PVP-coated AgNPs Research Articles

Visualization, quantification and coordination of Ag+ ions released from silver nanoparticles in hepatocytes.

Silver nanoparticles (AgNPs) can enter eukaryotic cells and exert toxic effects, most probably as a consequence of the release of Ag+ ions. Due to the elusive nature of Ag+ ionic species, quantitative information concerning AgNP intracellular dissolution is missing. By using a synchrotron nanoprobe, silver is visualized and quantified in hepatocytes (HepG2) exposed to AgNPs; the synergistic use of electron microscopy allows for the discrimination between nanoparticular and ionic forms of silver within a single cell. AgNPs are located in endocytosis vesicles, while the visualized Ag+ ions diffuse in the cell. The averaged NP dissolution rates, measured by X-ray absorption spectroscopy, highlight the faster dissolution of citrate-coated AgNPs with respect to the less toxic PVP-coated AgNPs; these results are confirmed at the single-cell level. The released Ag+ ions recombine with thiol-bearing biomolecules: the Ag-S distances measured in cellulo, and the quantitative evaluation of gene expression, provide independent evidence of the involvement of glutathione and metallothioneins in Ag+ binding. The combined use of cutting-edge imaging techniques, atomic spectroscopy and molecular biology brings insight into the fate of AgNPs in hepatocytes, and more generally into the physicochemical transformations of metallic nanoparticles in biological environments and the resulting disruption of metal homeostasis.

Size-dependent cytotoxicity of silver nanoparticles in human neutrophils assessed by multiple analytical approaches

AimsSilver nanoparticles (AgNPs) have emerged as an important class of nanomaterials with a wide range of industrial and medical applications. The assessment of AgNPs' biological effects in the human organism is therefore essential to evaluate the impact of these nanomaterials in public health and reassure the ratio benefit/risk. In the present study, the effect of polyvinyl pyrrolidone (PVP)-coated AgNPs with distinct sizes (10 and 50nm) on neutrophils' oxidative burst and toxicity were tested. Main methodsThe effect of AgNPs on human neutrophils viability was evaluated by trypan blue, neutral red and propidium iodide methods. The measurement of neutrophils' oxidative burst was performed using the probe dihydrorhodamine 123. The cytomorphological alterations of human neutrophils exposed to AgNPs were evaluated by optical microscopy and transmission electron microscopy. Key findingsIt was observed that PVP-coated AgNPs are toxic to human neutrophils being the 10nm AgNPs more toxic than the 50nm AgNPs. The smallest AgNPs lead to membrane damage, impaired lysosomal activity and induce neutrophils' oxidative burst. Despite the production of reactive species, the toxicity of AgNPs is not NADPH oxidase-dependent. SignificanceThese data indicate that AgNPs are toxic to human neutrophils in concentration-, time- and size-dependent manner, but independent of NADPH oxidase activation.

Mammalian Cells Exhibit a Range of Sensitivities to Silver Nanoparticles that are Partially Explicable by Variations in Antioxidant Defense and Metallothionein Expression.

While it is well known that there are interspecies differences in Ag sensitivity, differences in the cytotoxic responses of mammalian cells to silver nanoparticles (Ag NPs) are also observed. In order to explore these response outcomes, six cell lines, including epithelial cells (Caco-2, NHBE, RLE-6TN, and BEAS-2B) and macrophages (RAW 264.7 and THP-1) of human and rodent origin, are exposed to 20 nm citrate- and PVP-coated Ag NPs with Au cores, as well as 20 nm citrate-coated particles without cores. An MTS assay shows that while Caco-2 and NHBE cells are resistant to particles over a 0.1-50 μg mL(-1) dose range, RAW 264.7, THP-1, RLE-6TN, and BEAS-2B cells are more susceptible. While there are small differences in dissolution rates, there are no major differences in the cytotoxic potential of the different particles. However, differences in anti-oxidant defense and metallothionein expression among different cell types are observed, which can partially explain differential Ag NP sensitivity. So, it is important to consider these differences in understanding the potential heterogeneous effects of nano Ag on mammalian biological systems.

