Nitric oxide-releasing nanomaterials: from basic research to potential biotechnological applications in agriculture.

Nitric oxide (NO) is a multifunctional gaseous signal that modulates the growth, development and stress tolerance of higher plants. NO donors have been used to boost plant endogenous NO levels and to activate NO-related responses, but this strategy is often hindered by the relative instability of donors. Alternatively, nanoscience offers a new, promising way to enhance NO delivery to plants, as NO-releasing nanomaterials (e.g. S-nitrosothiol-containing chitosan nanoparticles) have many beneficial physicochemical and biochemical properties compared to non-encapsulated NO donors. Nano NO donors are effective in increasing tissue NO levels and enhancing NO effects both in animal and human systems. The authors believe, and would like to emphasize, that new trends and technologies are essential for advancing plant NO research and nanotechnology may represent a breakthrough in traditional agriculture and environmental science. Herein, we aim to draw the attention of the scientific community to the potential of NO-releasing nanomaterials in both basic and applied plant research as alternatives to conventional NO donors, providing a brief overview of the current knowledge and identifying future research directions. We also express our opinion about the challenges for the application of nano NO donors, such as the environmental footprint and stakeholder's acceptance of these materials.

Nanotechnology advances for sustainable agriculture: current knowledge and prospects in plant growth modulation and nutrition.

MAIN CONCLUSION: Advances in nanotechnology make it an important tool for improving agricultural production. Strong evidence supports the role of nanomaterials as nutrients or nanocarriers for the controlled release of fertilizers to improve plant growth. Scientific research shows that nanotechnology applied in plant sciences is smart technology. Excessive application of mineral fertilizers has produced a harmful impact on the ecosystem. Furthermore, the projected increase in the human population by 2050 has led to the search for alternatives to ensure food security. Nanotechnology is a promising strategy to enhance crop productivity while minimizing fertilizer inputs. Nanofertilizers can contribute to the slow and sustainable release of nutrients to improve the efficiency of nutrient use in plants. Nanomaterial properties (i.e., size, morphology and charge) and plant physiology are crucial factors that influence the impact on plant growth. An important body of scientific research highlights the role of carbon nanomaterials, metal nanoparticles and metal oxide nanoparticles to improve plant development through the modulation of physiological and metabolic processes. Modulating nutrient concentrations, photosynthesis processes and antioxidant enzyme activities have led to increases in shoot length, root development, photosynthetic pigments and fruit yield. In parallel, nanocarriers (nanoclays, nanoparticles of hydroxyapatite, mesoporous silica and chitosan) have been shown to be an important tool for the controlled and sustainable release of conventional fertilizers to improve plant nutrition; however, the technical advances in nanofertilizers need to be accompanied by modernization of the regulations and legal frameworks to allow wider commercialization of these elements. Nanofertilizers are a promising strategy to improve plant development and nutrition, but their application in sustainable agriculture remains a great challenge. The present review summarizes the current advance of research into nanofertilizers, and their future prospects.

Nitric-oxide releasing chitosan nanoparticles towards effective treatment of cutaneous leishmaniasis.

Cutaneous leishmaniasis (CL) is a major public health problem caused by Leishmania parasites that produce destructive and disfiguring skin conditions. There is an urgent need for alternative topical therapies due to the limitations of current systemic treatments. Recently, we have synthesized nitric oxide-releasing chitosan nanoparticles (NONPs) and shown their potential in vitro against Leishmania amazonensis. Herein we evaluated the application of NONPs for the treatment of CL on infected BALB/c mice. Mice were treated with topical administration of increasing concentrations of NONPs and disease progression was investigated regarding parasite load, lesion thickness, and pain score. As a result, we observed a dose-dependent NONPs effect. Parasite burden and lesion thickness were substantially lower on animals receiving NONPs at a 2 mM concentration compared to untreated control. Moreover, the clinical presentation of the lesions did not show any visible signs of ulcer, suggesting clinical healing in these animals. This successful outcome was sustained for at least 21 days after therapy even in one single dose. Thus, we demonstrate that NONPs are suitable for topical administration, and represent an attractive approach to treat CL.

