AgNPs Of Different Sizes Research Articles

Stimuli-responsive synthesis of silver nanoparticles applying green and chemical reduction approaches

Introduction: The current study reports the comparative stimuli-responsive synthesis of silver nanoparticles (AgNPs) with various sizes and morphologies employing Lycium ruthenicum extract and sodium citrate solutions. Methods: The morphology and size of AgNPs were regulated by varying the pH values, concentrations of the extract solution, and temperatures in the reaction medium. The prepared AgNPs were assessed via various instrumental analyses, including UV-Vis, FTIR, XRD, TEM, and DLS. Results: The L. ruthenicum extract displayed several functional groups that reduced the Ag ions to the AgNPs at different values of pH. However, the primary chemical structure of L. ruthenicum was virtually unaltered at these conditions. Variations in the pH and extract concentration of the reaction medium yielded AgNPs of different sizes and morphologies. Both bio- and chemo-synthesized AgNPs revealed a relatively dispersed sphere-shaped morphology under alkaline conditions (≈ 36 nm). Conclusion: This study introduced a simple, valuable, and green technique for stimuli-sensitive AgNPs synthesis employing the L. ruthenicum extract.

Use of Residual Malt from an Artisanal Beer Brewing Process in the Biosynthesis of Silver Nanoparticles Mediated by Nucleating and Structure-Directing Agents.

Biosynthesized silver nanoparticles (AgNPs) are widely used in varied applications, which are morphology dependent. Consequently, a morphology-controlled synthesis is mandatory. Although there are several studies focused on the plant extract-based biosynthesis of metallic nanoparticles, the use of extracts obtained from agro-wastes is scant. Furthermore, information regarding morphology modification through the use of additional agents is even more scarce. Thus, in this study, AgNPs were synthesized using a malt extract (ME) obtained from an artisanal beer brewing process residue. Additionally, sodium chloride (NaCl), gum arabic (GA), and talc (T) were used in an attempt to modify the morphology of AgNPs. XRD, DLS, SEM, and TEM results demonstrate that stable AgNPs of different sizes and shapes were synthesized. FTIR, HPLC analysis, and the quantification of total proteins, free amino acids, reducing sugars, and total polyphenols before and after AgNPs synthesis showed that ME biomolecules allowed them to act as a source of reducing and stabilizing agents. Therefore, this study provides evidence that ME can be successfully used to biosynthesize AgNPs. Additionally, the antibacterial activity of AgNPs against Gram-negative and Gram-positive bacteria was evaluated. Results indicate that AgNPs show a higher antibacterial activity against Gram-positive bacteria.

The Size Effect of Silver Nanoparticles on Reinforcing the Mechanical Properties of Regenerated Fibers.

Regenerated silk fibroin (RSF), made from discarded silk cocoons, can be processed into regenerated silk fibers by a simple, inexpensive, and environmentally friendly wet-spinning process. However, the breaking strength and toughness of most RSF fibers are lower than those of natural silk. In this study, Ag nanoparticles (NPs) of different sizes were introduced into RSF to form RSF/AgNPs hybrid fibers by wet spinning. The effects of AgNPs of different sizes on the mechanical properties and structure of the hybrid fibers were investigated. The results demonstrated that the mechanical properties of hybrid fibers were significantly improved, especially the breaking strain, after the addition of four different sizes of AgNPs. With the reduction in AgNPs size (2-60 nm), the breaking strength and breaking strain of hybrid fibers tended to increase. The results showed that the hybrid fibers containing 2 nm AgNPs were remarkable, with excellent mechanical properties and toughness, and the breaking strain reached 138.27%, which was far greater than blank RSF fibers (15.02%) and even natural silk (about 21%). The S-FTIR and WAXD showed that, compared with the larger AgNPs, the smaller AgNPs contributed more to the formation of silk fibroin β-sheet and crystallinity, and reduced the β-crystallite size. This study is helpful to understand the relationship between the size of nanoparticles and the mechanical properties of hybrid fibers.

Biological Synthesis of Monodisperse Uniform-Size Silver Nanoparticles (AgNPs) by Fungal Cell-Free Extracts at Elevated Temperature and pH.

