Cytotoxicity induced by engineered silver nanocrystallites is dependent on surface coatings and cell types

Coated silver nanoparticles: synthesis, cytotoxicity, and optical properties

Coated silver nanoparticles (AgNPs) have recently become a topic of interest due to the fact that they have several applications such as in electronic, antimicrobial, industrial, optical, and medical fields as biosensors and drug delivery systems. However, the use of AgNPs in medical fields remains somewhat limited due to their probable cytotoxic effect. Researchers have succeeded in reducing the toxicity of silver particles by coating them with different substances. Generally, the coating of AgNPs leads to change in their properties depending on the type of the coating material as well as the layer thickness. This review covers the state-of-the-art technologies behind (a) the synthesis of coated AgNPs including coating methods and coating materials, (b) the cytotoxicity of coated AgNPs and (c) the optical properties of coated AgNPs.

Coated silver nanoparticles (AgNPs) have recently become a topic of interest due to the fact that they have several applications such as in electronic, antimicrobial, industrial, optical, and medical fields as biosensors and drug delivery systems.

Antimicrobial Effects of Biogenic Nanoparticles

Infectious diseases pose one of the greatest health challenges in the medical world. Though numerous antimicrobial drugs are commercially available, they often lack effectiveness against recently developed multidrug resistant (MDR) microorganisms. This results in high antibiotic dose administration and a need to develop new antibiotics, which in turn requires time, money, and labor investments. Recently, biogenic metallic nanoparticles have proven their effectiveness against MDR microorganisms, individually and in synergy with the current/conventional antibiotics. Importantly, biogenic nanoparticles are easy to produce, facile, biocompatible, and environmentally friendly in nature. In addition, biogenic nanoparticles are surrounded by capping layers, which provide them with biocompatibility and long-term stability. Moreover, these capping layers provide an active surface for interaction with biological components, facilitated by free active surface functional groups. These groups are available for modification, such as conjugation with antimicrobial drugs, genes, and peptides, in order to enhance their efficacy and delivery. This review summarizes the conventional antibiotic treatments and highlights the benefits of using nanoparticles in combating infectious diseases.

Bioengineering of Functional Nanosilver Nanogels for Smart Healthcare Systems

Functional designing of nanogels has become an attractive domain of biomedical engineering to develop bioactive materials with innovative features for the human healthcare system. Nanosilver has attracted enormous attention due to its wide antimicrobial spectrum and ability to kill almost all types of bacteria in its vicinity. However, the most crucial challenge for bioscientists is the lack of binding ability of nanosilver with the material surfaces that allow nanosilver to leach out to the surrounding tissue and exert toxicity while the biomaterial is in contact with the living system. Designing nanosilver within a nanogel confinement offers enormous possibilities to develop functional bioactive nanoparticles that may be bonded to any biomaterial surface via the nanogel functionality. This approach requires the proper combination of material science with nanotechnology and biotechnology to innovate interesting domain of functional nanogels with unique features. This work aims at providing a critical review on the current progress, approaches, and vision in designing nanosilver-entrapped nanogel particles with diverse functionality, and their bioactivity against microorganisms for human healthcare devices.

Intracellular Transport of Silver and Gold Nanoparticles and Biological Responses: An Update

Medicine, food, and cosmetics represent the new promising applications for silver (Ag) and gold (Au) nanoparticles (NPs). AgNPs are most commonly used in food and cosmetics; conversely, the main applications of gold NPs (AuNPs) are in the medical field. Thus, in view of the risk of accidentally or non-intended uptake of NPs deriving from the use of cosmetics, drugs, and food, the study of NPs⁻cell interactions represents a key question that puzzles researchers in both the nanomedicine and nanotoxicology fields. The response of cells starts when the NPs bind to the cell surface or when they are internalized. The amount and modality of their uptake depend on many and diverse parameters, such as NPs and cell types. Here, we discuss the state of the art of the knowledge and the uncertainties regarding the biological consequences of AgNPs and AuNPs, focusing on NPs cell uptake, location, and translocation. Finally, a section will be dedicated to the most currently available methods for qualitative and quantitative analysis of intracellular transport of metal NPs.

Fungal silver nanoparticles: synthesis, application and challenges

PURPOSE

This paper aims to summarize recent developments regarding the synthesis, application and challenges of fungal AgNPs. Possible methods to overcome the challenge of synthesis and reduce the toxicity of AgNPs have been discussed.

MATERIALS AND METHODS

This review consults and summary a large number of papers.

RESULTS

Silver nanoparticles (AgNPs) have great potential in many areas, as they possess multiple novel characteristics. Conventional methods for AgNPs biosynthesis involve chemical agents, causing environmental toxicity and high energy consumption. Fungal bioconversion is a simple, low-cost and energy-efficient biological method, which could successfully be used for AgNPs synthesis. Fungi can produce enzymes that act as both reducing and capping agents, to form stable and shape-controlled AgNPs.

CONCLUSIONS

AgNPs have great potential in the medical and food industries, due to their antimicrobial, anticancer, anti-HIV, and catalytic activities. However, the observed in vitro and in vivo toxicity poses considerable challenges in the synthesis and application of AgNPs.