Chitosan chemically modified to deliver nitric oxide with high antibacterial activity.

The aim of the current study is to report a simple and efficient method to chemically modify chitosan in order to form S-nitroso-chitosan for antibacterial applications. Firstly, commercial chitosan (CS) was modified to form thiolated chitosan (TCS) based on an easy and environmental-friendly method. TCS was featured based on physicochemical and morphological techniques. Results have confirmed that thiol groups in TCS formed after CS's primary amino groups were replaced with secondary amino groups. Free thiol groups in TCS were nitrosated to form S-nitrosothiol moieties covalently bond to the polymer backbone (S-nitroso-CS). Kinetic measurements have shown that S-nitroso-CS was capable of generating NO in a sustained manner at levels suitable for biomedical applications. The antibacterial activities of CS, TCS and S-nitroso-CS were evaluated based on the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves determined for Escherichia coli, Staphylococcus aureus and Streptococcus mutans. MIC/MBC values reached 25/25, 0.7/0.7 and 3.1/3.1 µg mL-1 for CS/TCS and 3.1/3.1, 0.1/0.2, 0.1/0.2 µg mL-1 for S-nitroso-CS, respectively. Decreased MIC and MBC values have indicated that S-nitroso-CS has higher antibacterial activity than CS and TCS. Time-kill curves have shown that the bacterial cell viability decreased 5-fold for E. coli and 2-fold for S. mutans in comparison to their respective controls, after 0.5 h of incubation with S-nitroso-CS. Together, CS backbone chemically modified with S-nitroso moieties have yielded a polymer capable of generating therapeutic NO concentrations with strong antibacterial effect.

The Impact of Multiple Functional Layers in the Structure of Magnetic Nanoparticles and Their Influence on Albumin Interaction.

In nanomedicine, hybrid nanomaterials stand out for providing new insights in both the diagnosis and treatment of several diseases. Once administered, engineered nanoparticles (NPs) interact with biological molecules, and the nature of this interaction might directly interfere with the biological fate and action of the NPs. In this work, we synthesized a hybrid magnetic nanostructure, with antibacterial and antitumoral potential applications, composed of a magnetite core covered by silver NPs, and coated with a modified chitosan polymer. As magnetite NPs readily oxidize to maghemite, we investigated the structural properties of the NPs after addition of the two successive layers using Mössbauer spectroscopy. Then, the structural characteristics of the NPs were correlated to their interaction with albumin, the major blood protein, to evidence the consequences of its binding on NP properties and protein retention. Thermodynamic parameters of the NPs-albumin interaction were determined. We observed that the more stable NPs (coated with modified chitosan) present a lower affinity for albumin in comparison to pure magnetite and magnetite/silver hybrid NPs. Surface properties were key players at the NP-biological interface. To the best of our knowledge, this is the first study that demonstrates a correlation between the structural properties of complex hybrid NPs and their interaction with albumin.

Photochemistry of nitric oxide and S-nitrosothiols in human skin.

Nitric oxide (NO) is related to a wide range of physiological processes such as vasodilation, macrophages cytotoxicity and wound healing. The human skin contains NO precursors (NOx). Those are mainly composed of nitrite (NO2-), nitrate (NO3-), and S-nitrosothiols (RSNOs) which forms a large NO store. These NOx stores in human skin can mobilize NO to blood stream upon ultraviolet (UV) light exposure. The main purpose of this study was to evaluate the most effective UV light wavelength to generate NO and compare it to each NO precursor in aqueous solution. In addition, the UV light might change the RSNO content on human skin. First, we irradiated pure aqueous solutions of NO2- and NO3- and mixtures of NO2- and glutathione and NO3- and S-nitrosoglutathione (GSNO) to identify the NO release profile from those species alone. In sequence, we evaluated the NO generation profile on human skin slices. Human skin was acquired from redundant plastic surgical samples and the NO and RSNO measurements were performed using a selective NO electrochemical sensor. The data showed that UV light could trigger the NO generation in skin with a peak at 280-285 nm (UVB range). We also observed a significant RSNO formation in irradiated human skin, with a peak at 320 nm (UV region) and at 700 nm (visible region). Pre-treatment of the human skin slice using NO2- and thiol (RSHs) scavengers confirmed the important role of these molecules in RSNO formation. These findings have important implications for clinical trials with potential for new therapies.

