Cysteine-induced modifications of zero-valent silver nanomaterials: implications for particle surface chemistry, aggregation, dissolution, and silver speciation

Cytotoxicity and Genotoxicity Effects of a Magnetic Zeolite Composite in Daphnia magna (Straus, 1820)

Zeolite type 5A combined with the magnetic properties of maghemite nanoparticles facilitate the rapid absorption of heavy metals, which makes them an interesting proposal for the remediation of water contaminated with lead and arsenic. However, the physicochemical analysis related to concentration and size for the use of this magnetic zeolite composite (MZ0) in water bodies and the possible toxicological effects on aquatic fauna has not yet been carried out. The main objective of the research work is to determine lethal concentrations that cause damage to Daphnia magna based on LC50 tests, morphology, reproductive rate, and quantification of the expression of three genes closely involved in the morphological development of vital structures (Glass, NinaE, Pph13). To achieve this objective, populations of neonates and young individuals were used, and results showed that the LC50 for neonates was 11,314 mg L-1, while for young individuals, it was 0.0310 mg L-1. Damage to morphological development was evidenced by a decrease in eye size in neonates, an increase in eye size in young individuals, variations in the size of the caudal spine for both age groups, and slight increases in the heart size, body, and antenna for both age groups. The reproductive rate of neonates was not affected by the lower concentrations of MZ0, while in young individuals, the reproductive rate decreased by more than 50% from the minimum exposure concentration of MZ0. And for both ages, Glass gene expression levels decreased as the MZ0 concentration increased. Also, the MZ0 evidenced its affinity for the exoskeleton of D. magna, which was observed using both light microscopy and electron microscopy. It is concluded that MZ0 did not generate significant damage in the mortality, morphology, reproductive rate, or gene expression in D. magna at lower concentrations, demonstrating the importance of evaluating the possible impacts on different life stages of the cladoceran.

Sulfide in engineered methanogenic systems - Friend or foe?

Sulfide ions are regarded to be toxic to microorganisms in engineered methanogenic systems (EMS), where organic substances are anaerobically converted to products such as methane, hydrogen, alcohols, and carboxylic acids. A vast body of research has addressed solutions to mitigate process disturbances associated with high sulfide levels, yet the established paradigm has drawn the attention away from the multifaceted sulfide interactions with minerals, organics, microbial interfaces and their implications for performance of EMS. This brief review brings forward sulfide-derived pathways other than toxicity and with potential significance for anaerobic organic matter degradation. Available evidence on sulfide reactions with organic matter, interventions with key microbial metabolisms, and interspecies electron transfer are critically synthesized as a guidance for comprehending the sulfide effects on EMS apart from the microbial toxicity. The outcomes identify existing knowledge gaps and specify future research needs as a step forward towards realizing the potential of sulfide-derived mechanisms in diversifying and optimizing EMS applications.

Environmental effects and interaction of nanoparticles on beneficial soil and aquatic microorganisms

A steadily increasing production volume of nanoparticles reflects their numerous industrial and domestic applications. These economic successes come with the potential adverse effects on natural systems that are associated with their presence in the environment. Biological activities and effects of nanoparticles are affected by their entry method together with their specificities like their size, shape, charge, area, and chemical composition. Particles can be classified as safe or dangerous depending on their specific properties. As both aquatic and terrestrial systems suffer from organic and inorganic contamination, nanoparticles remain a sink for these contaminants. Researching the sources, synthesis, fate, and toxicity of nanoparticles has advanced significantly during the last ten years. We summarise nanoparticle pathways throughout the ecosystem and their interactions with beneficial microorganisms in this research. The prevalence of nanoparticles in the ecosystem causes beneficial microorganisms to become hazardous to their cells, which prevents the synthesis of bioactive molecules from undergoing molecular modifications and diminishes the microbe population. Recently, observed concentrations in the field could support predictions of ambient concentrations based on modeling methodologies. The aim is to illustrate the beneficial and negative effects that nanoparticles have on aqueous and terrestrial ecosystems, as well as the methods utilized to reduce their toxicity.

Ambivalent effects of dissolved organic matter on silver nanoparticles/silver ions transformation: A review

The numerous applications of silver nanoparticles (AgNPs) lead to their spread in aquatic systems and the release of silver ions (Ag⁺), which brings potential risks to environment and human health. Owing to the different toxicity, the mutual transformations between AgNPs and Ag⁺ has been a hot topic of research. Dissolved organic matter (DOM) is ubiquitous on the earth and almost participates in all the reactions in the nature. The previous studies have reported the roles of DOM played in the transformation between AgNPs and Ag⁺. However, different experiment conditions commonly caused contradictory results, leading to the difficulty to predict the fate of AgNPs in specific reactions. Here we summarized mechanisms of DOM-mediated AgNPs oxidation and Ag⁺ reduction, and analyzed the effects of environmental parameters. Moreover, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This review will promote the understanding of the fate and risk assessments of AgNPs in natural water systems.

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

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

Silver Nanoparticle Effects on Antioxidant Response in Tobacco Are Modulated by Surface Coating

The antimicrobial properties of silver and enhanced reactivity when applied in a nanoparticle form (AgNPs) led to their growing utilization in industry and various consumer products, which raises concerns about their environmental impact. Since AgNPs are prone to transformation, surface coatings are added to enhance their stability. AgNP phytotoxicity has been mainly attributed to the excess generation of reactive oxygen species (ROS), leading to the induction of oxidative stress. Herein, in vitro-grown tobacco (Nicotiana tabacum) plants were exposed to AgNPs stabilized with either polyvinylpyrrolidone (PVP) or cetyltrimethylammonium bromide (CTAB) as well as to ionic silver (AgNO₃), applied in the same concentrations, either alone or in combination with cysteine, a strong silver ligand. The results show a higher accumulation of Ag in roots and leaves after exposure to AgNPs compared to AgNO₃. This was correlated with a predominantly higher impact of nanoparticle than ionic silver form on parameters of oxidative stress, although no severe damage to important biomolecules was observed. Nevertheless, all types of treatments caused mobilization of antioxidant machinery, especially in leaves, although surface coatings modulated the activation of its specific components. Most effects induced by AgNPs or AgNO₃ were alleviated with addition of cysteine.

Purifying water with silver nanoparticles (AgNPs)-incorporated membranes: Recent advancements and critical challenges

In the face of the growing global water crisis, membrane technology is a promising means of purifying water and wastewater. Silver nanoparticles (AgNPs) have been widely used to improve membrane performance, for antibiofouling, and to aid in photocatalytic degradation, thermal response, and electro-conductivity. However, several critical issues such as short antimicrobial periods, trade-off effects and silver inactivation seriously restrict the engineering application of AgNPs-incorporated membranes. In addition, there is controversy around the use of AgNPs given the toxic preparation process and environmental/biological risks. Hence, it is of great significance to summarize and analyze the recent developments and critical challenges in the use of AgNPs-incorporated membranes in water and wastewater treatment, and to propose potential solutions. We reviewed the different properties and functions of AgNPs and their corresponding applications in AgNPs-incorporated membranes. Recently, multifunctional, novel AgNP-incorporated membranes combined with other functional materials have been developed with high-performance. We further clarified the synergistic mechanisms between AgNPs and these novel nanomaterials and/or polymers, and elucidated their functions and roles in membrane separation. Finally, the critical challenges of AgNPs-incorporated membranes and the proposed solutions were outlined: i) Prolonging the antimicrobial cycle through long-term and controlled AgNPs release; ii) Overcoming the trade-off effect and organic fouling of the AgNPs-incorporated membranes; iii) Preparation of sustainable AgNPs-incorporated membranes; iv) Addressing biotoxicity induced by AgNPs; and v) Deactivation of AgNPs-incorporated membrane. Overall, this review provides a comprehensive discussion of the advancements and challenges of AgNPs-incorporated membranes and guides the development of more robust, multi-functional and sustainable AgNPs-incorporated membranes.

