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

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.

Perturbation of cellular mechanistic system by silver nanoparticle toxicity: Cytotoxic, genotoxic and epigenetic potentials

Currently the applications of silver nanoparticles (Ag NPs) are gaining overwhelming response due to the advancement of nanotechnology. However, only limited information is available with regard to their toxicity mechanism in different species. It is very essential to understand the complete molecular mechanism to explore the functional and long term applications of Ag NPs. Ag NPs could be toxic at cellular, subcellular, biomolecular, and epigenetic levels. Toxicity effects induced by Ag NPs have been evaluated using numerous in vitro and in vivo models, but still there are contradictions in interpretations due to disparity in methodology, test endpoints and several other model parameters which needs to be considered. Thus, this review article focuses on the progressive elucidation of molecular mechanism of toxicity induced by Ag NPs in various in vitro and in vivo models. Apart from these, this review also highlights the various ignored factors which are to be considered during toxicity studies.

Comparative assessment of the apoptotic potential of silver nanoparticles synthesized by Bacillus tequilensis and Calocybe indica in MDA-MB-231 human breast cancer cells: targeting p53 for anticancer therapy

Background

Recently, the use of nanotechnology has been expanding very rapidly in diverse areas of research, such as consumer products, energy, materials, and medicine. This is especially true in the area of nanomedicine, due to physicochemical properties, such as mechanical, chemical, magnetic, optical, and electrical properties, compared with bulk materials. The first goal of this study was to produce silver nanoparticles (AgNPs) using two different biological resources as reducing agents, Bacillus tequilensis and Calocybe indica. The second goal was to investigate the apoptotic potential of the as-prepared AgNPs in breast cancer cells. The final goal was to investigate the role of p53 in the cellular response elicited by AgNPs.

Methods

The synthesis and characterization of AgNPs were assessed by various analytical techniques, including ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The apoptotic efficiency of AgNPs was confirmed using a series of assays, including cell viability, leakage of lactate dehydrogenase (LDH), production of reactive oxygen species (ROS), DNA fragmentation, mitochondrial membrane potential, and Western blot.

Results

The absorption spectrum of the yellow AgNPs showed the presence of nanoparticles. XRD and FTIR spectroscopy results confirmed the crystal structure and biomolecules involved in the synthesis of AgNPs. The AgNPs derived from bacteria and fungi showed distinguishable shapes, with an average size of 20 nm. Cell viability assays suggested a dose-dependent toxic effect of AgNPs, which was confirmed by leakage of LDH, activation of ROS, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells in MDA-MB-231 breast cancer cells. Western blot analyses revealed that AgNPs induce cellular apoptosis via activation of p53, p-Erk1/2, and caspase-3 signaling, and downregulation of Bcl-2. Cells pretreated with pifithrin-alpha were protected from p53-mediated AgNPs-induced toxicity.

Conclusion

We have demonstrated a simple approach for the synthesis of AgNPs using the novel strains B. tequilensis and C. indica, as well as their mechanism of cell death in a p53-dependent manner in MDA-MB-231 human breast cancer cells. The present findings could provide insight for the future development of a suitable anticancer drug, which may lead to the development of novel nanotherapeutic molecules for the treatment of cancers.

Toxicity of fungal-generated silver nanoparticles to soil-inhabiting Pseudomonas putida KT2440, a rhizospheric bacterium responsible for plant protection and bioremediation

Silver nanoparticles have attracted considerable attention due to their beneficial properties. But toxicity issues associated with them are also rising. The reports in the past suggested health hazards of silver nanoparticles at the cellular, molecular, or whole organismal level in eukaryotes. Whereas, there is also need to examine the exposure effects of silver nanoparticle to the microbes, which are beneficial to humans as well as environment. The available literature suggests the harmful effects of physically and chemically synthesised silver nanoparticles. The toxicity of biogenically synthesized nanoparticles has been less studied than physically and chemically synthesised nanoparticles. Hence, there is a greater need to study the toxic effects of biologically synthesised silver nanoparticles in general and mycosynthesized nanoparticles in particular. In the present study, attempts have been made to assess the risk associated with the exposure of mycosynthesized silver nanoparticles on a beneficial soil microbe Pseudomonas putida. KT2440. The study demonstrates mycosynthesis of silver nanoparticles and their characterisation by UV-vis spectrophotometry, FTIR, X-ray diffraction, nanosight LM20--a particle size distribution analyzer and TEM. Silver nanoparticles obtained herein were found to exert the hazardous effect at the concentration of 0.4 μg/ml, which warrants further detailed investigations concerning toxicity.

Pulmonary toxicity of instilled silver nanoparticles: influence of size, coating and rat strain

Particle size and surface chemistry are potential determinants of silver nanoparticle (AgNP) respiratory toxicity that may also depend on the lung inflammatory state. We compared the effects of intratracheally-administered AgNPs (20 nm and 110 nm; polyvinylpyrrolidone (PVP) and citrate-capped; 0.1 mg/Kg) in Brown-Norway (BN) and Sprague-Dawley (SD) rats. In BN rats, there was both a neutrophilic and eosinophilic response, while in SD rats, there was a neutrophilic response at day 1, greatest for the 20 nm citrate-capped AgNPs. Eosinophilic cationic protein was increased in bronchoalveolar lavage (BAL) in BN and SD rats on day 1. BAL protein and malondialdehyde levels were increased in BN rats at 1 and 7 days, and BAL KC, CCL11 and IL-13 levels at day 1, with increased expression of CCL11 in lung tissue. Pulmonary resistance increased and compliance decreased at day 1, with persistence at day 7. The 20 nm, but not the 110 nm, AgNPs increased bronchial hyperresponsiveness on day 1, which continued at day 7 for the citrate-capped AgNPs only. The 20 nm versus the 110 nm size were more proinflammatory in terms of neutrophil influx, but there was little difference between the citrate-capped versus the PVP-capped AgNPs. AgNPs can induce pulmonary eosinophilic and neutrophilic inflammation with bronchial hyperresponsiveness, features characteristic of asthma.