Current applications of nanotechnology to develop plant growth inducer agents as an innovation strategy.

Nanotechnology has been proposed as an important tool and strategy for applying new products in agriculture at the nanometer scale in order to improve the food crop at sustainability and productivity levels for contributing with the agriculture security. Nanoparticles (NPs) have been planted as an intelligent material with a large contact surface per unit mass respect to bulk-products, allowing its effect to be exerted with greater efficiency in a specific point on a plant target. Currently, NPs have been studied to be applied to various species of monocotyledonous and dicotyledonous plants. Some NPs properties such as concentration, shape, size, composition and surface functionality have the ability to regulate the NPs growth effects on the plant during germination and seedling stages under controlled and field conditions. Furthermore, several studies have tried to explain the mechanism of uptake, translocation and accumulation of NPs inside the plant at the organ and cell level, but further studies are needed to determine specific mechanisms and exact action. Nevertheless, evaluation of the toxicity effects of NPs on physiological indexes of the plant is needed to determine the effective dose without producing adverse effects on the plant and food chain. It is noteworthy that studies have indicated that nanoparticles, regardless of their nature, can be efficient inducers of plant growth. However, a series of laboratory tests are required to optimize their application conditions and their specific physiological impact on plants. In this review, we summarize the knowledge about NPs application to induce plant growth to direct future studies in order to propose NPs for technological innovation.

Delivering nitric oxide into human skin from encapsulated S-nitrosoglutathione under UV light: An in vitro and ex vivo study.

Nitric oxide (NO) is a crucial molecule in the human body. The encapsulation of exogenous NO donors into chitosan nanoparticles (CS NPs) has been widely used to overcome NO drawbacks in pharmacological applications, such as, its short half-life. The NO donor, S-nitrosoglutathione (GSNO), was encapsulated into CS NPs (GSNO-CS NPs) and characterized by AFM and DLS measurements. The nanoparticles presented a hydrodynamic size of 123.3 ± 1.5 nm and a polydispersity of 0.25 ± 0.01. The ability of GSNO-CS NPs, combined with UV irradiation, to deliver NO was evaluated using ex vivo human skin. The human skin was pre-treated with GSNO-CS NPs, in the presence and absence of UV irradiation. The results showed that the combined treatment significantly increased the NO and S-nitrosothiol levels in human skin. This effect can emulate the cardiovascular benefits related to NO without negative side effects of skin exposure to UV light.

Nitric oxide-loaded chitosan nanoparticles as an innovative antileishmanial platform.

Leishmaniasis is a neglected tropical disease that demands for new therapeutic strategies due to adverse side effects and resistance development promoted by current drugs. Nitric oxide (NO)-donors show potential to kill Leishmania spp. but their use is limited because of their instability. In this work, we synthesize, characterize, and encapsulate S-nitroso-mercaptosuccinic acid into chitosan nanoparticles (NONPs) and investigate their activity on promastigotes and intracellular amastigotes of Leishmania (Leishmania) amazonensis. Cytotoxicity on macrophages was also evaluated. We verified that NONPs reduced both forms of the parasite in a single treatment. We also noticed reduction of parasitophorous vacuoles as an evidence of inhibition of parasite growth and resolution of infection. No substantial cytotoxicity was detected on macrophages. NONPs were able to provide a sustained parasite killing for both L. (L.) amazonensis infective stages with no toxicity on macrophages, representing a promising nanoplatform for cutaneous leishmaniasis.