Physicochemical characteristics and toxicity of surface-modified zinc oxide nanoparticles to freshwater and marine microalgae

Because of wide applications of surface-modified zinc oxide nanoparticles (ZnO-NPs) in commercial sunscreens and their easiness of being released into water, concerns have been raised over their potential effects on aquatic organisms. This study compared physicochemical properties of silane-coated and uncoated ZnO-NPs to elucidate their toxic potencies toward three freshwater and three marine microalgae. Surfaces of ZnO-NPs (20 nm) were modified by coating with 3-aminopropyltrimethoxysilane (A-ZnO-NPs) that provides the particles with a more hydrophilic surface, or dodecyltrichlorosilane (D-ZnO-NPs) that turns the particles to hydrophobic. Uncoated ZnO-NPs formed larger aggregates and released more Zn²⁺ than did either of the two coated ZnO-NPs. The three nanoparticles formed larger aggregates but released less Zn²⁺ at pH 8 than at pH 7. Although sensitivities varied among algal species, A-ZnO-NPs and uncoated ZnO-NPs were more potent at inhibiting growth of algal cells than were D-ZnO-NPs after 96-h exposure to ZnO, uncoated ZnO-NPs, each of the coated ZnO-NPs or ZnSO₄ at 10 concentrations ranging from 0.1 to 100 mg/L. The marine diatom Thalassiosira pseudonana exposed to ZnO-NPs, A-ZnO-NPs or D-ZnO-NPs resulted in differential expressions of genes, suggesting that each of the coatings resulted in ZnO-NPs acting through different mechanisms of toxic action.

Probing the toxicity of nanoparticles: a unified in silico machine learning model based on perturbation theory

Nanoparticles (NPs) are part of our daily life, having a wide range of applications in engineering, physics, chemistry, and biomedicine. However, there are serious concerns regarding the harmful effects that NPs can cause to the different biological systems and their ecosystems. Toxicity testing is an essential step for assessing the potential risks of the NPs, but the experimental assays are often very expensive and usually too slow to flag the number of NPs that may cause adverse effects. In silico models centered on quantitative structure-activity/toxicity relationships (QSAR/QSTR) are alternative tools that have become valuable supports to risk assessment, rationalizing the search for safer NPs. In this work, we develop a unified QSTR-perturbation model based on artificial neural networks, aimed at simultaneously predicting general toxicity profiles of NPs under diverse experimental conditions. The model is derived from 54,371 NP-NP pair cases generated by applying the perturbation theory to a set of 260 unique NPs, and showed an accuracy higher than 97% in both training and validation sets. Physicochemical interpretation of the different descriptors in the model are additionally provided. The QSTR-perturbation model is then employed to predict the toxic effects of several NPs not included in the original dataset. The theoretical results obtained for this independent set are strongly consistent with the experimental evidence found in the literature, suggesting that the present QSTR-perturbation model can be viewed as a promising and reliable computational tool for probing the toxicity of NPs.

Green synthesis of silver nanoparticles using Mentha pulegium and investigation of their antibacterial, antifungal and anticancer activity

A simple and eco-friendly method for efficient synthesis of stable colloidal silver nanoparticles (AgNPs) using Mentha pulegium extracts is described. A series of reactions was conducted using different types and concentrations of plant extract as well as metal ions to optimize the reaction conditions. AgNPs were characterized by using UV-vis spectroscopy, transmission electron microscopy, atomic force microscopy, dynamic light scattering, zetasizer, energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR). At the optimized conditions, plate shaped AgNPs with zeta potential value of -15.7 and plasmon absorption maximum at 450 nm were obtained using high concentration of aqueous extract. Efficient adsorption of organic compounds on the nanoparticles was confirmed by FTIR and EDAX. The biogenic AgNPs displayed promising antibacterial activity on Escherichia coli, Staphylococcus aureus, and Streptococcus pyogenes. The highest antibacterial activity of 25 µg mL-1 was obtained for all the strains using aqueous extract synthesized AgNPs. The aqueous extract synthesised AgNPs also showed considerable antifungal activity against fluconazole resistant Candida albicans. The cytotoxicity assay revealed considerable anticancer activity of AgNPs on HeLa and MCF-7 cancer cells. Overall results indicated high potential of M. pulegium extract to synthesis high quality AgNPs for biomedical applications.