Atomistic Simulations of Coating of Silver Nanoparticles with Poly(vinylpyrrolidone) Oligomers: Effect of Oligomer Chain Length

Silver nanoparticles (AgNPs) possess unique physicochemical properties, which are different from those of matter of the same chemical composition on a larger scale. These features open up the opportunity for their use in many promising chemical and biomedical applications. In this study we have developed an atomistic model for molecular dynamics (MD) simulations of AgNP coated by poly(N-vinyl-2-pyrrolidone) (PVP) oligomers. We focus on identifying the relative length of PVP oligomers, enabling effective protecting of a crystalline silver core of 4.5 nm diameter from water contacts. Three different PVP-coated AgNP systems have been compared: (i) a nanoparticle coated by a mixture of short-chain PVP oligomers of the varying size and (ii,iii) the silver core wrapped by a single, long-chain PVP polymer with the number of monomers equal to 816 and 1440, respectively. We have validated the MD models of the PVP–AgNPs using a series of MD simulations reproducing adsorption, wrapping, and coating of PVP around a silver core either as short PVP oligomers or as a single-chain, long polymer of a varying length. Our simulations predict that the saturated coating of PVP around the silver core of the given diameter can occur when the polymer chain length approaches 2600–2800 units.

Asymmetric flow field-flow fractionation of manufactured silver nanoparticles spiked into soil solution

Manufactured metallic silver nanoparticles (AgNP) are intensively utilized in consumer products and this will inevitably lead to their release to soils. To assess the environmental risks of AgNP in soils, quantification of both their concentration and size in soil solution is essential. We developed a methodology consisting of asymmetric flow field-flow fractionation (AF4) in combination with on-line detection by UV–vis spectroscopy and off-line HR-ICP-MS measurements to quantify the concentration and size of AgNP, coated with either citrate or polyvinylpyrrolidone (PVP), in water extracts of three different soils. The type of mobile phase was a critical factor in the fractionation of AgNP by AF4. In synthetic systems, fractionation of a series of virgin citrate- and PVP-coated AgNP (10–90nm) with reasonably high recoveries could only be achieved with ultrahigh purity water as a mobile phase. For the soil water extracts, 0.01% (w:v) sodium dodecyl sulfate (SDS) at pH 8 was the key to a successful fractionation of the AgNP. With SDS, the primary size of AgNP in all soil water extracts could be determined by AF4, except for PVP-coated AgNP when clay colloids were present. The PVP-coated AgNP interacted with colloidal clay minerals, leading to an overestimation of their primary size. Similar interactions between PVP-coated AgNP and clay colloids can take place in the environment and facilitate their transport in soils, aquifers, and surface waters. In conclusion, AF4 in combination with UV–vis spectroscopy and HR-ICP-MS measurements is a powerful tool to characterize AgNP in soil solution if the appropriate mobile phase is used.

Effects of prenatal exposure to silver nanoparticles on spatial cognition and hippocampal neurodevelopment in rats

