Coating-Dependent Neurotoxicity of Silver Nanoparticles—An In Vivo Study on Hippocampal Oxidative Stress and Neurosteroids

Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials. The level of exposure to nanosilver is constantly raising, and a growing body of research highlights that it is harmful to the health, especially the nervous system, of humans. The potential pathways through which nanosilver affects neurons include the release of silver ions and the associated induction of oxidative stress. To better understand the mechanisms underlying the neurotoxicity of nanosilver, in this study we exposed male Wistar rats to 0.5 mg/kg body weight of AgNPs coated with bovine serum albumin (BSA), polyethylene glycol (PEG), or citrate, or to AgNO₃ as a source of silver ions for 28 days and assessed the expression of antioxidant defense markers in the hippocampus of the exposed animals after 1 week of spatial memory training. We also evaluated the influence of AgNPs coating on neurosteroidogenesis in the rat hippocampus. The results showed that AgNPs disrupted the antioxidant system in the hippocampus and induced oxidative stress in a coating-dependent manner, which could potentially be responsible for neurodegeneration and cognitive disorders. The analysis of the influence of AgNPs on neurosteroids also indicated coating-dependent modulation of steroid levels with a significant decrease in the concentrations of progesterone and 17α-progesterone in AgNPs(BSA), AgNPs(PEG), and Ag⁺ groups. Furthermore, exposure to AgNPs or Ag⁺ resulted in the downregulation of selected genes involved in antioxidant defense (Cat), neurosteroid synthesis (Star, Hsd3b3, Hsd17b1, and Hsd17b10), and steroid metabolism (Ar, Er1, and Er2). In conclusion, depending on the coating material used for their stabilization, AgNPs induced oxidative stress and modulated the concentrations of steroids as well as the expression of genes involved in steroid synthesis and metabolism.     

黑曲霉负载银纳米颗粒的制备及其抗菌性能

采用非酶还原法,以黑曲霉菌原位还原银氨离子制备一种新型银纳米颗粒（AgNPs）/菌体复合抗菌材料,着重考察了反应温度与pH值对还原过程和所得复合材料的抗菌性能及稳定性的影响。结果表明,在温度为30℃、60℃和pH 9.5、11.5条件下,能够合成出粒径为6.9～8.2 nm的近球形AgNPs。该AgNPs均匀地分布在菌体表面上,对E.coli显示出高的抗菌性能：最小抑菌浓度(MIC)为217～434 mg·L^-1（以菌粉总质量表示）或8～20 mg Ag·L^-1（以银含量表示）。提高反应温度有利于提高菌体银负载量,但AgNPs粒径增大,抗菌性能有所下降;提高反应pH值有利于提高还原速率,而对抗菌性能影响不显著。复合材料中AgNPs与菌体结合牢固,单位质量复合材料释出的Ag⁺含量为1.7～6.8 mg·g^-1,提高反应温度和pH值后Ag⁺的释出均减少。     

Development of silver nanoparticles‐loaded calcium alginate beads embedded in gelatin scaffolds for use as wound dressings

Silver nanoparticles (AgNPs)‐loaded calcium alginate beads embedded in gelatin scaffolds were developed to sustain and maintain the release of silver (Ag⁺) ions over an extended time period. The UV irradiation technique was used to reduce Ag⁺ ions in alginate solution to AgNPs. The average sizes of AgNPs ranged between ca 20 and ca 22 nm. The AgNPs‐loaded calcium alginate beads were prepared by electrospraying of a sodium alginate solution containing AgNPs into calcium chloride (CaCl₂) solution. The AgNPs‐loaded calcium alginate beads were then embedded into gelatin scaffolds. The release characteristics of Ag⁺ ions from both the AgNPs‐loaded calcium alginate beads and the AgNPs‐loaded calcium alginate beads embedded in gelatin scaffolds were determined in either deionized water or phosphate buffer solution at 37 °C for 7 days. Moreover, the AgNPs‐loaded calcium alginate beads embedded in gelatin scaffolds were tested for their antibacterial activity and cytotoxicity. © 2014 Society of Chemical Industry     

