Search

Silver nanoparticles were obtained in MeCN/0.05 M Bu4NPF6 medium by сyclobis(paraquat-p‑phenylene)-mediated reduction of the silver ions generated by anodic oxidation of metallic silver during the electrolysis in an undivided cell. Due to multipoint donor–acceptor interaction, the сyclobis(paraquat-p‑phenylene) binds the resulting electron-donor silver nanoparticles to each other, which leads to their enlargement, aggregation, and adsorption. This property of the macrocycle allows calling the сyclobis(paraquat-p-phenylene) a molecular glue for silver nanoparticles. In the absence of stabilizers, aggregated polydisperse silver nanoparticles of indeterminate shape are formed, sized 20 to 500 nm. Electrosynthesis in the presence of polyvinylpyrrolidone as a stabilizer also leads to the formation of aggregated smaller (55 ± 26 nm) metal particles which have, in addition to the quasi-spherical shape, the shape of a flat triangle and hexagon. Silver nanoparticles stabilized by polyvinylpyrrolidone are partially bound on the surface of nanocellulose. In the presence of nanocellulose, larger silver nanoparticles with an average size of 97 ± 29 nm are formed, mainly shaped quasi-spherical; cubic, tetrahedral, and rod-shaped silver nanoparticles are also formed; no silver nanoparticles with a flat structure has been formed. The catalytic activity of the obtained particles in the reduction of p-nitrophenol by sodium borohydride is extremely low due to their large size, aggregation, and coating of the silver nanoparticles' surface with the stabilizer polyvinylpyrrolidone and macrocycles. [ABSTRACT FROM AUTHOR]

Wound dressings were prepared by using polyethylene terephthalate (PET) fabric as the base material. The functionality of the fabric was enhanced by alkaline hydrolysis. The hydrolysis of the fabric led to the formation of carboxyl groups on its surface. FTIR and contact angle measurements were carried out to monitor the chemical and physical changes on the fabric surface. Silver was immobilized on the fabric as the bioactive component. The fabric was characterized by EDX in mapping mode to observe distribution of silver on the fabric. PEG 600 used as carrier for silver ions to be loaded of the material surface. Antimicrobial studies of the fabric was carried out by zone of inhibition and colony reduction methods against E. coli and S. aureus. Bacterial adhesion was completely inhibited in silver immobilized samples. On the basis of observations from mechanical analysis, EDX, carboxyl content estimation, and antibacterial resistance we concluded that material was the most suitable sample to develop wound dressing. [ABSTRACT FROM AUTHOR]

A comparative analysis has been performed for silver nanoparticle dispersions obtained by the chemical reduction of Ag+ ions using several samples of chitosan with different molecular masses as reductants and stabilizers. The structure and conductivity of ring deposits resulting from the evaporation of droplets of the obtained dispersion have been studied. It has been shown that the average size of silver nanoparticles, their number concentration, and the degree of precursor reduction weakly depend on chitosan molecular mass, while the geometric parameters and electrical conductivity of the ring deposits substantially change upon the passage from oligochitosans to high-molecular-mass chitosan. [ABSTRACT FROM AUTHOR]

