AgNP Suspensions Research Articles

Aqueous dispersions of ‘green’ silver nanoparticles for eco-applications: Synthesis, structure and biosafety

Sustainable agriculture requires the use of intelligent compounds with multifaceted effect on soil and plants. Such conditioners can be hydrogels enriched with nanoparticles, but only those synthesized using ‘green chemistry’ methods. Therefore, the main aim of the study was to synthesize and characterize innovative ‘green’ silver nanoparticles (AgNPs) for agricultural applications. AgNPs were created using water or alcohol extracts of eucalyptus (Eucalyptus viminalisLabill) and aloe (Aloë arborescens Mill) as well as tannin to reduce silver ions (Ag+) to zero valent form (Ag0). The synthesis was conducted under autoclave conditions or at room temperature, in the presence of potassium carbonate. The AgNPs characterization was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS) method, whereas stability of the AgNPs suspensions under various conditions was estimated using turbidimetry. Biosafety of the formed species was determined based on genotoxicity (comet test) and cytotoxicity (study with crystal violet and MTT) assays. The obtained results confirmed the presence of zero valent silver phase in the nanoparticles and showed that their crystallite size was 14–24 nm, with different degrees of polydispersity depending on the synthesis conditions. Hydrodynamic diameter of AgNPs and their aggregates in the aqueous dispersions varied from 6 nm to 103 nm, and the smallest aggregation degree was noted for the nanoparticles synthesized using tannin. All synthesized nanoparticles were biosafe. Thus, they can be applied in agro-industrial processes without damaging the environment.

Guide for Optimization of Olive Leaf Extraction and Silver Nanoparticles Biosynthesis as an Initial Step for Pilot Plant Design.

This account presents the results of two successful optimization processes. First, a polyphenol-rich aqueous olive extract was obtained and then silver nanoparticles (AgNPs) synthesized with high efficiency. Selected parameters for both processes were optimized based on the procedure of the Box-Behnken multifactorial design. The independent variables in the extraction process were the biomass/water ratio, temperature, and time. For AgNPs synthesis, the independent variables were the volume of olive extract, temperature, and process duration. The relationship between the process parameters was visualized graphically by using the response surface methodology. A high fit of the experimental data with the predicted models was shown. The regression coefficients were high, 0.9936 for extraction and 0.9757 for AgNPs biosynthesis. The extraction efficiency under its optimal conditions was as follows: biomass/solvent ratio 0.016, temperature 80 °C for 80 min, and yield 160.67 [μg GAE (gallic acid equivalent)/mL]. The highest yield of AgNPs synthesis, equal to 1.955, was obtained when it was carried out for 50 min at 75 °C with the application of 11 mL of extract. Studies on the AgNPs suspension's stability depending on the extract amount were demonstrated. A physicochemical analysis using dynamic light scattering, transmission electron microscopy images, and Fourier transform infrared spectroscopy for AgNPs obtained under optimal conditions was shown. Finally, a pilot-scale biosynthesis of AgNPs was designed.

Biosynthesis and assessment of antibacterial and antioxidant activities of silver nanoparticles utilizing Cassia occidentalis L. seed

This research explores the eco-friendly synthesis of silver nanoparticles (AgNPs) using Cassia occidentalis L. seed extract. Various analytical techniques, including UV–visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDX), were employed for comprehensive characterization. The UV–visible spectra revealed a distinct peak at 425 nm, while the seed extract exhibited peaks at 220 and 248 nm, indicating the presence of polyphenols and phytochemicals. High-resolution TEM unveiled spherical and oval-shaped AgNPs with diameters ranging from 6.44 to 28.50 nm. The SEM exhibiting a spherical shape and a polydisperse nature, thus providing insights into the morphology of the AgNPs. EDX analysis confirmed the presence of silver atoms at 10.01% in the sample. XRD results unequivocally confirm the crystalline nature of the AgNPs suspension, thereby providing valuable insights into their structural characteristics and purity. The antioxidant properties of AgNPs, C. occidentalis seed extract, and butylated hydroxytoluene (BHT) were assessed, revealing IC50 values of 345, 500, and 434 μg/mL, respectively. Antibacterial evaluation against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli demonstrated heightened sensitivity of bacteria to AgNPs compared to AgNO3. Standard antibiotics, tetracycline, and ciprofloxacin, acting as positive controls, exhibited substantial antibacterial efficacy. The green-synthesized AgNPs displayed potent antibacterial activity, suggesting their potential as a viable alternative to conventional antibiotics for combating pathogenic bacterial infections. Furthermore, potential biomedical applications of AgNPs were thoroughly discussed.