Conformationally engineering flexible peptides on silver nanoparticles

Molecular conformational engineering is to engineer flexible non-functional molecules into unique conformations to create novel functions just like natural proteins fold. Obviously, it is a grand challenge with tremendous opportunities. Based on the facts that natural proteins are only marginally stable with a net stabilizing energy roughly equivalent to the energy of two hydrogen bonds, and the energy barriers for the adatom diffusion of some metals are within a similar range, we propose that metal nanoparticles can serve as a general replacement of protein scaffolds to conformationally engineer protein fragments on the surface of nanoparticles. To prove this hypothesis, herein, we successfully restore the antigen-recognizing function of the flexible peptide fragment of a natural anti-lysozyme antibody on the surface of silver nanoparticles, creating a silver nanoparticle-base artificial antibody (Silverbody). A plausible mechanism is proposed, and some general principles for conformational engineering are summarized to guide future studies in this area.

•

A silver NP-based artificial antibody is created by conformational engineering

•

Function emerges on NPs from non-functional peptide by mimicking the protein folding

•

A general mechanism is proposed for the conformational engineering on metal NPs

Building the Bridge From Aquatic Nanotoxicology to Safety by Design Silver Nanoparticles

Nanotechnologies have rapidly grown, and they are considered the new industrial revolution. However, the augmented production and wide applications of engineered nanomaterials (ENMs) and nanoparticles (NPs) inevitably lead to environmental exposure with consequences on human and environmental health. Engineered nanomaterial and nanoparticle (ENM/P) effects on humans and the environment are complex and largely depend on the interplay between their peculiar properties such as size, shape, coating, surface charge, and degree of agglomeration or aggregation and those of the receiving media/body. These rebounds on ENM/P safety and newly developed concepts such as the safety by design are gaining importance in the field of sustainable nanotechnologies. This article aims to review the critical characteristics of the ENM/Ps that need to be addressed in the safe by design process to develop ENM/Ps with the ablility to reduce/minimize any potential toxicological risks for living beings associated with their exposure. Specifically, we focused on silver nanoparticles (AgNPs) due to an increasing number of nanoproducts containing AgNPs, as well as an increasing knowledge about these nanomaterials (NMs) and their effects. We review the ecotoxicological effects documented on freshwater and marine species that demonstrate the importance of the relationship between the ENM/P design and their biological outcomes in terms of environmental safety.

Functionalization and Antibacterial Applications of Cellulose-Based Composite Hydrogels

Pathogens, especially drug-resistant pathogens caused by the abuse of antibiotics, have become a major threat to human health and public health safety. The exploitation and application of new antibacterial agents is extremely urgent. As a natural biopolymer, cellulose has recently attracted much attention due to its excellent hydrophilicity, economy, biocompatibility, and biodegradability. In particular, the preparation of cellulose-based hydrogels with excellent structure and properties from cellulose and its derivatives has received increasing attention thanks to the existence of abundant hydrophilic functional groups (such as hydroxyl, carboxy, and aldehyde groups) within cellulose and its derivatives. The cellulose-based hydrogels have broad application prospects in antibacterial-related biomedical fields. The latest advances of preparation and antibacterial application of cellulose-based hydrogels has been reviewed, with a focus on the antibacterial applications of composite hydrogels formed from cellulose and metal nanoparticles; metal oxide nanoparticles; antibiotics; polymers; and plant extracts. In addition, the antibacterial mechanism and antibacterial characteristics of different cellulose-based antibacterial hydrogels were also summarized. Furthermore, the prospects and challenges of cellulose-based antibacterial hydrogels in biomedical applications were also discussed.

How the Physicochemical Properties of Manufactured Nanomaterials Affect Their Performance in Dispersion and Their Applications in Biomedicine: A Review

The growth in novel synthesis methods and in the range of possible applications has led to the development of a large variety of manufactured nanomaterials (MNMs), which can, in principle, come into close contact with humans and be dispersed in the environment. The nanomaterials interact with the surrounding environment, this being either the proteins and/or cells in a biological medium or the matrix constituent in a dispersion or composite, and an interface is formed whose properties depend on the physicochemical interactions and on colloidal forces. The development of predictive relationships between the characteristics of individual MNMs and their potential practical use critically depends on how the key parameters of MNMs, such as the size, shape, surface chemistry, surface charge, surface coating, etc., affect the behavior in a test medium. This relationship between the biophysicochemical properties of the MNMs and their practical use is defined as their functionality; understanding this relationship is very important for the safe use of these nanomaterials. In this mini review, we attempt to identify the key parameters of nanomaterials and establish a relationship between these and the main MNM functionalities, which would play an important role in the safe design of MNMs; thus, reducing the possible health and environmental risks early on in the innovation process, when the functionality of a nanomaterial and its toxicity/safety will be taken into account in an integrated way. This review aims to contribute to a decision tree strategy for the optimum design of safe nanomaterials, by going beyond the compromise between functionality and safety.

Towards Standardization for Determining Dissolution Kinetics of Nanomaterials in Natural Aquatic Environments: Continuous Flow Dissolution of Ag Nanoparticles

The dissolution of metal-based engineered nanomaterials (ENMs) in aquatic environments is an important mechanism governing the release of toxic dissolved metals. For the registration of ENMs at regulatory bodies such as REACH, their dissolution behavior must therefore be assessed using standardized experimental approaches. To date, there are no standardized procedures for dissolution testing of ENMs in environmentally relevant aquatic media, and the Organisation for Economic Co-operation and Development (OECD) strongly encourages their development into test guidelines. According to a survey of surface water hydrochemistry, we propose to use media with low concentrations of Ca²⁺ and Mg²⁺ for a better simulation of the ionic background of surface waters, at pH values representing acidic (5 < pH < 6) and near-neutral/alkaline (7 < pH < 8) waters. We evaluated a continuous flow setup adapted to expose small amounts of ENMs to aqueous media, to mimic ENMs in surface waters. For this purpose, silver nanoparticles (Ag NPs) were used as model for soluble metal-bearing ENMs. Ag NPs were deposited onto a 10 kg.mol⁻¹ membrane through the injection of 500 µL of a 5 mg.L⁻¹ or 20 mg.L⁻¹ Ag NP dispersion, in order to expose only a few micrograms of Ag NPs to the aqueous media. The dissolution rate of Ag NPs in 10 mM NaNO₃ was more than two times higher for ~2 µg compared with ~8 µg of Ag NPs deposited onto the membrane, emphasizing the importance of evaluating the dissolution of ENMs at low concentrations in order to keep a realistic scenario. Dissolution rates of Ag NPs in artificial waters (2 mM Ca(NO₃)₂, 0.5 mM MgSO₄, 0–5 mM NaHCO₃) were also determined, proving the feasibility of the test using environmentally relevant media. In view of the current lack of harmonized methods, this work encourages the standardization of continuous flow dissolution methods toward OECD guidelines focused on natural aquatic environments, for systematic comparisons of nanomaterials and adapted risk assessments.