Probing nanoparticles and nanoparticle-conjugated biomolecules using time-of-flight secondary ion mass spectrometry

Bio-conjugated nanoparticles have emerged as novel molecular probes in nano-biotechnology and nanomedicine and chemical analyses of their surfaces have become challenges. The time-of-flight (TOF) secondary ion mass spectrometry (SIMS) has been one of the most powerful surface characterization techniques for both nanoparticles and biomolecules. When combined with various nanoparticle-based signal enhancing strategies, TOF-SIMS can probe the functionalization of nanoparticles as well as their locations and interactions in biological systems. Especially, nanoparticle-based SIMS is an attractive approach for label-free drug screening because signal-enhancing nanoparticles can be designed to directly measure the enzyme activity. The chemical-specific imaging analysis using SIMS is also well suited to screen nanoparticles and nanoparticle-biomolecule conjugates in complex environments. This review presents some recent applications of nanoparticle-based TOF-SIMS to the chemical analysis of complex biological systems.

The oxidative potential of differently charged silver and gold nanoparticles on three human lung epithelial cell types

BACKGROUND

Nanoparticle (NPs) functionalization has been shown to affect their cellular toxicity. To study this, differently functionalized silver (Ag) and gold (Au) NPs were synthesised, characterised and tested using lung epithelial cell systems.

METHODS

Monodispersed Ag and Au NPs with a size range of 7 to 10 nm were coated with either sodium citrate or chitosan resulting in surface charges from -50 mV to +70 mV. NP-induced cytotoxicity and oxidative stress were determined using A549 cells, BEAS-2B cells and primary lung epithelial cells (NHBE cells). TEER measurements and immunofluorescence staining of tight junctions were performed to test the growth characteristics of the cells. Cytotoxicity was measured by means of the CellTiter-Blue ® and the lactate dehydrogenase assay and cellular and cell-free reactive oxygen species (ROS) production was measured using the DCFH-DA assay.

RESULTS

Different growth characteristics were shown in the three cell types used. A549 cells grew into a confluent mono-layer, BEAS-2B cells grew into a multilayer and NHBE cells did not form a confluent layer. A549 cells were least susceptible towards NPs, irrespective of the NP functionalization. Cytotoxicity in BEAS-2B cells increased when exposed to high positive charged (+65-75 mV) Au NPs. The greatest cytotoxicity was observed in NHBE cells, where both Ag and Au NPs with a charge above +40 mV induced cytotoxicity. ROS production was most prominent in A549 cells where Au NPs (+65-75 mV) induced the highest amount of ROS. In addition, cell-free ROS measurements showed a significant increase in ROS production with an increase in chitosan coating.

CONCLUSIONS

Chitosan functionalization of NPs, with resultant high surface charges plays an important role in NP-toxicity. Au NPs, which have been shown to be inert and often non-cytotoxic, can become toxic upon coating with certain charged molecules. Notably, these effects are dependent on the core material of the particle, the cell type used for testing and the growth characteristics of these cell culture model systems.

Impact of storage conditions and storage time on silver nanoparticles' physicochemical properties and implications for their biological effects

A multi-parametric assessment of the impact of storage time/conditions and capping agent charge on the stability and toxicity of AgNPs showed agglomeration, dissolution, oxidation, capping agent degradation and attachment of Ag⁺ ions all play a role.

Silver nanoparticles – wolves in sheep's clothing?

We review the cellular and molecular mechanisms behind silver nanoparticle toxicity and their intracellular fate. In addition, the role of silver ions in the toxicity of silver nanoparticles is discussed.

Dual effects of β-cyclodextrin-stabilised silver nanoparticles: enhanced biofilm inhibition and reduced cytotoxicity

The composition and mode of synthesis of nanoparticles (NPs) can affect interaction with bacterial and human cells differently. The present work describes the ability of β-cyclodextrin (β-CD) capped silver nanoparticles (AgNPs) to inhibit biofilm growth and reduce cytotoxicity. Biofilm formation of Staphylococcus epidermidis CSF 41498 was quantified by a crystal violet assay in the presence of native and capped AgNPs (Ag-10CD and Ag-20CD), and the morphology of the biofilm was observed by scanning electron microscope. The cytotoxicity of the AgNPs against HaCat cells was determined by measuring the increase in intracellular reactive oxygen species and change in mitochondrial membrane potential (ΔΨm). Results indicated that capping AgNPs with β-CD improved their efficacy against S. epidermidis CSF 41498, reduced biofilm formation and their cytotoxicity. The study concluded that β-CD is an effective capping and stabilising agent that reduces toxicity of AgNPs against the mammalian cell while enhancing their antibiofilm activity.

Effects of silver nanoparticles on human health

There has been a great deal of attention and research devoted on nanoparticels (NPs) over the last 10 years. From current knowledge in the field of nanotoxicology, it has become evident that the most NPs, if not all are more toxic than bulk materials. The rapid progress and developing has been leading to concerns about the potential risk associated with the use and application of NPs on human health and the environment. Silver nanoparticles (SNPs) are one of the most available and commercially distributed nanomaterials around the world. In order to understand how human health can be affected by SNPs, quantification and detection of SNPs in biological systems have to be conducted in different models. It seems that respiratory and gastrointestinal systems as well as the skin are the major routes of SNPs penetration into the body. Research on SNPs toxicity is mostly conducted in vitro, and the available human and animal data are relatively limited. This review attempts to focus on the characterization and quantification of the potential harmful effects of SNPs on human health.