BackgroundSilver nanoparticles (Ag-NPs) are among the most commonly used nanomaterials and may be exposed to human and ecosystem. Prior in vitro study showed that Ag-NPs compromised neurodevelopment of PC12 cells. This study aims to investigate the effect of prenatal exposure to Ag-NPs on spatial cognition and hippocampal neurodevelopment in rats. MethodsPregnant rats were exposed by intraperitoneal injection to various solutions during pregnancy, including vehicle (water and glycerol mixture, 1:1 in volume), uncoated Ag-NPs (0.427mg Ag perg rat), polyvinylpyrrolidine (PVP)-coated Ag-NPs (0.407mg Ag perg rat), silver nitrate (0.013mg Ag+ and 0.007mg NO3+ per g rat) and sodium nitrate (0.007mg NO3+ perg rat). Pregnant rats without any injection were used as blank control. Male offspring at postnatal day 35 (PND35) were randomly selected for Morris Water Maze (MWM) test. After the MWM test, the rats were decapitated and hippocampus were collected for analysis of tissue structure, silver content, GAP-43 mRNA and protein expressions. ResultsFor the spatial learning in MWM test, since the third test day, the escape latency of rats in the uncoated Ag-NPs group was significantly higher than those in the other groups. The behaviors of rats were not significantly different among the other groups. The averaged silver content in the hippocampus of rats in the uncoated Ag-NPs group was 17.51μg/g, significantly higher than those in the other groups. The hippocampal structure in rats of the uncoated Ag-NPs group was deformed as compared to those in the other groups. Compared with the rats in blank and vehicle controls, the levels of GAP-43 mRNA and protein in the uncoated Ag-NPs, PVP-coated Ag-NPs, silver nitrate and sodium nitrate groups were all significantly decreased. The levels of GAP-43 mRNA and protein of rats in the uncoated Ag-NPs group was significantly lower than those in the later three groups, while there was no significant difference among the later three groups. ConclusionsMaternal exposure to uncoated Ag-NPs during pregnancy impaired spatial cognition in rat offspring. GAP-43 reduction might be involved in the cognitive impairment. The toxicity was mainly associated with release of silver ion. Coating with PVP reduced the toxicity of Ag-NPs.

Persistence of silver nanoparticles in the rat lung: Influence of dose, size, and chemical composition

Increasing silver nanoparticle (AgNP) use in sprays, consumer products, and medical devices has raised concerns about potential health effects. While previous studies have investigated AgNPs, most were limited to a single particle size or surface coating. In this study, we investigated the effect of size, surface coating, and dose on the persistence of silver in the lung following exposure to AgNP. Adult male rats were intratracheally instilled with four different AgNPs: 20 or 110 nm in size and coated with either citrate or polyvinylpyrrolidone (PVP) at 0.5 or 1.0 mg/kg doses. Silver retention was assessed in the lung at 1, 7, and 21 d post exposure. ICP-MS quantification demonstrated that citrate-coated AgNPs persisted in the lung to 21 d with retention greater than 90%, while PVP-coated AgNP had less than 30% retention. Localization of silver in lung tissue at 1 d post exposure demonstrated decreased silver in proximal airways exposed to 110 nm particles compared with 20 nm AgNPs. In terminal bronchioles 1 d post exposure, silver was localized to surface epithelium but was more prominent in the basement membrane at 7 d. Silver positive macrophages in bronchoalveolar lavage fluid decreased more quickly after exposure to particles coated with PVP. We conclude that PVP-coated AgNPs had less retention in the lung tissue over time and larger particles were more rapidly cleared from large airways than smaller particles. The 20 nm citrate particles showed the greatest effect, increasing lung macrophages even 21 d after exposure, and resulted in the greatest silver retention in lung tissue.

Macroscopic assessment of nanosilver toxicity to soil denitrification kinetics.

A large increase in commercial and home use of silver nanoparticle (AgNP) products and technologies has raised concerns about their impact on environmental health. While several sources cite soils and sediments as the predominant sink for AgNPs in natural environments, few studies contribute to risk assessment of AgNPs in terrestrial environments. In this study, the effect of AgNPs ([Ag]: 1-100 mg/kg, 15-50 nm with 0-90% polyvinylpyrrolidone [PVP] capping agent) on soil denitrification processes was investigated with batch kinetic experiments using well-characterized AgNPs. Although the effects on denitrification kinetics and equilibrium end-points were variable among the AgNPs, denitrification kinetics were limited under certain conditions (e.g., PVP-coated AgNPs ≥ 10 mg/kg). In assessing the impact of AgNPs on ecosystem processes, it is important to consider the interactions of AgNPs with soils and sediments in addition to the physicochemical properties (size, coating agents, sedimentation rate, solubility, surface charge properties, dispersibility) of AgNPs.