Encapsulation of S-nitrosoglutathione into chitosan nanoparticles improves drought tolerance of sugarcane plants.

The entrapment of NO donors in nanomaterials has emerged as a strategy to protect these molecules from rapid degradation, allowing a more controlled release of NO and prolonging its effect. On the other hand, we have found beneficial effects of S-nitrosoglutathione (GSNO) - a NO donor - supplying to sugarcane plants under water deficit. Here, we hypothesized that GSNO encapsulated into nanoparticles would be more effective in attenuating the effects of water deficit on sugarcane plants as compared to the supplying of GSNO in its free form. The synthesis and characterization of chitosan nanoparticles containing GSNO were also reported. Sugarcane plants were grown in nutrient solution, and then subjected to the following treatments: control (well-hydrated); water deficit (WD); WD + GSNO sprayed in its free form (WDG) or encapsulated (WDG-NP). In general, both GSNO forms attenuated the effects of water deficit on sugarcane plants. However, the encapsulation of this donor into chitosan nanoparticles caused higher photosynthetic rates under water deficit, as compared to plants supplied with free GSNO. The root/shoot ratio was also increased when encapsulated GSNO was supplied, indicating that delayed release of NO improves drought tolerance of sugarcane plants. Our results provide experimental evidence that nanotechnology can be used for enhancing NO-induced benefits for plants under stressful conditions, alleviating the negative impact of water deficit on plant metabolism and increasing biomass allocation to root system.

Green synthesis of silver nanoparticles: effect of synthesis reaction parameters on antimicrobial activity.

In this work, the biosynthesis of silver nanoparticles by Galega officinalis extract using AgNO3 as a precursor was reported. The reaction parameters for the biosynthesis and efficiency in their antimicrobial control against Escherichia coli, Staphylococcus aureus and Pseudomonas syringae were determined. For biosynthesis, a central composite design combined with response surface methodology was used to optimize the process parameters (pH, AgNO3 and extract concentration), and the design was assessed through the size distribution, zeta potential and polydispersity index of the nanoparticles. The results demonstrated that at pH 11, 1.6 mM of AgNO3 and 15% vv-1 of G. officinalis extract were the optimal reaction parameters. Transmission electron microscope (TEM) images and X-ray diffraction (XRD) confirmed the formation of small spherical silver nanoparticles. Antimicrobial assays showed a high inhibitory effect against E. coli, S. aureus and P. syringae, and that effect was larger with silver nanoparticles of a smaller size (23 nm). This work demonstrates that G. officinalis extract is a feasible medium for the synthesis of silver nanoparticles and that the control of the reaction parameters can determine the nanoparticle characteristics and therefore their antimicrobial effectiveness.

Antitumor Potential of S-Nitrosothiol-Containing Polymeric Nanoparticles against Melanoma.

Melanoma is a malignant proliferative disease originated from melanocyte transformations, which are characterized by a high metastatic rate and mortality. Advances in Nanotechnology have provided useful new approaches and tools for antitumor chemotherapy. The aim of this study was to investigate the molecular mechanisms underlying chitosan nanoparticles containing S-nitrosomercaptosuccinic acid ( S-nitroso-MSA-CS) induced cytotoxicity in melanoma cells. S-Nitroso-MSA-CS induced concentration-dependent cell death against B16-F10 tumor cells, whereas non-nitroso nanoparticles (CS or MSA-CS) did not induce significant cytotoxicity. Additionally, melanoma cells were more sensitive to cell death than normal melanocytes. S-Nitroso-MSA-CS-induced cytotoxicity exhibited features of caspase-dependent apoptosis, and it was associated with oxidative stress, characterized by increased mitochondrial superoxide production and oxidation of protein thiol groups. In addition, tyrosine nitration and cysteine S-nitrosylation of amino acid residues in cellular proteins were observed. The potential use of these nanoparticles in antitumor chemotherapy of melanoma is discussed.