Inhalation of silver nanomaterials--seeing the risks

Demand for silver engineered nanomaterials (ENMs) is increasing rapidly in optoelectronic and in health and medical applications due to their antibacterial, thermal, electrical conductive, and other properties. The continued commercial up-scaling of ENM production and application needs to be accompanied by an understanding of the occupational health, public safety and environmental implications of these materials. There have been numerous in vitro studies and some in vivo studies of ENM toxicity but their results are frequently inconclusive. Some of the variability between studies has arisen due to a lack of consistency between experimental models, since small differences between test materials can markedly alter their behaviour. In addition, the propensity for the physicochemistry of silver ENMs to alter, sometimes quite radically, depending on the environment they encounter, can profoundly alter their bioreactivity. Consequently, it is important to accurately characterise the materials before use, at the point of exposure and at the nanomaterial-tissue, or "nanobio", interface, to be able to appreciate their environmental impact. This paper reviews current literature on the pulmonary effects of silver nanomaterials. We focus our review on describing whether, and by which mechanisms, the chemistry and structure of these materials can be linked to their bioreactivity in the respiratory system. In particular, the mechanisms by which the physicochemical properties (e.g., aggregation state, morphology and chemistry) of silver nanomaterials change in various biological milieu (i.e., relevant proteins, lipids and other molecules, and biofluids, such as lung surfactant) and affect subsequent interactions with and within cells will be discussed, in the context not only of what is measured but also of what can be visualized.

A combined toxicity study of zinc oxide nanoparticles and vitamin C in food additives

At present, safety evaluation standards for nanofood additives are made based on the toxic effects of a single additive. Since the size, surface properties and chemical nature influence the toxicity of nanomaterials, the toxicity may have dramatically changed when nanomaterials are used as food additives in a complex system. Herein, we investigated the combined toxicity of zinc oxide nanoparticles (ZnO NPs) and vitamin C (Vc, ascorbic acid). The results showed that Vc increased the cytotoxicity significantly compared with that of the ZnO only NPs. When the cells were exposed to ZnO NPs at a concentration less than 15 mg L(-1), or to Vc at a concentration less than 300 mg L(-1), there was no significant cytotoxicity, both in the case of gastric epithelial cell line (GES-1) and neural stem cells (NSCs). However, when 15 mg L(-1) of ZnO NPs and 300 mg L(-1) of Vc were introduced to cells together, the cell viability decreased sharply indicating significant cytotoxicity. Moreover, the significant increase in toxicity was also shown in the in vivo experiments. The dose of the ZnO NPs and Vc used in the in vivo study was calculated according to the state of food and nutrition enhancer standard. After repeated oral exposure to ZnO NPs plus Vc, the injury of the liver and kidneys in mice has been indicated by the change of these indices. These findings demonstrate that the synergistic toxicity presented in a complex system is essential for the toxicological evaluation and safety assessment of nanofood.

Computational tool for risk assessment of nanomaterials: novel QSTR-perturbation model for simultaneous prediction of ecotoxicity and cytotoxicity of uncoated and coated nanoparticles under multiple experimental conditions

Nanomaterials have revolutionized modern science and technology due to their multiple applications in engineering, physics, chemistry, and biomedicine. Nevertheless, the use and manipulation of nanoparticles (NPs) can bring serious damages to living organisms and their ecosystems. For this reason, ecotoxicity and cytotoxicity assays are of special interest in order to determine the potential harmful effects of NPs. Processes based on ecotoxicity and cytotoxicity tests can significantly consume time and financial resources. In this sense, alternative approaches such as quantitative structure-activity/toxicity relationships (QSAR/QSTR) modeling have provided important insights for the better understanding of the biological behavior of NPs that may be responsible for causing toxicity. Until now, QSAR/QSTR models have predicted ecotoxicity or cytotoxicity separately against only one organism (bioindicator species or cell line) and have not reported information regarding the quantitative influence of characteristics other than composition or size. In this work, we developed a unified QSTR-perturbation model to simultaneously probe ecotoxicity and cytotoxicity of NPs under different experimental conditions, including diverse measures of toxicities, multiple biological targets, compositions, sizes and conditions to measure those sizes, shapes, times during which the biological targets were exposed to NPs, and coating agents. The model was created from 36488 cases (NP-NP pairs) and exhibited accuracies higher than 98% in both training and prediction sets. The model was used to predict toxicities of several NPs that were not included in the original data set. The results of the predictions suggest that the present QSTR-perturbation model can be employed as a highly promising tool for the fast and efficient assessment of ecotoxicity and cytotoxicity of NPs.

The impact of aminated surface ligands and silica shells on the stability, uptake, and toxicity of engineered silver nanoparticles

Inherent nanomaterial characteristics, composition, surface chemistry, and primary particle size, are known to impact particle stability, uptake, and toxicity. Nanocomposites challenge our ability to predict nanoparticle reactivity in biological systems if they are composed of materials with contrasting relative toxicities. We hypothesized that toxicity would be dominated by the nanoparticle surface (shell vs core), and that modulating the surface ligands would have a direct impact on uptake. We exposed developing zebrafish (Danio rerio) to a series of ~70 nm amine-terminated silver nanoparticles with silica shells (AgSi NPs) to investigate the relative influence of surface amination, composition, and size on toxicity. Like-sized aminated AgSi and Si NPs were more toxic than paired hydroxyl-terminated nanoparticles; however, both AgSi NPs were more toxic than the Si NPs, indicating a significant contribution of the silver core to the toxicity. Incremental increases in surface amination did not linearly increase uptake and toxicity, but did have a marked impact on dispersion stability. Mass-based exposure metrics initially supported the hypothesis that smaller nanoparticles (20 nm) would be more toxic than larger particles (70 nm). However, surface area-based metrics revealed that toxicity was independent of size. Our studies suggest that nanoparticle surfaces play a critical role in the uptake and toxicity of AgSi NPs, while the impact of size may be a function of the exposure metric used. Overall, uptake and toxicity can be dramatically altered by small changes in surface functionalization or exposure media. Only after understanding the magnitude of these changes, can we begin to understand the biologically available dose following nanoparticle exposure.