The antibacterial and toxicological studies of mycosynthesis silver nanoparticles by isolated phenols from agaricus bisporus

Silver nanoparticles (AgNPs) are widely utilized in biomedical and antibacterial fields. However, their use poses a risk and danger of Ag+ absorption into human tissue via skin penetration. This study focuses on the facile and eco-friendly approach to synthesizing uniformly distributed and spherically shaped phenol capped AgNPs using Agaricus bisporus. The synthesis process was monitored by UV–vis spectroscopy peak at 430 nm. Further characterizations were performed by XRD, and TEM. The phenol-capped AgNPs (average diameter is 11.81 nm) exhibit excellent colloidal stability in an aqueous solution with a zeta potential of −32.9 mV. The presence of phenols in the AgNPs suspension, which include CAFFICACID, QUERCETIN, GALLIC ACID, ROSMARINIC ACID, SINAPIC, and SYNIRGIC was confirmed by HPLC analysis. The study investigated their antibacterial activity against colonies of palm-hand bacteria, Pseudomonas aeruginosa, and Streptococcus pyogenes bacteria even in small doses was investigated. Damage to the cell wall, mitochondria, and DNA by nanoparticles has been proposed as an antibacterial mechanism. Toxicological parameters such as histological study of skin and vital organ tissue, hematological, serum biochemistry, and fatality incidence were investigated. There were no harmful effects or damage caused by phenol-capped AgNPs in albino mouse organs when compared to the vehicle group. Toxicological evidence supports the use of mycosynthesized phenol-capped AgNPs in non-alcohol hand sanitizer.

Enhancement of Terahertz Emission by Silver Nanoparticles in a Liquid Medium.

Due to higher molecular density, lower ionization potential, and a better self-healing property compared with gases, liquid targets have been used for laser-induced terahertz generation for many years. In this work, a liquid target used for terahertz radiation is embedded with silver nanoparticles (Ag NPs), which makes the material have both the fluidity of liquids and conductivity of metals. Meanwhile, the experimental setup is easier to implement than that of liquid metals. Polyvinyl alcohol (PVA) is used as a stabilizing agent to avoid precipitation formation. It is observed that the power of 0.5 THz radiation from the Ag NP suspension is five times stronger than that from liquid water in identical experimental conditions. In addition, the reusability of the material is investigated using multiple excitations. UV-visible spectroscopy and TEM imaging are carried out to analyze the target material after each excitation. As a result, quasispherical Ag NP suspensions show good reusability for several excitations and only a decrease in particle concentration is observed. By contrast, the chain-like Ag NP suspension shows poor stability due to PVA damage caused by intense laser pulses, so it cannot be used in a recyclable manner.

Photocatalytic degradation of methylene blue and antibacterial activity of silver nanoparticles synthesized from Camellia sinensis leaf extract

Green synthesis of silver nanoparticles (AgNPs) has attracted substantial interest and achievement due to their environmental friendliness, ease of manipulation, and potential for large-scale production. By using aqueous Camellia sinensis leaf extract, suspensions of AgNPs, which possess photocatalytic and biological activity, were successfully synthesized in this study. The reduction of silver ions to AgNPs was visually inspected via the colour of the reaction mixture, which was altered from pale yellow to reddish brown. The methods of characterization of the as-synthesized AgNPs were performed using Ultraviolet-Visible spectroscopy (UV-Vis), dynamic light scattering technique (DLS), and X-ray diffraction analysis (XRD). The surface plasmon resonance bands of AgNPs at 420-430 nm in UV-Vis spectra indicated the presence of silver particles at the nanoscale. The size of AgNPs was determined by DLS, ranging from 25 nm to 40 nm. XRD analysis showed that AgNPs were highly pure and crystalline. The antibacterial activity of AgNPs against Gram-positive and Gram-negative bacterial strains, including Staphylococcus aureus and Escherichia coli, respectively, was demonstrated by the disc diffusion method. The examination of the photocatalytic activity of AgNPs was conducted through methylene blue (MB) degrading experiments, and the MB degrading performance was approximately 95% within 72 h under sunlight.