Engineered Nanoparticles as Potential Food Contaminants and Their Toxicity to Caco-2 Cells

Engineered nanoparticles (ENPs), such as metallic or metallic oxide nanoparticles (NPs), have gained much attention in recent years. Increasing use of ENPs in various areas may lead to the release of ENPs into the environment and cause the contamination of agricultural and food products by ENPs. In this study, we selected two important ENPs (zinc oxide [ZnO] and silver [Ag] NPs) as potential food contaminants and investigated their toxicity via an in vitro model using Caco-2 cells. The physical properties of ENPs and their effects on Caco-2 cells were characterized by electron microscopy and energy dispersive X-ray spectroscopic (EDS) techniques. Results demonstrate that a significant inhibition of cell viability was observed after a 24-h of exposure of Caco-2 cells to 3-, 6-, and 12-mM ZnO NPs or 0.5-, 1.5-, and 3-mM Ag NPs. The noticeable changes of cells include the alteration in cell shape, abnormal nuclear structure, membrane blebbing, and cytoplasmic deterioration. The toxicity of ZnO NPs, but not that of Ag NPs after exposure to simulated gastric fluid, significantly decreased. Scanning transmission electron microscopy shows that ZnO and Ag NPs penetrated the membrane of Caco-2 cells. EDS results also confirm the presence of NPs in the cytoplasm of the cells. This study demonstrates that ZnO and Ag NPs have cytotoxic effects and can inhibit the growth of Caco-2 cells.

Toxicity of silver ions and differently coated silver nanoparticles in Allium cepa roots

Silver nanoparticles (AgNPs) are the dominating nanomaterial in consumer products due to their well-known antibacterial and antifungal properties. To enhance their properties, different surface coatings may be used, which affect physico-chemical properties of AgNPs. Due to their wide application, there has been concern about possible environmental and health consequences. Since plants play a significant role in accumulation and biodistribution of many environmentally released substances, they are also very likely to be influenced by AgNPs. In this study we investigated the toxicity of AgNO₃ and three types of laboratory-synthesized AgNPs with different surface coatings [citrate, polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB)] on Allium cepa roots. Ionic form of Ag was confirmed to be more toxic than any of the AgNPs applied. All tested AgNPs caused oxidative stress and exhibited toxicity only when applied in higher concentrations. The highest toxicity was recorded for AgNPs-CTAB, which resulted with increased Ag uptake in the roots, consequently leading to strong reduction of the root growth and oxidative damage. The weakest impact was found for AgNPs-citrate, much bigger, negatively charged NPs, which also aggregated to larger particles. Therefore, we can conclude that the toxicity of AgNPs is directly correlated with their size, overall surface charge and/or surface coating.

Insight into the interactions between nanoparticles and cells

This review summarizes the latest advances in nanoparticle (NP)–cell interactions. The influence of NP size, shape, shell structure, surface chemistry and protein corona formation on cellular uptake and cytotoxicity is highlighted in detail. Their impact on other cellular responses such as cell proliferation, differentiation and cellular mechanics is also discussed.

Impacts of Morphology, Natural Organic Matter, Cations, and Ionic Strength on Sulfidation of Silver Nanowires

Silver nanowires (AgNWs) are being widely utilized in an increasing number of consumer products, which could release silver to aquatic environments during the use or washing process, and have received growing concerns on their potential risks to bio-organisms and humans. The present study demonstrated that AgNWs mainly experienced direct oxysulfidation by reacting with dissolved sulfide species (initial S^2- concentration at 1.6 mg/L) to produce silver sulfide nanostructures under environmentally relevant conditions. Granular Ag₂S nanoparticles were formed on the surface of the nanowires. The sulfidation rate constant (k_Ag) of AgNWs was compared with those of silver nanoparticles (AgNPs) at different particle sizes. It was found that the k_Ag positively correlated with the specific surface areas of the silver nanomaterials. Natural organic matter (NOM) suppressed the sulfidation of AgNWs to different extents depending on its concentration. Divalent cations (Mg²⁺ and Ca²⁺ ions) substantially accelerated the sulfidation rates of AgNWs compared to monovalent cations (Na⁺ and K⁺ ions). At the same ionic strengths, Ca²⁺ ions displayed the highest promoting effect among the four metallic ions.

Governing factors affecting the impacts of silver nanoparticles on wastewater treatment

Silver nanoparticles (nanosilver or AgNPs) enter municipal wastewater from various sources, raising concerns about their potential adverse effects on wastewater treatment processes. We argue that the biological effects of silver nanoparticles at environmentally realistic concentrations (μgL^-1 or lower) on the performance of a full-scale municipal water resource recovery facility (WRRF) are minimal. Reactor configuration is a critical factor that reduces or even mutes the toxicity of silver nanoparticles towards wastewater microbes in a full-scale WRRF. Municipal sewage collection networks transform silver nanoparticles into silver(I)-complexes/precipitates with low ecotoxicity, and preliminary/primary treatment processes in front of biological treatment utilities partially remove silver nanoparticles to sludge. Microbial functional redundancy and microbial adaptability to silver nanoparticles also greatly alleviate the adverse effects of silver nanoparticles on the performance of a full-scale WRRF. Silver nanoparticles in a lab-scale bioreactor without a sewage collection system and/or a preliminary/primary treatment process, in contrast to being in a full scale system, may deteriorate the reactor performance at relatively high concentrations (e.g., mgL^-1 levels or higher). However, in many cases, silver nanoparticles have minimal impacts on lab-scale bioreactors, such as sequencing batch bioreactors (SBRs), especially when at relatively low concentrations (e.g., less than 1mgL^-1). The susceptibility of wastewater microbes to silver nanoparticles is species-specific. In general, silver nanoparticles have higher toxicity towards nitrifying bacteria than heterotrophic bacteria.

