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Enhancement of antibacterial properties of Ag nanorods by electric field

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Enhancement of antibacterial properties of Ag nanorods by electric field

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The effect of an electric field on the antibacterial activity of columnar aligned silver nanorods was investigated. Silver nanorods with a polygonal cross section, a width of 20–60 nm and a length of 260–550 nm, were grown on a titanium interlayer by applying an electric field perpendicular to the surface of a Ag/Ti/Si(100) thin film during its heat treatment at 700 °C in an Ar+H2 environment. The optical absorption spectrum of the silver nanorods exhibited two peaks at wavelengths of 350 and 395 nm corresponding to the main surface plasmon resonance bands of the one-dimensional silver nanostructures. It was found that the silver nanorods with an fcc structure were bounded mainly by {100} facets. The antibacterial activity of the silver nanorods against Escherichia coli bacteria was evaluated at various electric fields applied in the direction of the nanorods without any electrical connection between the nanorods and the capacitor plates producing the electric field. Increasing the electric field from 0 to 50 V cm−1 resulted in an exponential increase in the relative rate of reduction of the bacteria from 3.9×10−2 to 10.5×10−2 min−1. This indicates that the antibacterial activity of silver nanorods can be enhanced by applying an electric field, for application in medical and food-preserving fields.

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... Rod-like Ag-NPs can be obtained by various routes [162,[174][175][176] but limited methods lead to pure rod-like Ag-NPs [176]. Methyl cellulose is used as soft template, at proper reaction conditions. ...
... For instance, at 90°C ~25% of reddish-yellow rod-like nanoparticles are obtained. High purity rod-like Ag-NPs with polygonal cross-section [174] (width of 20-60 nm and length of 260-550nm), were grown on a titanium interlayer by applying an electric field perpendicular to the surface of a Ag/Ti/Si(100) thin film during its heat treatment at 700°C in an Ar+H 2 environment. The Ag/Ti/Si(100) suprastructure was obtained starting from P-type Si(100) wafers by controlled dc magnetron sputtering without breaking the vacuum between the two depositions. ...
... These nanorods are suitable for biofunctionalization and could be further used for biomedical applications because of their high stability over time. [162,174] Wire Silver nanowires possess less SERS properties than the silver cubes and bipyramids, for instance but can be used in catalysis, microelectronic devices or nanometer-scale electrodes. [173] Cube Usually Ag-NPs are obtained by reduction of silver ions in ethylene glycol containing sulfide or hydrogensulfide at ppm level. ...
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... [7] In addition, ZnO is the main transparent material that is widely used in cosmetics, as drug carrier, filler in dentistry, in photodynamic therapy, anticancer (the destruction of cancer cells) and antibacterial applications in medical biotechnology and industrial fields. [7][8][9] The antibacterial properties of non-toxic ZnO are further improved by modifying its shell characteristics with various inorganic materials. The nanoparticles active oxygen radical species can attack and disrupt the bacterial cell wall, thereby resulting in cell death. ...
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... In recent times owing to advancement of some resistant bacterial strains to counter the antibiotics, the antibacterial activity of nanomaterials, such as zinc, silver and copper, with their unique size dependent properties has attracted great attentions [1][2][3][4][5]. For instance, ZnO with a quartzite hexagonal phase have a direct band gap of 3.37 eV possesses a wide range of technological applications. ...
... It is a unique material that exhibits optical, semiconducting, pyroelectric and piezoelectric properties [4,5]. It has attracted serious research attention because of its applicability to wide applications such as light emitting diode, [6,7], solar cells [8,9], chemical and gas sensors [10], ultraviolet (UV) light detector [11], stimulated emission with low loss and high gain [12], and transparent conducting oxide [13]. Due to these varied applications, several methods including thin films and polymeric approaches have been employed to deposit ZnO. ...
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... For example, in the need of increasing the efficacy of antibacterial properties of Ag metal, their nano forms are used like nanoparticles, nanosols, gels, etc. They have been employed in composite materials (anti-bacterial clothes), anti HIV, anti-cancer, ointments, sunscreen, anti-fungal cream, coating materials and many more devices [47,50]. Development in charac- terisation techniques, molecular modelling and extensive research, has made it pos- sible to predict and confirm the working mechanism of nano drugs [51,52]. ...
Chapter
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... For example, in the need of increasing the efficacy of antibacterial properties of Ag metal, their nano forms are used like nanoparticles, nanosols, gels, etc. They have been employed in composite materials (anti-bacterial clothes), anti HIV, anti-cancer, ointments, sunscreen, anti-fungal cream, coating materials and many more devices [47,50]. Development in characterisation techniques, molecular modelling and extensive research, has made it possible to predict and confirm the working mechanism of nano drugs [51,52]. ...
Chapter
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Article
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... The size of silver particles has been reduced to nano scale to improve their bioactivity [4,5]. Recently, many studies reconfirm the effective antimicrobial activity of nano silver [6][7][8]. Nanostructured silver has attracted great attention among various types of nanoparticles due to its inherent properties of high thermal stability, and little toxicity to mammalian cells and tissues [9,10] with applications in medicine as antibacterial agents [11]. ...
Article
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Article
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Article
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Article
Full-text available
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... In particular, zinc oxide (ZnO), an inexpensive material, with a wide band gap (3.37 eV) with optoelectronic, piezoelectric, and pyroelectric characteristics, has excellent application in sensors, anticorrosive, n-type semiconductor, optoelectronic devices, short wavelength laser diode, light-emitting diodes, thin film transistor energy storage devices, cosmetic and dermatological products and applications [11][12][13][14][15][16][17][18][19][20]. The versatility of ZnO has been reported in various morphologies such as nanowires, nanobelts, nanorods and many others for different applications [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. ZnO has a high exciton binding energy, which gives efficient emission at room temperature (11). ...
Article
Zinc oxide nanocomposites with Li and Ag doping were synthesized and were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), diffused reflectance spectroscopy (DRS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS). A peak shift was observed in XRD diffraction patterns, which was due to the lattice strain which was created by the doping of Li and Ag. Four phonon modes in Raman spectra corresponds to wurtzite structure with C6v space group. In ToF-SIMS, the presence of Li has been confirmed with its isotopes at m/z 6.01 and 7.01 respectively. For Candiasis albicans, the final microbial count after 10h were 2.1 x 104, 1.8 x 103, 1.1 x 103, 1.6 x 102, 1.0 x 102 and 3.0 x 101 in case of ZnO, lithium doped ZnO and Ag (0.5 mM, 1 mM, 3 mM, 5 mM) incorporation in Li doped ZnO matrices respectively, while the microbial count were 2.4 x 105, 1.6 x 104, 4.8 x 102, 3.2 x 102, 1.1 x 102 and 1.5 x 102 in the case of the ZnO, lithium doped ZnO, Ag (0.5 mM, 1 mM, 3 mM, 5 mM) incorporation in Li doped ZnO matrices, respectively.
... It also possesses various applications such as UV light emitting diodes, laser diodes and catalysts [21]. It has also been widely used in the treatment of a variety of skin conditions, in products such as baby powder, barrier creams to treat diaper rashes and in calamine lotion, antidandruff shampoos and antiseptic ointments [17,22]. Keeping these in mind, the present investigation was carried out to synthesize silver and zinc nanoparticles using the aqueous extracts of two potential mangrove plants namely H. fomes and S. apetala through photo-mediated bioreduction of metal ions to nanoparticles and determine their biological potential in terms of their, antioxidant, anti-diabetic, anti-inflammatory and antibacterial activities. ...