Construction of Silver Nanoparticle-Loaded Micelles Via Coordinate Interaction and Their Antibacterial Activity

Silver nanoparticles (AgNPs) loaded antibacterial micelles were fabricated utilizing the coordinate interaction between silver ion (Ag⁺) and methoxy-poly(ethylene glycol)-block-poly(acrylamide-co-acrylonitrile) followed by in situ reduction. This micelle was characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, and dynamic light scattering. The upper critical solution temperature of Ag⁺-loaded micelles was dependent on Ag⁺ concentration. The AgNPs were approximately 4 nm in diameter and homogenously distributed in the micelles. The AgNPs-loaded micelle displayed high stability during a one week study and excellent antibacterial activity against gram-negative Escherichia coli and was of acceptable toxicity toward human embryonic hepatocytes.     

Comparison of adsorptive features between silver ion and silver nanoparticles on nanoporous materials

The removal of Ag⁺ or AgNPs released from nano-products or effluent of WTP is important to reduce the potential risk of AgNPs. In this work, we prepared bimodal nanoporous silica (BNS) to compare the removal efficiency of Ag⁺ and AgNP with unimodal nanoporous silica (NS). To determine the adsorption capacity of Ag⁺ and AgNPs on NS and BNS, isotherm and kinetics studies was carried out at different concentrations. The results showed BNS with a bimodal nanoporous structure and a large external surface showed a higher uptake capacity and faster adsorption rate.     

Preparation and characterization of poly(styrene)/metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization

The expectant dithiocarbamate group end-functional poly(styrene) (PS) with a controlled molecular weight and low molecular weight distribution was synthesized conveniently via reversible addition-fragmentation chain transfer (RAFT) polymerization and was used to prepare polymer/metal composites with coordination chemistry. By the self-assembly technique, PS coordinated with the rare earth metal in N,N-dimethylformamide (DMF) to generate the fluorescent Eu–PS and Sm–PS complexes. Furthermore, PS-coated spherical silver nanoparticles (AgNPs) were prepared by reducing Ag⁺ to Ag⁰ under ultrasound irradiation in the presence of DMF and H₂O. The well core/shell structure of the AgNPs was characterized by transmission electron microscopy (TEM).     

Effects of Silver Nanoparticles on Physiological and Proteomic Responses of Tobacco (Nicotiana tabacum) Seedlings Are Coating-Dependent

The harmful effects of silver nanoparticles (AgNPs) have been confirmed in many organisms, but the mechanism of their toxicity is not yet fully understood. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by coatings that influence their physico-chemical properties. In this study, the effects of AgNPs with different coatings [polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB)] on oxidative stress appearance and proteome changes in tobacco (Nicotiana tabacum) seedlings have been examined. To discriminate between the nanoparticulate Ag form from the ionic one, the treatments with AgNO₃, a source of Ag⁺ ions, were also included. Ag uptake and accumulation were found to be similarly effective upon exposure to all treatment types, although positively charged AgNP-CTAB showed less stability and a generally stronger impact on the investigated parameters in comparison with more stable and negatively charged AgNP-PVP and ionic silver (AgNO₃). Both AgNP treatments induced reactive oxygen species (ROS) formation and increased the expression of proteins involved in antioxidant defense, confirming oxidative stress as an important mechanism of AgNP phytotoxicity. However, the mechanism of seedling responses differed depending on the type of AgNP used. The highest AgNP-CTAB concentration and CTAB coating resulted in increased H₂O₂ content and significant damage to lipids, proteins and DNA molecules, as well as a strong activation of antioxidant enzymes, especially CAT and APX. On the other hand, AgNP-PVP and AgNO₃ treatments induced the nonenzymatic antioxidants by significantly increasing the proline and GSH content. Exposure to AgNP-CTAB also resulted in more noticeable changes in the expression of proteins belonging to the defense and stress response, carbohydrate and energy metabolism and storage protein categories in comparison to AgNP-PVP and AgNO₃. Cysteine addition significantly reduced the effects of AgNP-PVP and AgNO₃ for the majority of investigated parameters, indicating that AgNP-PVP toxicity mostly derives from released Ag⁺ ions. AgNP-CTAB effects, however, were not alleviated by cysteine addition, suggesting that their toxicity derives from the intrinsic properties of the nanoparticles and the coating itself.     