Silver nanoparticles: Significance of physicochemical properties and assay interference on the interpretation of in vitro cytotoxicity studies

Silver nanoparticles (AgNPs) have generated a great deal of interest in the research, consumer product, and medical product communities due to their antimicrobial and anti-biofouling properties. However, in addition to their antimicrobial action, concerns have been expressed about the potential adverse human health effects of AgNPs. In vitro cytotoxicity studies often are used to characterize the biological response to AgNPs and the results of these studies may be used to identify hazards associated with exposure to AgNPs. Various factors, such as nanomaterial size (diameter), surface area, surface charge, redox potential, surface functionalization, and composition play a role in the development of toxicity in in vitro test systems. In addition, the interference of AgNPs with in vitro cytotoxicity assays may result in false negative or false positive results in some in vitro biological tests. The goal of this review is to: 1) summarize the impact of physical-chemical parameters, including size, shape, surface chemistry and aggregate formation on the in vitro cytotoxic effects of AgNPs; and 2) explore the nature of AgNPs interference in in vitro cytotoxicity assays.

Properties of silver nanoparticles influencing their uptake in and toxicity to the earthworm Lumbricus rubellus following exposure in soil

Physicochemical properties of nanoparticles influence their environmental fate and toxicity, and studies investigating this are vital for a holistic approach towards a comprehensive and adequate environmental risk assessment. In this study, we investigated the effects of size, surface coating (charge) of silver nanoparticles (AgNPs) - a most commonly-used nanoparticle-type, on the bioaccumulation in, and toxicity (survival, growth, cocoon production) to the earthworm Lumbricus rubellus. AgNPs were synthesized in three sizes: 20, 35 and 50 nm. Surface-coating with bovine serum albumin (AgNP_BSA), chitosan (AgNP_Chit), or polyvinylpyrrolidone (AgNP_PVP) produced negative, positive and neutral particles respectively. In a 28-day sub-chronic reproduction toxicity test, earthworms were exposed to these AgNPs in soil (0-250 mg Ag/kg soil DW). Earthworms were also exposed to AgNO₃ at concentrations below known EC₅₀. Total Ag tissue concentration indicated uptake by earthworms was generally highest for the AgNP_BSA especially at the lower exposure concentration ranges, and seems to reach a plateau level between 50 and 100 mg Ag/kg soil DW. Reproduction was impaired at high concentrations of all AgNPs tested, with AgNP_BSA particles being the most toxic. The EC₅₀ for the 20 nm AgNP_BSA was 66.8 mg Ag/kg soil, with exposure to <60 mg Ag/kg soil already showing a decrease in the cocoon production. Thus, based on reproductive toxicity, the particles ranked: AgNP_BSA (negative) > AgNP_PVP (neutral) > Chitosan (positive). Size had an influence on uptake and toxicity of the AgNP_PVP, but not for AgNP_BSA nor AgNP_Chit. This study provides essential information on the role of physicochemical properties of AgNPs in influencing uptake by a terrestrial organism L. rubellus under environmentally relevant conditions. It also provides evidence of the influence of surface coating (charge) and the limited effect of size in the range of 20-50 nm, in driving uptake and toxicity of the AgNPs tested.

Molecular Mechanism of Silver Nanoparticles-Induced Human Osteoblast Cell Death: Protective Effect of Inducible Nitric Oxide Synthase Inhibitor

BACKGROUND

Silver nanoparticles (AgNPs) show strong antibacterial properties, making them excellent candidates to be used in orthopaedic repair and regeneration. However, there are concerns regarding the cytotoxicity of AgNPs and molecular mechanisms underlying AgNPs-induced bone cells toxicity have not been elucidated. Therefore, the aim of our study was to explore mechanisms of AgNPs-induced osteoblast cell death with particular emphasis on the role of nitric oxide (NO) generated by inducible nitric oxide synthase (iNOS).

METHODS AND RESULT

Silver nanoparticles used in this study were 18.3±2.6 nm in size, uncoated, spherical, regular shape and their zeta potential was -29.1±2.4 mV as measured by transmission electron microscopy (TEM) and zetasizer. The release of silver (Ag) from AgNPs was measured in cell culture medium by atomic absorption spectroscopy (AAS). The exposure of human osteoblast cells (hFOB 1.19) to AgNPs at concentration of 30 or 60 μg/mL for 24 or 48 hours, respectively resulted in cellular uptake of AgNPs and changes in cell ultrastructure. These changes were associated with apoptosis and necrosis as shown by flow cytometry and lactate dehydrogenase (LDH) assay as well as increased levels of pro-apoptotic Bax and decreased levels of anti-apoptotic Bcl-2 mRNA and protein. Importantly, we have found that AgNPs elevated the levels of nitric oxide (NO) with concomitant upregulation of inducible nitric oxide synthase (iNOS) mRNA and protein. A significant positive correlation was observed between the concentration of AgNPs and iNOS at protein and mRNA level (r = 0.837, r = 0.721, respectively; p<0.001). Finally, preincubation of osteoblast cells with N-iminoethyl-l-lysine (L-NIL), a selective iNOS inhibitor, as well as treating cells with iNOS small interfering RNAs (siRNA) significantly attenuated AgNPs-induced apoptosis and necrosis. Moreover, we have found that AgNPs-induced cells death is not related to Ag dissolution is cell culture medium.