Chitosan Glutaraldegyde Cryogels for Wastewater Treatment and Extraction of Silver Nanoparticles

The discharge of nanoparticles into the environment, such as through industrial plants and municipal wastewater treatment plants, can pose a hazard to aquatic life. This study demonstrates the effective removal of silver nanoparticles (AgNPs) using a chitosan-based cryogel, which has potential applications in agriculture, as well as in water treatment or in industrial plants that discharge into environmentally sensitive water bodies. The adsorbent is economically viable, has high affinity toward metal nanoparticles, is biodegradable and biocompatible, and displays a good removal of nanoparticles. AgNP adsorption was monitored using UV/Vis spectroscopy and TEM analysis. SEM, nitrogen adsorption, TGA, and FTIR analysis were used for cryogel characterization. The BET model of nitrogen adsorption revealed a specific surface area of 7.7 m2/g for chitosan–glutaraldehyde (CHI–GA) cryogels. The elasticity modulus of the CHI–GA cryogel was estimated as 543 ± 54 kPa. The AgNPs were characterized by a negative charge (−38 ± 17 mV) and an average diameter of 64 nm with a polydispersity index of 0.16. The mechanism of AgNP adsorption involved electrostatic interactions between the oppositely charged surfaces of the cryogel and particles. The temperature of the cryogel preparation affected the water permeability and adsorption efficiency. CHI–GA illustrated a capacity of 63 mg/g at a flow rate of 0.8 mL/min under a solution pressure of 500–970 Pa. The increase in pressure of the model plant extract-stabilized AgNP suspension (14 mg/L AgNPs) to 3.42–3.9 kPa led to an increase in the water permeability rate to 10 mL/min and a significant decrease in the efficiency of particle removal. The CHI–GA adsorbent demonstrated up to 96.5% AgNP removal until the breakthrough point due to adsorbent saturation. The CHI–GA cryogel adsorbent (1 g) can be used for efficient filtering of about 4.5 L of contaminated water.

Development and Experimental Evaluation of Some Silver Nanoparticles with Antimicrobial Potential

By adjusting the synthesis process, silver nanoparticles (AgNp) of various shapes, sizes, and structures can be obtained, all of which have a substantial impact on the biological effect, notably, the regulation of antibacterial activity in the present circumstances of growing bacterial resistance. Due to their relatively small size, nanoparticles may be disseminated evenly throughout the body of the experimental animal, even at low doses, and exert more potent antibacterial activities. Our research was centered on the synthesis, production, and biological evaluation of antibacterial silver nanoparticles. Using the Turkevich method, we were able to effectively synthesize and characterize nanoscale silver particles, with an average crystallite size of 9.49 nm. We examined their acute toxicity and pharmacokinetic characteristics in rats after administering a single dosage. In addition, we evaluated the biological effect of topical AgNp suspension on the progression of burn-type lesions in the experimental animals. The pharmacokinetic profile demonstrated that the plasma concentration of silver nanoparticles, as well as their clearance rate, and dispersion throughout the body, are significantly enhanced in large rodent species. The restorative effect of synthesized silver nanoparticles in the form of a suspension in distilled water was corroborated by the values of the hematological parameters. These results demonstrated an intense stimulation of the cellular and molecular processes of the local immune defense, which has resulted in significantly faster regeneration in the AgNp-treated group.