Natural organic matter composition and nanomaterial surface coating determine the nature of platinum nanomaterial-natural organic matter corona

Natural organic matter corona (NOM corona) is an interfacial area between nanomaterials (NMs) and the surrounding environment, which gives rise to NMs' unique surface identity. While the importance of the formation of natural organic matter (NOM) corona on engineered nanomaterials (NMs) to NM behavior, fate, and toxicity has been well-established, the understanding of how NOM molecular properties affect NOM corona composition remains elusive due to the complexity and heterogeneity of NOM. This is further complicated by the variation of NOMs from different origins. Here we use eight NOM isolates of different molecular composition and ultrahigh resolution Fourier-transform ion cyclotron resonance-mass spectrometry (ESI-FT-ICR-MS) to determine the molecular composition of platinum NM-NOM corona as a function of NOM composition and NM surface coating. We observed that the composition of PtNM-NOM corona varied with the composition of the original NOM. The percentage of NOM formulas that formed PVP-PtNM-NOM corona was higher than those formed citrate-PtNM-NOM corona, due to increased sorption of NOM formulas, in particular condensed hydrocarbons, to the PVP coating. The relative abundance of heteroatom formulas (CHON, CHOS, and CHOP) was higher in the PVP-PtNM-NOM corona than in citrate-PtNM-corona which was in turn higher than those in the original NOM isolate, indicating preferential partitioning of heteroatom-rich molecules to NM surfaces. The relative abundance of CHO, CHON, CHOS, CHOP and condensed hydrocarbons in PtNM-NOM corona increased with their increase in NOM isolates. Furthermore, PtNM-NOM corona is rich with compounds with high molecular weight. This study demonstrates that the composition and properties of PtNM-NOM corona depend on NOM molecular properties and PtNM surface coating. The results here provide evidence of molecular interactions between NOM and NMs, which are critical to understanding NM colloidal properties (e.g., surface charge and stability), interaction forces (e.g., van der Waals and hydrophobic), environmental behaviors (e.g., aggregation, dissolution, sulfidation, etc.), and biological effects (e.g., uptake, bioaccumulation, and toxicity).

Surface Coating-Modulated Phytotoxic Responses of Silver Nanoparticles in Plants and Freshwater Green Algae

Silver nanoparticles (AgNPs) have been implemented in a wide range of commercial products, resulting in their unregulated release into aquatic as well as terrestrial systems. This raises concerns over their impending environmental effects. Once released into the environment, they are prone to various transformation processes that modify their reactivity. In order to increase AgNP stability, different stabilizing coatings are applied during their synthesis. However, coating agents determine particle size and shape and influence their solubility, reactivity, and overall stability as well as their behavior and transformations in the biological medium. In this review, we attempt to give an overview on how the employment of different stabilizing coatings can modulate AgNP-induced phytotoxicity with respect to growth, physiology, and gene and protein expression in terrestrial and aquatic plants and freshwater algae.

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

Background

Precisely 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.

Methods

Cells 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.

Results

We 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.

Conclusions

There 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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00430-1.

Antibacterial and Antifungal Properties of Silver Nanoparticles-Effect of a Surface-Stabilizing Agent

The biocidal properties of silver nanoparticles (AgNPs) prepared with the use of biologically active compounds seem to be especially significant for biological and medical application. Therefore, the aim of this research was to determine and compare the antibacterial and fungicidal properties of fifteen types of AgNPs. The main hypothesis was that the biological activity of AgNPs characterized by comparable size distributions, shapes, and ion release profiles is dependent on the properties of stabilizing agent molecules adsorbed on their surfaces. Escherichia coli and Staphylococcus aureus were selected as models of two types of bacterial cells. Candida albicans was selected for the research as a representative type of eukaryotic microorganism. The conducted studies reveal that larger AgNPs can be more biocidal than smaller ones. It was found that positively charged arginine-stabilized AgNPs (ARGSBAgNPs) were the most biocidal among all studied nanoparticles. The strongest fungicidal properties were detected for negatively charged EGCGAgNPs obtained using (-)-epigallocatechin gallate (EGCG). It was concluded that, by applying a specific stabilizing agent, one can tune the selectivity of AgNP toxicity towards desired pathogens. It was established that E. coli was more sensitive to AgNP exposure than S. aureus regardless of AgNP size and surface properties.

Grouping Hypotheses and an Integrated Approach to Testing and Assessment of Nanomaterials Following Oral Ingestion

The risk assessment of ingested nanomaterials (NMs) is an important issue. Here we present nine integrated approaches to testing and assessment (IATAs) to group ingested NMs following predefined hypotheses. The IATAs are structured as decision trees and tiered testing strategies for each decision node to support a grouping decision. Implications (e.g., regulatory or precautionary) per group are indicated. IATAs integrate information on durability and biopersistence (dissolution kinetics) to specific hazard endpoints, e.g., inflammation and genotoxicity, which are possibly indicative of toxicity. Based on IATAs, groups of similar nanoforms (NFs) of a NM can be formed, such as very slow dissolving, highly biopersistent and systemically toxic NFs. Reference NMs (ZnO, SiO2 and TiO2) along with related NFs are applied as case studies to testing the oral IATAs. Results based on the Tier 1 level suggest a hierarchy of biodurability and biopersistence of TiO2 > SiO2 > ZnO, and are confirmed by in vivo data (Tier 3 level). Interestingly, our analysis suggests that TiO2 and SiO2 NFs are able to induce both local and systemic toxicity along with microbiota dysbiosis and can be grouped according to the tested fate and hazard descriptors. This supports that the decision nodes of the oral IATAs are suitable for classification and assessment of the toxicity of NFs.

Eco-Interactions of Engineered Nanomaterials in the Marine Environment: Towards an Eco-Design Framework

Marine nano-ecotoxicology has emerged with the purpose to assess the environmental risks associated with engineered nanomaterials (ENMs) among contaminants of emerging concerns entering the marine environment. ENMs’ massive production and integration in everyday life applications, associated with their peculiar physical chemical features, including high biological reactivity, have imposed a pressing need to shed light on risk for humans and the environment. Environmental safety assessment, known as ecosafety, has thus become mandatory with the perspective to develop a more holistic exposure scenario and understand biological effects. Here, we review the current knowledge on behavior and impact of ENMs which end up in the marine environment. A focus on titanium dioxide (n-TiO₂) and silver nanoparticles (AgNPs), among metal-based ENMs massively used in commercial products, and polymeric NPs as polystyrene (PS), largely adopted as proxy for nanoplastics, is made. ENMs eco-interactions with chemical molecules including (bio)natural ones and anthropogenic pollutants, forming eco- and bio-coronas and link with their uptake and toxicity in marine organisms are discussed. An ecologically based design strategy (eco-design) is proposed to support the development of new ENMs, including those for environmental applications (e.g., nanoremediation), by balancing their effectiveness with no associated risk for marine organisms and humans.

Ionic-strength-dependent effect of suspended sediment on the aggregation, dissolution and settling of silver nanoparticles

Suspended sediment (SS) is ubiquitous in natural waters and plays a key role in the fate of engineered nanomaterials. In this study, the effect of SS on the aggregation, settling, and dissolution of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) was investigated under environmentally relevant conditions. The heteroaggregation of AgNPs with SS was not observed at low ionic strength (≤0.01 M) due to high electrostatic repulsion and steric forces. At higher NaCl concentrations (0.1 and 0.3 M), PVP-AgNPs were found to attach onto the SS surface, and the formation of AgNP-SS heteroaggregates strongly promoted settling of PVP-AgNPs due to the overwhelming gravity force. PVP-AgNP dissolution was reduced after the addition of sediment to ultrapure water because the presence of sediment-associated dissolved organic matter (SS-DOM). The formation of an AgCl layer on PVP-AgNP surface in 0.01 M NaCl solution resulted in the minor effect of SS on AgNP dissolution. After addition of SS, the dissolved silver concentrations of PVP-AgNP increased in 0.1 and 0.3 M NaCl solution. The interactions of SS-DOM with AgNPs under different NaCl concentrations interfered the dissolution of AgNPs in sediment-laden water. This study provides new insight into the fate of AgNPs in sediment-laden water under various environmental conditions.