... Antimicrobial resistance has an importance meaning of the use, mainly the waste of antimicrobial medicines and develops when a microorganism transforms or obtains a resistance gene. So we have to achieve and attainment of modern medicines [1] has been incorporated and integrated into the coatings of food cans, in packages for meat, fish, corn, and peas to protect colors and to inhibit spoilage due to its antimicrobial properties [2]. Nanotechnology tools are improving our understanding of how bacteria work, though providing new prospects to analyze the dynamic and physical features of molecules, molecular assemblies, and intact microbial cells, either through isolation or under in vivo settings [3]. ...
... However, different Ag NP-based composites have been synthesized including magnetic NPs (MNP)@Ag NPs, CNT-Ag NPs [103], graphene oxide(GO)-Ag NPs, and TiO2-Ag NPs [104,105] which can increase the permanency of Ag NPs, and offer antibacterial and antibiofilm effects other than naked Ag NPs [106]. In addition, it has been reported that by using electric field stimulation, the antibacterial activity of Ag nanostructures can be increased significantly [107]. ...
Article
Several pieces of research have been done on transition metal nanoparticles and their nanocomplexes as research on their physical and chemical properties and their relationship to biological features are of great importance. Among all their biological properties, the antibacterial and antimicrobial are especially important due to their high use for human needs. In this article, we will discuss the different synthesis and modification methods of silver (Ag) and gold (Au) nanoparticles and their physicochemical properties. We will also review some state-of-art studies and find the best relationship between the nanoparticles' physicochemical properties and potential antimicrobial activity. The possible antimicrobial mechanism of these types of nanoparticles will be discussed in-depth as well.
... Another model is toxic ions when thermodynamic properties in a suspended medium, or biological environment, support particle dissolution. NPs are typically aggregated in hard water and seawater and are strongly affected by the specific form of organic matter and other natural particles in fresh water (Phillips & Barbano, 1997;Vaidhyanathan et al., 1998;Babes et al., 1999;Saito, 1993;Li et al., 2004Li et al., , 2007Akhavan & Ghaderi, 2009;Kumar & Chen, 2008;Choi et al., 2010;Highsmith, 2014;Santosh & Yuanbing, 2021;Jiang et al., 2008;Kai et al., 2011;Baek et al., 2011;Huang et al., 2015;Chusuei et al., 2013;Wu et al., 2010). While the state of dispersion changes ecotoxicity, other abiotic influences, such as pH, salinity, and organic matter, remain routinely studied in ecotoxicological studies. ...
Chapter
Toxicity of Nanomaterials
... Recently, the application of nanomaterials with antibacterial activity, such as titanium nanoparticles (TiNPs) and silver nanoparticles (AgNPs), has been attracted due to the flexibility on the applications of these nanoparticles in various antibacterial purposes such as solar light-induced photocatalysis [8], chemical stability [9], electric fieldinduced activity [10], easy mesoporous [11], nanotube loading [12], applicability against a broad range of bacteria [13], lasting activity with controllable release [14] and possibility of green [15] or bio synthesis [16][17][18]. Moreover, green synthesis of metallic nanoparticles involves the use of short reaction times, relatively low temperatures, and the use of extracts as biocatalysts (such as leaves, plants, fungi, and seed) to reduce the metallic precursor [19]. ...
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Nowadays, microorganisms have been developing multidrug resistance, imposing a threat to the treatment of infections and increasing costs associated with health care systems. Moreover, these bacteria are responsible for several deaths worldwide. Nanocomposite consisting of metallic nanoparticles supported onto nanozeolites have been promising in the stabilization of nanoparticles and enhancement of the application of the antibacterial agent, resulting in a lesser extent of nanoparticle agglomeration and surface energy reduction. In this context, the present work aims to synthesize and characterize nanocomposites doping with silver (AgNPs@NZ-180) and titanium (TiNPs@NZ-180) nanoparticles. The samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), and zeta potential (ZP), respectively. Antibacterial activity of the nanocomposites was verified by minimum inhibitory concentration (MIC) determination against four bacterial strains. Results suggest that nanocomposites showed the regular shape and mesoporous structure, high purity, physio-chemical stability, and good dispersion of AgNPs and TiNPs on the support. FT-IR spectra showed some specific stretching such as was identified, such as Al–O, Si–O, TiO–O, Ag–O, Ti–O, and AgO–O stretching, confirming the successful incorporation of AgNPs and TiNPs. XRD diffractograms showed characteristic peaks of analcime structure, a type of nanozeolite with silver (2Ɵ = 33.26° and 47.88°) and titanium nanoparticles peaks (2Ɵ = 24.17°, 25.86, 47.59° and 52.28°). Moreover, all samples represented negative charge surface ranged between −29.69 ± 1.27 mV until −14.65 ± 6.14 mV. Moreover, AgNPs@NZ-180 showed antibacterial activity against all bacteria tested (K. pneumoniae, E. coli, S. aureus, and P. aeruginosa) at 250 µg mL⁻¹ by MIC method, while TiNPs@NZ-180 did not show antibacterial activity in all procedures performed (<500 µg mL⁻¹), indicating that AgNPs have relevance on the antibacterial activity for the nanocomposite. Therefore, nanocomposite with polymeric matrix of nanozeolite (NZ-180) incorporated with silver nanoparticles (AgNPs) have potential medical applicability as a promising antimicrobial agent, using a simple and low-cost method, correlating nanomedicine as nanostructured materials.
... Different engineered nanomaterials are present in everyday life used in products with direct exposure to humans. Several examples can be illustrated on this: Fe2O3 nanoparticles that are used in the final polish on metallic jewelry, TiO2 nanoparticles are used in food coloring, cosmetics, skin care products, and tattoo pigment [4][5][6], ZnO nanoparticles present in many products including cotton fabric, food packaging, and rubber for its deodorizing and antibacterial properties [7,8]. ...
Preprint
Nanotechnology has been one of the fastest growing fields in the last three decades. Nanomaterials (sized 1-100 nm) has a wide spectrum of potential applications in many fields, applied as coating materials or in treatment and diagnosis. Nowadays, nanoparticles of both metallic and non-metallic origin are under investigation and development for applications in various fields of biology/therapeutics. Specifically, we show the correlations between the physicochemistry and biophysical specificity of metal nanoparticles and their uptake, transport, and biodistribution in cells, at the molecular, cellular, and whole organism level. Physiologically important metals are present in the human body with a wide range of biological activities. Some of these metals are magnesium, chromium, manganese, iron, cobalt, copper, zinc, selenium and molybdenum. Metals used in nanotechnology have to be biocompatible with the human system in terms of absorption, assimilation, excretion, and side effects. These metals are synthesized in the form of nanoparticles by different physical and chemical methods. Nanotoxicological studies of metal nanoparticles are intended to determine whether and to what extent their properties may pose a threat to the environment and to human beings. An overview of metal and metal oxide nanoparticles, their applications, and the potential for human exposure is provided, and it is integrated by a discussion of general principles of nanoparticle-induced toxicity and methods for toxicity testing of nanomaterials. This review wants to focus on establishing metal nanoparticles of physiological importance to be the best candidates for future nanotechnological tools and medicines, owing to the acceptability and safety in the human body. This can only be successful if these particles are synthesized with a better biocompatibility and low or no toxicity.