Fabrication of Silver Nanoparticles in Aqueous Solution by Laser Technique and Study of Their Hemocompatibility and Antibacterial Effects Against Dental Decay Bacteria

Silver nanoparticles (Ag NPs) were prepared by laser ablation of a silver bulk immersed in cetrimonium bromide (CTAB). The immersed sheet was focused by a pulsed Nd:YAG laser at 1064 nm, 600 mJ at room temperature, a pulse duration of 10 ns, and a repetition rate of 5 Hz. The Ag NPs suspension was analyzed using UV–Vis spectroscopy, zeta potential (ZP), the Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The peak at 425 nm was observed in the absorption spectrum of Ag NPs colloidal solution.Ag NPs' colloidal results are 20 mV for positively charged CTAB. The XRD pattern of the NPs revealed the presence of Ag phase planes (111), (200), and (220). All samples show aggregation-induced spherical nanostructures and large particles in FESEM images. The TEM images revealed nearly spherical NPs, with sizes ranging from 5–70 nm, for Ag NPs prepared with CTAB. The Ag NPs with concentrations of (0.0, 25, 50, 100, and 200) µg/mL were tested for antibacterial activity against a clinical isolate of Streptococcus mutans, and the concentrations of (0.0, 50, 75, 100, and 200) µg/mL were tested for in vitro hemocompatibility effects by measuring the hemolysis rate of red blood cells. Ag NPs' antibacterial activity against Streptococcus mutans was size and concentration-dependent, and the hemolysis rate showed low effects at low concentrations, so Ag NPs could be employed to treat and prevent dental caries, but to transform this technology into therapeutic and preventive measures, more investigation and development are required.

Green Synthesis of Cellulose-Based Biofilms Doped with AgNPs with Antibacterial Activity

In this work, cellulose-based composite biofilms doped with silver nanoparticles (AgNPs) have been produced by eco-friendly process. The AgNPs were synthesized from Ilex paraguariensis with an average size of 45 nm, a characteristic plasmon band at 450 nm and zeta potential of -23 mV. The biofilm has been synthesized by casting method, using different volumes of AgNPs suspension with glycerol plasticizing agent (T6-T10) or not (T1-T5). The AgNPs were successfully incorporated into the biofilms that was confirmed by scanning electron microscopy. The mechanical and optical structural and the antimicrobial properties of the biofilms have been determined. In the presence of AgNPs, the mechanical properties, thermal stability and water vapor barrier of the biofilms have been not altered. However, the addition of glycerol decreased the tensile strength and the modulus of elasticity, in addition to increasing the elongation of the biofilms and the water vapor barrier. The biofilm T10 showed a transmittance of ca. 10%, with high potential to be used as a UV light blocker. Finally, the biofilms doped with AgNPs showed activity against the bacterium Pseudomonas fluorescens. Given the above, this work presented a new biofilm with activity against the bacterium Pseudomonus fluorescens obtained by eco-friendly process.

The Imbibition of Pea (Pisum sativum L.) Seeds in Silver Nitrate Reduces Seed Germination, Seedlings Development and Their Metabolic Profile.

The use of silver nanoparticles (Ag NPs) on plants is accompanied by the occurrence of Ag+ ions, so the research of the effects of both on plants should be related. Therefore, in our study, the effects of Ag NPs suspension (containing Ag0 at 20 mg/L) and AgNO3 solutions (with the concentration of Ag+ ions at 20 and 50 mg/L) on the seed germination and early seedling growth (4 days) of pea (Pisum sativum L.) were compared. Both Ag NPs and AgNO3 did not decrease seed germination, and even stimulated seedling growth. In seedlings developing in the Ag NPs suspension, an increase in monosaccharides, homoserine and malate was noted. In the next experiment, the effect of short-term seed imbibition (8 h) in AgNO3 at elevated concentrations, ranging from 100 to 1000 mg/L, on the further seed germination, seedling growth (in absence of AgNO3) and their polar metabolic profiles were evaluated. The seed imbibition in AgNO3 solutions at 500 and 1000 mg/L reduced seed germination, inhibited seedlings’ growth and caused morphological deformations (twisting and folding of root). The above phytotoxic effects were accompanied by changes in amino acids and soluble carbohydrates profiles, in both sprouts and cotyledons. In deformed sprouts, the content of homoserine and asparagine (major amino acids) decreased, while alanine, glutamic acid, glutamine, proline, GABA (γ-aminobutyric acid) and sucrose increased. The increase in sucrose coincided with a decrease in glucose and fructose. Sprouts, but not cotyledons, also accumulated malic acid and phosphoric acid. Additionally, cotyledons developed from seeds imbibed with AgNO3 contained raffinose and stachyose, which were not detectable in sprouts and cotyledons of control seedlings. The obtained results suggest the possible disturbances in the mobilization of primary (oligosaccharides) and presumably major storage materials (starch, proteins) as well as in the primary metabolism of developing seedlings.

