Spontaneous formation of silver nanoparticles in aminosilica

We report a rapid and spontaneous metallization process associated with sol–gel reaction of aminosilane that can be utilized to synthesise silver embedded silica nanocomposite without involving additional reducing agents. The reduction reaction induced by bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS) involves amine functional moieties, which drive the reduction reaction with presence of water. Cyclic voltammetry was used to investigate the redox potential of enTMOS and its relation to chemical environment. It was found that the oxidation potential of enTMOS depending on the amount of water (water:enTMOS (v/v) = 8:1–0:1) ranges from 0.48 to 0.68 V versus Ag/AgCl electrode in methanol. The oxidation potential of aminosilane decreases with water content and becomes more negative than that of Ag, suggesting the aminosilane acts as a silver reducing agent while serving as a matrix to encapsulate silver nanoparticles after reacting with water. This process has been utilized to produce evenly dispersed silver nanoparticles with sizes ranging from 5 to 20 nm in both liquid and solid forms of aminosilane, allowing us to prepare silver nanoparticles doped silica nanocomposite that exhibits enhanced electrochemical properties.     

Chitosan aerogel containing silver nanoparticles: From metal-chitosan powder to porous material

The work presents a synthetic approach that combines methods of metal vapor synthesis (MVS), gelation and supercritical drying in order to obtain chitosan aerogels containing silver nanoparticles. On the first stage, two types of silver organosols were prepared via the eco-sustainable MVS method. Then the prepared silver organosols were used to modify chitosan powders for producing metal-chitosan powder composites. Gelation of the powder composites was performed in oxalic acid at elevated temperatures. Supercritical drying of the gels was implemented in order to preserve the formed porous structures. Thus, the chitosan powders modified with MVS-produced silver nanoparticles were used to prepare metal-chitosan aerogels. Characterization of the structure and the morphology of both powder and aerogel silver-chitosan composites was conducted by means of low temperature nitrogen adsorption, X-ray photoelectron spectroscopy, X-ray powder diffraction, small-angle X-ray scattering, SEM and TEM. Changes in the structure and morphology of silver nanoparticles between powder and aerogel composites were analyzed.     

Keratin capped silver nanoparticles--synthesis and characterization of a nanomaterial with desirable handling properties

We report for the first time the stabilization of silver nanoparticles in good yield, average diameter 3.5 nm, using wool keratin hydrolysates as stabilizers. The nanoparticles are extremely stable as a suspension and can be lyophilized into a powder and easily reconstituted in solvent with no change in spectral properties relative to the initial suspension. The nanoparticles interact with nitrogen and oxygen moieties of the keratin hydrolysates under the pH conditions used in the synthesis and appear to act as cross-linkers between adjacent chains. The product has excellent handling properties which we believe will make it a very attractive biocompatible coating/additive, providing prolonged antimicrobial efficacy to a wide variety of products such as textiles, plastics, paints, orthopedic devices and others.     

Antioxidant and antibacterial activity of silver nanoparticles biosynthesized using Chenopodium murale leaf extract

Silver is known for its antimicrobial effects and silver nanoparticles are gaining their importance due to their antimicrobial activities. The aims of the current study were to use plant extract for the biosynthesis of silver nanoparticles and to evaluate their antibacterial and antioxidant activity in vitro. The results indicated that silver nanoparticles (AgNPs) can be synthesized in a simple method using Chenopodium murale leaf extract. The TEM analysis showed that the sizes of the synthesized AgNps ranged from 30 to 50 nm. The essential oil of C. murale leaf extract was formed mainly of α-Terpinene, (Z)-Ascaridole and cis-Ascaridole. The total phenolic compounds and total flavonides were higher in AgNPs-containing plant extract compared to the plant extract. AgNPs-containing leaf extract showed a higher antioxidant and antimicrobial activity compared to C. murale leaf extract alone or silver nitrate. It could be concluded that C. murale leaf extract can be used effectively in the production of potential antioxidant and antimicrobial AgNPs for commercial application.     

Interplay between amphiphilic peptides and nanoparticles for selective membrane destabilization and antimicrobial effects

As a result of an increasing number of bacteria developing resistance against antibiotics, antimicrobial peptides (AMPs) are attracting significant interest, particularly in relation to identification of peptides displaying potent but selective effects. Much less focus has been placed on delivery systems for AMPs, despite AMPs suffering from delivery challenges related to their size, cationicity, and amphiphilicity. Inorganic nanoparticles may provide opportunities for controlling peptide release, reducing infection-related AMP degradation, or increasing bioavailability. Numerous such nanomaterials display potent and triggerable antimicrobial effects on their own. When combined with AMPs, combinatorial and synergistic effects in relation to the behavior of such mixed systems as antimicrobials have been observed. The mechanistic origin of these effects are poorly understood that at present, however, precluding rational design of mixed nanoparticle antimicrobials/AMPs and nanoparticulate delivery systems for AMPs. Here, the area of membrane interactions and antimicrobial effects of inorganic nanomaterials are briefly outlined, in combination with AMPs.     