Critical experimental evaluation of key methods to detect, size and quantify nanoparticulate silver

Different analytical techniques, sedimentation flow field fractionation (SdFFF), asymmetrical flow field flow fractionation (AF4), centrifugal liquid sedimentation (CLS) and dynamic light scattering (DLS) have been used to give complementary size information about suspensions of silver nanoparticles (AgNPs) in the size range of 20-100 nm by taking advantage of the different physical principles on which are based. Particle morphology was controlled by TEM (Transmission Electron Microscopy). Both SdFFF and AF4 were able to accurately size all AgNPs; among sedimentation based techniques, CLS underestimated the average sizes of larger samples (70 and 100 nm), but it produced the best separation of bimodal mixtures Ag40/60 and Ag40/70 mix compared to SdFFF. On the contrary, DLS overestimated the average sizes of the smallest samples (20 and 30 nm) and it was unable to deal with bimodal mixtures. Quantitative mass and number particle size distributions were also calculated starting from UV-vis signals and ICP-MS data and the results evaluated as a means to address the issue of determining nanoparticle size distributions as required for implementation of European regulations relating to labeling of nanomaterials in consumer products. The results are discussed in light of possible particle aggregation state, analysis repeatability, size resolution and quantitative recoveries.

Silver nanoparticles augment releasing of pyrogenic factors by blood cells stimulated with LPS

Silver nanoparticles (AgNPs) have cytotoxic properties via generation of reactive oxygen species which are involved in the generalized sickness behavior of the host, including fever and lethargy among others. The aim of the present study was to investigate the impact of AgNPs on the ability of rat peripheral blood mononuclear cells (PBMCs) to release fever mediating factors after stimulation with lipopolysaccharide (LPS). Body temperature and motor activity of the Wistar rats were measured by biotelemetry system. Rat PBMCs were stimulated with LPS and after that the cells were washed and incubated alone or with AgNPs. The final supernatants were injected intraperitoneally. The levels of endogenous pyrogens such as interleukin-1β (IL−1β), IL-6 and tumor necrosis factor-α (TNF-α) released from the PBMCs into the final supernatants were also estimated. The results indicated that injection of the supernatants from the cells stimulated with LPS induced fever and inhibited motor activity. These effects were potentiated by the presence of AgNPs during the final incubation. The presence of the AgNPs also resulted in significant increases in levels of endogenous pyrogens. The augmentation of fever in the rats by the AgNPs treatment of the cultures seemed to be primarily associated with the changes in interleukin-1β levels.

A MD simulation and analysis for aggregation behaviors of nanoscale zero-valent iron particles in water via MS

With the development of nanotechnology, more nanomaterials will enter into water environment system. Studying the existing form of nanomaterials in water environment will help people benefit from the correct use of them and to reduce the harm to human caused by them for some nanomaterials can bring polluting effect. Aggregation is a main behavior for nanoparticle in water environment. NZVI are used widely in many fields resulting in more NZVI in water environment. Molecular dynamics simulations and Materials Studio software are used to investigate the microaggregation behaviors of NZVI particles. Two scenes are involved: (1) particle size of NZVI in each simulation system is the same, but initial distance of two NZVI particles is different; (2) initial distance of two NZVI particles in each simulation system is the same, but particle size of NZVI is different. Atomistic trajectory, NP activity, total energy, and adsorption of H₂O are analyzed with MS. The method provides new quantitative insight into the structure, energy, and dynamics of the aggregation behaviors of NZVI particles in water. It is necessary to understand microchange of NPs in water because it can provide theoretical research that is used to reduce polluting effect of NPs on water environment.

Differential stress reaction of human colon cells to oleic-acid-stabilized and unstabilized ultrasmall iron oxide nanoparticles

Therapeutic engineered nanoparticles (NPs), including ultrasmall superparamagnetic iron oxide (USPIO) NPs, may accumulate in the lower digestive tract following ingestion or injection. In order to evaluate the reaction of human colon cells to USPIO NPs, the effects of non-stabilized USPIO NPs (NS-USPIO NPs), oleic-acid-stabilized USPIO NPs (OA-USPIO NPs), and free oleic acid (OA) were compared in human HT29 and CaCo₂ colon epithelial cancer cells. First the biophysical characteristics of NS-USPIO NPs and OA-USPIO NPs in water, in cell culture medium supplemented with fetal calf serum, and in cell culture medium preconditioned by HT29 and CaCo₂ cells were determined. Then, stress responses of the cells were evaluated following exposure to NS-USPIO NPs, OA-USPIO NPs, and free OA. No modification of the cytoskeletal actin network was observed. Cell response to stress, including markers of apoptosis and DNA repair, oxidative stress and degradative/autophagic stress, induction of heat shock protein, or lipid metabolism was determined in cells exposed to the two NPs. Induction of an autophagic response was observed in the two cell lines for both NPs but not free OA, while the other stress responses were cell- and NP-specific. The formation of lipid vacuoles/droplets was demonstrated in HT29 and CaCo₂ cells exposed to OA-USPIO NPs but not to NS-USPIO NPs, and to a much lower level in cells exposed to equimolar concentrations of free OA. Therefore, the induction of lipid vacuoles in colon cells exposed to OA utilized as a stabilizer for USPIO NPs is higly amplified compared to free OA, and is not observed in the absence of this lipid in NS-USPIO NPs.