... ZnO material also has broad antimicrobial activity which can act against bacteria [6], virus [7] and fungus [8]. Moreover, ZnO is also used in biological application,for example, antidandruff shampoo, calamine lotion, baby powder and antiseptic cream [9] Nowadays, ZnO is one of the materials that have been used in forensic field for fingerprint detection [10][11][12]. Fingerprint are known as epidermal reliefs that found in the phalanges of each of our fingers which the most useful form of physical evidence in distinguishes all human beings and are unrepeatable. ...
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... Apart from being a precious metal, silver is known to possess antibacterial properties [32]. Nowadays, silver nanoparticles are finding widespread applications in medical science, textile industries, and also in the treatment of water [33,34]. ...
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... As referred above, silver is also known as an antibacterial agent [14][15][16][17], in particular in its nanocrystalline form [13,15], and an excellent material for biosensor applications [11]. Akhavan et al. [18,19] reported two studies about the antibacterial effect of silver, one in which an electric field was applied in the direction of silver nanorods grown on a Ti interlayer deposited by dc magnetron sputtering, and another which reported compact Ag nanorods capped by sol-gel mesoporous TiO 2 layer, both deposited onto silicon substrates. The two studies showed a strong, fast and lasting antibacterial activity against Escherichia coli (E. ...
... The silver has long been known to keep water pure and keep external wounds clean, because it kills bacteria. This is in part due to thiol group reactions that inactivate bacterial enzymes (Akhavan and Ghaderi, 2009). Moreover, the pure silver having the highest electrical and thermal conductivity of any metal (Chen and Schluesener, 2008). ...
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The present study was carried to examine phytotoxicity or biocompability of silver nanoparticles (Ag NPs) on tomato plant (Solanum lycopersicum L.) under in vitro culture by agar medium. The effects of colloidal Ag NPs were investigated on seed germination, total chlorophyll, carotenoids and reduced carbohydrates of tomato seedlings. The plants were grown in water agar and MS medium containing 0, 2.5, 5, 10, 20, 40, 80, and 100 ppm Ag NPs. The results shown that seed germination, total chlorophyll, carotenoids and reduced sugar contents were decreased under Ag NPs exposure. On the other hand, Ag NPs caused physiological phytotoxicities in tomato plants under the present study condition.
... 8 Elham Ghaderi and Omid Akhavan found that an electric field generation was responsible for the antibacterial activity of silver nano-rods against E. Coli bacteria. 9 B. Al Nanoparticle Aluminium nanoparticle are synthesized by all three, solid phase synthesis (mechanical ball milling, mechanochemical synthesis), liquid phase synthesis (laser ablation, exploding wire, solution reduction and decomposition processes) and gas phase synthesis (gas evaporation). Yamamoto et el. ...
... Antimicrobial resistance has an importance meaning of the use, mainly the waste of antimicrobial medicines and develops when a microorganism transforms or obtains a resistance gene. So we have to achieve and attainment of modern medicines [1] has been incorporated and integrated into the coatings of food cans, in packages for meat, fish, corn, and peas to protect colors and to inhibit spoilage due to its antimicrobial properties [2]. Nanotechnology tools are improving our understanding of how bacteria work, though providing new prospects to analyze the dynamic and physical features of molecules, molecular assemblies, and intact microbial cells, either through isolation or under in vivo settings [3]. ...
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In this paper, three types of zinc oxidenanoparticles (ZnO NPs) were prepared by a wet chemical method (precipitation method), the first type was ZnONPs capped with Polyethylene Glycol (ZnONPs@PEG) and other ZnO NPs were capped with Polyvinylpyrroli-done (ZnO NPs@PVP), and the last type of ZnO NPs was provided without polymer. The samples were characterized via X-ray diffraction (XRD). The average crystal size and shape of the prepared ZnOnanopowder were determined by Transmission Electron Microscope (TEM). The antibacterial activity of the three types of ZnO NPs were tested against four types of bacteria that were Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosaand Staphylococcus, All ZnO NPs were photo-activated under the exposure to UV light at 254 nm before being applied against the four types of bacteria. The antibacterial activity of ZnO NPs was determined based on the appearance of zones of inhibition and the standard deviation was calculated for all appeared inhibition zones. The results obtained from TEM imaging revealed the formation of spherical, rods and nano flowers shapes for uncapped ZnO NPs, ZnONPs@PEG and ZnO NPs@PVPrespectively. Also, it was found that the Bacillus subtilisinhabited usingZnONPs@PEG more than using the other types of ZnO NP.
... With these so-called "electropores", for a moment, the cell membrane becomes highly permeable to exogenous substances in the surrounding media [9,10]. Although electroporation is a powerful delivery technique for many molecules [13,23], silver nanoparticles are not so easy to be delivered into living cells, because, on one hand, electroporation efficiency is influenced by many factors, such as voltage, pulse width, cell condition, operation temperature, serum concentration in electrical buffer [10][11][12]15] and on the other hand, silver nanoparticles have shown bad biocompatibility with living cells [2,24]. Therefore, the primary objective of this study is to investigate the optimal electroporation parameters for obtaining the greatest delivery efficiency and at the same time ensuring cell viability. ...
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Electroporation assisted metallic nanoparticle delivery has been shown by our previous work to significantly reduce the time of sample preparation for surface-enhanced Raman spectroscopy (SERS) measurements of biological cells. In this paper, we report our experimental work to optimize the electroporation parameters, including adjustment of the pulse pattern, operation temperature, and electroporation buffer, for fastest delivery of silver nanoparticles into living C666 cells (a human nasopharyngeal carcinoma cell line). The delivery efficiency was evaluated by the integrated intensity of whole cell SERS spectrum. Our work concluded that the silver nanoparticle delivery rate is best under the electroporation condition of using 4 consecutive 350 V (875 V/cm) rectangular electric pulses of 1, 10, 10 and 1 ms durations, respectively. Low temperature (0–4°C) is necessary for keeping cell viability during the electroporation process and it also improves the delivery efficiency of silver nanoparticles. The serum in the buffer has no obvious effect on the delivery efficiency.
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For good or bad, the immediate future of humanity is irreversibly entwined with technologies of the nanoscale. One of the great contemporary paradoxes is that solutions to global problems, such as pandemics, environmental degradation as well as lack of energy and food security, may reside in how we decide to govern materials operating at the scale of one billionth of a meter and involving probabilistic quantum effects. Increasingly scientists have began to emphasize the importance of nanotechnology in systematically alleviating the critical problems facing humanity and its biosphere. One of the main ways nanotechnology can assist in this is via artificial photosynthesis and through its contribution to ensuring a global, equitable, domestic, or locally produced source of hydrogen fuel as well as ammonia fertilizer and starch-based food. The hypothesis explored in this chapter is that nanotechnology (once appropriately regulated) will emerge in the future as a close "friend of the earth," indeed that this is nanotechnology's "moral culmination." Further, we argue that embedded within a governance challenges related to such global deployment of nanotechnology are an array of exciting opportunities for transitioning toward a billion year period of human stewardship over planetary health known as the Sustainocene. The term "Sustainocene" was developed by Canberra-based eco-physician Dr. Bryan Furnass and has been promoted and expounded by the first author and others as a way of refocusing global policy discussion about the use of new technologies (such as nanotechnology) in assisting an indefinite number of future human generations to flourish as stewards over a sustainable and biodiverse environment. © 2014 Matthew S. Hull and Diana M. Bowman Published by Elsevier Inc. All rights reserved.