Molasses-Silver Nanoparticles: Synthesis,Optimization, Characterization,and Antibiofilm Activity

Biofilms are matrix-enclosed communities of bacteria that are highly resistant to antibiotics. Adding nanomaterials with antibacterial activity to the implant surfaces may be a great solution against biofilm formation. Due to its potent and widespread antibacterial effect, silver nanoparticles were considered the most potent agent with different biological activities. In the present investigation, silver nanoparticles (AgNPs) were newly synthesized as antibiofilm agents using sugarcane process byproduct (molasses) and named Mo-capped AgNPs. The synthesized nanoparticles showed promising antimicrobial activity against S. aureus ATCC 6538 and C. albicans DAY185. Statistically designed optimization through response surface methodology was evaluated for maximum activity and better physical characteristics, namely the nanoparticles’ size and polydispersity index (PDI), and it was revealed that molasses concentration was the main effective factor. Minimal biofilm eradication concentration (MBEC) of Mo-capped AgNPs against S. aureus ATCC 6538 and C. albicans DAY185 was 16 and 32 µg/mL, respectively. Scanning electron microscope study of Mo-capped AgNP-treated biofilm revealed that AgNPs penetrated the preformed biofilm and eradicated the microbial cells. The optimally synthesized Mo-capped AgNPs were spherically shaped, and the average size diameter ranged between 29 and 88 nm with high proportions of Ag⁺ element (78.0%) recorded. Fourier-transform infrared spectroscopy (FTIR) analysis indicated the importance of molasses ingredients in capping and stabilizing the produced silver nanoparticles.     

Characterization of Silver Particles in Silver-Containing Activated Carbon Fibers Prepared from Liquefied Wood

Silver particles in silver-containing activated carbon fibers prepared from liquefied wood were characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscope, and nitrogen adsorption isotherms. Silver irons (Ag⁺) and metallic silver (Ag⁰) were detected in fibers, and the amount of Ag⁰ was much higher than that of Ag⁺. Ag⁰ were migrated and aggregated together to form silver particles with a wide size (0–5μm), which were distributed in micropores, mesopores, and surface of fibers. The mean size of silver particles on the surface was directly related to soaking concentration, while the larger silver particles were easier to peel off from the surface. Also, the increasing micropores and mesopores were blocked by silver particles at higher concentration, and some blocked mesopores were converted into micropores. When the washing treatment was carried out, the silver particles on the surface were removed significantly, resulting in an increase in mesopore quantity. However, most of the silver particles in micropores were firmly supported. The silver-containing activated carbon fibers showed the high and lasting antibacterial activity.     

Ag+ ions imprinted cryogels for selective removal of silver ions from aqueous solutions

ABSTRACT

The removal of heavy metal ions from aquatic media or any conditions is crucial. Silver ions turn out to be the important example of this problem on earth when these are released to the environment. In the present study, silver ions (Ag⁺) imprinted poly(hydroxyethyl methacrylate) (PHEMA)-based cryogels were prepared using N-methacryloyl-L-cysteine as functional monomer, to be chelated with Ag⁺ ions. The maximum adsorption capacity of Ag⁺-imprinted polymeric cryogel was found to be 49.27 mg/g from aqueous solutions. To investigate the affinity of Ag⁺-imprinted PHEMAC cryogel column, photographic film material from the natural silver ion source was used. The recovery results were 72.8% for the Ag⁺-imprinted PHEMAC cryogel and 0.62% for the non-imprinted PHEMAC cryogels. These values clearly showed the selectivity of the Ag⁺-imprinted PHEMAC cryogel column. The adsorption–desorption cycle was performed more 10 times with use of the same Ag⁺-imprinted PHEMAC cryogel for the determination of reuse. These molecularly imprinted cryogels were used in adsorption process for a long time with no significant loss.     