Synthesis of Biogenic Silver Nanoparticles Using Caesalpinia digyna and Investigation of Their Antimicrobial Activity and In Vivo Biocompatibility

Among metallic nanoparticles, silver nanoparticles (AgNPs) have a wide spectrum of medical applications. Herein, biogenic silver nanoparticles (bAgNPs) were prepared from extracts of Caesalpinia digyna leaf as a reducing agent at different pH values (i.e., 5, 7, 8, and 10). The as-synthesized bAgNPs were characterized using UV-vis and Fourier transform infrared (FTIR) spectroscopies, scanning transmission electron microscopy, powder X-ray diffraction analysis, dynamic light scattering, and ζ-potential analysis. The sizes of bAgNPs prepared at pH 5, 7, 8, and 10 were 45.4, 11.3, 11.4, and 40.8 nm, respectively, and all of the nanoparticles were negatively charged. The antimicrobial activity of the as-prepared bAgNPs was investigated against Bacillus subtilis, Escherichia coli DH5α, E. coli K12, enteropathogenic E. coli (EPEC), and Salmonella typhi. The bAgNPs prepared at pH 8 showed the highest antibacterial propensity against all of the bacterial strains as exhibited in the zone of inhibition (ZOI) as well as the CellTox green assay, which can be due to their relatively small size, stability, and higher surface area-to-volume ratio. The bAgNPs synthesized at pH 8 showed the highest ZOI against B. subtilis, which was ∼25 mm in diameter. The lipid peroxidation assay demonstrated the formation of the malondialdehyde-thiobarbituric acid (MDA-TBA) adduct while treating the bacteria with bAgNPs due to the oxidation of fatty acids present in the membrane. The highest amount of MDA-TBA adduct was observed when Gram-positive B. subtilis was exposed to bAgNPs. On the contrary, rats treated with bAgNPs demonstrated no significant toxicity in terms of hematological and biochemical parameters. The bAgNPs also showed excellent compatibility with human red blood cells. Overall, bAgNPs synthesized at pH 8 have superior antimicrobial activity and excellent biocompatibility and, therefore, can be used as potential antibacterial agents.

Preparation of two types of silver-doped fluorescent carbon dots and determination of their antibacterial properties

The preparation and performance of doped antibacterial carbon dots (CDs) have been the research hotspot. In this paper, we report the preparation of two blue light-emitting silver-doped CDs, CD-1 and CD-2, through one- and two-step routes, respectively, by using polyethyleneimine, citric acid, and AgNO₃ as raw materials. Both CDs exhibited excellent and broad-spectrum activity against gram-positive bacteria, gram-negative bacteria, and fungi. We compared the emission wavelength, surface group, particle size, chargeability, and element content of the two CDs through various characterization methods. CD-2 exhibiting longer emission wavelength, larger particle size, and higher silver content displayed higher antibacterial activity against microorganisms than CD-1. On the other hand, CDs exhibited varying antibacterial properties against different microorganisms because of differences in the cell wall structure of gram-positive bacteria (peptidoglycan), gram-negative bacteria (lipopolysaccharides), and fungi (chitin). Based on scanning electron microscopy observations, circular dichroism spectroscopy and agarose gel electrophoresis, we speculate that CDs exert antibacterial activity mainly through membrane disruption and their effect on intracellular DNA and proteins. At the same time, CDs have multicolor imaging capabilities of Staphylococcus aureus. The antibacterial activity and versatility of bioimaging make them more potential antibacterial agents than traditional agents.

Transformation of Nanomaterials and Its Implications in Gut Nanotoxicology

Ingestion of engineered nanomaterials (ENMs) is inevitable due to their widespread utilization in the agrifood industry. Safety evaluation has become pivotal to identify the consequences on human health of exposure to these ingested ENMs. Much of the current understanding of nanotoxicology in the gastrointestinal tract (GIT) is derived from studies utilizing pristine ENMs. In reality, agrifood ENMs interact with their microenvironment, and undergo multiple physicochemical transformations, such as aggregation/agglomeration, dissolution, speciation change, and surface characteristics alteration, across their life cycle from synthesis to consumption. This work sieves out the implications of ENM transformations on their behavior, stability, and reactivity in food and product matrices and through the GIT, in relation to measured toxicological profiles. In particular, a strong emphasis is given to understand the mechanisms through which these transformations can affect ENM induced gut nanotoxicity.

A voltammetric investigation of the sulfidation of silver nanoparticles by zinc sulfide

Silver nanoparticles (Ag NPs) are among the most common forms of nanoparticles in consumer products, yet the environmental implications of their widespread use remain unclear due to uncertainties about their fate. Because sulfidation of Ag NPs results in the formation of a stable silver sulfide (Ag₂S) product, it is likely an important removal mechanism of bioavailable silver in natural waters. In addition to sulfide, the complete conversion of Ag NPs to Ag₂S will require dissolved oxygen or some other oxidant so dispersed metal sulfides may be an important pool of reactive sulfide for such reactions in oxygenated systems. The reaction of Ag NPs with zinc sulfide (ZnS) was investigated using a voltammetric method, anodic stripping voltammetry (ASV). ASV provided sensitive, in situ measurements of the release of zinc (Zn²⁺) cations resulting from the cation exchange reaction between Ag NPs and ZnS. The effects of Ag NP size and surface coatings on the initial rates of sulfidation by ZnS were examined. Sulfidation of smaller Ag NPs generally occurred faster and to a greater extent due to their larger relative surface areas. Sulfidation of Ag NPs capped by citrate and lipoic acid occurred more rapidly relative to polyvinylpyrrolidone (PVP) and branched polyethylene (BPEI). This study demonstrates the utility of voltammetry for such investigations and provides insights into important factors controlling Ag NP sulfidation such as availability of dissolved oxygen, Ag NP size and Ag NP surface coating. Furthermore, this work demonstrates the importance of cation exchange reactions between silver and metal sulfides, and how the environmental release of Ag NPs could alter the speciation of other metals of environmental significance.

Dispersibility and Size Control of Silver Nanoparticles with Anti-Algal Potential Based on Coupling Effects of Polyvinylpyrrolidone and Sodium Tripolyphosphate

In nearly all the cases of biotoxicity studies of silver nanoparticles (AgNPs), AgNPs used often have general dispersibility and wide size distribution, which may inevitably generate imprecise results. Herein, a kind of synthesis method by coupling effects of polyvinylpyrrolidone (PVP) and sodium tripolyphosphate (STPP) was proposed, in order to prepare AgNPs with better dispersibility and a stable size. Based on this, the preparation mechanism of AgNPs and the potential anti-algae toxicity were analyzed. UV-vis analysis showed that the particle size distribution of AgNPs prepared by co-protective agents was more uniform. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) were used to confirm that the obtained nano silver was of a high purity and stable size (~30 nm in diameter). Zeta potential and Fourier transform infrared spectroscopy (FTIR) analysis results indicated the synthesis mechanism of AgNPs by co-protective agents, more precisely, PVP limited the polynegative effect and prevented the linear induction of P₃O₁₀^5- produced by STPP during the growth of silver nuclei. Subsequently, Chlorella and Scenedesmus obliquus were utilized to test the toxicity of AgNPs, confirming that AgNPs synthesized through co-protective agents have potential inhibitory ability on algae, but not severe. This study provides a basic theory for the induction of synthetic AgNPs by various factors in the natural environment and a scientific reference for the environmental risk assessment.