Chapter
Water treatment is important to protect people from water-borne diseases. Traditional chemical disinfection creates a lot of disinfection by-products which are harmful to human health. Thus, there is a growing need for new water disinfection methods to effectively move pathogens from water sources. Nanotechnology has the potential to meet the challenge to provide new water treatment methods. In this chapter, we introduce several antimicrobial nanomaterials including oligodynamic metals (e.g., nAg), photocatalytic semiconductors (e.g., TiO2), and carbon nanomaterials (e.g., CNT) and their disinfection mechanisms. Moreover, we use cases to illustrate how these materials are designed and used in real water treatment devices.
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The present work reports study on antimicrobial activity of pure and doped ZnO nanocomposites. Polyvinyl pyrrolidone capped Mn- and Fe-doped ZnO nanocomposites were synthesised using simple chemical co-precipitation technique. The synthesised materials were characterised using transmission electron microscope (TEM), X-ray powder diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), Fourier transform infrared (FTIR) spectroscopy and ultraviolet (UV) visible spectroscopy. The XRD and TEM studies reveal that the synthesised ZnO nanocrystals have a hexagonal wurtzite structure with average crystalline size ∼7-14 nm. EDXRF and FTIR study confirmed the doping and the incorporation of impurity in ZnO nanostructure. The antimicrobial activities of nanoparticles (NPs) were studied against fungi, gram-positive and gram-negative bacteria using the standard disc diffusion method. The photocatalytic activities of prepared NPs were evaluated by degradation of methylene blue dye in aqueous solution under UV light irradiation. Experimental results demonstrated that ZnO NPs doped with 10% of Mn and Fe ions showed maximum antimicrobial and photodegradation efficiency in contrast with that of the 1% loading. The enhancement in antimicrobial effect and photocatalytic degradation is attributed to the generation of reactive oxygen species due to the synergistic effects of Mn and Fe loading.
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In this paper, ZnO nanoparticles were prepared by a wet chemical method. The sample was characterized by X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence. The average crystal size of the prepared ZnO nanopowder was determined by XRD. UV absorption spectrum revealed three bands at 448 nm, 536 nm and 818 nm respectively. The quality and purity of ZnO nanomaterial crystalline samples were confirmed by photoluminescence spectra. Disk diffusion method was used to determine the antibacterial activity of various classes of antibiotics in the presence of ZnO nanoparticles.
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The catalytic activity of a material highly had been dependent on the nature of the matrix. To address this issue, a detailed study was aimed. TiO2 nanoparticles were fabricated with an unusual anatase crystal phase and an interesting porous morphology. The development of porosity in TiO2 was skillfully achieved by using hexamine during the synthesis, followed by its selective removal by calcination at an optimum temperature. The route was found to be template‐free, green and thoroughly reproducible. Surface of the as prepared TiO2 was modified with oleic acid expecting an interaction between Lewis acidic TiO2 and electron rich oleic acid. This modification enabled adhesion of Ag nanoparticles on TiO2 surface, since oleic acid had already been reported as an effective capping agent for Ag nanoparticles. A comparison was made between the photocatalytic activities of TiO2 and TiO2‐Ag nanocomposites. This was further compared with commercial variety of TiO2. A very interesting trend was observed establishing that porous morphology of the nanoparticles could boost photocatalytic activities towards dye degradation in water medium. All the samples were systematically characterized by FTIR, XRD, XPS, BET and TEM.
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Surface modification is considered to be an important approach for improving the antibacterial activity and cytocompatibility of titanium alloys. Silver has been extensively studied for improving the antibacterial ability of implants due to its powerful antibacterial activity. Therefore, in this study, TiN/Ag multilayers were deposited on the surface of medical titanium alloys by a multi-arc ion plating system with the top TiN, Ag, and TiN and Ag composite (TiN-Ag) layers. The structure and chemical characteristics of the three groups were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) respectively. Scanning electron microscopy (SEM) was used to elucidate the cross-section structures of the multilayers. The surface topography, roughness, friction coefficients, hardness and elastic modulus values for different top layers were obtained by atomic force microscopy (AFM), wear tester and nanoindenter. The biological assays, including cytocompatibility experiments and antibacterial activity, were evaluated by MC3T3-E1 cells, bovine serum albumin (BSA) and Escherichia coli (E. coli) in vitro. These results confirm that the TiN/Ag multilayers with the exposed TiN-Ag top layer show excellent mechanical properties, antibacterial properties and ideal cytocompatibility, leading to the potential application of these multilayers as body-implanted materials.
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The adhesion of pathogenic bacteria in medical implants and surfaces is a health-related problem that requires strong inhibition against bacterial growth and attachment. In this work, we have explored the enhancement of antibacterial activity of metal free-based composites under external electric field. It affects the oxidation degree of polypyrrole- based electrodes and consequently the antibacterial activity of material. A conductive layer of carbon nanotubes (graphite) was deposited on porous substrate of polyurethane (sandpaper) and covered by polypyrrole, providing highly conductive electrodes characterized by intrinsic antibacterial activity reinforced by electro-enhanced effect due to the external electric field. The bacterial inhibition of composites was monitored from counting of viable cells at different voltage/ time of treatment and determination of biofilm inhibition on electrodes and reactors. The external voltage on electrodes reduces the threshold time for complete bacterial inactivation of PPy-based composites to values in order of 30 min for Staphylococcus aureus and 60 min for Escherichia coli.
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Metal nanoparticles (MNs) are the center of attention in different branches of applied sciences as they have unique features in comparison with bulk ones. They are very effective, low cost and stable antibacterial agents which resisting them requires many mutations. Metal nanoparticles first anchor to the bacterial cell wall and interact with thiol and phosphorus groups of respiratory enzymes resulting in their inactivation. These nanostructures can penetrate into the cell via various mechanisms that distort cell integrity leading to cell content leakage followed with weakening of proton motive force functioning and inhibition of ATP synthesis. After penetration, MNs implement denaturation in DNA and RNA molecular structures hinder cellular replication, transcription and translation mechanisms. Metal nanoparticles induce ROS generation which has a detrimental effect on cell viability. Beside, sum of these effects and mechanisms may lead to inhibition of bacterial cell division, cell disruption and the decline of bacterial populations.
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Biodegradable Zn-0.05Mg-(0.5, 1 wt.%) Ag alloy was manufactured by indirectly extruding the alloy ingot at 200 °C with an extrusion ratio of 16:1. Dynamic recrystallization took place during the extrusion process, leading to the formation of equiaxed crystals with twins in both cross-sectional and longitudinal direction. There was no detectable Ag-related phase present except the Mg2Zn11 in the alloys. Tensile strength was increased with an increase in Ag content, reaching 202 MPa when Ag content is 1 wt.%. As-extruded Zn-0.05Mg-0.5Ag showed better corrosion performance with a low corrosion current density of 2.2 A/cm² and low corrosion rate of 0.15 mm/year. The antibacterial property improved for both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) by addition of Ag. The antibacterial rates were more than 99% when Ag content is up to 1 wt.%. The biodegradable Zn-Mg-Ag alloys with high antibacterial behavior show great potential in medical devices.