A facile route to tailoring peptide-stabilized gold nanoparticles using glutathione as a synthon

The preparation of gold nanoparticles (AuNPs) of high purity and stability remains a major challenge for biological applications. This paper reports a simple synthetic strategy to prepare water-soluble peptide-stabilized AuNPs. Reduced glutathione, a natural tripeptide, was used as a synthon for the growth of two peptide chains directly on the AuNP surface. Both nonpolar (tryptophan and methionine) and polar basic (histidine and dansylated arginine) amino acids were conjugated to the GSH-capped AuNPs. Ultracentrifugation concentrators with polyethersulfone (PES) membranes were used to purify precursor materials in each stage of the multi-step synthesis to minimize side reactions. Thin layer chromatography, transmission electron microscopy, UV-Visible, 1H-NMR, and fluorescence spectroscopies demonstrated that ultracentrifugation produces high purity AuNPs, with narrow polydispersity, and minimal aggregation. More importantly, it allows for more control over the composition of the final ligand structure. Studies under conditions of varying pH and ionic strength revealed that peptide length, charge, and hydrophobicity influence the stability as well as solubility of the peptide-capped AuNPs. The synthetic and purification strategies used provide a facile route for developing a library of tailored biocompatible peptide-stabilized AuNPs for biomedical applications.

Designing nanogel carriers for antibacterial applications

We have developed a novel and simple synthesis route to create nanosized (∼5nm) silver nanoparticles (Ag NPs) embedded in a biocompatible nanogel (NG) comprising degradable, natural polymers, namely dextran and lysozyme. In this study, we prepared hybrid nanogels with varying lysozyme content, evaluated their potential to reduce Ag NPs in situ (using ultraviolet-visible spectroscopy, cryo-transmission electronic microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy) and determined their antibacterial properties against Escherichia coli and Staphylococcus aureus. Lysozyme was found to enhance nucleation and stabilization of Ag NPs while limiting their growth. As lysozyme concentration increased, larger nanogels with greater loading of smaller Ag NPs were obtained. The antibacterial properties of hybrid NGs were found to depend upon nanogel type and bacterial conditions. Hybrid nanogels with the largest Ag NPs showed the lowest minimum inhibition concentration. However, the greatest bacterial killing efficiency (up to 100%) occurred within 1h if the bacteria were exposed to hybrid nanogels with smaller Ag NPs while agitating the medium. These results suggest that nanogel properties as well as antibacterial activity can be tuned by varying the lysozyme content. By targeting drug delivery (e.g. ligand grafted surface), these nanogels can be used to prevent biofilm formation and control infection without the complications (i.e. overexposure) associated with classical antibiotic delivery platforms.

Organic-coated silver nanoparticles in biological and environmental conditions: fate, stability and toxicity

This review paper presents the overview of processes involved in transformation of organic-coated silver nanoparticles (AgNPs) in biological systems and in the aquatic environment. The coating on AgNPs greatly influences the fate, stability, and toxicity of AgNPs in aqueous solutions, biological systems, and the environment. Several organic-coated AgNP systems are discussed to understand their stability and toxicity in biological media and natural water. Examples are presented to demonstrate how a transformation of organic-coated AgNPs in an aqueous solution is affected by the type of coating, pH, kind of electrolyte (mono- or divalent), ionic strength, organic ligands (inorganic and organic), organic matter (fulvic and humic acids), redox conditions (oxic and anoxic), and light. Results of cytotoxicity, genotoxicity, and ecotoxicity of coated AgNPs to food chain members (plants, bacteria, and aquatic and terrestrial organisms) are reviewed. Key factors contributing to toxicity are the size, shape, surface coating, surface charge, and conditions of silver ion release. AgNPs may directly damage the cell membranes, disrupt ATP production and DNA replication, alternate gene expressions, release toxic Ag(+) ion, and produce reactive oxygen species to oxidize biological components of the cell. A progress made on understanding the mechanism of organic-coated AgNP toxicity using different analytical techniques is presented.

Applications of inorganic nanoparticles as therapeutic agents

During the last decade, various functional nanostructured materials with interesting optical, magnetic, mechanical and chemical properties have been extensively applied to biomedical areas including imaging, diagnosis and therapy. In therapeutics, most research has focused on the application of nanoparticles as potential delivery vehicles for drugs and genes, because nanoparticles in the size range of 2-100 nm can interact with biological systems at the molecular level, and allow targeted delivery and passage through biological barriers. Recent investigations have even revealed that several kinds of nanomaterials are intrinsically therapeutic. Not only can they passively interact with cells, but they can also actively mediate molecular processes to regulate cell functions. This can be seen in the treatment of cancer via anti-angiogenic mechanisms as well as the treatment of neurodegenerative diseases by effectively controlling oxidative stress. This review will present recent applications of inorganic nanoparticles as therapeutic agents in the treatment of disease.

Caging of plumbagin on silver nanoparticles imparts selectivity and sensitivity to plumbagin for targeted cancer cell apoptosis

Nano-caging of plumbagin for selective killing of cancer cells.

Green synthesis of anisotropic silver nanoparticles with potent anticancer activity using Taxus baccata extract

Highly stable colloidal silver nanoparticles with potent anticancer activity against MCF-7 cells were synthesized using Taxus baccata extracts.