Evaluating the antimicrobial activity and cytotoxicity of polydopamine capped silver and silver/polydopamine core-shell nanocomposites

Fabrication of bioactive nanomaterials with improved stability and low toxicity towards healthy mammalian cells have recently been a topic of interest. Bioactive metal nanomaterials such as silver nanoparticles (AgNPs) tend to lose their stability with time and become toxic to some extent, limiting their biological applications. AgNPs were separately encapsulated and loaded on the surface of a biocompatible polydopamine (PDA) to produce Ag-PDA and Ag@PDA nanocomposites to unravel the issue of agglomeration. PDA was coated through the self-polymerization of dopamine on the surface of AgNPs to produce Ag-PDA core-shells nanocomposites. For Ag@PDA, PDA spheres were first designed through self-polymerization of dopamine followed by in situ reduction of silver nitrate (AgNO3) without any reductant. AgNPs sizes were controlled by varying the concentration of AgNO₃. The TEM micrograms showed monodispersed PDA spheres with an average diameter of 238 nm for Ag-PDA and Ag@PDA nanocomposites. Compared to Ag@PDA, Ag-PDA nanocomposites have shown insignificant toxicity towards human embryonic kidney (HEK-293T) and human dermal fibroblasts (HDF) cells with cell viability of over 95% at concentration of 250 µg/mL. A excellent antimicrobial activity of the nanocomposites was observed; with Ag@PDA possessing bactericidal effect at concentration as low as 12.5 µg/mL. Ag-PDA on the other hand were only found to be bacteriostatic against gram-positive and gram-negative bacteria was also observed.     

Ganoderma applanatum-mediated green synthesis of silver nanoparticles: Structural characterization,and in vitro and in vivo biomedical and agrochemical properties

This study presents the use of basidiomycete extracts as an effective platform for “green synthesis” of silver nanoparticles (AgNPs). Out of seven basidiomycete species, Ganoderma applanatum displayed the highest antimicrobial properties against the tested pathogens. Thus, G. applanatum methanol crude extract was fractionated using column chromatography, and the obtained fractions were subjected to an antimicrobial assay followed by phytochemical analyses using high-performance liquid chromatography to select the best fraction for synthesis of AgNPs. Fraction 3 displayed potent antimicrobial activities as evidenced by its high phenolic content, and thus was used for AgNP biosynthesis. The G. applanatum fraction 3-synthesized AgNPs were then characterized using various microscopy, spectroscopy and X-ray diffraction techniques. The characteristic features of the synthesized AgNPs indicated the spherical shape of AgNPs with an average size of 20–25 nm. The synthesized AgNPs exhibit high antioxidant capacity, in vitro antibacterial activity against Staphylococcus aureus and Escherichia coli, and in vivo antifungal properties against Botrytis cinerea and Colletotrichum gloeosporioides in tomato and strawberry leaflet assays, respectively. Our results demonstrated that G. applanatum can be efficiently used in synthesis of AgNPs with potent antimicrobial properties, which can be used for both clinical and agrochemical purposes.     

Electrospinning of ultrafine cellulose acetate fibers: Studies of a new solvent system and deacetylation of ultrafine cellulose acetate fibers

Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004     

Biodegradable electrospun poly(l-lactide) fibers containing antibacterial silver nanoparticles

Biodegradable poly(l-lactide) (PLA) ultrafine fibers containing nanosilver particles were prepared via electrospinning. Morphology of the Ag/PLA fibers and distribution of the silver nanoparticles were characterized. The release of silver ions from the Ag/PLA fibers and their antibacterial activities were investigated. These fibers showed antibacterial activities (microorganism reduction) of 98.5% and 94.2% against Staphylococcus aureus and Escherichia coli, respectively, because of the presence of the silver nanoparticles.     

Hexazamacrocycle assisted sensing of silver ion through facile synthesis of silver nanoparticles

The ease of generation of silver nanoparticles by using hexazamacrocycle ligand, L1 is utilized for the visual detection of the presence of silver ions at lower concentrations.     