The Effect of Bio-Synthesized Silver Nanoparticles on Germination, Early Seedling Development, and Metabolome of Wheat (Triticum aestivum L.).

Changes in the metabolome of germinating seeds and seedlings caused by metal nanoparticles are poorly understood. In the present study, the effects of bio-synthesized silver nanoparticles ((Bio)Ag NPs) on grains germination, early seedlings development, and metabolic profiles of roots, coleoptile, and endosperm of wheat were analyzed. Grains germinated well in (Bio)Ag NPs suspensions at the concentration in the range 10–40 mg/L. However, the growth of coleoptile was inhibited by 25%, regardless of (Bio)Ag NPs concentration tested, whereas the growth of roots gradually slowed down along with the increasing concentration of (Bio)Ag NPs. The deleterious effect of Ag NPs on roots was manifested by their shortening, thickening, browning of roots tips, epidermal cell death, progression from apical meristem up to root hairs zone, and the inhibition of root hair development. (Bio)Ag NPs stimulated ROS production in roots and affected the metabolic profiles of all tissues. Roots accumulated sucrose, maltose, 1-kestose, phosphoric acid, and some amino acids (i.e., proline, aspartate/asparagine, hydroxyproline, and branched-chain amino acids). In coleoptile and endosperm, contrary to roots, the concentration of most metabolites decreased. Moreover, coleoptile accumulated galactose. Changes in the concentration of polar metabolites in seedlings revealed the affection of primary metabolism, disturbances in the mobilization of storage materials, and a translocation of sugars and amino acids from the endosperm to growing seedlings.

Minimizing the Silver Free Ion Content in Starch Coated Silver Nanoparticle Suspensions with Exchange Cationic Resins.

This work describes the optimization of a methodology for the reduction of silver ions from silver nanoparticle suspensions obtained from low-yield laboratory procedures. The laboratory synthesis of silver nanoparticles following a bottom-up approach starting from silver nitrate, originates silver ions that were not reduced to their fundamental state for nanoparticles creation at the end of the process. However, it is well known that silver ions can easily influence chemical assays due to their chemical reactivity properties and can limit biological assays since they interfere with several biological processes, namely intracellular ones, leading to the death of living cells or organisms. As such, the presence of silver ions is highly undesirable when conducting biological assays to evaluate the influence of silver nanoparticles. We report the development of an easy, low-cost, and rapid methodology that is based on cation exchange resins to minimize the silver ion content in a raw suspension of silver nanoparticles while preserving the integrity of the nanomaterials. This procedure preserves the physical-chemical properties of the nanoparticles, thus allowing the purified nanoparticulate systems to be biologically tested. Different types of cationic resins were tested, and the developed methodology was optimized by changing several parameters. A reduction from 92% to 10% of free silver/total silver ratio was achieved when using the Bio-Rad 50W-X8 100–200 mesh resin and a contact time of 15 min. Filtration by vacuum was used to separate the used resin from the nanoparticles suspension, allowing it to be further reused, as well as the purified AgNPs suspension.

Preparing AgNPs via Biosynthesis and Chemical Reduction Techniques and Evaluating Their Antibacterial Effects