Chapter
This chapter presents various substrates and their capabilities for biofilm formation, taking into account influential factors like van der Waals forces, hydrophobicity, hydrophilicity, the presence of polar side chains on polymers, and more. It includes information about natural substrates such as roots of plants and rocks (which are slimy in rivers when covered with biofilm). Also the artificial substrates of metals, ceramics, and polymers are described in terms of their interaction with bacteria and the formation/control of biofilms. Studies have been carried out with ceramic materials used in dentistry. The results showed that the greater the surface roughness in crowns, etc. the greater the accumulation of biofilm (called plaque in its hardened form). As for metals, silver has an antibacterial action that depends on the silver ion. It interrupts the ability of a bacterial cell to form chemical bonds that are necessary for survival.
Chapter
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Increased microorganisms resistance to drugs is currently a challenging problem as more powerful drugs are necessary for successful treatments. Current research is investigating for the first time reinforced bactericidal effects in wastewater resulted by simultaneous use of metallic thin films deposited on water filter papers combined with electrical power directly applied to the coated structures. Silver and copper were deposited at room temperature onto water filter papers by using high vacuum magnetron sputtering system. The metallic coated structures efficiently eliminated common types of wastewater bacteria (e.g. Escherichia coli and other coliforms). The antibacterial effects were reinforced by using electrical power applied to the structures. Increasing the electricity levels resulted in stronger bactericidal effects and subsequently shorter exposure times were required to reduce bacteria from contaminated water. Thin films adherence to filter fibers and the morphology of the coated structures were examined using digital optical microscopy and Scanning Electron Microscopy (SEM). The method used for assessing antibacterial performance was the standardized membrane filtering technique for wastewater examination. Water was collected from local basins and the bacterial content was monitored before and after exposure to uncoated, silver and copper coated filter fibers, and electrically activated metallic coated filter fibers. The metallic thin films were retained on the fibers surface after water treatment consequently reducing the nanoparticles release to the surroundings.
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Ferroelectric functional materials are known for a wide range of applications including sensors, actuators, energy harvesting devices. Very recent studies based on ferroelectric materials for environmental cleaning and bacterial remediation add a further up-and-coming field of application of these materials. They possess several advantages over conventional methods such as biocompatible range and sustainability. Although the research area is relatively new, some substantial experimental work has been done in the last couple of years. The rationale and underlying mechanisms of different published reports were compiled and explained to offer a better understanding of the subject. The three major mechanisms can be divided into catalysis via a change in surface potential, mediated catalysis by the formation of reactive oxide species on the ceramic surface due to piezoelectric or pyroelectric excitation, and enhanced photocatalysis due to internal electric fields. Our goal is to provide a comprehensive report on ferroelectric materials application in the prevention of bacterial infections and to give an outlook on further possible research strategies.
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In this study, Ag/BiOCl/diatomite composite material was prepared by simple hydrothermal method on the basis of diatomite, which has the dual effect of degrading tetracycline and inactivation of microorganisms (E. coli). The structure and properties of the composites were analyzed by various characterization methods. According to the obtained data, the degradation rate of tetracycline (TC) reached 97.8% by Ag(7.5%)/BiOCl/diatomite composites within 60 minutes of visible light irradiation. Under natural conditions, the antibacterial activity of the composite to E. coli decreased to 99.9% after 25 minutes. After three repeated experiments, the prepared composite samples still have good catalytic performance, which shows the stability of the catalyst. Finally, a possible photocatalytic degradation mechanism was proposed. Oxygen vacancies (OVs), superoxide radicals (•O2-), holes (h+) and hydroxyl radicals (•OH) are significance active substances, which play an important role in the photodegradation of TC. In this experiment, Ag/BiOCl/diatomite composite material was prepared to degrade tetracycline in water with high antimicrobial activity, which provides a simple method and has a certain application prospect.
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Green synthesis of silver nanoparticles (AgNPs) is a widely accepted approach due to its ecofriendly use of non-toxic materials. AgNPs are extensively used in the agriculture and medicine industry as antioxidant, antibacterial, and antifungal agents. In this study, AgNPs were synthesized using phytochemical sinigrin as both reducing and capping agent. Sinigrin present in cruciferous vegetables can be hydrolyzed by endogenous myrosinase (MYR) to produce allyl isothiocyanate (AITC) which has reported antibacterial properties. We hypothesized that sinigrin-capped AgNPs (SIN-AgNPs) will have enhanced antibacterial activity in the presence of MYR enzyme due to the release of AITC from hydrolysis of sinigrin. The formation of SIN-AgNPs was confirmed by UV-Vis absorption spectra which exhibited a peak around 405 nm. The particle size was determined to be ~20 nm using dynamic light scattering. The size was also confirmed through transmission electron microscopy (TEM) imaging with morphology close to spherical shape. Fourier transform infrared analysis confirmed the functional groups of sinigrin capped on the surface of AgNPs. Myrosinase gene (TGG1) sequence was cloned in pET-20b(+) plasmid and expressed in BL21(DE3) E. coli competent cells. The collected bacterial lysate was purified by immobilized metal affinity chromatography to obtain MYR protein which was characterized by SDS-PAGE, Western blot, and enzyme activity. The antibacterial efficacy was evaluated against E. coli using disc diffusion assay and growth kinetics study. Our results showed that SIN-AgNPs in combination with MYR protein exhibited ⁓25% more zone of inhibition by disk diffusion assay at a concentration of 25 µg/ml and inhibited bacterial growth for a longer time in the range of 0.5 to 1 µg/ml in growth kinetic assay.
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This study reports the synthesis of silver nanoparticles (Ag NPs) by the sodium borohydride reduction method and their embedding in a silica shell functionalized with several antibiotics (ampicillin, penicillin G and isoniazide). The characterization of the novel materials was made by UV-visible absorption spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, dynamic light scattering and thermal analysis. TEM micrographs revealed the formation of spherical nanoparticles with size ranging between 20 and 50 nm. The Ag NPs embedded in the silica network exhibited a good antimicrobial efficiency, comparable or even superior to that of antibiotic-containing formulations. This is the first report regarding the synergic antimicrobial effect of Ag NPs embedded in silica and ampicillin, both against planktonic cells and biofilms formed by P. aeruginosa and S. aureus, two of the most fearful resistant bugs. These results are demonstrating the great potential of these nanocomposites to be used in developing novel antimicrobial agents or improving the existent ones, by increasing their efficiency, extending their spectrum of activity and decreasing the probability to select resistance, by simultaneously targeting multiple targets in the microbial cells.
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A carbon monolith with a silver coating was prepared and its antimicrobial behaviour in a flow system was examined. The functional groups on the surface of the carbon monolith were determined by temperature-programmed desorption and Boehm's method, and the point of zero charge was determined by mass titration. The specific surface area was examined by N2 adsorption using the Brunauer, Emmett and Teller (BET) method. As a test for the surface activity, the deposition of silver from an aqueous solution of a silver salt was used. The morphology and structure of the silver coatings were characterized by scanning electron microscopy and x-ray diffraction. The resistance to the attrition of the silver deposited on the carbon monolith was tested. The antimicrobial activity of the carbon monolith with a silver coating was determined using standard microbiological methods. Carbon monolith samples with a silver coating showed good antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans, and are therefore suitable for water purification, particularly as personal disposable water filters with a limited capacity.