Fungi’s ability to convert organic materials into bioactive products offers environmentally friendly solutions for diverse industries. In the nanotechnology field, fungi metabolites have been explored for green nanoparticle synthesis. Silver nanoparticle (AgNP) research has grown rapidly over recent years mainly due to the enhanced optical, antimicrobial and anticancer properties of AgNPs, which make them extremely useful in the biomedicine and biotechnology field. However, the biological synthesis mechanism is still not fully established. Therefore, this study aimed to evaluate the combined effect of time, temperature and pH variation in AgNP synthesis using three different fungi phyla (Ascomycota, Basidiomycota and Zygomycota) represented by six different fungi species: Cladophialophora bantiana (C. bantiana), Penicillium antarcticum (P. antarcticum), Trametes versicolor (T. versicolor), Trichoderma martiale (T. martiale), Umbelopsis isabellina (U. isabellina) and Bjerkandera adusta (B. adusta). Ultraviolet–visible (UV-Vis) spectrophotometry and transmission electron microscopy (TEM) results demonstrated the synthesis of AgNPs of different sizes (3 to 17 nm) and dispersity percentages (25 to 95%, within the same size range) using fungi extracts by changing physicochemical reaction parameters. It was observed that higher temperatures (90 °C) associated with basic pH (9 and 12) favoured the synthesis of monodisperse small AgNPs. Previous studies demonstrated enhanced antibacterial and anticancer properties correlated with smaller nanoparticle sizes. Therefore, the biologically synthesised AgNPs shown in this study have potential as sustainable substitutes for chemically made antibacterial and anticancer products. It was also shown that not all fungi species (B. adusta) secrete metabolites capable of reducing silver nitrate (AgNO3) precursors into AgNPs, demonstrating the importance of fungal screening studies.

Interaction of silver nanoparticles with plasma transport proteins: A systematic study on impacts of particle size, shape and surface functionalization

Metallic nanoparticles are an important and widely used materials in development of nano-enabled medicine. For that reason, their interaction with biological molecules has to be systematically examined, as use of nanoparticles can lead to altered biological functions. In this study, we evaluated the interaction between silver nanoparticles (AgNPs) and two important plasma transport proteins - albumin and α-1-acid glycoprotein. To investigate comprehensively how different physico-chemical properties impact interaction of proteins with nanosurface, AgNPs of different size, shape and surface coating was prepared. The study was conducted using UV–Vis absorption, fluorescence, inductively coupled plasma mass spectrometry, circular dichroism spectroscopy, transmission electron microscopy, dynamic and electrophoretic light scattering techniques. The results showed significant complexities of the nano-bio interface and binding affinities of proteins onto surface of different AgNPs, which were affected by both AgNPs and protein properties. The most significant role on AgNPs-protein interaction had the coating agents used for AgNPs surface stabilization. Our findings should improve safe-by-design approach to development of the metallic nanomaterials for medical use.

Silver Nanoparticle Interactions with Surfactant-Based Household Surface Cleaners.

Silver nanoparticles (AgNPs) are the most widely used engineered nanomaterials in consumer products, primarily due to their antimicrobial properties. This widespread usage has resulted in concerns regarding potential adverse environmental impacts and increased probability of human exposure. As the number of AgNP consumer products grows, the likelihood of interactions with other household materials increases. AgNP products have the potential to interact with household cleaning products in laundry, dishwashers, or during general use of all-purpose surface cleaners. This study has investigated the interaction between surfactant-based surface cleaning products and AgNPs of different sizes and with different capping agents. One AgNP consumer product, two laboratory-synthesized AgNPs, and ionic silver were selected for interaction with one cationic, one anionic, and one nonionic surfactant product to simulate AgNP transformations during consumer product usage before disposal and subsequent environmental release. Changes in size, morphology, and chemical composition were detected during a 60 min exposure to surfactant-based surface cleaning products using ultraviolet-visible (UV/Vis) spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX), and dynamic light scattering (DLS). Generally, once AgNP suspensions were exposed to surfactant-based surface cleaning products, all the particles showed an initial aggregation, likely due to disruption of their capping agents. Over the 60 min exposure, cleaning agent-1 (cationic) showed more significant particle aggregates than cleaning agent-2 (anionic) and cleaning agent-3 (nonionic). In addition, UV/Vis, TEM-EDX, and DLS confirmed formation of incidental AgNPs from interaction of ionic silver with all surfactant types.