Comparative toxicity of silver nanoparticles on oxidative stress and DNA damage in the nematode, Caenorhabditis elegans

This study examined the effects of polyvinylpyrrolidone (PVP) surface coating and size on the organismal and molecular toxicity of silver nanoparticles (AgNPs) on the nematode, Caenorhabditis elegans. The toxicity of bare AgNPs and 8 and 38nm PVP-coated AgNPs (PVP8-AgNPs, PVP38-AgNPs) were compared. The toxicity of AgNO3 was also tested because ion dissolution and particle-specific effects are often important characteristics determining Ag nanotoxicity. Comparative toxicity across AgNO3 and the three different types of AgNPs was first evaluated using a C. elegans mortality test by a direct comparison of the LC50 values. Subsequently, mutant screening followed by oxidative stress, mitochondrial toxicity and DNA damage assays were carried out at equitoxic (LC10 and LC50) concentrations to further assess the toxicity mechanism of AgNO3 and AgNPs. AgNO3 and bare AgNPs had similar toxicities, whereas PVP coating reduced the toxicity of the AgNPs significantly. Of the PVP-AgNPs, the smaller NPs were more toxic. Different groups of mutants responded differently to AgNO3 and AgNPs, which indicates that their toxicity mechanism might be different. AgNO3 and bare AgNPs induced mitochondrial membrane damage. None of the silver materials tested caused detectable polymerase-inhibiting DNA lesions in either the nucleus or mitochondria as measured by a quantitative PCR assay, but AgNO3, bare AgNPs and PVP8-AgNPs induced oxidative DNA damage. These results show that coatings on the AgNPs surface and the particle size make a clear contribution to the toxicity of the AgNPs, and oxidative stress-related mitochondrial and DNA damage appear to be potential mechanisms of toxicity.

Residence time effects on phase transformation of nanosilver in reduced soils

Residence time effects on phase transformation of silver nanoparticles (AgNPs) (15-50 nm, with and without polyvinylpyrrolidone (PVP) coating) were investigated in reducing soils using experimental geochemistry and synchrotron-based x-ray techniques. After 30 days of anaerobic incubation, a substantial fraction of PVP-coated AgNPs (15 nm) were transformed into Ag₂S and or humic acid (HA) complexed Ag(I), whereas only the HA fraction was dominant in uncoated AgNPs (50 nm). Several investigations recently reported that sulfidation of AgNPs to Ag₂S was the predominant mechanism controlling the fate of AgNP in soil-water environments. However, this investigation showed each AgNP underwent particle-specific chemical transformations to different end compounds after 30 days. Considering the small contribution of Ag(I) dissolution from all AgNPs (less than 5%), we concluded that changes in solid-state chemical speciation of sorbed AgNPs was promoted by particle-specific interactions of NPs in soil chemical constituents, suggesting a critical role of soil absorbents in predicting the fate of AgNPs in terrestrial environments.

Effects of Silver Nanoparticle on Soil-Nitrification Processes

The release of silver (Ag) nanoparticles (NPs) from the use of consumer products to the environment has raised concern about the risk to ecosystems because of its unpredictable toxicological impact to microorganisms in terrestrial environment. In this study, the impact of Ag chemical speciation (Ag(+) and Ag-NPs [50-nm uncoated and 15-nm polyvinylpyrrolidone (PVP)-coated Ag-NPs]) to soil nitrification kinetics was investigated using a batch soil-slurry nitrification method along with sorption isotherm and dissolution experiments. The results of nitrification potential (i.e., kinetic rate) suggest that Ag(+)/Ag-NPs, which strongly sorb in soils, suppressed the nitrification processes. Among each chemical species, the degree of suppression increased with increasing [Ag]total. Although ionic Ag (Ag(+)) species is known to exhibit greater antimicrobial effects than the solid state Ag species, such as Ag-NPs, in most studies, PVP-coated 15-nm Ag-NPs, however, more effectively suppressed the soil nitrification process than did Ag(+) under the same dose. Although several physicochemical-based toxicity mechanisms of dispersed Ag-NPs were discussed in pure culture and aquatic systems, it is not clearly understood how PVP-coated Ag-NPs could exhibit greater toxicity to nitrifying bacteria than Ag(+) in soils. In assessing the impact of Ag-NPs to microbial mediated processes (e.g., N cycles) in the terrestrial environment, it might be critical to understand the interactions and reactivity of Ag-NPs at the soil-water interface.