Coating-Dependent Effects of Silver Nanoparticles on Tobacco Seed Germination and Early Growth

Silver nanoparticles (AgNPs) are used in a wide range of consumer products because of their excellent antimicrobial properties. AgNPs released into the environment are prone to transformations such as aggregation, oxidation, or dissolution so they are often stabilised by coatings that affect their physico-chemical properties and change their effect on living organisms. In this study we investigated the stability of polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB) coated AgNPs in an exposure medium, as well as their effect on tobacco germination and early growth. AgNP-CTAB was found to be more stable in the solid Murashige and Skoog (MS) medium compared to AgNP-PVP. The uptake and accumulation of silver in seedlings was equally efficient after exposure to both types of AgNPs. However, AgNP-PVP induced only mild toxicity on seedlings growth, while AgNP-CTAB caused severe negative effects on all parameters, even compared to AgNO3. Moreover, CTAB coating itself exerted negative effects on growth. Cysteine addition generally alleviated AgNP-PVP-induced negative effects, while it failed to improve germination and growth parameters after exposure to AgNP-CTAB. These results suggest that the toxic effects of AgNP-PVP are mainly a consequence of release of Ag+ ions, while phytotoxicity of AgNP-CTAB can rather be ascribed to surface coating itself.

Protective effect of N-acetylcysteine on the toxicity of silver nanoparticles: Bioavailability and toxicokinetics in Enchytraeus crypticus

We previously demonstrated that N-acetylcysteine (NAC) could reduce the toxicity of silver (Ag) materials (nanoparticles (NPs) and Ag nitrate) to the soil invertebrate Enchytraeus crypticus (Oligochaeta). It remains however, unclear whether the antitoxic mechanism of NAC was caused by NAC-Ag binding in the soil or inside the organisms. This study aimed at determining the bioavailability of Ag in the soil in a 21-day toxicity test as well as the Ag uptake and elimination kinetics in E. crypticus exposed to AgNPs in LUFA 2.2 standard soil amended with low (100 mg/kg dry soil) and high (600 mg/kg dry soil) NAC concentrations. The addition of NAC to the soil alleviated the toxicity of AgNPs by decreasing the internal Ag concentration of E. crypticus in a dose-dependent manner. Indeed, NAC reduced the binding of Ag to the soil, which probably was due to the formation of soluble but biologically unavailable Ag-cysteine complexes. The reduced Ag uptake in the enchytraeids was explained from an increased elimination at high NAC levels. These findings reinforce the view that metal complexing-compounds like NAC play a key role in the modulation of AgNP toxicity and bioavailability in terrestrial environments. Further, it may inform on the potential of NAC as a remediation solution for Ag or other metal-contaminated soils.

Transformation pathways and fate of engineered nanoparticles (ENPs) in distinct interactive environmental compartments: A review

The ever increasing production and use of nano-enabled commercial products release the massive amount of engineered nanoparticles (ENPs) in the environment. An increasing number of recent studies have shown the toxic effects of ENPs on different organisms, raising concerns over the nano-pollutants behavior and fate in the various environmental compartments. After the release of ENPs in the environment, ENPs interact with various components of the environment and undergoes dynamic transformation processes. This review focus on ENPs transformations in the various environmental compartments. The transformation processes of ENPs are interrelated to multiple environmental aspects. Physical, chemical and biological processes such as the homo- or hetero-agglomeration, dissolution/sedimentation, adsorption, oxidation, reduction, sulfidation, photochemically and biologically mediated reactions mainly occur in the environment consequently changes the mobility and bioavailability of ENPs. Physico-chemical characteristics of ENPs (particle size, surface area, zeta potential/surface charge, colloidal stability, and core-shell composition) and environmental conditions (pH, ionic strength, organic and inorganic colloids, temperature, etc.) are the most important parameters which regulated the ENPs environmental transformations. Meanwhile, in the environment, organisms encountered multiple transformed ENPs rather than the pristine nanomaterials due to their interactions with various environmental materials and other pollutants. Thus it is the utmost importance to study the behavior of transformed ENPs to understand their environmental fate, bioavailability, and mode of toxicity.

A hybrid lipid membrane coating "shape-locks" silver nanoparticles to prevent surface oxidation and silver ion dissolution

The controlled synthesis of stable silver nanoparticles (AgNPs), that do not undergo surface oxidation and Ag+ ion dissolution, continues to be a major challenge. Here the synthesis of robust hybrid lipid-coated AgNPs, comprised of l-α-phosphatidylcholine (PC) membranes anchored by a stoichiometric amount of long-chained hydrophobic thiols and sodium oleate (SOA) as hydrophobic binding partners, that do not undergo surface oxidation and Ag+ ion dissolution, is described. UV-Visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometry (ICP-MS) demonstrate that in the presence of strong oxidants, such as potassium cyanide (KCN), the hybrid lipid-coated AgNPs are stable and do not undergo surface oxidation even in the presence of membrane destabilizing surfactants. UV-Vis studies show that the stability of hybrid lipid-coated AgNPs of various sizes and shapes is dependent on the length of the thiol hydrocarbon chain and can be ranked in the order of increasing stability as follows: propanethiol (PT) < hexanethiol (HT) ≤ decanethiol (DT). UV-Vis and ICP-MS studies show that the hybrid lipid-coated AgNPs do not change in size or shape confirming that the AgNPs do not undergo surface oxidation and Ag+ ion dissolution when placed in the presence of strong oxidants, chlorides, thiols, and low pH. Long-term stability studies, over 21 days, show that the hybrid lipid-coated AgNPs do not release Ag+ ions and are more stable. Overall, these studies demonstrate hybrid membrane encapsulation of nanomaterials is a viable method for stabilizing AgNPs in a "shape-locked" form that is unable to undergo surface oxidation, Ag+ ion release, aging, or shape conversion. More importantly, this design strategy is a simple approach to the synthesis and stabilization of AgNPs for a variety of biomedical and commercial applications where Ag+ ion release and toxicity is a concern. With robust and shielded AgNPs, investigators can now evaluate and correlate how the physical features of AgNPs influence toxicity without the confounding factor of Ag+ ions present in samples. This design strategy also provides an opportunity where the membrane composition can be tuned to control the release rate of Ag+ ions for optimizing antimicrobial activity.

Effects of Chloride Concentration on the Water Disinfection Performance of Silver Containing Nanocellulose-based Composites

The availability of microbially-safe drinking water is a challenge in many developing regions. Due to the well-known antibacterial effect of silver ions, materials used for their controlled release have been widely studied for point-of-use water disinfection. However, even if it is in principle known that chloride anions can suppress the antibacterial efficiency of silver, the majority of previous studies, surprisingly, have not focused on chloride concentrations relevant for freshwaters and thus for practical applications. Here, we prepared low-cost nanocellulose-aluminium oxyhydroxide nanocomposites functionalized with silver nanoparticles. Field samples obtained from Chennai, India were used as a guideline for choosing relevant chloride concentrations for the antibacterial studies, i.e., 10, 90, and 290 ppm. The antibacterial performance of the material against Escherichia coli and Bacillus subtilis was demonstrated and the influence of chloride concentration on the antibacterial effect was studied with E. coli. A 1 h contact time led to bacterial reductions of 5.6 log₁₀, 2.9 log₁₀, and 2.2 log₁₀, respectively. This indicates that an increase of chloride concentration leads to a substantial reduction of antibacterial efficiency, even within chloride concentrations found in freshwaters. This work enables further insights for designing freshwater purification systems that utilize silver-releasing materials.