Potent antiviral effect of silver nanoparticles on SARS-CoV-2

The pandemic of COVID-19 is spreading unchecked due to the lack of effective antiviral measures. Silver nanoparticles (AgNP) have been studied to possess antiviral properties and are presumed to inhibit SARS-CoV-2. Due to the need for an effective agent against SARS-CoV-2, we evaluated the antiviral effect of AgNPs. We evaluated a plethora of AgNPs of different sizes and concentration and observed that particles of diameter around 10 nm were effective in inhibiting extracellular SARS-CoV-2 at concentrations ranging between 1 and 10 ppm while cytotoxic effect was observed at concentrations of 20 ppm and above. Luciferase-based pseudovirus entry assay revealed that AgNPs potently inhibited viral entry step via disrupting viral integrity. These results indicate that AgNPs are highly potent microbicides against SARS-CoV-2 but should be used with caution due to their cytotoxic effects and their potential to derange environmental ecosystems when improperly disposed.

Synthesis, characterization and antibacterial application of silver nanoparticle embedded composite cryogels

Water treatment applications; they consist of processes that desalination, softening, removals of dissolved organic matter, color, particle and microorganism. In traditional treatment processes, microorganisms cause thick film layer on the membrane to be used and not enough treatment. Silver nanoparticles (AgNPs), known to stop bacterial growth due to their superior antibacterial properties even at low concentrations due to their contact with microorganisms, are used for water disinfection. Membrane production with a combination of AgNPs and polymers has started to attract attention in recent years due to advanced optics, conductivity and antibacterial properties. The ability of AgNP to exhibit its antibacterial effect depends on the property of this material to be homogeneously dispersed in the polymer. In this study, Poly(2-hydroxyethyl methacrylate-glycidyl methacrylate), Poly(HEMA-GMA), cryogels were synthesized as solid support. In order to gain antibacterial properties to synthesized cryogels, AgNPs of different sizes were embedded in cryogels. These structures have been used as a kind of antibacterial filter in the purification of water obtained from natural sources used as drinking and using water in the local region. Particle Size analysis was used to determine the size of synthesized AgNPs. Swelling test, Scanning Electron Microscopy (SEM), Elemental Analysis, Fourier Transform Infrared Spectroscopy (FT-IR), and surface area (BET) analysis were performed for characterization of cryogels.

One‐pot microwave‐assisted synthesis of size‐dependent l‐glutathione‐capped spherical silver nanoparticles suitable for materials with antibacterial properties

AbstractIn the last years, there has been an alarming increase in antibiotic resistance by pathogenic microbes, which has become a major public health concern. There is a great interest in developing new antimicrobial for reducing the impact. Silver nanoparticles (AgNPs) as antibacterial agents are currently being studied to be used to fight these pathogenic microbes. The aim of the present study was to synthesize AgNPs of different sizes through the use of microwave and determine their antimicrobial activities. Synthesis of size‐dependent l‐glutathione‐capped spherical nanoparticles through one‐pot microwave synthesis was achieved, and their antimicrobial properties were determined. Different sizes of AgNPs between 5–10, 15–35, and 50–80 nm were made by varying the concentration of silver nitrate and using sodium borohydride (NaBH4) as a reducing agent. l‐glutathione was used to stabilize the AgNPs to prevent them from aggregation in the colloidal solution. The synthesized AgNPs showed ultraviolet absorption at around 400 nm with high concentration of AgNO3 having sharp peaks. The formed particles were crystalline in nature with uniform spherical shape. The formed AgNPs were of crystalline size of 9.94, 18.45, 34.96, 52.40, and 58.50 nm. Fourier transform infrared analysis confirmed conjugation of glutathione as a capping agent to AgNPs as the result of the formed spectra showing the absence of ─SH stretch. The high temperature generated by microwave helped to synthesize nanoparticles within a short time and by varying the concentration of AgNO3 helped obtain the desired particle size. Glutathione conjugated well with AgNPs as a result of interaction of negative thiol resulting to colloidal stabilization and reduced aggregation. The antibacterial activity of AgNPs was found to be size dependent with the smaller size of 9.94 nm being more efficient than 18.45, 34.96, 52.40, and 58.50 nm against the tested strains Bacillus subtilis (ATCC 6633), Escherichia coli (ATCC 25922), Salmonella spp. (ATCC 700623), and Staphylococcus aureus (ATCC 25923). Of the four stains, E. coli was found to be the least affected by all three different particle sizes of the synthesized AgNPs.