Influence of the Eu2+ on the Silver Aggregates Formation in Ag+–Na+ Ion‐Exchanged Eu3+‐Doped Sodium–Aluminosilicate Glasses

Europium‐doping sodium–aluminosilicate glasses are prepared by melt‐quenching method, in which europium ions were spontaneously reduced from their trivalent to divalent state. The silver was introduced into glasses by Ag⁺–Na⁺ ion exchange and the interactions between europium ions and silver species were investigated. Owing to energy transfer (ET) from Ag⁺/silver aggregates to Eu³⁺, significant enhancements of Eu³⁺ emission were observed for 285/350‐nm excitation, respectively. The divalent europium ions promote the formation of silver aggregates in the process of ion exchange.     

Comportement electrochimique et reactivite du systeme Ag(II)-Ag(I)-bipyridine dans le carbonate de propylene

The electrochemical behaviour of silver(I)- and silver(II)-bipyridyl complexes has been investigated using voltammetry, cyclic voltammetry and coulometry in propylene carbonate. In unbuffered non-acidic medium, when the stoichiometry of the solutions is C_L/C_Ag = 2, the Ag^I(bipy)⁺ concentration is low; the preponderant species is Ag^I(bipy)₂⁺. Under such conditions, the Ag^II(bipy)₂²⁺/Ag^I(bipy)₂⁺ couple hs a reversible behaviour and is one of the must powerful oxidants used in the solvent (E^′° = 0.790 V vsE_Fc^′° + _Fc). As a function of the acidity level of the solutions, one observes the oxidation of either Ag^I(bipy)⁺ or Ag⁺ in the presence of the protonated ligand to complexed Ag(II). The silver(II) species produced oxidizes water and the excess of ligand (C_L/C_Ag > 2).     

Physicochemical and antimicrobial properties of sodium alginate/gelatin-based silver nanoformulations

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.     

Fabrication and evolution of multilayer silver nanofilms for surface-enhanced Raman scattering sensing of arsenate

Surface-enhanced Raman scattering (SERS) has recently been investigated extensively for chemical and biomolecular sensing. Multilayer silver (Ag) nanofilms deposited on glass slides by a simple electroless deposition process have been fabricated as active substrates (Ag/GL substrates) for arsenate SERS sensing. The nanostructures and layer characteristics of the multilayer Ag films could be tuned by varying the concentrations of reactants (AgNO₃/BuNH₂) and reaction time. A Ag nanoparticles (AgNPs) double-layer was formed by directly reducing Ag⁺ ions on the glass surfaces, while a top layer (3rd-layer) of Ag dendrites was deposited on the double-layer by self-assembling AgNPs or AgNPs aggregates which had already formed in the suspension. The SERS spectra of arsenate showed that characteristic SERS bands of arsenate appear at approximately 780 and 420 cm^-1, and the former possesses higher SERS intensity. By comparing the peak heights of the approximately 780 cm^-1 band of the SERS spectra, the optimal Ag/GL substrate has been obtained for the most sensitive SERS sensing of arsenate. Using this optimal substrate, the limit of detection (LOD) of arsenate was determined to be approximately 5 μg·l^-1.     

Dispersion mechanisms of Arabic gum in the preparation of ultrafine silver powder

Finely divided silver micro-spheres were prepared with Arabic gum (AG) as dispersant through the chemical reaction of AgNO₃ and ascorbic acid. AG dispersive mechanisms in the preparation of silver powder are proposed in the paper. The -COOH and -NH₂ groups of AG reacted with Ag⁺ to form Ag⁺-AG complexes, followed by the nucleation of silver on AG polymer chains, which yielded silver spheres with an AG protection layer by reducing Ag⁺-AG complexes with ascorbic acid. With the steric effect of AG, the prepared silver particles exhibit improved dispersibility. UV-Vis and FTIR spectra confirmed that silver particles were stabilized by AG.     