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Silver (Ag) nanomaterials with well-defined crystal structures have been rapidly synthesized in three minutes by a microwave (MW)-polyol method. Various precursors such as H2PtCl6 and Pt(acac)2 have been used to detect real roles of Pt seeds and anions for the formation of the Ag nanomaterials. Furthermore, effect of Cl− anions to final morphologies of the Ag nanostructures has also been explored by pre-adding Cl− precursor such as NaCl or KCl in the ethylene glycol (EG) solutions only including AgNO3 and poly(vinylpyrrolidone) (PVP). The experimental results show that pre-formed metallic Pt seeds are probably not responsible for nucleation and subsequent evolution of 1D Ag products, but Cl− ions indeed influence the formation of the 1D Ag nanostructures as well as perfect crystallization of other Ag nanoparticles with well-defined crystal structures including single- and twinned-FCC crystals. It has been further evidenced that the presence of Cl− ions can accelerate re-dissolution of formed spherical Ag particles and is favorable to the growth of the 1D Ag and other Ag nanostructures with well-defined crystal structures such as single-crystal cubes and twinned bi-pyramids in the MW-assisted polyol reduction process. At the same time, it also indicates that H2PtCl6 probably does not act as a nucleation agent for the 1D Ag products but as a precursor of Cl− ions to affect final morphologies of the Ag products. Possible factors affecting shape-selected process of the Ag nanostructures have been discussed in detail.
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Silver nanostructures have been synthesized by a microwave (MW)-polyol method. When AgNO3 was reduced by ethylene glycol (EG) in the presence of Pt seeds and polyvinylpyrrolidone (PVP), mixtures of one-dimensional (1-D) nanorods and nanowires, 2-D nanosheets and nanoplates, and 3-D spherical and cubic nanoparticles were prepared within a few minutes. It was found that morphologies and sizes of silver nanostructures depended strongly on such experimental parameters as concentrations of Pt, PVP, and AgNO3, and heating time. Possible growth mechanism of each silver nanostructure was discussed. The growth mechanism of nanorods was especially discussed on the basis of crystal structure of rod type of Au core-Ag shell nanoparticle.
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Silver nanorods and nanowires have been synthesized by using a microwave (MW)-polyol method. When AgNO3 was reduced by ethylene glycol (EG) in the presence of Pt seeds and a long chain length of poly(vinylpyrrolidone) (PVP: Mw = 360 k), mixtures of one-dimensional (1-D) silver nanorods and nanowires and three-dimensional (3-D) spherical, triangular-bipyramidal, and cubic nanoparticles were synthesized within a few minutes. The average diameters, lengths, and yields of these products were measured as a function of concentration of Pt, PVP, or AgNO3, heating time, or MW power to determine optimum conditions for the synthesis of 1-D products. 1-D products could be easily separated from other 3-D nanoparticles by repeating centrifugal separation in water. Longer and thicker 1-D products could be prepared by using 1-D products as seeds and repeating the reduction of AgNO3 in EG under MW irradiation. In this two-step preparation, some bent 1-D wires due to the combination of {111} facets of two rods and wires were produced. Possible growth mechanisms of 1-D products involving bent structures, and 3-D spherical, triangular-bipyramidal, and cubic nanoparticles were discussed by reference to growth mechanisms of Au core-Ag shell nanocrystals prepared using the two-step MW polyol method.
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Thermal stability of Ag layer on Ti coated Si substrate for different thicknesses of the Ag layer have been studied. To do this, after sputter-deposition of a 10 nm Ti buffer layer on the Si(1 0 0) substrate, an Ag layer with different thicknesses (150–5 nm) was sputtered on the buffer layer. Post annealing process of the samples was performed in an N2 ambient at a flow rate of 200 ml/min in a temperature range from 500 to 700 °C for 30 min. The electrical property of the heat-treated multilayer with the different thicknesses of Ag layer was examined by four-point-probe sheet resistance measurement at the room temperature. Phase formation and crystallographic orientation of the silver layers were studied by θ–2θ X-ray diffraction analysis. The surface topography and morphology of the heat-treated films were determined by atomic force microscopy, and also, scanning electron microscopy. Four-point- probe electrical measurement showed no considerable variation of sheet resistance by reducing the thickness of the annealed Ag films down to 25 nm. Surface roughness of the Ag films with (1 1 1) preferred crystallographic orientation was much smaller than the film thickness, which is a necessary condition for nanometric contact layers. Therefore, we have shown that the Ag layers with suitable nano-thicknesses sputtered on 10 nm Ti buffer layer were thermally stable up to 700 °C.
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The present work highlights the high efficiency of silver nano-particles deposited over carbon covered alumina (CCA), by electro-chemical deposition method over impregnation method, in controlling microorganisms in water. The anti-microbial activities of the catalysts are determined quantitatively by serial dilution followed by inoculation method. The catalytic characterization of these materials obtained by using transmission electron microscopy (TEM), X-ray diffraction (XRD) and temperature programmed reduction (TPR). TEM and X-ray line broadening technique results indicate the presence of Ag particles in nanometer size. The main advantage of Ag supported catalysts prepared by electro-chemical deposition over that made by conventional impregnation technique is that only small amount is needed and no pretreatment conditions like reduction are required for deactivation of microorganism in water. Thus, silver catalysts prepared by this method are not only efficient but also economical in restoring hydrogen economy. The combined characteristics of Al2O3 and carbon like low acidity, high mechanical strength and presence of meso pores in CCA are also helpful for getting good activity.
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Conductivity of silver pastes using nanoparticles was investigated with sintering temperatures. Nano-sized silver particles with 50–100nm in size were prepared by chemical reduction method. Silver pastes composed of nanoparticles (80wt%), Pb-free frit (1.0wt%) and organic vehicle (19wt%) were screen printed on alumina substrates and sintered at temperatures ranging from 250 to 450°C. As increasing the sintering temperatures, densification and grain growth were observed. When sintered at 400°C, a distinct decrease in film thickness and a sharp increase in the rate of shrinkage took place, which in turn densification was developed at this temperature. With sintering temperatures, electrical resistivity of the films decreased due to denser microstructure and the films sintered at 450°C showed 4.11μΩcm which can be compatible for various electronic devices.
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A chelating monomer, glycidyl methacrylate–iminodiacetic acid (GMA–IDA), was grafted onto cotton fibers to form cotton fiber-graft-GMA–IDA (CFGI). The quantity of GMA–IDA grafting on CFGI was dependent on the concentration of GMA–IDA solution in the reaction system. The weight of Ag+ adsorbed by CFGI increased with increasing the amount of GMA–IDA on CFGI. After the CFGI–Ag+ complexes were irradiated by ultraviolet lamp, scanning electron microscope and energy-dispersive X-ray spectrometer confirmed that CFGI/silver nanocomposites were prepared successfully. As the weight of Ag+ adsorbed by CFGI increased, the diameter of the Ag nanoparticles increased. The cotton fibers containing Ag nanoparticles with an average size of 75 nm exhibited high antibacterial activity against Escherichia coli.
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Silver nanoparticles have been prepared in a hyperbranched polyamine matrix by using a reductive technique. The hyperbranched polyamine has been synthesized by an A2+B3 approach using 2,4,6-trichloro-1,3,5-triazine and 4,4′-(4,4′-isopropylidene diphenyl-1,1′-diyldioxy) dianiline in the presence of diisopropyl ethyl amine as an active base. The synthesized hyperbranched polyamine and silver nanoparticles were characterized by different spectroscopic and analytical techniques such as FT-IR, UV–vis, 1H NMR, 13C NMR, elemental analysis, solution viscosity, X-ray diffraction, TEM, etc. UV–vis and TEM studies confirm the formation of well-dispersed nanoparticles with average size of 7.2nm. The thermal behavior of pure polymer and polymer with silver nanoparticles has been studied by thermogravimetric (TG) analysis and differential scanning calorimetric (DSC) studies. These studies indicate the enhancement of thermostability of 40°C and an increment of 34°C in glass transition temperature (Tg) of polyamine with silver nanoparticles compared to pure polyamine. The antibacterial activity of silver nanoparticles was tested against Bacillus subtilis and Staphylococcus aureus bacteria at different concentrations by using the diffusion disc technique. The result shows that the antibacterial activity increases with the increase of concentration of the active agent.
