Behavior Of Silver Nanoparticles Research Articles

Behavior of Silver Nanoparticles in Chlorinated Lettuce Wash Water

Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food crops, thus raising food safety and environmental concerns. Because little is known about Ag NP behavior in wash water during typical commercial washing of fresh produce, this study assessed the temporal changes in Ag NP behavior when exposed to 2 to 100 mg/L free chlorine (Cl2) in simulated lettuce wash water for up to 10 days. Aggregate size and zeta potential of Ag NPs (5 mg/L) were evaluated in the presence and absence of dissolved lettuce extract (DLE, 0.1%), with Ag NPs in deionized water serving as the control treatment. In the presence of chlorine, greater aggregation of Ag NPs occurred over time (49 to 431 nm) compared with the control treatment (P < 0.05). Lower zeta potentials (-39 to -95 mV) were observed in the chlorine-only treatments, likely due to the formation of AgCl particles. Larger aggregates and lower zeta potentials were also observed in DLE (84 to 273 nm and -28 to -32 mV, respectively), as compared with the control treatment. After 7 to 10 days, larger aggregates were seen in the chlorine-only treatments as compared with the DLE treatments, despite lower zeta potentials, probably facilitated by nucleation and crystal growth of AgCl. Transmission electron microscopy with energy dispersive spectroscopy confirmed the formation of AgCl-Ag NP composite particles with chlorine and the embedding of AgCl and Ag NPs in the DLE matrix. Thus, DLE might stabilize and protect Ag NPs from chlorine. These findings indicate that chlorine and plant-released organic material can substantially change the behavior of Ag NPs, which may, in turn, impact both removal from fresh-cut produce during washing and their environmental fate.

Simultaneous Influence of Gradients in Natural Organic Matter and Abiotic Parameters on the Behavior of Silver Nanoparticles in the Transition Zone from Freshwater to Saltwater Environments.

As nanoparticles have been found to cause a range of harmful impacts in biota, understanding processes and transformations which may stabilize and increase their persistence time in the environment are of great importance. As nanoparticles carried in riverine or wastewaters will eventually reach estuaries, understanding their behavior and transport potential in this transition zone from fresh to marine waters is essential, particularly as estuaries are sensitive ecological zones, oftentimes encompassing ornithologically important areas. In this direction, we report on the influence of combined gradients of riverine and marine natural organic matter (NOM) on the temporal stability of biocorona-encapsulated silver nanoparticles in terms of ion release kinetics. In parallel, salinity, pH and oxygen saturation were simultaneously varied to create a model to mimic the complex estuarine environment. While humic acid (HA) and alginate (Alg) disrupted the stabilizing ability of the nanoparticle protein corona to a greater and lesser degree, respectively, they slowed the rate of ion release in freshwater at pH 6.6 and in saltwater at pH 8, respectively, while oxygen saturation was also found to be an important factor. Thus, as the type of NOM changes with pH along a salinity gradient in an estuary, conditions required to increase the persistence time of nanoparticles are serendipitously met, with greater colloidal stability achieved in cases where there is more rapid replacement of HA with Alg. Despite the strong gradients in ionic strength, pH and oxygen saturation, the protein corona was not sufficiently disrupted at the nanoparticle surface to be substituted by NOM indicating the greater adsorption energy of the protein’s hydrophobic domains. Ultimately, it is the specific NOM profile of individual estuaries that may provide the best indicator for predicting the stability and persistence of silver nanoparticles as they transition from fresh to salt water environments.

Environmental fate and behavior of silver nanoparticles in natural estuarine systems

Silver nanoparticles (AgNPs) are widely used in many consumer products, whereas their environmental behaviors in natural aquatic systems remain unknown, especially in natural brackish media. Therefore, it is urgent to investigate the environmental fate of AgNPs in natural brackish waters. Here, we investigated the stability of citrate-coated AgNPs in natural brackish water collected from 6 different sites with distinct salinities in the Xinglinwan Reservoir, located in Xiamen City, southeast China. The obtained results showed that AgNP colloids remained stable in low-salinity waters, which was mainly determined by the effects of dissolved organic matter (DOM) promoting the stability of the nanoparticles. However, the environmental fate of AgNPs in high-salinity waters was dominated by the salinity or ionic strength, especially the free ion concentrations of Cl−, SO42−, or S2−, resulting in rapid sedimentation and dissolution. In addition, both DOM and salinity contributed to the environmental behavior of AgNPs in moderate-salinity waters, ultimately resulting in either colloidal stability or sedimentation. Overall, these results may reveal that AgNPs remain relatively stable for a long period in low-salinity natural waters, and that the stability might gradually decrease as AgNPs are transferred from freshwaters through brackish waters and eventually end up in seawater along the bay. Our findings also further indicate that the toxicity and potential risks of AgNPs may present more serious threats to the environment and organisms in natural freshwaters than in natural estuarine systems or seawater.