Phytogenic-mediated silver nanoparticles using Persicaria hydropiper extracts and its catalytic activity against multidrug resistant bacteria

Multidrug resistance (MDR) is one of the major global threats of this century. So new innovative approaches are needed for the development of existing antibiotics to limit antibacterial resistance. The current study was aimed to utilize extracts of root, stem, and leaves of Persicaria hydropiper for the synthesis of silver nanoparticles (AgNPs) using standard procedure. Synthesis of AgNPs was evident from the change in color of the solution to dark brownish and then it was further revealed by UV–Vis and Fourier Transformed Infrared Spectroscopy (FTIR). UV–Vis spectroscopy has revealed absorbance peak at 370 nm while, FTIR spectrum displayed that aromatics amines were used as reducing agent in the fabrication of AgNPs. In addition, Scanning Electron Microscopy (SEM micrograph) displaying tetrahedron, spherical and oval shapes of synthesized AgNPs whereas, average size of synthesized AgNPs was found in the range of 32–77 nm. Beside this, it was also observed that the potency of antibiotics against MDR bacteria increased after coating with synthesized AgNPs i.e., the potency of Ceftazidime and Ciprofloxacin increased up to 450% and 500% against Bacillus respectively while, the potency of Gentamicin, Vancomycin and Linezolid increased up to 150%, 200% and 58% against Bacillus, Staphylococcus, and Proteus species respectively. Furthermore, it was concluded that utilizing AgNPs in combination with commercially available antibiotics would provide an alternate therapy for the treatment of infectious diseases caused by MDR bacteria.     

Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis

Colloidal silver nanoparticles were synthesized by an easy green method using thermal treatment of aqueous solutions of silver nitrate and natural rubber latex (NRL) extracted from Hevea brasiliensis. The UV–Vis spectra detected the characteristic surface plasmonic absorption band around 435 nm. Both NRL and AgNO₃ contents in the reaction medium have influence in the Ag nanoparticles formation. Lower AgNO₃ concentration led to decreased particle size. The silver nanoparticles presented diameters ranging from 2 nm to 100 nm and had spherical shape. The selected area electron diffraction (SAED) patterns indicated that the silver nanoparticles have face centered cubic (fcc) crystalline structure. FTIR spectra suggest that reduction of the silver ions are facilitated by their interaction with the amine groups from ammonia, which is used for conservation of the NRL, whereas the stability of the particles results from cis-isoprene binding onto the surface of nanoparticles. Therefore natural rubber latex extracted from H. brasiliensis can be employed in the preparation of stable aqueous dispersions of silver nanoparticles acting as a dispersing and/or capping agent. Moreover, this work provides a new method for the synthesis of silver nanoparticles that is simple, easy to perform, pollutant free and inexpensive.     

Ecofriendly synthesis of silver nanoparticles using Kei-apple (Dovyalis caffra) fruit and their efficacy against cancer cells and clinical pathogenic microorganisms

Green fabrication has become a safe approach for producing nanoparticles. Plant-based biogenic synthesis of silver nanoparticles (AgNPs) has emerged as a possible alternative to traditional chemical production. In this paper, we provide a low-cost, green synthesis of AgNPs utilizing using Kei-apple (Dovyalis caffra) fruit extract. Ultraviolet–visible (UV–Vis) spectroscopy, Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Scanning-Electron Microscope (SEM), and Dynamic Light Scattering (DLS) analyses were used to characterize green produced AgNPs. The formation of AgNPs was shown to have a surface resonance peak of 415 nm in UV–visible spectra, and FTIR spectra verified the participation of biological molecules in Synthesis of AgNPs. The TEM revealed that the biosynthesized AgNPs were mostly spherical in form, with size range of 12–53 nm. XRD diffractogram was used to demonstrate the face cubic centre (fcc) character of AgNPs. Excellent anticancer activity of AgNPs was recorded where more than 80% of Prostate Cancer (PC-3) cell lines was inhibited by 100–150 µg/mL of AgNPs, while 38% only was recorded using AgNO₃ and 55.62% was recorded D. caffra fruit extract at 150 µg/mL. Destructions of PC-3 cell was observed as a result of exposed to AgNPs, followed by D. caffra fruit extract, while minor alterations were recorded as exposed to AgNO₃. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) scavenging using AgNPs was three fold using fruit extract at 100 µg/mL indicating good antioxidant activity. Excellent inhibitory activity of AgNPs was recorded against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus fumigatus with inhibition diameter zone 28.22 ± 0.25 mm, 23.21 ± 0.35 mm, 27.25 ± 0.03 mm, 28.40 ± 0.15 mm, 29.23 ± 0.44 mm, and 9.52 ± 0.5 mm, respectively compared with AgNO₃. D. caffra fruits considered a promising and safe source for fabrication of AgNPs with multi-biological functions.     