Silver nanoparticles (AgNPs) is one the most important metal in medical aspect specially as antibiotics. AgNPs show very interesting antimicrobial properties, even when used at low concentrations. Also, these cost-efficient materials have negligible immunological responses and cytotoxicity. In this study evaluation chemical reduction and biosynthesis methods of Synthesis of silver nanoparticles and this affect on antibacterial application. For this reason we prepared both of chemical nano particles and biosynthesied nanoparticles of silver and evaluated the antibacterial effects on Both of gram negative and gram positive bacteria. Size, morphology and composition of NPs were studied by scanning electron microscopy (SEM), laser particle analyzer (LPA) and ultraviolet-visible spectroscopy (UV-Vis). Our results showed that UV-Vis spectroscopy was performed to represent AgNP suspensions’ plasmon bands. The results show a sharp absorbance peak for AgNPs at 430 nm. For the biological synthesis of AgNPs, the preparation process was monitored through the color variations. Afterward, UV-Vis spectrophotometry was performed to measure its optical parameters. The results revealed an absorbance peak at 420 nm for the AgNPs. AgNPs produced by biological and chemical reduction methods were tested for their antimicrobial activity. To this end, Gram-negative and Gram-positive bacteria were taken using the Agar well diffusion technique. presents the diameter of inhibition zones around each well with chemically prepared AgNPs, biologically synthesized AgNPs, and AgNO3. The highest antibacterial activity of NPs was observed in E. coli, which was more than that of S. aureus. In addition, the biosynthesized NPs showed higher antibacterial activity than those prepared using the chemical method. Finally as conclusion The results  of our study showed that producing NPs by the biosynthesis technique was more powerful than chemical processes, and the produced NPs offer a higher antibacterial activity against s,arouse.

Influence of Inorganic Metal (Ag, Cu) Nanoparticles on Biological Activity and Biochemical Properties of Brassica napus Rhizosphere Soil

Two separate forms of application of silver and copper nanoparticles (AgNP and CuNP in a nanocolloidal suspension) to winter oilseed rape seeds were used: (1) seed soaking (S) for 1 h at 20 °C in a NP suspension and (2) additional seed soaking and spraying plants 21-day-old seedlings (SP) with NP. The AgNP and CuNP colloidal suspensions in sterile distilled water were applied in three different NP concentrations (50, 100, 150 mg L−1). However, the changes in the biology and biochemistry of the Brassica napus rhizospheric soil after the application of CuNPs and AgNPs are not considerable, although mostly statistically significant, and the application of CuNPs is more beneficial for this activity than the application of AgNPs. The number of CFUs (colony–forming units) of the tested groups of culturable microorganisms (fungi and copiotrophic, oligotrophic, and siderophore-producing bacteria) indicates the following trend: the abundance of all the tested groups was slightly positively correlated with CuNPs and clearly negatively correlated with AgNPs in each version of application. The soil pH value and tested biochemical soil parameters (IAA: indole-3-acetic acid, PhC: phenolic compounds, FeCC: Fe–chelating compounds) were negatively correlated with AgNPs applied to the seeds (S) at all the tested concentrations and to the seeds and plants (SP) at the concentration of 50 mg L−1. In turn, these parameters were strongly positively correlated with CuNPs applied to the S and SP groups at the concentration of 50 mg L−1 as well as Ag applied to SP at 100 mg L−1. Decrease in dehydrogenase activity (DHA) was lower after the application of CuNPs and AgNPs in S than in the SP way, and the DHA activity was equal to the activity in the control sample after the CuNP application in 100 and 150 mg L−1 concentrations.

Comparative assessment of the fate and toxicity of chemically and biologically synthesized silver nanoparticles to juvenile clams

Nanoparticles (NPs) can be produced via physical, chemical, or biological approaches. Yet, the impact of the synthesis approaches on the environmental fate and effects of NPs is poorly understood. Here, we synthesized AgNPs through chemical and biological approaches (cit-AgNPs and bio-AgNPs), characterized their properties, and toxicities relative to commercially available Ag nanopowder (np-AgNPs) to the clam Mercenaria mercenaria. The chemical synthesis is based on the reduction of ionic silver using sodium borohydride as a reducing agent and trisodium citrate as a capping agent. The biological synthesis is based on the reduction of ionic silver using biomolecules extracted from an atoxigenic strain of a filamentous fungus Aspergillus parasiticus. The properties of AgNPs were determined using UV–vis, dynamic light scattering, laser Doppler electrophoresis, (single particle)-inductively coupled plasma-mass spectroscopy, transmission electron microscopy, and asymmetric flow-field flow fractionation. Both chemical and biological synthesis approaches generated spherical AgNPs. The chemical synthesis produced AgNPs with narrower size distributions than those generated through biological synthesis. The polydispersity of bio-AgNPs decreased with increases in cell free extract (CFE):Ag ratios. The magnitude of the zeta potential of the cit-AgNPs was higher than those of bio-AgNPs. All AgNPs formed aggregates in the test media i.e., natural seawater. Based on the same total Ag concentrations, all AgNPs were less toxic than AgNO3. The toxicity of AgNPs toward the juvenile clam, Mercenaria mercenaria, decreased following the order np-AgNPs > cit-AgNPs > bio-AgNPs. Expressed as a function of dissolved Ag concentrations, the toxicity of Ag decreased following the order cit-AgNPs > bio-AgNPs > AgNO3 ~ np-AgNPs. Therefore, the toxicity of AgNP suspensions can be attributed to a combined effect of dissolved and particulate Ag forms. These results indicate that AgNP synthesis methods determine their environmental and biological behaviors and should be considered for a more comprehensive environmental risk assessment of AgNPs.