Cytotoxic and proinflammatory effects of PVP-coated silver nanoparticles after intratracheal instillation in rats

Silver nanoparticles (AgNP) are among the most promising nanomaterials, and their usage in medical applications and consumer products is growing rapidly. To evaluate possible adverse health effects, especially to the lungs, the current study focused on the cytotoxic and proinflammatory effects of AgNP after the intratracheal instillation in rats. Monodisperse, PVP-coated AgNP (70 nm) showing little agglomeration in aqueous suspension were instilled intratracheally. After 24 hours, the lungs were lavaged, and lactate dehydrogenase (LDH), total protein, and cytokine levels as well as total and differential cell counts were measured in the bronchoalveolar lavage fluid (BALF). Instillation of 50 µg PVP-AgNP did not result in elevated LDH, total protein, or cytokine levels in BALF compared to the control, whereas instillation of 250 µg PVP-AgNP caused a significant increase in LDH (1.9-fold) and total protein (1.3-fold) levels as well as in neutrophil numbers (60-fold) of BALF. Furthermore, while there was no change in BALF cytokine levels after the instillation of 50 µg PVP-AgNP, instillation of 250 µg PVP-AgNP resulted in significantly increased levels of seven out of eleven measured cytokines. These finding suggest that exposure to inhaled AgNP can induce moderate pulmonary toxicity, but only at rather high concentrations.

The role of the glutamatergic NMDA receptor in nanosilver-evoked neurotoxicity in primary cultures of cerebellar granule cells

Nanoparticles are known to enter the vertebrate brain, but little is known about their neurotoxicity. The aim of this study is to investigate mechanisms of the contribution of AgNPs to neuronal cell death using primary cultures of rat cerebellar granule cells (CGCs). We tested the role of glutamatergic N-methyl-d-aspartate receptors (NMDA) in AgNP-evoked neurotoxicity using MK-801, a noncompetitive inhibitor of NMDAR. We used commercially available 0.2% PVP-coated AgNPs <100nm in a concentration range of 2.5–75μg/ml sonicated with fetal calf serum. After a 10min incubation period, a dose-dependent increase in the uptake of 45Ca2+ into neurons was observed in the presence of 25–75μg/mL AgNPs which was completely abolished by addition of MK-801. Using the fluorescent dye fluo3 AM we observed an increase in the intracellular calcium level by 87% compared to control. ROS production was found to increase by about 30% over control after a 30-min incubation with 75μg/mL AgNPs. Further, we observed a significant decrease in the mitochondrial potential during a 30-min incubation with AgNPs. Administration of MK-801 was found to provide a protective effect. Our results show that excitotoxicity via activation of NMDA receptor, followed by calcium imbalance, destabilization of mitochondrial function and ROS production, indicate an important mechanism involved in neurotoxicity evoked by AgNPs in cultured neurons.