Understanding the stability and durability of laser-generated Ag nanoparticles and effects on their antibacterial activities

Ag NPs of different sizes prepared using laser ablation of an Ag solid target in pure deionised water and in polyvinylpyrrolidone (PVP) surfactant liquid were subjected to different storage conditions for up to six months. Ag NPs with sizes less than 10 nm were more susceptible to agglomeration over time. However, the samples of Ag NPs produced and stored in the PVP solutions in the dark at 4 °C temperature presented longest stability for at least six months. The antibacterial activity of ultra-fine Ag NPs in the range of 2 to 10 nm and Ag NPs larger than 10 nm lasted at least six months against E. coli bacteria.

Modification of Spectral Behavior of Ketocyanine Dyes by Silver Nanoparticles of Different Sizes

The spectral behavior of two ketocyanine dyes 2,5-di[(E)-1-(4-dimethylaminophenyl) methylidine]-1-cyclopentanone(2,5-DMAPMC) and 2,5-di[(E)-1-(4-diethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DEAPMC) is investigated in the presence of silver nanoparticles (AgNPs) of sizes 32[Formula: see text]nm, 52[Formula: see text]nm and 60[Formula: see text]nm using absorption and fluorescence spectroscopy. The absorption spectral changes of dyes with the addition of AgNPs of different sizes suggest their possible interaction with AgNPs. Fluorescence quenching has been observed for both the dyes with the addition of AgNPs of all the sizes. The possible quenching mechanisms including energy transfer and electron transfer are discussed. The fluorescence quenching rate parameter is found to increase with increase in the size of AgNPs and is explained based on the varying ability of silver AgNPs of different sizes to accommodate dye molecules. The effect of functional groups on quenching rate parameters is also discussed.

The Influence of Silver Nanoparticle Sizes on Antibacterial Activity, Cytotoxicity and Genotoxicity of Alginate Hydrogel Beads Containing Silver Nanoparticles

Sizes of silver nanoparticles (AgNPs) have been shown to affect the biological activity of AgNPs. Hydrogel beads loaded with AgNPs have been extensively employed for biomedical applications. However, the influence of AgNPs sizes on biological activity of AgNP-loaded hydrogel beads has not much studied. Our objectives were to investigate the effect of AgNP sizes on the antibacterial activity, the cyto- and genotoxicity of AgNPs/alginate hydrogel beads. AgNPs of different sizes (⁓10 nm for S-AgNPs, and ⁓50 nm for L-AgNPs) were incorporated into alginate hydrogel beads during the preparation. The results showed that, S-AgNPs/alginate hydrogel beads (⁓89% inhibition) at AgNP concentration of 10 µg/ml tended to inhibit the growth of E. coli greater than L-AgNPs/alginate hydrogel beads (⁓49% inhibition) at the same dose. Moreover, at this effective antibacterial concentration (10 µg/ml), S-AgNPs/alginate hydrogel beads exhibited weak cytotoxic effect to HaCaT cells whereas L-AgNPs/alginate hydrogel beads showed non-cytotoxicity to this cell line. Furthermore, treatment of HaCaT cells with 10 µg/ml of S-AgNPs/ or L-AgNPs/alginate hydrogel beads did not result in a significant change in %DNA in tail when compared to untreated cells. Therefore, these AgNPs/alginate hydrogel beads, especially with smaller sized AgNPs, can be used as an antibacterial biomaterial with low cytotoxicity and genotoxicity to human cells.