Investigation of the Antibacterial Activity and in vivo Cytotoxicity of Biogenic Silver Nanoparticles as Potent Therapeutics

Biogenic nanoparticles are the smartest weapons to deal with the multidrug-resistant "superbugs" because of their broad-spectrum antibacterial propensity as well as excellent biocompatibility. The aqueous biogenic silver nanoparticles (Aq-bAgNPs) and ethanolic biogenic silver nanoparticles (Et-bAgNPs) were synthesized using aqueous and ethanolic extracts of Andrographis paniculata stem, respectively, as reducing agents. Electron microscopic images confirmed the synthesis of almost spherical shaped biogenic silver nanoparticles (bAgNPs). The zeta potentials of the nanoparticles were negative and were -22 and -26 mV for Aq-bAgNPs and Et-bAgNPs, respectively. The antibacterial activity of bAgNPs was investigated against seven pathogenic (i.e., enteropathogenic Escherichia coli, Salmonella typhi, Staphylococcus aureus, Vibrio cholerae, Enterococcus faecalis, Hafnia alvei, Acinetobacter baumannii) and three nonpathogenic (i.e., E. coli DH5α, E. coli K12, and Bacillus subtilis) bacteria at different time points (i.e., 12, 16, 20, and 24 h) in a dose-dependent manner (i.e., 20, 40, and 60 μg) through broth dilution assay, disk diffusion assay, CellTox^TM Green uptake assay, and trypan blue dye exclusion assay. The lowest minimum inhibitory concentration value for both the bAgNPs was 0.125 μg. Et-bAgNPs showed the highest antibacterial activity against S. aureus at 60 μg after 16 h and the diameter of inhibited zone was 28 mm. Lipid peroxidation assay using all the bacterial strains revealed the formation of malondialdehyde-thiobarbituric acid adduct due to the oxidation of cell membrane fatty acids by bAgNPs. The bAgNPs showed excellent hemocompatibility against human as well as rat red blood cells. Furthermore, there was no significant toxicity observed when the levels of rat serum ALT, AST, γ-GT (i.e., liver function biomarkers), and creatinine (i.e., kidney function biomarker) were determined.

Study on the dissolution of hollow mesoporous silica nanosphere-supported nanosized platinum oxide in biorelevant media for evaluating its potential as chemotherapeutics

Platinum oxide (PtO_x) nanoparticles (NPs) have been shown to possess anticancer activity by releasing ionic Pt species under biological conditions. However, the dissolution kinetics and the changes in the chemical state of Pt during PtO_x dissolution have not yet been studied. To fill this gap, we prepared a composite (designated as PtO_x@MMT-2) containing PtO_x NPs on hollow mesoporous silica nanospheres and studied the dissolution of the material in different biorelevant media. We found that the release of Pt was retarded due to the adsorption of biomolecules on PtO_x NPs during the degradation of host silica. The biomolecules adsorption also lowered the accessibility of PtO_x NPs, resulting in the reduced catalase-like activity of the NPs. In line with the results, the cytotoxicity of PtO_x@MMT-2, which was positively correlated to the amount of Pt uptake, was reduced by biomolecules adsorption. Our findings should be applicable to other metal (oxide) NPs under biological conditions and may provide implications for the design of nanomaterials for practical therapeutic applications.

Bifunctionalized Silver Nanoparticles as Hg2+ Plasmonic Sensor in Water: Synthesis, Characterizations, and Ecosafety

In this work, hydrophilic silver nanoparticles (AgNPs), bifunctionalized with citrate (Cit) and L-cysteine (L-cys), were synthesized. The typical local surface plasmon resonance (LSPR) at λ _max = 400 nm together with Dynamic Light Scattering (DLS) measurements (<2R_H> = 8 ± 1 nm) and TEM studies (Ø = 5 ± 2 nm) confirmed the system nanodimension and the stability in water. Molecular and electronic structures of AgNPs were investigated by FTIR, SR-XPS, and NEXAFS techniques. We tested the system as plasmonic sensor in water with 16 different metal ions, finding sensitivity to Hg²⁺ in the range 1–10 ppm. After this first screening, the molecular and electronic structure of the AgNPs-Hg²⁺ conjugated system was deeply investigated by SR-XPS. Moreover, in view of AgNPs application as sensors in real water systems, environmental safety assessment (ecosafety) was performed by using standardized ecotoxicity bioassay as algal growth inhibition tests (OECD 201, ISO 10253:2006), coupled with determination of Ag⁺ release from the nanoparticles in fresh and marine aqueous exposure media, by means of ICP-MS. These latest studies confirmed low toxicity and low Ag⁺ release. Therefore, these ecosafe AgNPs demonstrate a great potential in selective detection of environmental Hg²⁺, which may attract a great interest for several biological research fields.

Complementary techniques (spICP-MS, TEM, and HPLC-ICP-MS) reveal the degradation of 40 nm citrate-stabilized Au nanoparticles in rat liver after intraperitoneal injection

BACKGROUND

Due to the increased use of engineered nanoparticles (NPs), their tracing in environmental and biological systems is of utmost importance. Besides their accumulation within a biological specimen, little is known about their degradation and transformation into corresponding low-molecular species that might influence any toxicological impact.

ANALYTICAL METHODS

Wistar rats underwent intraperitoneal injections of 40 nm citrate-stabilized gold nanoparticles. Different liver samples were analysed for the occurrence of nanoparticles and potential degradation products by means of spICP-MS, TEM and HPLC-ICP-MS.

MAIN FINDINGS

Studies using spICP-MS revealed the presence of the originally administrated Au NPs (40 nm diameter) and some evidences of other Au-containing species due to the increased background signal. Images obtained by transmission electron microscopy (TEM) showed the predominant presence of particles of significantly smaller diameter (6 ± 2 nm). As complementary method, HPLC-ICP-MS confirmed the presence of both particle types indicating a degradation of the Au NPs accompanied by detection of low-molecular Au species.

CONCLUSIONS

This study underlines that degradation of gold nanoparticles to low-molecular gold species might have to be taken into account in future for studies on their toxicological behaviour and their potential use in clinical applications.

Impacts of Continuous Inflow of Low Concentrations of Silver Nanoparticles on Biological Performance and Microbial Communities of Aerobic Heterotrophic Wastewater Biofilm

Attached-growth wastewater processes are currently used in water resource recovery facilities (WRRFs) for required upgrades due to an increase in influent loading or to reach more stringent discharge criteria. Yet, the distribution and long-term inhibitory effects of silver nanoparticles (AgNPs) in attached-growth biological wastewater processes and their impact on involved microbial communities are poorly understood at relevant, low concentrations. Retention, distribution, and long-term inhibitory effect of polyvinylpyrrolidone (PVP)-coated AgNPs were evaluated in bench-scale moving bed biofilm reactors (MBBRs), achieving soluble organic matter removal, over a 64 day exposure to nominal concentrations of 10 and 100 μg/L. Distributions of continuously added AgNPs were characterized in the influent, bioreactor, and effluent of MBBRs using single particle inductively coupled plasma mass spectroscopy (spICP-MS). Aerobic heterotrophic biofilms in MBBRs demonstrated limited retention capacity for AgNPs over long-term exposure, with release of AgNPs, and Ag-rich biofilm sloughed from the carriers. Continuous exposure to both influent AgNP concentrations significantly decreased soluble chemical oxygen demand (S_COD) removal efficiency (11% to 31%) and reduced biofilm viability (8% to 30%). Specific activities of both intracellular dehydrogenase (DHA) and extracellular α-glucosidase (α-Glu) and protease (PRO) enzymes were significantly inhibited (8% to 39%) with an observed NP dose-dependent intracellular reactive oxygen species (ROS) production and shift in biofilm microbial community composition by day 64. Our results indicated that long-term exposure to AgNPs in biofilm processes at environmentally relevant concentrations can impact the treatment process stability and the quality of the discharged effluent.