Investigating oxidative stress and inflammatory responses elicited by silver nanoparticles using high-throughput reporter genes in HepG2 cells: Effect of size, surface coating, and intracellular uptake

Silver nanoparticles (Ag NP) have been shown to generate reactive oxygen species; however, the association between physicochemical characteristics of nanoparticles and cellular stress responses elicited by exposure has not been elucidated. Here, we examined three key stress-responsive pathways activated by Nrf-2/ARE, NFκB, and AP1 during exposure to Ag NP of two distinct sizes (10 and 75nm) and coatings (citrate and polyvinylpyrrolidone), as well as silver nitrate (AgNO3), and CeO2 nanoparticles. The in vitro assays assessed the cellular response in a battery of stable luciferase-reporter HepG2 cell lines. We further assessed the impact of Ag NP and AgNO3 exposure on cellular redox status by measuring glutathione depletion. Lastly, we determined intracellular Ag concentration by inductively coupled plasma mass spectroscopy (ICP-MS) and re-analyzed reporter-gene data using these values to estimate the relative potencies of the Ag NPs and AgNO3. Our results show activation of all three stress response pathways, with Nrf-2/ARE displaying the strongest response elicited by each Ag NP and AgNO3 evaluated here. The smaller (10-nm) Ag NPs were more potent than the larger (75-nm) Ag NPs in each stress-response pathway, and citrate-coated Ag NPs had higher intracellular silver concentrations compared with both PVP-coated Ag NP and AgNO3. The cellular stress response profiles after Ag NP exposure were similar to that of AgNO3, suggesting that the oxidative stress and inflammatory effects of Ag NP are likely due to the cytotoxicity of silver ions.

Transport of silver nanoparticles in saturated columns of natural soils

With industrialization and urbanization soils are increasingly exposed to engineered nanoparticles (ENP), yet knowledge regarding the transport of ENP in natural soils is lacking, a process that was examined further in the current study. Saturated columns of 11 natural soils with varying physical and chemical properties were spiked with two pore volumes of a solution containing 1.7mgAgL−1 as polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP) (40nm actual diameter) and eluted at a constant flow rate of 1mlmin−1. Breakthrough of Ag was analyzed using filtration theory and a HYDRUS-1D transport model that incorporated two-site kinetic attachment–detachment. Separate kinetic batch studies suggested fast heteroaggregation between negatively charged AgNP and positively charged sites on the common soil colloids maghemite or montmorillonite. The concentration of such sites in the soil correlates positively with the oxalate-extractable aluminum concentration of the soils, a measure that correlated positively with collision efficiency. This correlation thus suggested favorable deposition of AgNP and/or enhanced straining following heteroaggregation of AgNP with mobile soils colloids. Occurrence of heteroaggregation was supported by the batch studies, enhanced size-exclusion in the soil with the highest porosity, and reversible attachment–detachment predicted from HYDRUS modeling, whereas straining and favorable deposition were suggested by irreversible attachment. Our study suggests that under similar experimental conditions, PVP-coated AgNP would rapidly interact with natural colloids in soils significantly reducing their mobility and hence potential risk from off-site transport.

The impact of size on the fate and toxicity of nanoparticulate silver in aquatic systems

The increased use of silver nanomaterials presents a risk to aquatic systems due to the high toxicity of silver. The stability, dissolution rates and toxicity of citrate- and polyvinylpyrrolidone-coated silver nanoparticles (AgNPs) were investigated in synthetic freshwater and natural seawater media, with the effects of natural organic matter investigated in freshwater. When sterically stabilised by the large PVP molecules, AgNPs were more stable than when charge-stabilised using citrate, and were even relatively stable in seawater. In freshwater and seawater, citrate-coated AgNPs (Ag–Cit) had a faster rate of dissolution than PVP-coated AgNPs (Ag–PVP), while micron-sized silver exhibited the slowest dissolution rate. However, similar dissolved silver was measured for both AgNPs after 72h in freshwater (500–600μgL−1) and seawater (1300–1500μgL−1), with higher concentrations in seawater attributed to chloride complexation. When determined on a mass basis, the 72-h IC50 (inhibitory concentration giving 50% reduction in algal growth rate) for Pseudokirchneriella subcapitata and Phaeodactylum tricornutum and the 48-h LC50 for Ceriodaphnia dubia exposure to Ag+ (1.1, 400 and 0.11μgL−1, respectively), Ag–Cit (3.0, 2380 and 0.15μgL−1, respectively) and Ag–PVP (19.5, 3690 and 2.0μgL−1, respectively) varied widely, with toxicity in the order Ag+>Ag–Cit>Ag–PVP. Micron-sized silver treatments elicited much lower toxicity than ionic Ag+ or AgNP to P. subcapitata. However, when related to the dissolved silver released from the nanoparticles the toxicities were similar to ionic silver treatments. The presence of natural organic matter stabilised the particles and reduced toxicity in freshwater. These results indicate that dissolved silver was responsible for the toxicity and highlight the need to account for matrix components such as chloride and organic matter in natural waters that influence AgNP fate and mitigate toxicity.