Determination of silver nanoparticles by atomic absorption spectrometry after dispersive suspended microextraction followed by oxidative dissolution back-extraction

This study presents a liquid phase microextraction method for the quantification of silver nanoparticles (AgNPs) in environmental samples by means of directly suspended microextraction and atomic absorption spectrometry. The method is based on the dispersion of octanol into fine droplets where AgNPs are partitioned and extracted from the bulk aqueous phase. Then octanol is re-dispersed again in a strongly acidic and oxidizing aqueous medium in order to selectively decompose AgNPs to silver ions. The aqueous extract is then analyzed by atomic absorption spectrometry. Under the working conditions, the method offers high selectivity for AgNPs since most nanoparticle species cannot be extracted into the octanol phase, while the selective back-extraction procedure ensures that only AgNPs are dissolved to the final extract medium. The method works equally well for AgNPs of different size and coatings, thus enabling the determination of the total concentration AgNPs in real samples. Method application in different water samples was used to evaluate the utility of the method in the analysis of real samples of variable complexity with satisfactory results in terms of detection limit (less than 100 femto-mole of AgNPs), recoveries (90–104%) and reproducibility (lower than 7%).

Simultaneous determination of the size and concentration of AgNPs in water samples by UV–vis spectrophotometry and chemometrics tools

The combination of UV–vis spectrophotometry with a chemometric calibration tool based on partial least squares (PLS) has allowed us the development of a multivariate analytical method that simultaneously estimates the concentration and size of mixtures of silver nanoparticles (AgNPs) in environmental water samples. The method is based on changes in the surface plasmon resonance band (SPRB) of AgNPs when they form aggregated/assembled structures with L-cysteine (L-cys). Measurementts were performed by employed a fixed-time kinetics method that implies that the final spectra (response) are obtained by subtstracting the solutions spectra at fixed times. Optimization of experimental conditions affecting aggregation such as time, temperature, pH and concentration of aggregating substance was performed by experimental design and response surface methodologies (RSM). A multivariate calibration model using AgNPs of known diameter size ((20 ± 3), (41 ± 3), (59 ± 5) and (79 ± 7) nm) within a concentration range between 0.62 and 2.5 mg L−1 was constructed by using a mixture experimental design and PLS. The method was finally applied to estimate size and concentration of AgNPs in AgNPs-spiked river and tap water samples. Water samples were spiked with individual, binary and ternary mixtures of AgNPs of different sizes and by using two types of AgNPs: citrate-coated AgNPs (cit-AgNPs) and polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs). A good correspondence was obtained between predicted values and the total amount of AgNPs added with recovery values ranged within 80–160% for the individual mixtures, 68–108% for the binary mixtures and 60–64% for the ternary mixtures of AgNPs. Finally, transmission electron microscopy (TEM) measurements were performed for those cases where discrepancies between the expected and the obtained values were observed. TEM micrographs evidenced the presence of agglomerates or aggregates of AgNPs in some of the mixtures or water tested.

Influence of gastrointestinal environment on free radical generation of silver nanoparticles and implications for their cytotoxicity

With the increasing number of applications of silver nanoparticles (Ag NPs) in consumer products, including food contact applications, it is important to understand potential health effects of ingestion of Ag NPs. The biosafety analysis of Ag NPs in various mammalian cells has been widely studied; however, the influence of the gastrointestinal environment on the physicochemical properties and toxicity of Ag NPs has not been fully addressed. In the present study, we investigated the impact of simulated human gastrointestinal tract (GIT) fluids on the physicochemical properties of Ag NPs and their impact on the in vitro cytotoxicity of Ag NPs in intestinal epithelial (Caco-2) cells. Polyvinylpyrrolidone (PVP)-coated Ag NPs of different sizes (30, 50, 100 nm) were incubated in three GIT fluids that differed in composition and pH (1.6, 5.0, 6.5) and were designed to mimic human gastric fluid in a fasted state (FaSSGF), human intestinal fluid in a fasted state (FaSSIF), and human intestinal fluid in a fed state (FeSSIF). Time-dependent decreases in UV–Vis absorption and increases in dynamic light scattering (DLS) were observed during the three-hour incubation of Ag NPs in GIT fluids. The results of transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS) suggested that the Ag NPs aggregated and precipitated as AgCl salts in the presence of FaSSGF and FeSSIF. In the presence of FaSSGF and hydrogen peroxide (H2O2), a particle size- and concentration-dependent generation of hydroxyl radicals (OH) was detected by electron spin resonance (ESR) spectroscopy. When compared to the effects observed with the incubation of Ag NPs in H2O, incubation of Ag NPs in FaSSGF showed decreased cellular uptake in Caco-2 cells. In contrast, the incubation of Ag NPs in FeSSIF demonstrated increased cellular uptake and cytotoxicity. The results of this study demonstrate that GIT fluids have a significant influence on the physicochemical properties and cytotoxicity of Ag NPs and they provide valuable information that may be used in the safety evaluation of Ag NPs for consumer products.

