [ABSTRACT FROM AUTHOR]

Nanoparticle (NP) tracking in complex media is still a challenge since NP concentrations are expected to be low compared to elemental background levels as it can be found in environmental matrices. This study presents a new method for radiolabeling of commercial silver nanopowder (Ag-NPs, dp < 100 nm) with Ag radionuclides ( t = 249.9 days) that provide an adequate time frame for particle detection, localization, and tracking under various experimental conditions. The radiolabeling procedure insures high efficiency, stability, and consistency of important particle properties such as size and morphology. Detection of Ag-NP in concentrations as low as 125 ng kg could be reached. For the first time, an appropriate tool for life-cycle studies of commercial Ag-NPs is provided without changing chemical composition of the material. This is of great importance e.g., for research in the field of nanotoxicology. [ABSTRACT FROM AUTHOR]

Metal nanoparticles need coating material so as to avoid aggregating to each other. On the contrary, there are occasions when the coating materials are required to be removed. Here, a theoretical model to relate removability of coating materials to their molecular structure is suggested. The model is used to find an optimum coating material, secondary amine, for use in low-temperature interconnection material. An interconnection made of methyloctylamine-coated silver nanoparticles was formed between a pair of copper electrodes by heating and pressurizing the nanoparticles and electrodes at 250 °C and 2.5 MPa, respectively, for 150 s. Shear strength and thermal conductivity of the formed interconnection were 17.8 MPa and 219 W/mK, respectively. This thermal conductivity value is greater than that obtained using Pb–Sn and silver solders. [ABSTRACT FROM AUTHOR]

Here, we present a review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms. For purpose of this review, silver nanomaterials include silver nanoparticles, stabilized silver salts, silver–dendrimer, polymer and metal oxide composites, and silver-impregnated zeolite and activated carbon materials. While there is some evidence that silver nanoparticles can directly damage bacteria cell membranes, silver nanomaterials appear to exert bacteriocidal activity predominantly through release of silver ions followed (individually or in combination) by increased membrane permeability, loss of the proton motive force, inducing de-energization of the cells and efflux of phosphate, leakage of cellular content, and disruption DNA replication. Eukaryotic cells could be similarly impacted by most of these mechanisms and, indeed, a small but growing body of literature supports this concern. Most antimicrobial studies are performed in simple aquatic media or cell culture media without proper characterization of silver nanomaterial stability (aggregation, dissolution, and re-precipitation). Silver nanoparticle stability is governed by particle size, shape, and capping agents as well as solution pH, ionic strength, specific ions and ligands, and organic macromolecules—all of which influence silver nanoparticle stability and bioavailability. Although none of the studies reviewed definitively proved any immediate impacts to human health or the environment by a silver nanomaterial containing product, the entirety of the science reviewed suggests some caution and further research are warranted given the already widespread and rapidly growing use of silver nanomaterials. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNP) are among the fastest growing product categories in the nanotechnology industry. Despite the importance of AgNP in consumer products and clinical applications, relatively little is known regarding AgNP toxicity and its associated risks. We investigated the effects of AgNP on gene expression in the mouse brain using Affymetrix Mouse Genome Arrays. C57BL/6 mice were exposed to AgNP (geometric mean diameter, 22.18 ± 1.72 nm; 1.91 × 107 particles/cm3) for 6 h/day, 5 days/week using the nose-only exposure system for 2 weeks. Total RNA isolated from the cerebrum and cerebellum was subjected to hybridization. From over 39,000 probe sets, 468 genes in the cerebrum and 952 genes in the cerebellum were identified as AgNP-responsive (one-way analysis of variance; p < 0.05). The largest groups of gene products affected by AgNP exposure included 73 genes in the cerebrum and 144 genes in the cerebellum. AgNP exposure modulated the expression of several genes associated with motor neuron disorders, neurodegenerative disease, and immune cell function, indicating potential neurotoxicity and immunotoxicity associated with AgNP exposure. Real-time PCR data for five genes analyzed from whole blood showed good correlation with the observed changes in the brain. Following rigorous validation and substantiation, these genes may assist in the development of surrogate markers for AgNP exposure and/or toxicity. [ABSTRACT FROM AUTHOR]