S-nitrosoglutathione spraying improves stomatal conductance, Rubisco activity and antioxidant defense in both leaves and roots of sugarcane plants under water deficit.

Water deficit is a major environmental constraint on crop productivity and performance and nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. This study aims to test the hypothesis that leaf spraying of S-nitrosoglutathione (GSNO), an NO donor, improves the antioxidant defense in both roots and leaves of sugarcane plants under water deficit, with positive consequences for photosynthesis. In addition, the roles of key photosynthetic enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) in maintaining CO2 assimilation of GSNO-sprayed plants under water deficit were evaluated. Sugarcane plants were sprayed with water or GSNO 100 µM and subjected to water deficit, by adding polyethylene glycol (PEG-8000) to the nutrient solution. Sugarcane plants supplied with GSNO presented increases in the activity of antioxidant enzymes such as superoxide dismutase in leaves and catalase in roots, indicating higher antioxidant capacity under water deficit. Such adjustments induced by GSNO were sufficient to prevent oxidative damage in both organs and were associated with better leaf water status. As a consequence, GSNO spraying alleviated the negative impact of water deficit on stomatal conductance and photosynthetic rates, with plants also showing increases in Rubisco activity under water deficit.

Synthesis and Characterization of Methylene Blue-Containing Silica-Coated Magnetic Nanoparticles for Photodynamic Therapy.

Superparamagnetic iron oxide nanoparticles (SPIONs), with appropriate surface coating, are commonly used for biomedical applications such as photodynamic therapy (PDT). This work describes the preparation and characterization of methylene blue (MB)-containing silica-coated SPIONs. Upon exposure to light, MB reacts with molecular oxygen and generates singlet oxygen (1O2) which is cytotoxic and causes irreversible damage to tumor tissues. In this work, SPIONs were synthesized by co-precipitation and coated with a single/double silica layer. The photoactive molecule MB was entrapped in the silica layer deposited on the surface of SPIONs, leading to the formation of hybrid nanomaterials composed of a magnetic core and silica layer. The nanocomposite exhibited magnetic behavior at room temperature due to the presence of its Fe3O4 core. Structural and morphological characterizations were performed by X-ray diffraction (XRD), Fourier transformed infrared (FTIR), SQUID magnetic measurements, ultraviolet-visible spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and dynamic light scattering. The results showed the presence of a crystalline Fe3O4 magnetic core and amorphous silica phases. Kinetic measurements revealed 1O2 generation by the nanoparticles upon irradiation with visible light (λ = 532 nm or λ = 633 nm). The results highlight the potential uses of SPIONs coated with MB-entrapped silica for PDT, whereby a sustained and localized generation of 1O2 was successfully achieved.

New approaches from nanomedicine for treating leishmaniasis.

Leishmaniasis, a vector-borne disease caused by obligate intramacrophage protozoa, threatens 350 million people in 98 countries around the world. There are already 12 million infected people worldwide and two million new cases occur annually. Leishmaniasis has three main clinical presentations: cutaneous (CL), mucosal (ML), and visceral (VL). It is considered an opportunistic, infectious disease and the HIV-leishmaniasis correlation is well known. Antimonial compounds are used as first-line treatment drugs, but their toxicity, which can be extremely high, leads to a number of undesirable side effects and resultant failure of the patients to adhere to treatment. There is also a reported increase in Leishmania sp. resistance to these drugs. Nanotechnology has emerged as an attractive alternative because of its improved bioavailability and lower toxicity, and other characteristics that help to relieve the burden of this disease. In this review we will present some of the recent advances in the nanotechnological research regarding the treatment of leishmaniasis. The preclinical results regarding the approaches for a biomedical treatment of the disease have been encouraging, but further efforts will still be necessary for this therapy to have greater clinical applicability in humans.

Exogenous nitric oxide improves sugarcane growth and photosynthesis under water deficit.