How Temperature and Photosynthetically Active Radiation Impact the Green Synthesis of Silver Nanoparticles Using Aqueous Extracts of Mentha Leaves?

Green synthesis highlights sustainable methods to produce silver nanoparticles (AgNPs). Here, extracts from fresh and lyophilized Mentha leaves produced AgNPs when performing reactions in the dark at 25ºC or 75ºC; also under photosynthetically active radiation (PAR) at 25ºC aiming to compare hydrothermal and photochemical methods. AgNPs formation was spectrophotometrically monitored and characterized by dynamic light scattering (DLS) and Zeta potential (ZP). The most polydisperse AgNPs suspension was synthesized at 25ºC (dark), presenting polydispersity index (PdI) of 0.574±0.061, and exhibited the lowest hydrodynamic diameter (HD) of 44.34±1.60 nm. In contrast, the highest HD was 80.15±2.88 nm to AgNPs produced at 25ºC with PAR which exhibited ZP of -27.8±0.7 mV. The lowest polydisperse suspension was produced at 75ºC (dark), presenting PdI of 0.369±0.009 and ZP of -12.8±0.6 mV. Concluding, we compared reliable green synthesis’ methods to determine which would efficiently produce AgNPs using Mentha leaves.

The mechanism of cell death induced by silver nanoparticles is distinct from silver cations

BackgroundPrecisely how silver nanoparticles (AgNPs) kill mammalian cells still is not fully understood. It is not clear if AgNP-induced damage differs from silver cation (Ag+), nor is it known how AgNP damage is transmitted from cell membranes, including endosomes, to other organelles. Cells can differ in relative sensitivity to AgNPs or Ag+, which adds another layer of complexity to identifying specific mechanisms of action. Therefore, we determined if there were specific effects of AgNPs that differed from Ag+ in cells with high or low sensitivity to either toxicant.MethodsCells were exposed to intact AgNPs, Ag+, or defined mixtures of AgNPs with Ag+, and viability was assessed. The level of dissolved Ag+ in AgNP suspensions was determined using inductively coupled plasma mass spectrometry. Changes in reactive oxygen species following AgNP or Ag+ exposure were quantified, and treatment with catalase, an enzyme that catalyzes the decomposition of H2O2 to water and oxygen, was used to determine selectively the contribution of H2O2 to AgNP and Ag+ induced cell death. Lipid peroxides, formation of 4-hydroxynonenol protein adducts, protein thiol oxidation, protein aggregation, and activation of the integrated stress response after AgNP or Ag+ exposure were quantified. Lastly, cell membrane integrity and indications of apoptosis or necrosis in AgNP and Ag+ treated cells were examined by flow cytometry.ResultsWe identified AgNPs with negligible Ag+ contamination. We found that SUM159 cells, which are a triple-negative breast cancer cell line, were more sensitive to AgNP exposure less sensitive to Ag+ compared to iMECs, an immortalized, breast epithelial cell line. This indicates that high sensitivity to AgNPs was not predictive of similar sensitivity to Ag+. Exposure to AgNPs increased protein thiol oxidation, misfolded proteins, and activation of the integrated stress response in AgNP sensitive SUM159 cells but not in iMEC cells. In contrast, Ag+ cause similar damage in Ag+ sensitive iMEC cells but not in SUM159 cells. Both Ag+ and AgNP exposure increased H2O2 levels; however, treatment with catalase rescued cells from Ag+ cytotoxicity but not from AgNPs. Instead, our data support a mechanism by which damage from AgNP exposure propagates through cells by generation of lipid peroxides, subsequent lipid peroxide mediated oxidation of proteins, and via generation of 4-hydroxynonenal (4-HNE) protein adducts.ConclusionsThere are distinct differences in the responses of cells to AgNPs and Ag+. Specifically, AgNPs drive cell death through lipid peroxidation leading to proteotoxicity and necrotic cell death, whereas Ag+ increases H2O2, which drives oxidative stress and apoptotic cell death. This work identifies a previously unknown mechanism by which AgNPs kill mammalian cells that is not dependent upon the contribution of Ag+ released in extracellular media. Understanding precisely which factors drive the toxicity of AgNPs is essential for biomedical applications such as cancer therapy, and of importance to identifying consequences of unintended exposures.