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We have recently demonstrated an approach based on the polyol process for the large-scale synthesis of silver nanowires with uniform diameters (see Sun, Y.; Gates, B.; Mayers, B.; Xia, Y. Nano Lett. 2002, 2, 165. Sun, Y.; Xia, Y. Adv. Mater. 2002, 14, 833. Sun, Y.; Yin, Y.; Mayers, B. T.; Herricks, T.; Xia, Y. Chem. Mater. 2002, 14, 4736). Although the capability and feasibility of this method have been successfully illustrated with the production of silver nanowires 30−60 nm in diameter and 1−50 μm in length, the growth mechanism of this process is yet to be elucidated. Here we report some progress on this matter:  First, electron microscopy studies on microtomed samples indicated that the cross sections of such silver nanowires had a pentagonal shape, together with a 5-fold twinned crystal structure. Second, the side surfaces (bounded by {100} facets) and the ends (bounded by {111} facets) of each nanowire were shown to have significant difference in reactivity toward dithoil molecules, with the side surfaces being completely passivated by poly(vinyl pyrrolidone) (PVP) and the ends being partially passivated (or essentially uncovered) by PVP. This result implied that the PVP macromolecules interacted more strongly with the {100} planes than with the {111} planes of silver. On the basis of these new results, we proposed that each silver nanowire evolved from a multiply twinned nanoparticle (MTP) of silver with the assistance of PVP at the initial stage of the Ostwald ripening process. The anisotropic growth was maintained by selectively covering the {100} facets with PVP while leaving the {111} facets largely uncovered by PVP and thus highly reactive.
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This paper describes a soft, solution-phase approach to the large-scale synthesis of uniform nanowires of bicrystalline silver whose lateral dimensions could be controlled in the range of 30−40 nm, and lengths up to 50 μm. The first step of this procedure involved the formation of platinum nanoparticles by reducing PtCl2 with ethylene glycol heated to 160 °C. Due to their close match in crystal structure and lattice constants, these platinum nanoparticles could serve as seeds for the heterogeneous nucleation and growth of silver that was produced in the solution via the reduction of AgNO3 with ethylene glycol. When surfactants such as poly(vinyl pyrrolidone) (PVP) were present in this solution, the silver could be directed to grow into uniform nanowires with aspect ratios as high as 1000. Measurements of transport property at room temperature indicated that these nanowires were electrically continuous with a conductivity of approximately 0.8 × 105 S/cm.
Article
Silver (Ag) nanowires with a pentagonal cross section have been synthesized by polyvinylpyrrolidone (PVP)-assisted polyol reduction in the presence of Pt nanoparticle seeds. The UV–visible absorption spectra and scanning electron microscopy have been used to trace the growth process of the Ag nanowires. X-ray photoelectron spectroscopy investigation further shows that the PVP molecules are adsorbed on the surface of the Ag nanowires through Ag : O coordination. Comparing with the growth process of Ag nanoparticles, a possible growth mechanism of the Ag nanowires has been proposed. It is implied that the PVP molecules are used as both a protecting agent and a structure-directing agent for the growth of Ag nanowires. It is concluded that the five-fold twinning Ag nanoparticles are formed through heterogenous nucleation after the introduction of Pt nanoparticle seeds and then grow anisotropically along the 110 direction, while the growth along 100 is relatively depressed.
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Homogeneous glasses in the Na2O–B2O3–Al2O3–SiO2 system doped with proper amount of AgCl were obtained by melting at a temperature of 1450 �C. Then, with several steps of treatment, including crystallization, elongation and reduction, the glass with oriented arrangement of needle-like micro–nano silver particles was produced. The microstructure and the optical properties of the glass samples in different stages were studied by SEM-EDAX, FE-SEM and UV–Vis spectrum. The results showed that the glass after elongation and reduction exhibits excellent polarization performance in the wavelength range from 600 nm to 900 nm, with an extinction ratio larger than 45 dB. The glass only elongated shows also slight polarizing performance, which may result from the formation of filament structure of Ag during elongation processing.
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Silver nanoparticles obtained by the electro-exploding wire technique were used to deposit on polypyrrole films prepared electrochemically. The presence of silver nanoparticles deposited was confirmed by X-ray diffraction. Energy dispersive X-ray spectroscopy was used to estimate the amount of silver nanoparticles deposited on polypyrrole.The current–voltage characteristics obtained from scanning tunneling microscopy showed remarkable changes in the electrical and the electronic properties of polypyrrole, which was also observed by the conventional two-probe method.The new approaches are the novel process used to produce pure silver nanoparticles and the simple and clean electro-deposition without the use of any chemical agents.
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The aqueous-phase synthesis of crystalline silver nanowires with different aspect ratios has been achieved by altering seeds. Cyclic voltammetry and tafel results showed that silver nanowires with high aspect ratio exhibited better activity and alcohol-tolerant stability for oxygen electroreduction in alkaline media than nanowires with low aspect ratio.
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This paper deals with the antibacterial efficacy of nanosized silver colloidal solution on the cellulosic and synthetic fabrics. Two kinds of Bacteria; Gram-positive and Gram-negative, were used. TEM observation of silver nanoparticles showed their shape, and size distribution. The particles were very small (2–5 nm) and had narrow distribution. SEM images of treated fabrics indicated silver nanoparticles were well dispersed on the surfaces of specimens. WAXS patterns did not show any peak of silver as the fabric had very small quantity of silver particles. However, ICP-MS informed the residual concentration of silver particles on fabrics before/after laundering. The antibacterial treatment of the textile fabrics was easily achieved by padding them with nanosized silver colloidal solution. The antibacterial efficacy of the fabrics was maintained after many times laundering.
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Two SiO2 supported Ag catalysts with 5 wt% Ag in each were prepared by impregnation and radiolysis methods. These catalysts were characterized by BET surface area, temperature programmed reduction (TPR) and X-ray diffraction techniques. TPR results indicate the presence of metallic silver in the catalyst prepared by radiolysis method whereas Ag+ precursor is formed in the catalyst prepared by impregnation method. The Ag particle size as calculated from the XRD patterns, in the catalyst prepared by radiolysis method is relatively smaller compared to that of the impregnated catalyst. The two catalysts are tested for decomposition of N2O and it is observed that the catalyst prepared by radiolysis gives higher conversion and better N2 selectivity. These results suggest that radiolysis method yields metallic Ag nanoparticles directly without any reduction treatment and that the catalyst exhibits good activity in N2O decomposition.
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In this study, we investigated the antimicrobial activity of silver nanoparticles (Ag-NPs) and platinum nanoparticles (Pt-NPs) aqueous solution, which were prepared using different stabilizer, such as sodium dodecylsulfate (SDS) and poly-(N-vinyl-2-pyrrolidone) (PVP), for Staphylococcus aureus (S. aureus) and Escherichia coli (E.coli) by measuring the minimum inhibitory concentration (MIC). Antimicrobial effect of Ag-NPs for S. aureus and E. coli was investigated using cup diffusion method. The growth of Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria were inhibited by Ag-NPs. The MIC of Ag-NPs for S. aureus and E. coli were 5 and 10 ppm, respectively. But the Au-NPs stabilized with SDS did not show antimicrobial activity. Also, the Pt-NPs stabilized with PVP (or SDS) did not show antimicrobial activity for the test organisms.