The increasing use of manufactured nanoparticles ensures these materials will make their way into the environment. Silver nanoparticles in particular, due to use in a wide range of applications, have the potential to get into water systems, e.g., drinking water systems, ground water systems, estuaries, and/or lakes. One important question is what is the chemical and physical state of these nanoparticles in water? Are they present as isolated particles, agglomerates or dissolved ions, as this will dictate their fate and transport. Furthermore, does the chemical and physical state of the nanoparticles change as a function of size or differ from micron-sized particles of similar composition? In this study, an electrospray atomizer coupled to a scanning mobility particle sizer (ES-SMPS) is used to investigate the state of silver nanoparticles in water and aqueous nitric acid environments. Over the range of pH values investigated, 0.5–6.5, silver nanoparticles with a bimodal primary particle size distribution with the most intense peak at 5.0 ± 7.4 nm, as determined from transmission electron microscopy (TEM), show distinct size distributions indicating agglomeration between pH 6.5 and 3 and isolated nanoparticles at pH values from 2.5 to 1. At the lowest pH investigated, pH 0.5, there are no peaks detected by the SMPS, indicating complete nanoparticle dissolution. Further analysis of the solution shows dissolved Ag ions at a pH of 0.5. Interestingly, silver nanoparticle dissolution shows size dependent behavior as larger, micron-sized silver particles show no dissolution at this pH. Environmental implications of these results are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The development of rapid and ecofriendly processes for the synthesis of silver (Ag) and gold (Au) nanoparticles is of great importance in the field of nanotechnology. In this study, the extracellular production of Ag and Au nanoparticles was carried out from the leaves of the plants, Tridax procumbens L. (Coat buttons), Jatropa curcas L. (Barbados nut), Calotropis gigantea L. (Calotropis), Solanum melongena L. (Eggplant), Datura metel L. (Datura), Carica papaya L. (Papaya) and Citrus aurantium L. (Bitter orange) by the sunlight exposure method. Qualitative comparisons of the synthesized nanoparticles between the plants were measured. Among these T. procumbens, J. curcas and C. gigantea plants synthesized <20 nm sized and spherical-shaped Ag particles, whereas C. papaya, D. metel and S. melongena produced <20 nm sized monodispersed Au particles. The amount of nanoparticles synthesized and its qualitative characterization was done by UV–vis spectroscopy and transmission electron microscopy (TEM), respectively. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used for structural confirmation. Further analysis carried out by fourier transform infrared spectroscopy (FTIR), provided evidence for the presence of amino groups, which increased the stability of the synthesized nanoparticles. [ABSTRACT FROM AUTHOR]

This work demonstrates a single-step method for synthesis and printing of metallic nanoparticles (NPs) in 2D micropatterns. The method is based on femtosecond laser writing, enabling fast and high precision deposition of silver, gold, or copper NPs in space-selective areas, which in general is not achieved by the traditional chemical routes or laser ablation of metal. Such finds were accomplished by employing laser-induced forward transfer in the femtosecond pulse regime (fs-LIFT). The results are promising for application, since metallic NPs, with a lognormal diameter distribution averaging between ~ 4 and 30 nm, allow exploring plasmon bands throughout the visible spectrum. The mechanisms behind NP formation by fs-LIFT are discussed based on the thermomechanical response of the material. An estimative based on the heat transfer suggests the occurrence of mechanical fragmentation rather than material vaporization. The main result addressed herein, however, is the ability to deposit silver, gold, and copper nanoparticles in selected regions, supporting the development of NP-based devices via one-step processing and their application in sensors and photonic circuits. [ABSTRACT FROM AUTHOR]

One of the new applications of silver nanoparticles is their use in plasmonic applications determined by the strong interaction of the electromagnetic wave and free electrons in nanostructures. Silver particles of a size smaller than the visible light wavelength can strongly absorb light due to the surface plasmonic resonance caused by the collective oscillation of the conduction electrons. The frequency and intensity of the plasmonic resonance depends on the distribution of the nanostructure polarized charge, which is determined by the shape and structure of the nanoparticle. But the rapid oxidation/sulfidation due to the ambient atmosphere dramatically reduces all the advantages of silver and causes difficulties from the view point of practical applications. Possible solution to this problem could be the formation of very pure particles of a perfect crystal structure, which should be more resistant to the abovementioned phenomena. We believe that unaccounted possibility of increasing the plasmon efficiency can be the usage of silver nanoparticles with a size equal to the magic numbers of various structures. To test this hypothesis, computer simulation was performed to determine the stability of the structure of silver clusters with a size of up to 2.0 nm. It shows that the use of small silver clusters in plasmonic applications strongly requires considering the problem of the thermal stability of their cluster structure with consideration of various kinds of "magic" numbers. [ABSTRACT FROM AUTHOR]

Commercially available 10- to 60-nm silver nanoparticles with different surface functional groups were tested for biological activity in different cell lines. Particle uptake and stability were examined in cell culture media to determine the correlation between particle stability, uptake, and cytotoxicity. Trends in rising toxicity with decreasing particle diameter were observed; however, correlations with particle stability or uptake were not observed. The effects of different cell culture media conditions on cellular toxicity were also measured and show a need to better understand how antibiotics, routinely used in cell culture, can transform particle surfaces and how exposure timelines are important to understand how particles that change over time might have different phases of cellular activity over their lifecycles. [ABSTRACT FROM AUTHOR]

A method for the preparation of a pure colloidal solution of silver (silver hydrosol) containing only small metal nanoparticles and carbonate ions stabilizing them was developed. For this purpose, a solution containing silver and oxalic acid salts was exposed to UV radiation of a low-pressure pulsed xenon lamp. The irradiation initiated Ag+ reduction with oxalate ions to give metal nanoparticles and carbonate ions. The latter ensure the electrostatic protection of nanoparticles via the formation of an electric double layer. Variation of the process conditions (silver and oxalate concentrations, UV irradiation conditions, the presence of air, and so on) allows the preparation of silver hydrosols with nanoparticle size ranging from 5 to 30 nm. The hydrosol is aggregatively stable for several months. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]