Efficacy of MTA Modified by Nanosilver for the Prevention of Coronal Leakage

Background:Numerous materials have been introduced as coronal barriers, however, they have shown various degrees of microleakage. Therefore, attempts are undertaken to introduce more reliable materials with the potential to provide a long-term coronal seal.Introduction:Thisin vitrostudy aimed to assess the efficacy of gray ProRoot Mineral Trioxide Aggregate (MTA) modified by a suspension of silver nanoparticles (AgNPs) as an orifice plug using a bacterial leakage method.Methods:40 extracted human teeth were prepared and filled (except for the negative control group) using the lateral compaction technique. The coronal 2 mm of the root filling was removed in the experimental groups. The teeth were randomly divided into two experimental (n = 15) and two control (n = 5) groups. In the experimental group 1 (MTA group) and the experimental group 2 (Ag-MTA group), MTA modified by a suspension of AgNPs was used as an orifice plug. In the negative control group, the entire root surfaces were covered with two layers of nail varnish. In the positive control group, the root canals were filled with a single gutta-percha cone without a sealer and no orifice plug. Bacterial leakage was assessed using a two-chamber system. The teeth were incubated at 37°C and 100% humidity for 120 days, and human saliva was added to the samples every 3 days. Bacterial microleakage was assessed by daily monitoring and observating the turbidity of the Brain Heart Infusion (BHI) broth. The data were analyzed using the log-rank test.Results:All positive controls showed contamination after 5 days. None of the negative controls were contaminated during the experiment. The Ag-MTA group demonstrated a significantly better coronal seal than the MTA group (p = 0.031).Conclusion:Gray ProRoot MTA modified by AgNPs has the potential for being used as an orifice plug in endodontically treated teeth.

Antioxidant-modulated cytotoxicity of silver nanoparticles.

The properties of silver nanoparticles (AgNPs) synthesized using compounds exhibiting biological activity seem to constitute an interesting issue worthy of examination. In these studies, two types of AgNPs were synthesized by a chemical reduction method using well-known antioxidants: gallic acid (GA) and ascorbic acid (AA). Transmission electron microscopy (TEM) and atomic force microscopy (AFM) revealed that the AgNPs were spherical. The average size was equal to 26 ± 6 nm and 20 ± 7 nm in the case of ascorbic acid-silver nanoparticles (AAgNPs) and gallic acid-silver nanoparticles (GAAgNPs), respectively. Surface-enhanced Raman spectroscopy (SERS) confirmed that the AgNPs were not stabilized by pure forms of applied antioxidants. Changes in mitochondrial activity and secretion of inflammatory and apoptosis mediators after the exposure of human promyelocytic (HL-60) and histiocytic lymphoma (U-937) cells to the AgNPs were studied to determine the impact of stabilizing layers on nanoparticle toxicity. The GAAgNPs were found to be more toxic for the cells than the AAgNPs. Their toxicity was manifested by a strong reduction in mitochondrial activity and induction of the secretion of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and caspase-9. The addition of pure antioxidants to the AgNP suspensions was found to influence their toxicity. There was a significant positive effect in the case of the mixture of AA with AAgNPs and GA with GAAgNPs. The results obtained suggest that the presence of stabilizing agents adsorbed on the surface of AgNPs is the main factor in shaping their toxicity. Nevertheless, the toxic effect can be also tuned by the introduction of free antioxidant molecules to the AgNP suspensions.