Article
Silver (Ag) nanodecahedrons have been synthesized for the first time by liquid-phase reduction of AgNO3 with assistance of polyvinylpyrrolidone (PVP) in a large scale. The edge size of Ag decahedrons is estimated to be ca. 80 nm. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) have been employed to elucidate the five-twinned structure of Ag decahedrons. The results show that the Ag decahedrons capped by PVP molecules hold five-twinning structure with distinct twinning boundaries. The growth process of Ag decahedrons has been investigated and their growth mechanism has been proposed. Combined with our previous reports on Ag nanowires with pentagonal cross section, it is revealed that the Ag nanodecahedrons might be assembled from five tetrahedrons step by step. Further studies on the role of PVP conformation in different solution reduction systems are required.
Article
Silver quantum dots (QDs) embedded silica/PAAc hybrid nanoparticles were prepared by copolymerization of acrylic acid (AAc) onto γ-Methacryloxypropyltrimethoxysilane (MPS) modified silica nanoparticles followed by reduction of the immobilized Ag+ ions to metallic Ag. The prepared hybrid nanoparticles were characterized using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The hybrid nanoparticles dispersed well in aqueous media and showed effective bactericidal activities. The results suggest that the hybrid nanoparticles have potential application as a water-soluble agent in many fields.
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A technique for synthesizing a composite electrode structure comprised of silver nanowires and carbon nanotubes (CNTs) for use as cathode catalysts in alkaline fuel cells was developed. The Ag nanowires were produced using electroless template-based deposition and sprayed as an electrocatalytically active surface coating on CNT matrices. Four different types of electrodes were prepared; blank matrices of CNTs and PTFE, CNTs and PTFE matrices sprayed with a layer of CNTs, CNTs and PTFE matrices sprayed with a layer of CNTs and 5 wt% Ag nanowires, and CNTs and PTFE matrices sprayed with a layer of CNTs and 9 wt% Ag nanowires. The catalytic performance with respect to the oxygen reduction reaction (ORR) was determined utilizing potential step voltammetry. The electrochemical test results showed that the electrode activity increased with increasing Ag concentration when mixed with CNTs.
Article
The super-resolution near-field structure (super-RENS) is a high-density near-field optical data storage medium which can achieve superior spatial resolution beyond the diffraction limit. Our previous studies found that enhanced local optical intensity occurred at the near fields of super-RENS disks, and the nonlinear near-field optical enhancement is related to the localized surface plasmons of silver clusters dissociated from the AgOx layer in the super-RENS disks. In this paper, we studied the near-field and far-field properties of AgOx-type super-RENS with different distributions of silver nanoparticles using finite-difference time-domain (FDTD) simulations. Highly localized enhancements are found between adjacent silver nanoparticles in the near fields. The far-field signals of different silver nanoparticles distributions confirm the super-resolution capability of AgOx-type Super-RENS disks, and a simplified Fourier optics model is used to describe the relation between highly localized near-field distributions and enhanced resolution of far-field signals.
Over the last decade, staphylococci with reduced susceptibility to vancomycin have been reported with increasing frequency. The appearance of Staphylococcus aureus isolates with thickened cell walls for which the vancomycin MICs were 8 or 16 μg/ml (vancomycin-intermediate S. aureus, or VISA) were followed by reports of isolates for which the vancomycin MICs were ≥ 32 pg/ml (vancomycin-resistant S. aureus, or VRSA). The latter isolates harbor the vanA vancomycin resistance gene from enterococci. Both VISA and VRSA isolates may escape detection in the clinical microbiology laboratory, depending on the method of susceptibility testing in use. The use of a brain heart infusion agar plate containing 6 pg of vancomycin/ml can aid in detecting these clinically significant isolates. The clinical significance and optimal methods for detecting heterogeneously vancomycin-intermediate S. aureus (hVISA) isolates remains controversial.
Article
Uniform silver (Ag) nanowires with an average length of 6 μm and diameter of 70 nm have been synthesized via PVP-assisted (polyvinylpyrrolidone, PVP-K30) polyol reduction. The structure of thus-obtained Ag nanowires has been investigated thoroughly through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Combined with the previous results, it is concluded that the Ag nanowires possess five-fold twinned crystal structure with [1 1 0] growth direction, bounded by five [1 0 0] planes and capped by ten [1 1 1] planes. The SAED of the pentagonal cross-section gives direct evidence of the five-fold symmetry of the Ag nanowires. The high-resolution TEM image clearly shows the five twinning boundaries with various defects. UV–visible absorption spectra, which are related to the well-defined structure of the Ag nanowires, exhibit unique transversal modes of the Ag nanowries. IR spectra of the Ag nanowires, compared with the pure PVP, indicate that the Ag atoms on the surface of the Ag nanowires are coordinated with oxygen atoms in the carbonyl group of the PVP. It has been proposed that the PVP main chain might lie on the surface of the Ag nanowires with the pyrrolidone ring tilted on them.
Article
Chronic wounds such as leg ulcers and pressure ulcers are often slow to heal. One of the causes of delayed wound healing is the presence of micro-organisms in the wound. A strategy for the prevention and treatment of wound colonisation or infection, which is receiving renewed attention, is the use of silver-based dressings. Silver has been used as an antimicrobial agent for centuries. It is effective against a broad range of bacteria (including methicillin and vancomycin-resistant strains), yeast, fungi and viruses. A number of new silver-based dressings, some of which act by the sustained release of silver ions to the wound bed, have recently become available, but there are wide variations in the amount of data supporting the use of individual products. This article reviews the evidence base for silver-containing dressings to help practitioners select the most appropriate product for the type of wound being treated.
Article
The bacterial inactivation efficiencies of silver metal and oxides and their combinations on textile fabrics was investigated to evaluate the disinfectant action on airborne bacteria. The inactivation performance was seen to depend on the amount of silver on the textile surface. The preparation of the polyester-polyamide Ag-loaded textiles was carried out by RF-plasma and vacuum-UV (V-UV) surface activation followed by chemical reduction of silver salts. The rate of bacterial inactivation by the silver loaded textile was tested on Escherichia coli K-12 and showed long lasting residual effect. Specular reflectance has been employed to assess the optical properties of the Ag-loaded fabrics. By elemental analysis it was found that levels of Ag loading >0.118% (w/w) for the vacuum-UV samples lead to complete inhibition of bacterial growth. X-ray photoelectron spectroscopy (XPS) shows that for textiles activated by RF or V-UV methods, the silver in the topmost layer increases with increasing concentration of the Ag used in the precursor solution. The exact determination of the oxidation state of the Ag-clusters on the textile is difficult because of the variation of particle size and electrostatic charging of the supported particles. Ag metal was found to be the main component of the Ag-clusters and not Ag2O and AgO as identified by the binding peak energies (BE). By transmission electron spectroscopy (TEM) it was seen that the Ag-clusters were deposited on the two polymer components of the textile fabric but having widely different sizes. (C) 2003 Elsevier Science B.V. All rights reserved.
Article
The inhibitory and bactericidal concentrations of electrically generated silver ions were 10 to 100 times lower than for silver sulfadiazine. Effects on normal mammalian cells were minimal.