Preparation and Characterization of Silver‐Doped Cu(In,Ga)Se2 Films via Nonvacuum Solution Process

Cu(In,Ga)Se₂ films doped with different contents of silver ions (Ag⁺) were successfully prepared using nonvacuum spin coating followed by selenization at elevated temperatures. Increasing the Ag⁺ ion content increased the lattice parameters of the chalcopyrite structure, and shifted the A1 mode in the Raman signals to low frequencies. The band gaps of the prepared (Ag,Cu)(In,Ga)Se₂ (ACIGS) films were considerably increased, thereby increasing the open‐circuit voltage (V_oc) of the solar cells. As Ag⁺ ion content increased, the microstructures of ACIGS films became densified because the formed (Cu,Ag)₂In alloy phase with a low melting point facilitated liquid‐phase sintering. The evaporation of selenium species was correspondingly suppressed in the films during selenization, thereby reducing the selenium vacancies. The improvement in the microstructures and the defects of ACIGS films increased short‐circuit current (J_sc) and fill factor of the solar cells. The spectral response of the solar cells was also enhanced remarkably. This study demonstrated that incorporation of Ag⁺ ions into Cu(In,Ga)Se₂ films substantially improved the efficiency of the solar cells.     

Silver deposition from its nitrate solutions by hydrogenated palladium

The currentless deposition of Ag⁺ cations from silver nitrate solutions has been found on the surface of hydrogenated Pd (Pd?H). This process has been shown to proceed via a chemico-catalytic mechanism. It has been demonstrated that the major fraction of silver deposited onto the Pd-H system from the nitrate solutions in the first 0.5–1 h of holding in the solution. A minimal size of silver crystallites (26–40 nm) was found when deposited from the diluted nitrate solutions that contain 0.32–2.5 g/L of Ag. The study has revealed that the currentless Ag deposition on the Pd–H surface is accompanied by the formation of the colloid phase of Ag crystallites. It has been established that the Pd–H system could purify solutions of Ag⁺ when the amount of hydrogen in Pd exceeded the amount of Ag⁺ in the solution.     

A Novel Approach to Prepare Poly(Vinyl Acetate)/Ag Nanocomposite for Effective Antimicrobial Coating Applications

Polyvinyl acetate nanocomposites were successfully prepared based on silver nanoparticles. First, silver nanoparticles were directly prepared during the in situ emulsion polymerization of vinyl acetate monomer using AgNO₃ as a source of Ag⁺ ions and poly(vinyl alcohol) was used for dual functions as emulsifier for emulsion polymerization and as a stabilizing agent, trisodium citrate (C₆H₅O₇Na₃) was used as reducing agent for Ag⁺ ions during the polymerization process. The prepared polyvinyl acetate/Ag nanocomposites were assessed using X-ray diffraction, scanning electron microscopy, Fourier transform infrared, transmission electron microscopy, and ultraviolet spectra. The antibacterial properties of the prepared polyvinyl acetate/Ag nanocomposites were investigated as antimicrobial activity against pathogenic bacteria, i.e., Staphylococcus aureus (G^+ve bacteria) and Escherichia coli (G^?ve bacteria). These polyvinyl acetate nanocomposites could be used as a promising material for enhanced and continuous antibacterial applications as coating and packaging materials.     

Silver containing bioactive glasses prepared by molten salt ion-exchange

Bioactive glasses containing silver on their surface were produced by ion-exchange from dilute silver nitrate melts. This technique allowed introducing Ag⁺ ions only on the surface of the base glass while maintaining its bioactivity. The ion-exchanged glasses were characterized by means of X-Ray diffraction, SEM observations and compositional analysis (EDS). The control of the Ag⁺ content on the surface, as well as its diffusion profile throughout the ion-exchanged layer, was obtained by a careful choice of the ion-exchange parameters (temperature, time and silver concentration in the molten bath). A very good repeatability in the diffusion profile and in the silver concentration throughout the ion-exchanged layer was achieved. In vitro tests were performed on the ion-exchanged samples in order to verify their bioactive behavior (soaking in a simulated body fluid). On the soaked samples, the precipitation of a hydroxycarbonate apatite layer (HCAp) was investigated. The amount of released Ag⁺ into simulated body fluid from the exchanged glass was detected by atomic absorption spectroscopy with heated graphite furnace (GFAAS).     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.