Discrimination between ionic silver and silver nanoparticles in consumer products using graphite furnace atomic absorption spectrometry

GFAAS method allows for rapid discrimination between Ag+ and AgNPs of different size extracted from fabrics and hygiene products.

Effect of different physicochemical conditions on the synthesis of silver nanoparticles using fungal cell filtrate of Aspergillus oryzae (MTCC No. 1846) and their antibacterial effect

Synthesis of silver nanoparticles (AgNPs) under different physicochemical conditions like concentration of silver nitrate (AgNO3), pH and temperature, using fungal cell filtrate of Aspergillus oryzae (MTCC No. 1846) and its antibacterial properties were demonstrated. When fungal cell filtrate having neutral pH was exposed to different concentrations of aqueous solution AgNO3 (1–10 mM), formation of stable AgNPs of different sizes was observed. The size of the AgNPs decreased with the increase of AgNO3 concentration from 1 mM to 8 mM, however, the particles size increased with the increase of AgNO3 concentration from 9 mM to 10 mM. When fungal cell filtrate exposed to aqueous solution of 1 mM AgNO3 at different pH (4–10), the silver ions (Ag+) were reduced leading to the formation of stable AgNPs of different sizes. The size of the AgNPs decreased with the increase of alkaline conditions. When aqueous solution of 1mM AgNO3 with fungal cell filtrate, having neutral pH, was exposed to different temperatures (10, 30, 50, 70 and 90 °С), formation of stable AgNPs having different sizes were obtained. The size of the AgNPs decreased with the increase of temperature. Synergetic effect with antibiotics and size dependent antibacterial activities were also demonstrated against Escherichia coli (MTCC 1687), Staphylococcus aureus (MTCC 737), Bacillus subtilis (MTCC 441) and Klebseilla pneumoniae (MTCC 4030). The formation AgNPs was characterized by UV–vis spectrophotometer. Transmission electron microscope (TEM) confirmed the sizes of the obtained nanoparticles. X-ray diffractometer (XRD) spectrum confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy (FTIR) confirmed the presence of protein as stabilizing agent around AgNPs. Scanning electron microscope (TEM) confirmed the morphological changes in the treated bacterial organisms.

Direct and indirect effects of silver nanoparticles on freshwater and marine microalgae (Chlamydomonas reinhardtii and Phaeodactylum tricornutum)

The last decade has seen a considerable increase in the use of silver nanoparticles (AgNPs), which are found in many every-day consumer products including textiles, plastics, cosmetics, household sprays and paints. The release of those AgNPs into aquatic environments could be causing ecological damage. In this study we assess the toxicity of AgNPs of different sizes to two species of microalgae, from freshwater and marine environment (Chlamydomonas reinhardtii and Phaeodactylum tricornutum respectively). Dissolution processes affect the form and concentration of AgNPs in both environments. Dissolution of Ag from AgNPs was around 25 times higher in marine water. Nevertheless, dissolution of AgNPs in both culture media seems to be related to the small size and higher surface area of NPs. In marine water, the main chemical species were AgCl2− (53.7%) and AgCl3−2 (45.2%). In contrast, for freshwater, the main chemical species were Ag+ (26.7%) and AgCl− (4.3%). The assessment of toxicological responses, specifically growth, cell size, cell complexity, chlorophyll a, reactive oxygen species, cell membrane damage and effective quantum yield of PSII, corroborated the existence of different toxicity mechanisms for microalgae. Indirect effects, notably dissolved Ag ions, seem to control toxicity to freshwater microalgae, whereas direct effects, notably attachment onto the cell surface and the internalization of AgNPs inside cells, seem to determine toxicity to the marine species studied. This research contributes to knowledge on the role of intrinsic and extrinsic factors in determining the behavior of NPs in different aquatic environments and the interaction with microalgae.