Comparison of toxicity of uncoated and coated silver nanoparticles

This study compares toxic effects of uncoated (20, 40, 60 and 80 nm) and OECD (Organization for Economic Co-operation and Development) standard citrate- and polyvinylpyrrolidone (PVP)-coated (10, 50, and 75 nm) silver nanoparticles (Ag-NPs) in J774A. 1 macrophage and HT29 epithelial cells. The cells were exposed to different concentrations (silver content) of Ag-NPs for 24 h. Analysis showed that uncoated Ag-NPs, at a concentration of 1 μg/ml, decreased cell viability by 20–40% and that 20 and 40 nm particles were 10% more cytotoxic than the 60 and 80 nm particles. In exposures to coated Ag-NPs, cell viability dropped at 25 μg/ml or higher concentrations, and the effects were also size-dependent. PVP-coated particles induced greater cytotoxicity than citrate-coated particles. Changes in sub-cellular architecture were observed in J774A. 1 cells upon exposure to test Ag-NPs. Furthermore, uncoated Ag-NPs (1 μg/mL) decreased the expression of selected cytokines including TNF-α, IL-1β, and IL-12 (p70) in J774A. 1 and IL-8 in HT29 cells. In contrast, both citrate- and PVP-coated Ag-NPs increased the expression of these cytokines at higher concentrations (25 μg/ml), and PVP-coated particles elevated cytokine levels the most. Moreover, while uncoated Ag-NPs resulted in decreased glutathione (GSH) content and increased superoxide dismutase (SOD) activity in test cells in a size-dependent manner at 1 μg/ml, coated Ag-NPs caused non-significant changes in GSH and SOD, even at the highest test concentrations. Lastly, uncoated (20 and 40 nm) at 1 μg/ml and coated Ag-NPs (10 nm PVP) at 50 μg/ml slightly increased the production of reactive oxygen species (ROS). Our data showed that uncoated Ag-NPs are more toxic than coated Ag-NPs. While uncoated Ag-NPs appear to suppress inflammatory responses and enhance oxidative stress in the test cells, coated Ag-NPs induce toxic effects through up-regulation of cytokines. Our findings support the toxicity of Ag-NPs as being size- and coating- dependent while providing additional insight on the health impact of Ag-NPs.

Toxicity and stability of silver nanoparticles to the green alga Pseudokirchneriella subcapitata in boreal freshwater samples and growth media

The toxicity of silver nanoparticles (AgNPs) to green alga Pseudokirchneriella subcapitata was evaluated in standard nutrient medium (ISO 8692), lake water samples from an oligotrophic and an eutrophic lake, and in lake waters supplemented with the standard nutrient medium. Prior to toxicity testing the agglomeration of polyvinylpyrrolidone (PVP) and starch-coated AgNPs was studied in each test medium. Agglomeration was studied by determining the hydrodynamic diameter (HDD). The HDDs for the PVP- and starch-capped AgNP dispersions in deionized water were 40 and 175 nm respectively, indicating the presence of agglomerates. The HDDs of AgNPs remained stable throughout the exposure time in all media used for the toxicity tests. The algae growth inhibition test was performed as a microplate modification of the ISO method using fluorescence detection. The effect of concentration at a 50% inhibition value for PVPcoated AgNPs in standard medium was 115 ± 3 µg/L, and for starchcoated AgNPs 51 ± 32 µg/L. The eutrophic freshwater conditions suppressed the toxicity of the PVP- coated AgNPs, but not the starchcoated NPs. This finding emphasizes the importance of using different AgNPs and natural waters in assessing the environmental risks of silver nanoparticles.