A paper-based visual fluorescence immunoassay is presented for the detection of matrix metalloproteinase-7 (MMP7) that is related to renal cancer. The method is based on the distance-dependent fluorescence quenching of CdTe quantum dots (QDs) on a nitrocellulose membrane by Ag+ following a sandwich-type immunoreaction on microtiter wells using silver nanoparticle (AgNP)–labeled secondary antibody– and primary antibody–coated microtiter wells. The silver nanoparticles captured in the well are dissolved with HNO3, while the quenching effect of QDs is based on silver ion-exchange reaction under 365-nm excitation light irradiation. Increasing concentration of released Ag+, thus higher concentration of the protein, leads to an increased distance of quenching on the nitrocellulose membrane. The paper-based immunoassay by combination of AgNP-assisted ion-exchange reaction with QD gives good distance-dependent responses and allows the detection of MMP7 at a concentration as low as 7.3 pg mL−1. The coefficients of variation are less than 6.9% and 12.4% for intra-assay and inter-assay, respectively. High specificity and long-term stability are achieved during the assay. Importantly, the testing of human serum samples using our strategy shows well-matched results with commercial human MMP7 ELISA kits. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) catalyze the mild reaction between the weak reducing agent kojic acid (KA) and silver ions (Ag+) to form Au@Ag bimetallic NPs by the combination of the intrinsic catalysis with plasmonic properties This is proposed as a novel optical assay to determine the tyrosinase (TYRase) concentration. The nanoparticles have been characterized by UV-vis spectroscopy, transmission electron microscope (TEM) images, and X-ray photoelectron spectroscopy (XPS). The sensing mechanism is based on the fact that KA binds to TYRase by chelating with dicopper active site of TYRase and the introduction of TYRase restrains the Au@Ag bimetallic NP formation by the precedent binding with KA. A clear color variation from yellow to pink and UV-vis spectral changes are observed at the optimal wavelength of 410 nm. The assay works in the range 0.13~0.73 U mL−1 with a detection limit (LOD) of 0.019 U mL−1. The impact from matrix interfering substances including glucose, uric acid, common oxidases, and amino acids is negligible. The applicability is demonstrated by quantitative determination of TYRase in human serum samples with 74 to 89% recovery and RSD less than 4.0%, which accords with the level for bio-sample analysis. [ABSTRACT FROM AUTHOR]

Using mulberry silkworm pupae as an alternative source of renewable raw materials, a water-soluble Bombyx mori chitosan derivative N-carboxymethylchitosan is synthesized. A method for the photochemical reduction of silver ions into silver nanoparticles in an N-carboxymethylchitosan matrix is developed. The presence of silver nanoparticles in a colloidal solution is confirmed by UV spectroscopy, and their shape and size are determined by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Recently revised OECD inhalation toxicity testing guidelines require measurements of lung burden immediately after and for periods following exposure for nanomaterials. Lung burden is a function of pulmonary deposition and retention of nanoparticles. Using lung burden studies as per OECD guidelines, it may be possible to assess clearance mechanisms of nanoparticles. In this study, male rats were exposed to silver nanoparticle (AgNP) aerosols (18.1–19.6 nm) generated from a spark generator. Exposure groups consisted of (1) control (fresh air), (2) low (31.2 ± 8.5 µg/m3), (3) moderate (81.8 ± 11.4 µg/m3), and (4) high concentrations (115.6 ± 30.5 µg/m3). Rats were exposed for 6-h/day, 5-days/week for 4 weeks (28-days) based on the revised OECD test guideline 412. Bronchoalveolar lavage (BAL) fluids were collected on post-exposure observation (PEO)-1 and PEO-7 days and analyzed for inflammatory cells and inflammatory biomarkers. The lung burdens of Ag from AgNPs were measured on PEO-1, PEO-7, and PEO-28 days to obtain quantitative mass concentrations per lung. Differential counting of blood cells and inflammatory biomarkers in BAL fluid and histopathological evaluation of lung tissue indicated that exposure to the high concentrations of AgNP aerosol induced inflammation at PEO-1, slowly resolved at PEO-7 and completely resolved at PEO-28 days. Lung burden measurement suggested that Ag from AgNPs was cleared through two different modes; fast and slow clearance. The fast clearance component was concentration-dependent with half-times ranging from two to four days and clearance rates of 0.35–0.17/day−1 from low to high concentrations. The slow clearance had half-times of 100, 57, and 76 days and clearance rates of 0.009, 0.012, and 0.007/day−1 for the high, moderate and low concentration exposure. The exact mechanism of clearance is not known currently. The fast clearance component which was concentration-dependent could be dependent on the dissolution of AgNPs and the slow clearance would be due to slow clearance of the low dissolution AgNPs secondary particles originating from silver ions reacting with biogenic anions. These secondary AgNPs might be cleared by mechanisms other than dissolution such as mucociliary escalation, translocation to the lymphatic system or other organs. [ABSTRACT FROM AUTHOR]