Size Dependent Catalytic Activity of Actinodaphne madraspatana Bedd Leaves Mediated Silver Nanoparticles

Green synthesis of metal nanoparticles using earth abundant materials in the absence of any toxic solvent, reducing agent and protecting group is one of the emerging areas of research in materials chemistry. Herein, we report a green method for the synthesis of silver nanoparticles (AgNPs) using Actinodaphne madraspatana Bedd leaf extract as reducing as well as stabilizing agent. To our delight, AgNPs of different sizes could be readily synthesized by simply changing the pH of plant extract and the average size of AgNPs were found to be 60, 35 and 20 nm at pH 6, 9 and 12 respectively. The efficacy of prepared AgNPs towards the catalytic reduction of 4-nitrophenol (4-NP) has been investigated and the nanocatalysts have demonstrated excellent catalytic activity as evidenced from the rate constants. The kinetics of reduction reaction follows Langmuir–Hinshelwood mechanism, based on which the rate constant ‘k’ was calculated. The effect of catalyst dosage, concentration of 4-NP, concentration of NaBH4 and size of AgNPs towards catalytic reduction of 4-NP has been systematically investigated. It was interesting to notice that the AgNPs have exhibited size dependent catalytic activity towards reduction of 4-NP and the catalytic activity was found to increase with decrease in particle size.

Digestive cell lysosomes as main targets for Ag accumulation and toxicity in marine mussels, Mytilus galloprovincialis, exposed to maltose-stabilised Ag nanoparticles of different sizes

Bioavailability and toxicity of maltose-stabilised AgNPs of different sizes (20, 40 and 100 nm) in mussels were compared with bulk and aqueous forms of the metal through a two-tier experimental approach. In the first tier, mussels were exposed for 3 d to a range of concentrations (0.75, 75, 750 μg Ag/l) in the form of Ag20-Mal, Ag40-Mal, Ag100-Mal, bulk Ag and aqueous Ag (as AgNO3), as well as to the concentrations of maltose used in the formulation of NPs. Mortality, bioaccumulation, tissue and cell distribution and lysosomal responses were investigated. In the second tier, mussels were exposed for 21 d to Ag20-Mal, Ag100-Mal, bulk Ag and aqueous Ag at the lowest effective concentration selected after Tier 1 (0.75 μg Ag/l), biomarkers and toxicopathic effects were investigated. Aqueous Ag was lethal within 3 d at 75 μg Ag/l; Ag NPs or bulk Ag did not produce significant mortality at 750 μg Ag/l. Ag accumulation was limited and metallothionein gene transcription was not regulated although metal accumulation occurred in digestive, brown and stomach epithelial cells and in gut lumen after exposure to AgNPs and aqueous Ag starting at low concentrations after 1 d. Electrondense particles (<10 nm) in lysosomes and residual bodies after exposure to AgNPs contained Ag and S (X-ray). Intralysosomal metal accumulation and lysosomal membrane destabilisation were enhanced after exposure to all the forms of Ag and more marked after exposure to Ag20-Mal than to larger NPs. 21 d exposure to AgNPs provoked digestive cell loss and loss of digestive gland integrity, resulting in atrophy-necrosis in digestive alveoli and oedema/hyperplasia in gills (Ag NP), vacuolisation in digestive cells (aqueous Ag) and haemocyte infiltration of connective tissue (all treatments). Intralysosomal metal accumulation, lysosomal responses and toxicopathic effects are enhanced at decreasing sizes and appear to be caused by Ag+ ions released from NPs, although the metal was not substantially accumulated.