High-resolution analytical electron microscopy reveals cell culture media-induced changes to the chemistry of silver nanowires

There is a growing concern about the potential adverse effects on human health upon exposure to engineered silver nanomaterials (particles, wires, and plates). However, the majority of studies testing the toxicity of silver nanomaterials have examined nominally "as-synthesized" materials without considering the fate of the materials in biologically relevant fluids. Here, in-house silver nanowires (AgNWs) were prepared by a modified polyol process and were incubated in three cell culture media (DMEM, RPMI-1640, and DCCM-1) to examine the impact of AgNW-medium interactions on the physicochemical properties of the AgNWs. High-resolution analytical transmission electron microscopy revealed that Ag2S crystals form on the surface of AgNWs within 1 h of incubation in DCCM-1. In contrast, the incubation of AgNWs in RPMI-1640 or DMEM did not lead to sulfidation. When the DCCM-1 cell culture medium was separated into its small molecule solutes and salts and protein components, the AgNWs were found to sulfidize in the fraction containing small molecule solutes and salts but not in the fraction containing the protein component of the media. Further investigation showed the AgNWs did not readily sulfidize in the presence of isolated sulfur containing amino acids or proteins, such as cysteine or bovine serum albumin (BSA). The results demonstrate that the AgNWs can be transformed by the media before and during the incubation with cells, and therefore, the effects of cell culture media must be considered in the analysis of toxicity assays. Appropriate media and material controls must be in place to allow accurate predictions about the toxicity and, ultimately, the health risk of this commercially relevant class of nanomaterial.

Silver nanoparticles induce anti-proliferative effects on airway smooth muscle cells. Role of nitric oxide and muscarinic receptor signaling pathway

Silver nanoparticles (AgNPs) are used to manufacture materials with new properties and functions. However, little is known about their toxic or beneficial effects on human health, especially in the respiratory system, where its smooth muscle (ASM) regulates the airway contractility by different mediators, such as acetylcholine (ACh) and nitric oxide (NO). The aim of this study was to evaluate the effects of AgNPs on ASM cells. Exposure to AgNPs induced ACh-independent expression of the inducible nitric oxide synthase (iNOS) at 100 μg/mL, associated with excessive production of NO. AgNPs induced the muscarinic receptor activation, since its blockage with atropine and blockage of its downstream signaling pathway inhibited the NO production. AgNPs at 10 and 100 μg/mL induced ACh-independent prolonged cytotoxicity and decreased cellular proliferation mediated by the muscarinic receptor-iNOS pathway. However, the concentration of 100 μg/mL of AgNPs induced muscarinic receptor-independent apoptosis, suggesting the activation of multiple pathways. These data indicate that AgNPs induce prolonged cytotoxic and anti-proliferative effects on ASM cells, suggesting an activation of the muscarinic receptor-iNOS pathway. Further investigation is required to understand the full mechanisms of action of AgNPs on ASM under specific biological conditions.

The effect of particle agglomeration on the formation of a surface-connected compartment induced by hydroxyapatite nanoparticles in human monocyte-derived macrophages

Agglomeration dramatically affects many aspects of nanoparticle–cell interactions. Here we show that hydroxyapatite nanoparticles formed large agglomerates in biological medium resulting in extensive particle uptake and dose-dependent cytotoxicity in human macrophages. Particle citration and/or the addition of the dispersant Darvan 7 dramatically reduced mean agglomerate sizes, the amount of particle uptake and concomitantly cytotoxicity. More surprisingly, agglomeration governed the mode of particle uptake. Agglomerates were sequestered within an extensive, interconnected membrane labyrinth open to the extracellular space. In spite of not being truly intracellular, imaging studies suggest particle degradation occurred within this surface-connected compartment (SCC). Agglomerate dispersion prevented the SCC from forming, but did not completely inhibit nanoparticle uptake by other mechanisms. The results of this study could be relevant to understanding particle–cell interactions during developmental mineral deposition, in ectopic calcification in disease, and during application of hydroxyapatite nanoparticle vectors in biomedicine.

Sulfidation of silver nanowires inside human alveolar epithelial cells: a potential detoxification mechanism

Silver nanowires (AgNWs) are being developed for use in optoelectronics. However before widespread usage, it is crucial to determine their potential effects on human health. It is accepted that Ag nanoparticles (AgNPs) exert toxic effects by releasing Ag(+) ions, but much less is known about whether Ag(+) reacts with compounds, or any downstream bioactive effects of transformed AgNPs. Analytical high-resolution transmission electron microscopy has been employed to elucidate cellular uptake and reactivity of AgNWs inside human alveolar epithelial type 1-like cells. AgNWs were observed in the cytoplasm and membrane-bound vesicles, and precipitation of Ag2S within the cell occurred after 1 h exposure. Cell viability studies showed no evidence of cytotoxicity and reactive oxygen species were not observed on exposure of cells to AgNWs. We suggest that Ag2S formation acts as a 'trap' for free Ag(+), significantly limiting short-term toxicological effects - with important consequences for the safety of Ag-nanomaterials to human health.

Mechanisms of Silver Nanoparticle Release, Transformation and Toxicity: A Critical Review of Current Knowledge and Recommendations for Future Studies and Applications

Nanosilver, due to its small particle size and enormous specific surface area, facilitates more rapid dissolution of ions than the equivalent bulk material; potentially leading to increased toxicity of nanosilver. This, coupled with their capacity to adsorb biomolecules and interact with biological receptors can mean that nanoparticles can reach sub-cellular locations leading to potentially higher localized concentrations of ions once those particles start to dissolve or degrade in situ. Further complicating the story is the capacity for nanoparticles to generate reactive oxygen species, and to interact with, and potentially disturb the functioning of biomolecules such as proteins, enzymes and DNA. The fact that the nanoparticle size, shape, surface coating and a host of other factors contribute to these interactions, and that the particles themselves are evolving or ageing leads to further complications in terms of elucidating mechanisms of interaction and modes of action for silver nanoparticles, in contrast to dissolved silver species. This review aims to provide a critical assessment of the current understanding of silver nanoparticle toxicity, as well as to provide a set of pointers and guidelines for experimental design of future studies to assess the environmental and biological impacts of silver nanoparticles. In particular; in future we require a detailed description of the nanoparticles; their synthesis route and stabilisation mechanisms; their coating; and evolution and ageing under the exposure conditions of the assay. This would allow for comparison of data from different particles; different environmental or biological systems; and structure-activity or structure-property relationships to emerge as the basis for predictive toxicology. On the basis of currently available data; such comparisons or predictions are difficult; as the characterisation and time-resolved data is not available; and a full understanding of silver nanoparticle dissolution and ageing under different conditions is observed. Clear concerns are emerging regarding the overuse of nanosilver and the potential for bacterial resistance to develop. A significant conclusion includes the need for a risk-benefit analysis for all applications and eventually restrictions of the uses where a clear benefit cannot be demonstrated.