Paramagnetic behaviour of silver nanoparticles generated by decomposition of silver oxalate

Silver oxalate Ag₂C₂O₄, was already proposed for soldering applications, due to the formation when it is decomposed by a heat treatment, of highly sinterable silver nanoparticles. When slowly decomposed at low temperature (125 °C), the oxalate leads however to silver nanoparticles isolated from each other. As soon as these nanoparticles are formed, the magnetic susceptibility at room temperature increases from −3.14 10⁻⁷ emu.Oe⁻¹.g⁻¹ (silver oxalate) up to −1.92 10⁻⁷ emu.Oe⁻¹.g⁻¹ (metallic silver). At the end of the oxalate decomposition, the conventional diamagnetic behaviour of bulk silver, is observed from room temperature to 80 K. A diamagnetic-paramagnetic transition is however revealed below 80 K leading at 2 K, to silver nanoparticles with a positive magnetic susceptibility. This original behaviour, compared to the one of bulk silver, can be ascribed to the nanometric size of the metallic particles.     

Spin-crossover nanoparticles and nanocomposite materials

This contribution reports on the state of the art of the elaboration and the application of nanoparticles (NPs) and nanohybrid/nanocomposite materials based on spin-crossover (SCO) complexes. The first part of this review concerns the syntheses and the characterizations of the physical properties of SCO NPs. All of the methods including homogeneous and heterogeneous media syntheses developed for the elaboration of such NPs and the associated methods used for their morphological characterization are presented. A particular attention is paid on the effects of the size reduction and the influence of the environment on the SCO properties and to specific and recent remarkable advanced physical measurements realized on a batch of NPs or on an isolated object. The second part presents the elaboration of various nanocomposite or nanohybrid materials for which SCO NPs have been associated with magnetic entities, noble metals, different fluorescent dyes, and different active polymers with the objectives to go toward specific applications based on synergistic effects between the two components.     

Phytofabrication of silver nanoparticles from Limonia acidissima leaf extract and their antimicrobial,antioxidant and its anticancer prophecy

Green synthesis of nanoparticles by eco-friendly methods is a recent technique which draws the attention of researchers because of the reward over many conventional chemical methods. The present work focuses on aqueous Limonia acidissima leaf extract in synthesizing silver nanoparticles and its applications in a simple way. The silver nanoparticles formed were characterized by Infrared, Ultra violet-visible, X-ray diffraction, transmission electron microscopic, and atomic force microscopic techniques. The powder X-ray diffraction studies and transmission electron microscopic images reveal that the silver nanoparticles synthesized were approximately 10–40 nm and have a spherical structure. The nanoparticles were assayed for their antibacterial, antifungal and antioxidant activity. The antimicrobial studies for the silver nanoparticles show a maximum zone of inhibition of 8.8 mm for Bacillus subtilis bacteria and 8.5 mm for Candida albicans fungi at 3 and 1 μg/mL respectively. In-silico ADMET studies reveal that the toxicity, bioactivity, pharmacokinetics and drug-likeness properties of Limonia acidissima leaf extract is good. The molecular docking studies show that the microbial activity is high for Bacillus subtilis and Candida albicans showing the coincidence of the in silico and in vitro studies as expected. The free radical scavenging activity of nanoparticles is 80 for 100 μg/mL. The 50% of inhibition of silver nanoparticles against human breast cancer cell lines is 18 μg/mL. It is evident that silver nanoparticles would be helpful in treating cancer cell lines and have great perspectives in the biomedical sector.     

Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Silver nanoparticles were synthesized by UV irradiation of [Ag(NH₃)₂]⁺ aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag₂O was much quicker than that from AgNO₃, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength (λ_max) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH₃)₂]⁺ (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (25 °C).     

A comparative study of the antibacterial mechanisms of silver ion and silver nanoparticles by Fourier transform infrared spectroscopy

In this study, we performed the first comparative study of the antibacterial mechanisms of silver ion (Ag⁺) and silver nanoparticles (AgNPs) on Escherichia coli (E. coli) using Fourier transform infrared (FTIR) spectroscopy. Through a thorough analysis of the FTIR spectra of E. coli after silver treatment in the spectral regions corresponding to thiol group, protein, lipopolysaccharide (LPS), and DNA, we were able to reveal a multifaceted antibacterial mechanism of silver at the molecular level for both Ag⁺ and AgNPs. Features of such mechanism include: (1) silver complexes with thiol group; (2) silver induces protein misfolding; (3) silver causes loss of LPS from bacterial membrane; (4) silver changes the overall conformation of DNA. Despite the similarities between Ag⁺ and AgNPs with respect to their antibacterial mechanisms, we further revealed that Ag⁺ and AgNPs display quite different kinetics for silver-thiol complexation and loss of LPS, with Ag⁺ displaying fast kinetics and AgNPs displaying slow kinetics. At last, we proposed a hypothesis to interpret the observed different behaviors between Ag⁺ and AgNPs when interacting with E. coli.     

Morphology and size-controlled synthesis of silver nanoparticles in aqueous surfactant polymer solutions

We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies. The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter were obtained when 1 wt% aqueous starch solution of AgNO₃ precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized by NaOH reduction of AgNO₃ in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time.