CONCLUSION

These results unambiguously demonstrate that increased expression of iNOS and generation of NO as well as NO-derived reactive species is involved in AgNPs-induced osteoblast cell death. Our findings may help in development of new strategies to protect bone from AgNPs-induced cytotoxicity and increase the safety of orthopaedic tissue repair.

Silver Nanoparticle-Mediated Cellular Responses in Various Cell Lines: An in Vitro Model

Silver nanoparticles (AgNPs) have attracted increased interest and are currently used in various industries including medicine, cosmetics, textiles, electronics, and pharmaceuticals, owing to their unique physical and chemical properties, particularly as antimicrobial and anticancer agents. Recently, several studies have reported both beneficial and toxic effects of AgNPs on various prokaryotic and eukaryotic systems. To develop nanoparticles for mediated therapy, several laboratories have used a variety of cell lines under in vitro conditions to evaluate the properties, mode of action, differential responses, and mechanisms of action of AgNPs. In vitro models are simple, cost-effective, rapid, and can be used to easily assess efficacy and performance. The cytotoxicity, genotoxicity, and biocompatibility of AgNPs depend on many factors such as size, shape, surface charge, surface coating, solubility, concentration, surface functionalization, distribution of particles, mode of entry, mode of action, growth media, exposure time, and cell type. Cellular responses to AgNPs are different in each cell type and depend on the physical and chemical nature of AgNPs. This review evaluates significant contributions to the literature on biological applications of AgNPs. It begins with an introduction to AgNPs, with particular attention to their overall impact on cellular effects. The main objective of this review is to elucidate the reasons for different cell types exhibiting differential responses to nanoparticles even when they possess similar size, shape, and other parameters. Firstly, we discuss the cellular effects of AgNPs on a variety of cell lines; Secondly, we discuss the mechanisms of action of AgNPs in various cellular systems, and try to elucidate how AgNPs interact with different mammalian cell lines and produce significant effects; Finally, we discuss the cellular activation of various signaling molecules in response to AgNPs, and conclude with future perspectives on research into AgNPs.

Silver Nanoparticles: Synthesis, Characterization, Properties, Applications, and Therapeutic Approaches

Recent advances in nanoscience and nanotechnology radically changed the way we diagnose, treat, and prevent various diseases in all aspects of human life. Silver nanoparticles (AgNPs) are one of the most vital and fascinating nanomaterials among several metallic nanoparticles that are involved in biomedical applications. AgNPs play an important role in nanoscience and nanotechnology, particularly in nanomedicine. Although several noble metals have been used for various purposes, AgNPs have been focused on potential applications in cancer diagnosis and therapy. In this review, we discuss the synthesis of AgNPs using physical, chemical, and biological methods. We also discuss the properties of AgNPs and methods for their characterization. More importantly, we extensively discuss the multifunctional bio-applications of AgNPs; for example, as antibacterial, antifungal, antiviral, anti-inflammatory, anti-angiogenic, and anti-cancer agents, and the mechanism of the anti-cancer activity of AgNPs. In addition, we discuss therapeutic approaches and challenges for cancer therapy using AgNPs. Finally, we conclude by discussing the future perspective of AgNPs.

Factors affecting the in vitro micronucleus assay for evaluation of nanomaterials

A number of in vitro methodologies have been used to assess the genotoxicity of different nanomaterials, including titanium dioxide nanoparticles (TiO₂ NPs) and silver nanoparticles (AgNPs). The in vitro micronucleus assay is one of the most commonly used test methods for genotoxicity evaluation of nanomaterials. However, due to the novel features of nanomaterials, such as high adsorption capacity and fluorescence properties, there are unexpected interactions with experimental components and detection systems. In this study, we evaluate the interference by two nanoparticles, AgNPs and TiO₂ NPs, with the in vitro micronucleus assay system and possible confounding factors affecting cytotoxicity and genotoxicity assessment of the nanomaterials including cell lines with different p53 status, nanoparticle coatings and fluorescence, cytochalasin B, fetal bovine serum in cell treatment medium and different measurement methodologies for detecting micronuclei. Our results showed that micronucleus induction by AgNPs was similar when evaluated using flow cytometry or microscope, whereas the induction by TiO₂ NPs was different using the two methods due to TiO₂'s fluorescence interference with the cytometry equipment. Cells with the mutated p53 gene were more sensitive to micronucleus induction by AgNPs than the p53 wild-type cells. The presence of serum during treatment increased the toxicity of AgNPs. The coatings of nanoparticles played an important role in the genotoxicity of AgNPs. These collective data highlight the importance of considering the unique properties of nanoparticles in assessing their genotoxicity using the in vitro micronucleus assay.