Non-antibacterial as well as non-anticancer activity of flower extract and its biogenous silver nanoparticles

Silver nanoparticles were synthesized by using the white flower extract of Albizia lebbeck as a source of reducing and capping agents. A. lebbeck white flower extract and silver nanoparticles were checked for their antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeroginosa and Ba cillus subtilis by using Mueller Hinton agar, nutrient agar and Luria Bertani agar using the well diffusion method. The synthesized silver nanoparticles did not show antibacterial activity at lower (0.1-0.4 mg ml^-1) or higher (0.5-2.5 mg ml^-1) concentrations against any of the four organisms on either of the media, even though silver nanoparticles have been well known to show antibacterial activity even at lower concentrations. The non-antibacterial properties of the synthesized silver nanoparticles against all four bacteria were confirmed using viability counting. With this unique non-antibacterial property of biogenous silver nanoparticles observed in this study, it can be stated that case by case evaluation of every synthesized silver nanoparticle needs to be done as there are multiple factors influencing their properties. Anticancer activity of these nanoparticles at different concentrations against A549 cancer cells did not show any significant decrease in cell viability highlighting its biocompatible nature. Thus, these silver nanoparticles can be a best suited candidate for drug delivery.

In the Search for Nanospecific Effects of Dissolution of Metallic Nanoparticles at Freshwater-Like Conditions: A Critical Review

Knowledge on relations between particle properties and dissolution/transformation characteristics of metal and metal oxide nanoparticles (NPs) in freshwater is important for risk assessment and product development. This critical review aims to elucidate nanospecific effects on dissolution of metallic NPs in freshwater and similar media. Dissolution rate constants are compiled and analyzed for NPs of silver (Ag), copper (Cu), copper oxide/hydroxide (CuO, Cu(OH)₂), zinc oxide (ZnO), manganese (Mn), and aluminum (Al), showing largely varying (orders of magnitude) constants when modeled using first order kinetics. An effect of small primary sizes (<15 nm) was observed, leading to increased dissolution rate constants and solubility in some cases. However, the often extensive particle agglomeration can result in reduced nanospecific effects on dissolution and also an increased uncertainty related to the surface area, a parameter that largely influence the extent of dissolution. Promising ways to model surface areas of NPs in solution using fractal dimensions and size distributions are discussed in addition to nanospecific aspects related to other processes such as corrosion, adsorption of natural organic matter (NOM), presence of capping agents, and existence of surface defects. The importance of the experimental design on the results of dissolution experiments of metal and metal oxide NPs is moreover highlighted, including the influence of ionic metal solubility and choice of particle dispersion methodology.

Stability of silver nanoparticle sulfidation products

The adoption of silver nanoparticles in consumer goods has raised concerns about the potential environmental harm of their widespread use. We studied chemical transformations that Ag NPs may undergo as they pass through sulfide-rich conditions common in waste water treatment plants (WWTPs), which may limit the release of Ag⁺ from Ag NPs due to the formation of low-solubility silver sulfide (Ag₂S). However, it is uncertain whether sulfidation is complete and if sulfidized Ag NPs continue to release Ag⁺. To address these uncertainties, we monitored the reaction of Ag NPs with various levels of sulfide with an ion selective electrode and UV/visible spectrophotometry over the course of two months. We characterized the products of the sulfidation reactions with a purge-and-trap acid volatile sulfide (AVS) analysis, which served as a measure of the stability of the sulfidized products because sulfide would be readily lost to oxidation unless it is stabilized as Ag₂S. The Ag NP surface plasmon resonance (SPR) absorbance peak was initially diminished and then returned over the course of several days after reaction with limited amounts of sulfide, suggesting a dynamic system that may retain some characteristics of the pristine Ag NPs. However, ICP-MS analysis of sulfidized Ag NP suspensions over a two-month period demonstrates that sulfidation limits the release of Ag⁺ ions from nanosilver that pass through a WWTP, even when sulfide concentrations are limited relative to silver.

Effects of ionic strength on physicochemical properties and toxicity of silver nanoparticles

In the environment, silver nanoparticles (AgNPs) undergo a number of potential transformations, such as aggregation, dissolution, and redox reactions. However, the transformation in ionic strength condition, as well as their related toxicity was not quite clear, especially in the in vivo system. In the present study, we comprehensively evaluated three different characteristics (ddH₂O, EPA water and K⁺ medium (KM)) mediated changes in the physical morphology of AgNPs and the alteration of the toxicity to Caenorhabditis elegans (C. elegans). Our results showed besides the changes of AgNPs behavior such as the transformation of morphological, with the transmission electron microscopy we found for the first time that smaller nanoparticles (<5 nm) appeared around the pristine AgNPs after incubation in EPA or KM for 5 days. Together with these changes, the toxicity of AgNPs to C. elegans changed significantly, showing that a higher ionic strength medium resulted in greater toxicity to C. elegans, as measured by germ cell apoptosis, brood size and lifespan. More importantly, our results indicated that the higher toxicity of AgNPs to C. elegans reproduction was probably related to the appearance of the smaller-size AgNPs in higher ionic strength media. These findings highlight that toxicity assessments for the release of nanomaterial to the environment need to be improved to assess environmental safety more accurately.

Protein-activated transformation of silver nanoparticles into blue and red-emitting nanoclusters

Protein capping can trigger nanoparticle to nanocluster transformation at elevated pH.

Nanoparticle modification in biological media: implications for oral nanomedicines

Nanomedicine has shown potential in enabling oral administration of poorly absorbable drugs, such as biologics. As part of the process related to optimisation of the safety and efficacy of nanomedicines, it is imperative that the interaction of nanoparticles with the biological systems – including the gut – is fully characterised. In this article, we provide an overview of the major mechanisms by which nanoparticles may transform upon introduction in biological media. Specifically, the phenomena of association, dissolution and biomolecule adsorption are discussed, together with factors which influence the occurrence of each phenomenon. The implications of these phenomena within the context of therapeutic action of nanomedicines, which includes reduced targeting efficiency, are also explored. Finally, we will comment on nanoparticle modification within the gut environment, including the currently available gastrointestinal models for the study of nano-bio interactions, with implications in the area of nanomedicines for oral administration.

Nanomedicines undergo transformation in biological media, which impacts biological effects. Such transformation in the gut environment has implications in use of nanomedicines for oral administration.