Effect of ionic strength on bioaccumulation and toxicity of silver nanoparticles in Caenorhabditis elegans

The behavior of silver nanoparticles (AgNPs) is influenced by environmental factors which altered their bioaccumulation and toxicity. In this study, we comprehensively investigated the influence of ionic strength on the ecotoxicity of AgNPs to Caenorhabditis elegans (C. elegans) through the transfer from Escherichia coli (E. coli). Three different exposure media (deionized water, EPA water and KM) were used to pretreat AgNPs. E. coli was then exposed to these transformed AgNPs and fed to C. elegans. Our results indicated that ionic strength significantly enhanced the reproductive toxicity (germ cell corpses, brood size and lifespan) and neurotoxicity (head trash and body bend) of AgNPs in C. elegans. Moreover, ICP-MS analysis showed that higher ionic strength increased bioaccumulation of AgNPs in E. coli and the resulting Ag body burden of E. coli affected the transfer of AgNPs to C. elegans, which might be responsible for the increased toxicity to nematodes. Furthermore, we also found that the reactive oxygen species (ROS) level in C. elegans was significantly increased after exposed to E. coli contaminated with ionic strength-treated AgNPs, which might play another important role for the enhanced toxicity of AgNPs. Overall, this study showed that the bioavailability and potential ecotoxicity of AgNPs are associated with the environmental factors.

Behavior of silver nanoparticles and ions in food simulants and low fat cow milk under migration conditions

Research on the potential migration of nanoparticles (NPs) from nano-based food contact materials (FCMs) has often reached inconsistency in previous studies. Conventional food simulants and traditional migration tests, which are established for small molecules, have been used for studying the potential migration of NPs from nano-based FCMs. The suitability of conventional food simulants and migration tests was investigated by studying the behavior of 40 nm polyethylene glycol (PEG) coated AgNPs and silver ions in food simulants (10% ethanol, 20% ethanol, 50% ethanol, 3% acetic acid, olive oil) under migration conditions. Particle mass and number concentrations, ionic concentration and particle size distributions were determined by single particle inductively coupled plasma-mass spectrometry (spICP-MS) before and after incubation for 4 h or 10 days at 40 °C. In agreement with similar studies, 50% ethanol preserved the AgNPs, while acetic acid induced dissolution of AgNPs. Dissolution of the PEG-AgNPs obeyed pseudo-first-order reaction kinetics. PEG-AgNPs showed similar behavior in low fat cow milk during storage at 4 °C for 5 days as in the corresponding food simulant, 50% ethanol. Addition of sodium chloride to ultrapure water led to enhanced dissolution. The potential reduction of silver ions to NPs in food simulants, low fat milk and in alkaline conditions in the presence of reducing agents was studied. Based on the obtained results, it is unlikely that AgNPs are formed from Ag ions at the low concentration which are typically observed for the migration of Ag from polymeric FCMs.

Behavior of silver nanoparticles in wastewater: systematic investigation on the combined effects of surfactants and electrolytes in model systems

pH, electrolytes and surfactants affected the stability of AgNPs in artificial test water system.

Seasonal variability of natural water chemistry affects the fate and behaviour of silver nanoparticles

Understanding the environmental behaviour of nanoparticles (NPs) after release into aquatic systems is essential to predict the environmental implications of nanotechnology. Silver nanoparticles (AgNPs) represent a major class of engineered NPs with a significant potential for environmental impact. Therefore, investigating their transformations in natural waters will help predict their long term environmental fate and behaviour. AgNPs were characterized in natural lake water collected seasonally from the same freshwater source, using column microcosms to assess their behaviour and transport at different depths. Building on our previous work using similar systems with synthetic waters, the influence of water chemistry and NP surface modifications on colloidal stability and dissolution in natural lake water over time was investigated. A simple sedimentation-diffusion model parameterized by the particle properties and total Ag concentration was successfully used to understand AgNPs transport behaviour. PVP coated AgNPs remained colloidally stable, with their transport in the water column dominated by diffusion, and exhibited no significant or substantial changes in data or model parameters for different seasons. Citrate coated AgNPs were susceptible to rapid aggregation, sedimentation, dissolution and reprecipitation; their transport in the water column was determined by both diffusion and sedimentation.