By using the method of cyclic voltammetry, we study the anodic dissolution of silver in a sodium polyacrylate (NaPA) solution. The influence of the concentration of NaPA, temperature, and рН value of the solution on the electrochemical characteristics of silver in the process of its polarization in a solution is investigated. It is shown that, for E = 0.3–1 V, the dissolution currents of silver become much stronger as the polyacrylate concentration increases. The diffusion character of anodic currents within the temperature range 20–50°С is established. It is discovered that, under the conditions of cathodic polarization (E = 0.15 V), silver ions are reduced with the formation of nanoparticles (7–10 nm). We propose to use the procedure of anodic dissolution of silver in order to get polyacrylate complexes of silver, which are precursors for the synthesis of stabilized silver nanoparticles. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of materials are greatly influenced by the state of their surface layers. In turn, the characteristics of the surface depend, for example, on the processes of absorption from a gas medium. In this study, by in situ measurements, the surface layers of polycrystalline silver exposed to external activated oxygen from different sources are investigated. For sources of activated oxygen, water vapor at a temperature of 1073 K and an ion source that makes it possible to obtain an oxygen ion beam with the energy 100–300 eV (5 μA/cm2) are used. It is established that, after treatment, the composition of AgO and Ag2O in the surface layers of silver includes, apart from atomic oxygen, molecular oxygen and silver in the zero-valence state. From estimates of the ratio between the intensities of spectroscopy peaks related to silver and oxygen components, it can be concluded that there exist associative forms of oxygen in the surface layers of silver. An increase in Ag 3d5/2–Ag 3d3/2 spin–orbit splitting is detected, which suggests that there are oxidized silver nanoparticles on the surface. [ABSTRACT FROM AUTHOR]

In the present investigation, synthesis of silver nanoparticles (AgNPs) has been successfully carried out in a very simple and cost-effective manner by reducing Ag ions in sodium alginate solution and further stabilizing the colloidal mixture with gelatin solution. The ultraviolet-visible (UV-vis) spectra were in excellent agreement with the nanostructure morphology obtained from dynamic light scattering transmission electron microscopy and their size distributions. Increase in precursor concentration was found to promote agglomeration of AgNPs. Antibacterial assays revealed that the nanoformulations were more active against Gram-negative bacteria. Swelling studies of the hydrogel films demonstrated a rapid increase in water uptake. However, an increase in swelling % was observed with decreasing AgNP content. The use of biocompatible materials such as sodium alginate and gelatin not only provides green and economic attributes to this piece of research work but, at the same time, also opens up possibilities of using the nanoformulations in wound dressings, active packaging and several other biomedical applications. [ABSTRACT FROM AUTHOR]

In the last two decades, a large number of literature had focused on the biosynthesis of silver nanoparticles (AgNPs) from silver ions by bacteria and other microorganisms. This study infers that bacteria and other microorganisms do not per se synthesize AgNPs. All tested auto- and heterotrophic microorganisms in this study were killed by silver ions and could not as viable cells produce AgNPs. Microbial cell viability represented in colony-forming units and metabolic viability represented in aerobic respiration in all investigated microorganisms as well as photosynthesis in photoautotrophic microorganisms ceased by silver ions too early before AgNPs formation. The time required for AgNPs synthesis inversely related to the incubation temperature of the investigated microorganisms with silver ions where it requires only few minutes for nanoparticles formation at high temperature or autoclaving. The minimum inhibitory and minimum bactericidal and fungicidal concentrations of silver ions were significantly lower than AgNPs, indicating that silver ions are more efficient antimicrobial. The results presented in this study indicate that formation of AgNPs by eubacteria, cyanobacteria and fungi is not a vitally regulated cellular metabolic process and the mechanism occurs via bioreduction of silver ions to nanoparticles by organics released from the dead cells. [ABSTRACT FROM AUTHOR]

In the present study, tailor-made ethylene vinyl alcohol copolymer (EVOH) fibers containing different amounts of antimicrobial silver ions and nanoparticles were developed by electrospinning and subsequent thermal annealing. The morphology of the fibers was examined by scanning and transmission electron microscopy and thermal properties were characterized by differential scanning calorimetry. Speciation and controlled release of silver from the fibers was monitored by anodic stripping voltammetry and energy dispersive X-ray spectroscopy. Before aging, 100 % of the silver recovered from the electrospun structures was in ionic form to be instantly released in contact with moisture with varying temperature-dependent kinetics. Thermal annealing of the fibers at 100 °C for 1, 2, and 4 days prompted the gradual transformation of 70, 93-94, and 98-99 % of the total silver into nanoparticles homogeneously distributed along the fibers, which were mostly retained within them, producing a substantial decrease in their release capacity. Speciation and release profiles from the fibers were correlated with their antibacterial performance against Listeria monocytogenes and Salmonella enteric. This study is a step forward in the understanding of silver-based electrospun antimicrobial polymers and puts forth the suitability of EVOH for the development of targeted delivery systems in a number of applications. [ABSTRACT FROM AUTHOR]