Study of charge-dependent transport and toxicity of peptide-functionalized silver nanoparticles using zebrafish embryos and single nanoparticle plasmonic spectroscopy

Nanomaterials possess unusually high surface area-to-volume ratios and surface-determined physicochemical properties. It is essential to understand their surface-dependent toxicity in order to rationally design biocompatible nanomaterials for a wide variety of applications. In this study, we have functionalized the surfaces of silver nanoparticles (Ag NPs, 11.7 ± 2.7 nm in diameter) with three biocompatible peptides (CALNNK, CALNNS, CALNNE) to prepare positively (Ag-CALNNK NPs(+ζ)), negatively (Ag-CALNNS NPs(-2ζ)), and more negatively charged NPs (Ag-CALNNE NPs(-4ζ)), respectively. Each peptide differs in a single amino acid at its C-terminus, which minimizes the effects of peptide sequences and serves as a model molecule to create positive, neutral, and negative charges on the surface of the NPs at pH 4-10. We have studied their charge-dependent transport into early developing (cleavage-stage) zebrafish embryos and their effects on embryonic development using dark-field optical microscopy and spectroscopy (DFOMS). We found that all three Ag-peptide NPs passively diffused into the embryos via their chorionic pore canals, and stayed inside the embryos throughout their entire development (120 h), showing charge-independent diffusion modes and charge-dependent diffusion coefficients. Notably, the NPs create charge-dependent toxic effects on embryonic development, showing that the Ag-CALNNK NPs(+ζ) (positively charged) are the most biocompatible while the Ag-CALNNE NPs(-4ζ) (more negatively charged) are the most toxic. By comparing with our previous studies of the same sized citrated Ag and Au NPs, the Ag-peptide NPs are much more biocompatible than the citrated Ag NPs, and nearly as biocompatible as the Au NPs, showing the dependence of nanotoxicity upon the surface charges, surface functional groups, and chemical compositions of the NPs. This study also demonstrates powerful applications of single NP plasmonic spectroscopy for quantitative analysis of single NPs in vivo and in tissues, and reveals the possibility of rational design of biocompatible NPs.

Tissue distribution and kinetics of dissolved and nanoparticulate silver in Iceland scallop (Chlamys islandica)

The fast expansion of the global nanotechnology market entails a higher environmental and human exposure to nanomaterials. Silver nanoparticles (AgNP) are used for their antibacterial properties; however, their environmental fate is yet poorly understood. Iceland scallops (Chlamys islandica) were exposed for 12 h to three different silver forms, dissolved Ag(I) (Agdiss), small (S-NP, Ø = 10-20 nm) and large AgNP (L-NP, Ø = 70-80 nm), labeled with (110m)Ag, and bioaccumulation kinetics and tissue distribution using in vivo gamma counting and whole-body autoradiography were determined. All Ag forms were readily and rapidly accumulated. Elimination process was also fast and bi-exponential, with mean biological half-life ranging from 1.4 to 4.3 days and from 17 to 50 days for fast and slow compartments, respectively. Most of the radioactivity concentrated in the hepatopancreas. Agdiss and S-NP tissue distributions were similar indicating a rapid dissolution of the latter in the tissues, contrarily to L-NP which appeared to form long lasting aggregates in the digestive system. Estimated steady-state bioconcentration factors (BCF), ranging between 2700 and 3800 ml g(-1) for dissolved and particulate silver forms, showed that C. islandica can accumulate significant quantities of Ag in a short time followed by an efficient depuration process.

Silver nanoparticle toxicity in the embryonic zebrafish is governed by particle dispersion and ionic environment

The mechanism of action of silver nanoparticles (AgNPs) is unclear due to the particles' strong tendency to agglomerate. Preventing agglomeration could offer precise control of the physicochemical properties that drive biological response to AgNPs. In an attempt to control agglomeration, we exposed zebrafish embryos to AgNPs of 20 or 110 nm core size, and polypyrrolidone (PVP) or citrate surface coatings in media of varying ionic strength. AgNPs remained unagglomerated in 62.5 μM CaCl2 (CaCl2) and ultrapure water (UP), but not in standard zebrafish embryo medium (EM). Zebrafish embryos developed normally in the low ionic strength environments of CaCl2 and UP. Exposure of embryos to AgNPs suspended in UP and CaCl2 resulted in higher toxicity than suspensions in EM. 20 nm AgNPs were more toxic than 110 nm AgNPs, and the PVP coating was more toxic than the citrate coating at the same particle core size. The silver tissue burden correlated well with observed toxicity but only for those exposures where the AgNPs remained unagglomerated. Our results demonstrate that size- and surface coating-dependent toxicity is a result of AgNPs remaining unagglomerated, and thus a critical-design consideration for experiments to offer meaningful evaluations of AgNP toxicity.