Investigation of effect of electric field on silver nanoparticles in order to separation of them from aqueous medium using electrocoagulation process

Abstract The behavior of silver nanoparticles (AgNPs) under an applied electric field depends primarily on their stabilizing agent. This research aimed at investigating the behavior of AgNPs and their stabilizers under the electrocoagulation (EC) process. In two separate experiments, sodium citrate and polyvinylpyrrolidone (PVP) were used as the nanoparticles’ stabilizers. Stability of the particles was studied while applying an electrical current with various voltages. Efficiency of the EC process was investigated for these different AgNPs sols. In the case of sodium citrate for various voltages, the plasmon resonance peak of the sample was disappeared after applying the electric field for 90 min, reflecting the removal of AgNPs in the sol by 99.91%. In the case of PVP for various voltages of the EC process for 10 min, the absorbance peak disappeared, and removal efficiency of AgNPs reached 99.98%. Effect of stabilizer concentration on the EC process was investigated. As sodium citrate concentration increased, the stability of AgNPs under an equall applied electric field increased, while the increase of the PVP concentration did not influence on the stability of AgNPs. Kinetic of AgNPs removal was also studied.

Influence of Phytochemical Reductive Capacity on Ultraviolet–visible Spectroscopic Behavior of Silver Nanoparticles

ABSTRACTA widely used method for obtaining silver nanoparticles uses plant extracts for reduction because of the presence of phytochemicals such as terpenoids, tannins, and flavonoids. Extracts of Flores sambuci, Hypericum perforatum, Lavandula angustifolia, Origanum vulgare, Rosmarinus officinalis, and Salvia officinalis were used for generating silver nanoparticles. The ultraviolet–visible spectra of silver nanoparticle solutions were correlated with variations of phytochemical characteristics to evaluate the plant extracts. These parameters were the antioxidant activity, total flavonoids, total tannins, total terpenoids, and total phenolics. Correlations between measurements of extracts’ phytoreductive characteristics were explained using Pearson coefficients. The results showed medium linear positive correlations for total tannins with the spectra of silver nanoparticle solutions. The antioxidant activity and total terpenoids presented medium linear negative correlations. Pearson coefficients between total phenolics and relative areas from ultraviolet–visible spectra from 350 to 600 nm were close to zero indicating no linear correlation.

Behaviour of silver nanoparticles in simulated saliva and gastrointestinal fluids

Continuously increasing application of silver nanoparticles (AgNPs) requires information on their safety and performance under biological conditions. Assessment of AgNPs in biological systems is also related to availability of robust toxicological methods for evaluation of toxic potential of AgNPs and information on their physicochemical state. Silver nanoparticles were subjected to action of simulated saliva, gastric and intestinal fluids, appropriately supplemented with digestive enzymes pepsin or pancreatin. The behaviour of AgNPs was determined using dynamic light scattering and transmission electron microscopy, and their toxicity as well as capability to induce inflammatory reactions were assessed using reconstructed human tissue models (EpiOral, EpiGingival, EpiIntestinal). The study revealed that during exposure to the fluids, AgNPs size and morphology changed and depended on composition and pH of the respective fluid. If present, the change in terms of growth of AgNPs size occurred immediately after contact of AgNPs with the respective fluid and continued with prolonged time of contact. A pilot study on reconstituted human tissue models revealed low toxicity and inflammatory effects of AgNPs and confirmed the suitability of 3-D models for toxicological studies including bioavailability.

Heat transfer behaviour of silver particles containing oleic acid surfactant: application in a two phase closed rectangular cross sectional thermosyphon (RTPTC)

This article focuses on heat transfer behaviour of silver nanoparticles containing oleic acid surfactant (OA) applied as a working fluid in a two-phase closed rectangular cross sectional thermosyphon (RTPTC). Thus, the OA could reduce the surface tension of the working fluid, which improved the colloidal ability and increased the lead-time period for nanoparticles to be uniformly dispersed. It highlights theories for investigating the effects on heat transfer characteristics of RTPTC such as heat transfer rate, thermal resistance, heat transfer coefficients and nanofluids behaviour. The most important heat transfer characteristic to be examined in this experiment is the relative thermal efficiency (RT). Five working fluids were tested, these include: de-ionized water; de-ionized water base with a silver nanoparticles concentration of 0.5 wt% (NP); and NP containing 0.5; 1; and 1.5 wt% of OA respectively. The results showed that 0.5 wt% NP containing 1 wt% OA produced the best results. It was further found that the heat transfer rate of 0.5 wt% NP containing 1 wt% of OA with a RT value of 1, was the highest across all experimental parameters studied. The NP containing OA demonstrated approximately 80 % higher heat transfer rate than the de-ionized water.

Assessing silver nanoparticles behaviour in artificial seawater by mean of AF4 and spICP-MS

The use of nanotechnology-based products is constantly increasing and there are concerns about the fate and effect on the aquatic environment of antimicrobial products such as silver nanoparticles. By combining different characterization techniques (asymmetric flow field-flow fractionation, single particle ICP-MS, UV–Vis) we show that it is possible to assess in detail the agglomeration process of silver nanoparticles in artificial seawater. In particular we show that the presence of alginate or humic acid differentially affects the kinetic of the agglomeration process. This study provides an experimental methodology for the in-depth analysis of the fate and behaviour of silver nanoparticles in the aquatic environment.