Genotoxicity of polyvinylpyrrolidone-coated silver nanoparticles in BEAS 2B cells

Silver nanoparticles (AgNPs) are widely utilized in various consumer products and medical devices, especially due to their antimicrobial properties. However, several studies have associated these particles with toxic effects, such as inflammation and oxidative stress in vivo and cytotoxic and genotoxic effects in vitro. Here, we assessed the genotoxic effects of AgNPs coated with polyvinylpyrrolidone (PVP) (average diameter 42.5±14.5nm) on human bronchial epithelial BEAS 2B cells in vitro. AgNPs were dispersed in bronchial epithelial growth medium (BEGM) with 0.6mg/ml bovine serum albumin (BSA). The AgNP were partially well-dispersed in the medium and only limited amounts (ca. 0.02μgAg+ ion/l) could be dissolved after 24h. The zeta-potential of the AgNPs was found to be highly negative in pure water but was at least partially neutralized in BEGM with 0.6mg BSA/ml. Cytotoxicity was measured by cell number count utilizing Trypan Blue exclusion and by an ATP-based luminescence cell viability assay. Genotoxicity was assessed by the alkaline single cell gel electrophoresis (comet) assay, the cytokinesis-block micronucleus (MN) assay, and the chromosomal aberration (CA) assay. The cells were exposed to various doses (0.5–48μg/cm2 corresponding to 2.5–240μg/ml) of AgNPs for 4 and 24h in the comet assay, for 48h in the MN assay, and for 24 and 48h in the CA assay. DNA damage measured by the percent of DNA in comet tail was induced in a dose-dependent manner after both the 4-h and the 24-h exposures to AgNPs, with a statistically significant increase starting at 16μg/cm2 (corresponding to 60.8μg/ml) and doubling of the percentage of DNA in tail at 48μg/cm2. However, no induction of MN or CAs was observed at any of the doses or time points. The lack of induction of chromosome damage by the PVP-coated AgNPs is possibly due to the coating which may protect the cells from direct interaction with the AgNPs, either by reducing ion leaching from the particles or by causing extensive agglomeration of the nanoparticles, with a possible reduction of the cellular uptake.

Polymeric Coatings on Silver Nanoparticles Hinder Autoaggregation but Enhance Attachment to Uncoated Surfaces

The propensity of silver nanoparticles (AgNPs) having two different polymer coatings (poly(vinylpyrrolidone), PVP, or gum arabic, GA) to aggregate, or to deposit to a reference surface (silica), was explored as a basis for differentiating the effect of surface coating on the stability of nanoparticles in aggregation and in deposition. Surface polymeric coatings stabilize nanoparticles against aggregation as shown by either an increased critical coagulation concentration as for PVP-coated AgNPs (AgPVP) or the absence of observable aggregation even at a high ionic strength as for GA-coated AgNPs (AgGA). In experiments of AgNPs deposition in a silica porous medium, dissimilar surfaces favored deposition, such as the case where polymer coatings were present on the AgNPs but were absent on the porous medium. The increased affinity of the AgNPs for the porous medium in this case may be explained by a shifted contact frontier where electrical double layer interaction is weaker. When coating polymers were introduced to the porous medium and allowed to preadsorb to the silica surfaces, the attachment efficiencies for both the AgPVP and AgGA were reduced due to steric and electrosteric stabilization, respectively. The results suggest that polymeric coatings that are usually deemed as stabilizers (as they indeed are in the case of autoaggregation) might not necessarily stabilize nanoparticles against deposition unless the collector surfaces are also coated with polymer.