Relating nanomaterial properties and microbial toxicity

Metal and metal oxide nanoparticles are among the most commonly used nanomaterials and their potential for adversely affecting environmental systems raises concern. Complex microbial consortia underlie environmental processes, and the potential toxicity of nanoparticles to microbial systems, and the consequent impacts on trophic balances, is particularly worrisome. The diverse array of metal and metal oxides, the different sizes and shapes that can be prepared and the variety of possible surface coatings complicate assessments of toxicity. Further muddling biocidal interpretations are the diversity of microbes and their intrinsic tolerances to stresses. Here, we review a range of studies focused on nanoparticle-microbial interactions in an effort to correlate the physical-chemical properties of engineered metal and metal oxide nanoparticles to their biological response. General conclusions regarding the parent material of the nanoparticle and the nanoparticle's size and shape on potential toxicity can be made. However, the surface coating of the material, which can be altered significantly by environmental conditions, can ameliorate or promote microbial toxicity. Understanding nanoparticle transformations and how the nanoparticle surface can be designed to control toxicity represents a key area for further study. Additionally, the vast array of microbial species and the structuring of these species within communities complicate extrapolations of nanoparticle toxicity in real world settings. Ultimately, to interpret the effect and eventual fate of engineered materials in the environment, an understanding of the relationship between nanoparticle properties and responses at the molecular, cellular and community levels will be essential.

Silver nanowires as prospective carriers for drug delivery in cancer treatment: an in vitro biocompatibility study on lung adenocarcinoma cells and fibroblasts

Lung cancer is a major and increasing global health problem. While there have been significant advances in the understanding of lung cancer biology, still no current therapy exists to reduce the inevitable and lethal progression of this disease. Silver nanowires (AgNWs) are promising candidates for a wide range of biomedical applications and the treatment of life-threatening diseases due to their unique physico-chemical and biochemical properties. However, the safety of this nanomaterial and its use as a biomedical tool are still under debate. This study evaluates the in vitro internalisation, cytotoxicity and influence on the cell cycle of AgNWs in lung adenocarcinoma (A549) cells and lung normal fibroblasts (MRC-5 cells). Our results demonstrate that AgNWs could be internalised effectively into A549 and MRC-5 cells without inducing detectable cytotoxicity, thus providing preliminary evidence on the future potential of AgNWs as biocompatible drug delivery platforms applicable in lung cancer therapies.

The antibacterial effects of silver, titanium dioxide and silica dioxide nanoparticles compared to the dental disinfectant chlorhexidine on Streptococcus mutans using a suite of bioassays

Metal-containing nanomaterials have the potential to be used in dentistry for infection control, but little is known about their antibacterial properties. This study investigated the toxicity of silver (Ag), titanium dioxide and silica nanoparticles (NPs) against the oral pathogenic species of Streptococcus mutans, compared to the routine disinfectant, chlorhexidine. The bacteria were assessed using the minimum inhibitory concentration assay for growth, fluorescent staining for live/dead cells, and measurements of lactate. All the assays showed that Ag NPs had the strongest antibacterial activity of the NPs tested, with bacterial growth also being 25-fold lower than that in chlorhexidine. The survival rate of bacteria under the effect of 100 mg l⁻¹ Ag NPs in the media was 2% compared to 60% with chlorhexidine, while the lactate concentration was 0.6 and 4.0 mM, respectively. Silica and titanium dioxide NPs had limited effects. Dialysis experiments showed negligible silver dissolution. Overall, Ag NPs were the best disinfectant and performed better than chlorhexidine. Improvements to the MIC assay are suggested.

Effects of silver nanoparticles in diatom Thalassiosira pseudonana and cyanobacterium Synechococcus sp

The aim of the present study was to investigate the effect of silver nanoparticles (AgNP) of different sizes toward two primary producer aquatic species. Thalassiosira pseudonana and Synechococcus sp. have been selected as representative models for the lower trophic organisms in marine and freshwater habitats, respectively. Time-dependent cellular growth was measured upon exposure to both AgNP and silver nitrate (AgNO(3)). In addition, AgNP behavior in freshwater and marine waters has been followed by CPS disc centrifuge, in the time frame of AgNP exposure studies, and the kinetic release of silver from AgNP of different sizes was measured by dialysis and inductively coupled plasma mass spectrometry (ICP-MS). The combination and interpretation of all these data suggest that a shared effect of AgNP and released silver was responsible for the toxicity in both organisms. Furthermore, the toxic effects induced by AgNP exposure in the present study seem to result from a mixture of parameters including aggregated state, size of the AgNP, stability of the preparation, and speciation of the released silver.

The influence of the surface chemistry of silver nanoparticles on cell death

The influence of the surface chemistry of silver nanoparticles (AgNPs) on p53 mediated cell death was evaluated using human dermal fibroblast (HDF) and lung cancer (A549) cells. The citrate reduced AgNPs (C-AgNPs) were modified with either lactose (L-AgNPs) or a 12-base long oligonucleotide (O-AgNPs). Both unmodified and modified AgNPs showed increased concentration and time dependent cytotoxicity and genotoxicity causing an increased p53 up-regulation within 6 h and led to apoptotic or necrotic cell deaths. The C-AgNPs induced more cytotoxicity and cellular DNA damage than the surface modified AgNPs. Modifying the C-AgNPs with lactose or the oligonucleotide reduced both necrotic and apoptotic cell deaths in the HDF cells. The C-AgNPs caused an insignificant necrosis in A549 cells whereas the modified AgNPs caused necrosis and apoptosis in both cell types. Compared to the O-AgNPs, the L-AgNPs triggered more cellular DNA damage, which led to up-regulation of p53 gene inducing apoptosis in A549 cells compared to HDF cells. This suggests that the different surface chemistries of the AgNPs cause different cellular responses that may be important not only for their use in medicine but also for reducing their toxicity.