Background: Knowledge about silver nanoparticles in soils is limited even if soils are a critical pathway for their environmental fate. In this paper, speciation results have been acquired using a silver ion selective electrode in three different soils. Results: Soil organic matter and pH were the most important soil properties controlling the occurrence of silver ions in soils. In acidic soils, more free silver ions are available while in the presence of organic matter, ions were tightly bound in complexes. The evolution of the chemical speciation of the silver nanoparticles in soils was followed over six months. Conclusion: During the first few hours, there appeared to be a strong sorption of the silver with soil ligands, whereas over time, silver ions were released, the final concentration being approximately 10 times higher than at the beginning. Ag release was associated with either the oxidation of the nanoparticles or a dissociation of adsorbed silver from the soil surfaces. [ABSTRACT FROM AUTHOR]

A simple and green chemical method has been developed to synthesize stable bare and capped silver nanoparticles based on the reduction of silver ions by glucose and capping by poly(α,γ, l-glutamic acid) (PGA). The use of ammonia during synthesis was avoided. PGA has had a dual role in the synthesis and was used as a capping agent to make the silver nanoparticle more biocompatible and to protect the nanoparticles from agglomerating in the liquid medium. The synthesized PGA-capped silver nanoparticles in the size range 5-45 nm were stable over long periods of time, without signs of precipitation. Morphological examination has shown that the silver nanoparticles had a nearly spherical, multiply twinned structure. The effects of the reaction temperature and the reaction time during the synthesis were investigated too. The biocompatibility of the PGA-capped silver nanoparticles is discussed in terms of in vitro toxicity with human intestinal Caco-2 cells. The samples were characterized by UV-Visible spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and zeta potential measurements. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag NPs) were efficiently generated by in situ reduction of silver ions via butylated hydroxytoluene (BHT), in poly(methyl methacrylate). The characterization of Ag/PMMA by TEM, SEM, XRD, and FTIR indicated that Ag NPs with a face center cubic (fcc) crystal structure and a mean diameter of about 30 nm were dispersed in PMMA matrix with a relatively uniform distribution. In addition, the results of UV-Vis spectroscopy indicated that optical properties of the nanocomposite appeared mainly dependent on the reaction time and temperature. Increasing the reaction time and temperature make higher yield of Ag NPs. A provisional reduction mechanism was also proposed for the formation of the Ag NPs. [ABSTRACT FROM AUTHOR]

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

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

A method is described for surface-enhanced Raman scattering (SERS) discrimination of formaldehyde (FA) and acetaldehyde (AA) in aqueous sample solutions. It is based on the use of a paper strip containing 4-aminothiophenol (Atp)-modified reduced graphene oxide (rGO)/[Ag(NH3)2]+ (rGO/[Ag(NH3)2]+/Atp). The addition of FA or AA induces the conversion of [Ag(NH3)2]+ complex to silver nanoparticles (AgNPs) because of aldehyde-induced silver reduction reaction. The AgNPs possess strong SERS activity. The average interparticle gaps between the AgNPs can be fine-tuned by controlling the experimental conditions, this leading to the formation of optimized SERS hot spots. It is also found that the changes in the spectral shapes and the relative intensity ratio of the bands at 1143 and 1072 cm−1 result from the difference in the pH value of the surrounding solution. This effect enables the selective discrimination of FA and AA. The paper strip can be used as a SERS dipstick and swab for on-site determination of FA or AA in wine and human urine via the differences in the intensity of the SERS peaks. The assay works over a wide range of concentrations (0.45 ng·L−1 to 480 μg·L−1) for FA and AA, and the respective detection limits are 0.15 and 1.3 ng·L−1.Schematic presentation of the preparation procedure of 4-aminothiophenol (Atp)-modified reduced graphene oxide (rGO)/[Ag(NH3)2]+ hybrid paper and its surface-enhanced Raman scattering discrimination of formaldehyde and acetaldehyde based on silver reduction. [ABSTRACT FROM AUTHOR]