Mechanistic Insights into Interaction of Humic Acid with Silver Nanoparticles

Humic acid (HA) is one of the major components of the natural organic matter present in the environment that alters the fate and behavior of silver nanoparticles (Ag NPs). Transformation of Ag NPs happens upon interaction with HA, thereby, changing both physical and chemical properties. Fluorescence spectroscopy and scanning electron microscopy (SEM) were used to analyze the interaction of Ag NPs with HA. In pH and time-dependent studies, the near field electro dynamical environment of Ag NPs influenced the fluorescence of HA, indicated by fluorescence enhancement. SEM revealed not only morphological changes, but also significant reduction in size of Ag NPs after interaction with HA. Based on these studies, a probable mechanism was proposed for the interaction of HA with Ag NPs, suggesting the possible transformation that these nanoparticles can undergo in the environment.

An investigation into the simultaneous enzymatic and SERRS properties of silver nanoparticles

Investigation into the use of artificial enzymes has become an increasingly popular area of research due to the numerous advantages offered in comparison to protein enzymes. One particular area of research interest involves the use of metal nanoparticles as artificial enzymes. The peroxidase-like activity of a variety of nanoparticles has recently been shown and their use in a range of assay formats for the detection of various analytes has been explored. Herein the enzyme mimicking activity of silver nanoparticles is investigated using the peroxidase substrate 3,3',5',5'-tetramethylbenzidine (TMB). The peroxidase-like nature of these nanoparticles can be used in combination with surface enhanced resonance Raman scattering (SERRS) to provide a novel spectroscopic method of analysis. Negatively charged silver nanoparticles were investigated in combination with TMB using SERRS and it was found that upon formation of the oxidation intermediate of TMB, small clusters of positively charged nanoparticles were formed. The enzyme like behaviour of silver nanoparticles along with their use as a SERRS substrate is combined to demonstrate a simple and rapid method for the direct detection of hydrogen peroxide with a detection limit of 100 nM.

Behaviour of silver nanoparticles and silver ions in an in vitro human gastrointestinal digestion model

Oral ingestion is an important exposure route for silver nanoparticles (AgNPs), but their fate during gastrointestinal digestion is unknown. This was studied for 60 nm AgNPs and silver ions (AgNO3) using in vitro human digestion model. Samples after saliva, gastric and intestinal digestion were analysed with SP-ICPMS, DLS and SEM-EDX. In presence of proteins, after gastric digestion the number of particles dropped significantly, to rise back to original values after the intestinal digestion. SEM-EDX revealed that reduction in number of particles was caused by their clustering. These clusters were composed of AgNPs and chlorine. During intestinal digestion, these clusters disintegrated back into single 60 nm AgNPs. The authors conclude that these AgNPs under physiological conditions can reach the intestinal wall in their initial size and composition. Importantly, intestinal digestion of AgNO3 in presence of proteins resulted in particle formation. These nanoparticles (of 20–30 nm) were composed of silver, sulphur and chlorine.

Superoxide-Mediated Formation and Charging of Silver Nanoparticles

Contemporary studies indicate that reactive oxygen species (ROS) such as superoxide play a key role in the toxicity and behavior of silver nanoparticles (AgNPs). While there have been suggestions that superoxide is able to reduce silver(I) ions with resultant production of AgNPs, no experimental evidence that this process actually occurs has been produced. Here we present definitive experimental evidence for the reduction of silver(I) by superoxide. A second-order rate constant of 64.5 ± 16.3 M(-1)·s(-1) is determined for this reaction in the absence of AgNPs. The overall rate constant, however, increases by at least 4 orders of magnitude in the presence of AgNPs. A model based on electron charging and discharging of AgNPs satisfactorily describes the kinetics of this process. The ability for AgNPs to undergo catalytic cycling provides a pathway for the continual generation of ROS and the regeneration of AgNPs following oxidation.

Interaction of silver with oxygen on sputtered pyrolytic graphite

Using core level spectra, it has been observed previously that the oxidation of silver nanoparticles deposited on sputter-damaged highly ordered pyrolytic graphite (HOPG) surfaces is very different from that taking place on surfaces composed entirely of silver. It is generally accepted that the final stage of the oxidation of silver is the formation of Ag2O/AgO. However, in the case of silver nanoparticles on HOPG, Ag2O/AgO can be further oxidized to give a species of unknown composition. In the present work it has been demonstrated that under these oxidizing conditions silver nanoparticles deposited on HOPG form silver carbonate. This implies that strong metal support interactions are responsible for the different behavior of silver nanoparticles on HOPG compared to that of silver in bulk. Carbonate formation is further suggested to be responsible for the deactivation of silver catalysts. # 2007 Elsevier B.V. All rights reserved.