All that is silver is not toxic: silver ion and particle kinetics reveals the role of silver ion aging and dosimetry on the toxicity of silver nanoparticles

BACKGROUND

When suspended in cell culture medium, nano-objects composed of soluble metals such as silver can dissolve resulting in ion formation, altered particle properties (e.g. mass, morphology, etc.), and modulated cellular dose. Cultured cells are exposed not just to nanoparticles but to a complex, dynamic mixture of altered nanoparticles, unbound ions, and ion-ligand complexes. Here, three different cell types (RAW 264.7 macrophages and bone marrow derived macrophages from wild-type C57BL/6 J mice and Scavenger Receptor A deficient (SR-A(-/-)) mice) were exposed to 20 and 110 nm silver nanoparticles, and RAW 264.7 cells were exposed to freshly mixed silver ions, aged silver ions (ions incubated in cell culture medium), and ions formed from nanoparticle dissolution. The In Vitro Sedimentation, Diffusion, Dissolution, and Dosimetry Model (ISD3) was used to predict dose metrics for each exposure scenario.

RESULTS

Silver nanoparticles, freshly mixed ions, and ions from nanoparticle dissolution were toxic, while aged ions were not toxic. Macrophages from SR-A(-/-) mice did not take up 20 nm silver nanoparticles as well as wild-types but demonstrated no differences in silver levels after exposure to 110 nm nanoparticles. Dose response modeling with ISD3 predicted dose metrics suggest that amount of ions in cells and area under the curve (AUC) of ion amount in cells are the most predictive of cell viability after nanoparticle and combined nanoparticle/dissolution-formed-ions exposures, respectively.

CONCLUSIONS

Results of this study suggest that the unbound silver cation is the ultimate toxicant, and ions formed extracellularly drive toxicity after exposure to nanoparticles. Applying computational modeling (ISD3) to better understand dose metrics for soluble nanoparticles allows for better interpretation of in vitro hazard assessments.

N-Acetylcysteine reverses silver nanoparticle intoxication in rats

The increasing use of silver nanoparticles (AgNPs) in consumer products raises the risk of human toxicity. Currently, there are no therapeutic options or established treatment protocols in cases of AgNPs intoxication. We demonstrated previously that thiol antioxidants compounds can reverse the cytotoxicity induced by AgNPs in Huh-7 hepatocarcinoma cells. Here, we investigated the use of N-acetylcysteine (NAC) against the systemic toxic effects of AgNPs (79.3 nm) in rats. Biochemical, histopathological, hematological, and oxidative parameters showed that a single intravenous injection of AgNPs (5 mg/kg b.w.) induced deleterious effects such as hepatotoxicity, potentially as a result of AgNPs accumulation in the liver. Treatment with a single intraperitoneal injection of NAC (1 g/kg b.w.) one hour after AgNPs exposure significantly attenuated all toxic effects evaluated and altered the bioaccumulation and release patterns of AgNPs in rats. The findings show that NAC may be a promising candidate for clinical management of AgNPs intoxication.

Influence of Organic Ligands on the Colloidal Stability and Removal of ZnO Nanoparticles from Synthetic Waters by Coagulation

The large-scale production and usage of zinc oxide nanoparticles (ZnO NPs) may lead to their post-release into the aquatic environment. In this study, the effect of hydrophobic/hydrophilic organic ligands on sorption and sedimentation of ZnO NPs has been systematically investigated. In addition, the coagulation efficiency of ZnO NPs, Zn2+, dissolved organic carbon (DOC), and UV254 with varying ferric chloride (FC) dosages in synthetic waters were also evaluated. The results showed that the higher concentration of organic ligands, i.e., humic acid (HA), salicylic acid (SA), and L-cysteine (L-cys) reduced the ζ-potential and hydrodynamic diameter (HDD) of particles, which enhanced the NPs stability. The adsorption of organic ligands onto ZnO NPs was fitted with the Langmuir model, with maximum adsorption capacities of 143, 40.47, and 66.05 mg/g for HA, SA and L-cys respectively. Removal of up to 95% of ZnO NPs and Zn2+ was achieved in studied waters at the effective coagulation zone (ECR), above which excess charge induced by coagulant restabilized the NPs in suspension. Moreover, the removal rate of DOC and UV254 were found to be higher in hydrophobic waters than hydrophilic waters. The width of ECR strongly depends on the characteristics of source water. The waters with hydrophobic ligand and higher UV254 values require more coagulant than hydrophilic waters to achieve the similar ZnO NPs and Zn2+ removal. The results of Fourier transform infrared (FT-IR) analysis of ZnO NPs composite contaminant flocs indicated that the combined effect of enmeshment and charge neutralization might be a possible removal mechanism. These findings may facilitate the prediction of fate, transport, and removal of ZnO NPs in the natural waters, and might contribute to risk assessment, as well as decision making about engineered nanoparticles (ENPs) in aquatic systems.

Differential behaviors of silver nanoparticles and silver ions towards cysteine: Bioremediation and toxicity to Phanerochaete chrysosporium

Potential transformations of silver nanoparticles (AgNPs) upon interaction with naturally ubiquitous organic ligands in aquatic environments influence their transport, persistence, bioavailability, and subsequent toxicity to organisms. In this study, differential behaviors of AgNPs and silver ions (Ag⁺) towards cysteine (Cys), an amino acid representative of thiol ligands that easily coordinate to Ag⁺ and graft to nanoparticle surfaces, were investigated in the aspects of bioremediation and their toxicity to Phanerochaete chrysosporium. Total Ag removal, 2,4-dichlorophenol (2,4-DCP) degradation, extracellular protein secretion, and cellular viability were enhanced to some extent after supplement of various concentrations of cysteine under stress of AgNPs and Ag⁺. However, an obvious decrease in total Ag uptake was observed after 5-50 μM cysteine addition in the groups treated with 10 μM AgNPs and 1 μM Ag⁺, especially at a Cys:Ag molar ratio of 5. More stabilization in uptake pattern at this ratio was detected under Ag⁺ exposure than that under AgNP exposure. Furthermore, in the absence of cysteine, all Ag⁺ treatments stimulated the generation of reactive oxygen species (ROS) more significantly than high-dose AgNPs did. However, cysteine supply under AgNP/Ag⁺ stress aggravated ROS levels, albeit alleviated at 100 μM Ag⁺, indicating that the toxicity profiles of AgNPs and Ag⁺ to P. chrysosporium could be exacerbated or marginally mitigated by cysteine. The results obtained were possibly associated with the lability and bioavailability of AgNP/Ag⁺-cysteine complexes.

Antimicrobial Potential and Cytotoxicity of Silver Nanoparticles Phytosynthesized by Pomegranate Peel Extract

The phytosynthesis of metal nanoparticles is nowadays attracting the increased attention of researchers and is much needed given the worldwide matter related to environmental contamination. The antimicrobial activity of colloidal and spray formulation of silver nanoparticles (AgNPs) synthesized by pomegranate peel extract against Candida albicans and Staphylococcus aureus, and their cytotoxicity in mammalian cells were tested in the present study. Dry matter, pH, total phenolics, and ellagic acid in the extract were determined. Then, AgNPs were phytosynthesized and characterized by X-ray diffraction, electron transmission microscopy, dynamic light scattering, zeta potential, and Ag⁺ dosage. Spray formulations and respective chemical-AgNP controls were prepared and tested. The peel extract reduced more than 99% of Ag⁺, and produced nanoparticles with irregular forms and an 89-nm mean size. All AgNP presented antimicrobial activity, and the spray formulation of green-AgNP increased by 255 and 4 times the effectiveness against S. aureus and C. albicans, respectively. The cytotoxicity of colloidal and spray green-AgNP was expressively lower than the respective chemical controls. Pomegranate peel extract produced stable AgNP with antimicrobial action and low cytotoxicity, stimulating its use in the biomedical field.