Size- and coating-dependent cytotoxicity and genotoxicity of silver nanoparticles evaluated using in vitro standard assays

The physicochemical characteristics of silver nanoparticles (AgNPs) may greatly alter their toxicological potential. To explore the effects of size and coating on the cytotoxicity and genotoxicity of AgNPs, six different types of AgNPs, having three different sizes and two different coatings, were investigated using the Ames test, mouse lymphoma assay (MLA) and in vitro micronucleus assay. The genotoxicities of silver acetate and silver nitrate were evaluated to compare the genotoxicity of nanosilver to that of ionic silver. The Ames test produced inconclusive results for all types of the silver materials due to the high toxicity of silver to the test bacteria and the lack of entry of the nanoparticles into the cells. Treatment of L5718Y cells with AgNPs and ionic silver resulted in concentration-dependent cytotoxicity, mutagenicity in the Tk gene and the induction of micronuclei from exposure to nearly every type of the silver materials. Treatment of TK6 cells with these silver materials also resulted in concentration-dependent cytotoxicity and significantly increased micronucleus frequency. With both the MLA and micronucleus assays, the smaller the AgNPs, the greater the cytotoxicity and genotoxicity. The coatings had less effect on the relative genotoxicity of AgNPs than the particle size. Loss of heterozygosity analysis of the induced Tk mutants indicated that the types of mutations induced by AgNPs were different from those of ionic silver. These results suggest that AgNPs induce cytotoxicity and genotoxicity in a size- and coating-dependent manner. Furthermore, while the MLA and in vitro micronucleus assay (in both types of cells) are useful to quantitatively measure the genotoxic potencies of AgNPs, the Ames test cannot.

A comparative study on the in vitro cytotoxic responses of two mammalian cell types to fullerenes, carbon nanotubes and iron oxide nanoparticles

The present study was designed to evaluate and compare the time- and dose-dependent cellular response of human periodontal ligament fibroblasts (hPDLFs), and mouse dermal fibroblasts (mDFs) to three different types of nanoparticles (NPs); fullerenes (C₆₀), single walled carbon nanotubes (SWCNTs) and iron (II,III) oxide (Fe₃O₄) nanoparticles via in vitro toxicity methods, and impedance based biosensor system. NPs were characterized according to their morphology, structure, surface area, particle size distribution and zeta potential by using transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, dynamic light scattering and zeta sizer analyses. The Mössbauer spectroscopy was used in order to magnetically characterize the Fe₃O₄ NPs. The hPDLFs and mDFs were exposed to different concentrations of the NPs (0.1, 1, 10, 50 and 100 μg/mL) for predetermined time intervals (6, 24 and 48 h) under controlled conditions. Subsequently, NP exposed cells were tested for viability, membrane leakage and generation of intracellular reactive oxygen species. Additional to in vitro cytotoxicity assays, the cellular responses to selected NPs were determined in real time using an impedance based biosensor system. Taken together, information obtained from all experiments suggests that toxicity of the selected NPs is cell type, concentration and time dependent.

The MTT and Crystal Violet Assays: Potential Confounders in Nanoparticle Toxicity Testing

The toxicological effects of nanoparticles (NPs) on humans, animals, and environment are largely unknown. Assessment of NPs cytotoxicity depends on the choice of the test system. Due to NPs optical activity and absorption values, they can influence the classical cytotoxicity assay. Eight NPs were spiked in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet assays and tested with HaCaT human skin cells. The MTT assay standard curve optical density (OD) measurements were altered by the presence of trisilanol phenyl and trisilanol isooctyl polyhedral oligomeric silsesquioxane particles. The crystal violet standard curve OD measurements were significantly shifted by gold NPs, but they did not affect the MTT assay. Carbon black decreased ODs in the MTT and crystal violet assays and was localized in the cell cytoplasm. These findings strongly indicate that a careful choice of in vitro viability systems is required to avoid flawed measurement of NPs toxicity.

Biogenic synthesis of metallic nanoparticles and prospects toward green chemistry

The immense importance of nanoparticles and their applications is a strong motivation for exploring new synthetic techniques. However, due to strict regulations that manage the potential environmental impacts greener alternatives for conventional synthesis are the focus of intense research. In the scope of this perspective, a concise discussion about the use of green reducing and stabilizing agents toward the preparation of metal nanoparticles is presented. Reports on the synthesis of noble metal nanoparticles using plant extracts, ascorbic acid and sodium citrate as green reagents are summarized and discussed, pointing toward an urgent need of understanding the mechanistic aspects of the involved reactions.

Avoiding artefacts during electron microscopy of silver nanomaterials exposed to biological environments

Electron microscopy has been applied widely to study the interaction of nanomaterials with proteins, cells and tissues at nanometre scale. Biological material is most commonly embedded in thermoset resins to make it compatible with the high vacuum in the electron microscope. Room temperature sample preparation protocols developed over decades provide contrast by staining cell organelles, and aim to preserve the native cell structure. However, the effect of these complex protocols on the nanomaterials in the system is seldom considered. Any artefacts generated during sample preparation may ultimately interfere with the accurate prediction of the stability and reactivity of the nanomaterials. As a case study, we review steps in the room temperature preparation of cells exposed to silver nanomaterials (AgNMs) for transmission electron microscopy imaging and analysis. In particular, embedding and staining protocols, which can alter the physicochemical properties of AgNMs and introduce artefacts thereby leading to a misinterpretation of silver bioreactivity, are scrutinized. Recommendations are given for the application of cryogenic sample preparation protocols, which simultaneously fix both particles and diffusible ions. By being aware of the advantages and limitations of different sample preparation methods, compromises or selection of different correlative techniques can be made to draw more accurate conclusions about the data.

The Antimicrobial Properties of Silver Nanoparticles in Bacillus subtilis Are Mediated by Released Ag+ Ions

The superior antimicrobial properties of silver nanoparticles (Ag NPs) are well-documented, but the exact mechanisms underlying Ag-NP microbial toxicity remain the subject of intense debate. Here, we show that Ag-NP concentrations as low as 10 ppm exert significant toxicity against Bacillus subtilis, a beneficial bacterium ubiquitous in the soil. Growth arrest and chromosomal DNA degradation were observed, and flow cytometric quantification of propidium iodide (PI) staining also revealed that Ag-NP concentrations of 25 ppm and above increased membrane permeability. RedoxSensor content analysis and P_hag-GFP expression analysis further indicated that reductase activity and cytosolic protein expression decreased in B. subtilis cells treated with 10–50 ppm of Ag NPs. We conducted X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses to directly clarify the valence and fine structure of Ag atoms in B. subtilis cells placed in contact with Ag NPs. The results confirmed the Ag species in Ag NP-treated B. subtilis cells as Ag₂O, indicating that Ag-NP toxicity is likely mediated by released Ag⁺ ions from Ag NPs, which penetrate bacterial cells and are subsequently oxidized intracellularly to Ag₂O. These findings provide conclusive evidence for the role of Ag⁺ ions in Ag-NP microbial toxicity, and suggest that the impact of inappropriately disposed Ag NPs to soil and water ecosystems may warrant further investigation.

Role of surface charge in determining the biological effects of CdSe/ZnS quantum dots

The growing potential of quantum dots (QDs) in biomedical applications has provoked the urgent need to thoroughly address their interaction with biological systems. However, only limited studies have been performed to explore the effects of surface charge on the biological behaviors of QDs. In the present study, three commercially available QDs with different surface coatings were used to systematically evaluate the effects of surface charge on the cellular uptake, cytotoxicity, and in vivo biodistribution of QDs. Our results demonstrated that charged QDs entered both cancer cells and macrophages more efficiently than neutral ones, while negative QDs internalized mostly. Upon entry into cells, QDs were localized in different subcellular compartments (eg, cytoplasm and lysosomes) depending on the surface charge. Interestingly, inconsistent with the result of internalization, positive QDs but not negative QDs exhibited severe cytotoxicity, which was likely due to their disruption of cell membrane integrity, and production of reactive oxygen species. Biodistribution studies demonstrated that negative and neutral QDs preferentially distributed in the liver and the spleen, whereas positive QDs mainly deposited in the kidney with obvious uptake in the brain. In general, surface charge plays crucial roles in determining the biological interactions of QDs.

Impact of nanosilver on various DNA lesions and HPRT gene mutations - effects of charge and surface coating

Background

The main goal of this research was to study the interactions of a fully characterized set of silver nanomaterials (Ag ENMs) with cells in vitro, according to the standards of Good Laboratory Practices (GLP), to assure the quality of nanotoxicology research. We were interested in whether Ag ENMs synthesized by the same method, with the same size distribution, shape and specific surface area, but with different charges and surface compositions could give different biological responses.

Methods

A range of methods and toxicity endpoints were applied to study the impacts of interaction of the Ag ENMs with TK6 cells. As tests of viability, relative growth activity and trypan blue exclusion were applied. Genotoxicity was evaluated by the alkaline comet assay for detection of strand breaks and oxidized purines. The mutagenic potential of Ag ENMs was investigated with the in vitro HPRT gene mutation test on V79-4 cells according to the OECD protocol. Ag ENM agglomeration, dissolution as well as uptake and distribution within the cells were investigated as crucial aspects of Ag ENM toxicity. Ag ENM stabilizers were included in addition to positive and negative controls.

Results

Different cytotoxic effects were observed including membrane damage, cell cycle arrest and cell death. Ag ENMs also induced various kinds of DNA damage including strand breaks and DNA oxidation, and caused gene mutation. We found that positive Ag ENMs had greater impact on cyto- and genotoxicity than did Ag ENMs with neutral or negative charge, assumed to be related to their greater uptake into cells and to their presence in the nucleus and mitochondria, implying that Ag ENMs might induce toxicity by both direct and indirect mechanisms.

Conclusion

We showed that Ag ENMs could be cytotoxic, genotoxic and mutagenic. Our experiments with the HPRT gene mutation assay demonstrated that surface chemical composition plays a significant role in Ag ENM toxicity.

Mechanistic lessons learned from studies of planktonic bacteria with metallic nanomaterials: implications for interactions between nanomaterials and biofilm bacteria

Metal and metal-oxide nanoparticles (NPs) are used in numerous applications and have high likelihood of entering engineered and natural environmental systems. Careful assessment of the interaction of these NPs with bacteria, particularly biofilm bacteria, is necessary. This perspective discusses mechanisms of NP interaction with bacteria and identifies challenges in understanding NP-biofilm interaction, considering fundamental material attributes and inherent complexities of biofilm structure. The current literature is reviewed, both for planktonic bacteria and biofilms; future challenges and complexities are identified, both in light of the literature and a dataset on the toxicity of silver NPs toward planktonic and biofilm bacteria. This perspective aims to highlight the complexities in such studies and emphasizes the need for systematic evaluation of NP-biofilm interaction.

Application of Multi-Species Microbial Bioassay to Assess the Effects of Engineered Nanoparticles in the Aquatic Environment: Potential of a Luminous Microbial Array for Toxicity Risk Assessment (LumiMARA) on Testing for Surface-Coated Silver Nanoparticles

Four different manufactured surface-coated silver nanoparticles (AgNPs) with coating of citrate, tannic acid, polyethylene glycol, and branched polyethylenimine were used in this study. The toxicity of surface-coated AgNPs was evaluated by a luminous microbial array for toxicity risk assessment (LumiMARA) using multi-species of luminescent bacteria. The salt stability of four different AgNPs was measured by UV absorbance at 400 nm wavelength, and different surface-charged AgNPs in combination with bacteria were observed using scanning electron microscopy (SEM). Both branched polyethylenimine (BPEI)-AgNPs and polyethylene glycol (PEG)-AgNPs were shown to be stable with 2% NaCl (non-aggregation), whereas both citrate (Cit)-AgNPs and tannic acid (Tan)-AgNPs rapidly aggregated in 2% NaCl solution. The values of the 50% effective concentration (EC₅₀) for BPEI-AgNPs in marine bacteria strains (1.57 to 5.19 mg/L) were lower than those for the other surface-coated AgNPs (i.e., Cit-AgNPs, Tan-AgNPs, and PEG-AgNPs). It appears that the toxicity of AgNPs could be activated by the interaction of positively charged AgNPs with the negatively charged bacterial cell wall from the results of LumiMARA. LumiMARA for toxicity screening has advantageous compared to a single-species bioassay and is applicable for environmental samples as displaying ranges of assessment results.

Reducing the cytotoxicity of inhalable engineered nanoparticles via in situ passivation with biocompatible materials

The cytotoxicity of model welding nanoparticles was modulated through in situ passivation with soluble biocompatible materials. A passivation process consisting of a spark discharge particle generator coupled to a collison atomizer as a co-flow or counter-flow configuration was used to incorporate the model nanoparticles with chitosan. The tested model welding nanoparticles are inhaled and that A549 cells are a human lung epithelial cell line. Measurements of in vitro cytotoxicity in A549 cells revealed that the passivated nanoparticles had a lower cytotoxicity (>65% in average cell viability, counter-flow) than the untreated model nanoparticles. Moreover, the co-flow incorporation between the nanoparticles and chitosan induced passivation of the nanoparticles, and the average cell viability increased by >80% compared to the model welding nanoparticles. As a more convenient way (additional chitosan generation and incorporation devices may not be required), other passivation strategies through a modification of the welding rod with chitosan adhesive and graphite paste did also enhance average cell viability (>58%). The approach outlined in this work is potentially generalizable as a new platform, using only biocompatible materials in situ, to treat nanoparticles before they are inhaled.

Static and Dynamic Microscopy of the Chemical Stability and Aggregation State of Silver Nanowires in Components of Murine Pulmonary Surfactant

The increase of production volumes of silver nanowires (AgNWs) and of consumer products incorporating them may lead to increased health risks from occupational and public exposures. There is currently limited information about the putative toxicity of AgNWs upon inhalation and incomplete understanding of the properties that control their bioreactivity. The lung lining fluid (LLF), which contains phospholipids and surfactant proteins, represents a first contact site with the respiratory system. In this work, the impact of dipalmitoylphosphatidylcholine (DPPC), Curosurf, and murine LLF on the stability of AgNWs was examined. Both the phospholipid and protein components of the LLF modified the dissolution kinetics of AgNWs, due to the formation of a lipid corona or aggregation of the AgNWs. Moreover, the hydrophilic proteins, but neither the hydrophobic surfactant proteins nor the phospholipids, induced agglomeration of the AgNWs. Finally, the generation of a secondary population of nanosilver was observed and attributed to the reduction of Ag(+) ions by the surface capping of the AgNWs. Our findings highlight that combinations of spatially resolved dynamic and static techniques are required to develop a holistic understanding of which parameters govern AgNW behavior at the point of exposure and to accurately predict their risks on human health and the environment.