MAIN CONCLUSION: Nitric oxide (NO)-mediated redox signaling plays a role in alleviating the negative impact of water stress in sugarcane plants by improving root growth and photosynthesis. Drought is an environmental limitation affecting sugarcane growth and yield. The redox-active molecule nitric oxide (NO) is known to modulate plant responses to stressful conditions. NO may react with glutathione (GSH) to form S-nitrosoglutathione (GSNO), which is considered the main reservoir of NO in cells. Here, we investigate the role of NO in alleviating the effects of water deficit on growth and photosynthesis of sugarcane plants. Well-hydrated plants were compared to plants under drought and sprayed with mock (water) or GSNO at concentrations ranging from 10 to 1000 µM. Leaf GSNO sprayed plants showed significant improvement of relative water content and leaf and root dry matter under drought compared to mock-sprayed plants. Additionally, plants sprayed with GSNO (≥ 100 µM) showed higher leaf gas exchange and photochemical activity as compared to mock-sprayed plants under water deficit and after rehydration. Surprisingly, a raise in the total S-nitrosothiols content was observed in leaves sprayed with GSH or GSNO, suggesting a long-term role of NO-mediated responses to water deficit. Experiments with leaf discs fumigated with NO gas also suggested a role of NO in drought tolerance of sugarcane plants. Overall, our data indicate that the NO-mediated redox signaling plays a role in alleviating the negative effects of water stress in sugarcane plants by protecting the photosynthetic apparatus and improving shoot and root growth.

Nitric oxide-releasing chitosan nanoparticles alleviate the effects of salt stress in maize plants.

Nitric oxide (NO) is a signaling molecule involved in plant response to various abiotic stresses. However, the application of NO donors in agriculture is hampered by the instability of these compounds. Despite the successful uses of NO-releasing nanoparticles for biomedical purposes and the variety of nanomaterials developed as carrier systems of agrochemicals, the potential applications of nanocarriers for NO delivery in plants have not yet been tested. Herein, we report the synthesis and characterization of chitosan nanoparticles (CS NPs) containing the NO donor S-nitroso-mercaptosuccinic acid (S-nitroso-MSA). The efficiency of these NO-releasing NPs in mitigating the deleterious effects of salinity on maize plants was compared to that of the non-encapsulated NO donor. The NPs were synthesized through ionotropic gelation process, and mercaptosuccinic acid (MSA), the NO donor precursor, was encapsulated into CS NPs (91.07% encapsulation efficiency). Free thiol groups of MSA-CS NPs were nitrosated, leading to S-nitroso-MSA-CS NPs (NO-releasing NPs). The incorporation of S-nitroso-MSA into CS NPs allowed a sustained NO release. Treatments of salt-stressed maize plants with S-nitroso-MSA-CS NPs resulted in a higher leaf S-nitrosothiols content compared to that of free S-nitroso-MSA. Moreover, S-nitroso-MSA-CS NPs were more efficient than was the free NO donor in the amelioration of the deleterious effects of salinity in photosystem II activity, chlorophyll content and growth of maize plants because the protective action of the nanoencapsulated S-nitroso-MSA was achieved at lower dosages. Overall, these results demonstrate the positive impact of S-nitroso-MSA nanoencapsulation in increasing NO bioactivity in maize plants under salt stress.

Antimicrobial activity of biogenic silver nanoparticles, and silver chloride nanoparticles: an overview and comments.

The antimicrobial impact of biogenic-synthesized silver-based nanoparticles has been the focus of increasing interest. As the antimicrobial activity of nanoparticles is highly dependent on their size and surface, the complete and adequate characterization of the nanoparticle is important. This review discusses the characterization and antimicrobial activity of biogenic synthesized silver nanoparticles and silver chloride nanoparticles. By revising the literature, there is confusion in the characterization of these two silver-based nanoparticles, which consequently affects the conclusion regarding to their antimicrobial activities. This review critically analyzes recent publications on the synthesis of biogenic silver nanoparticles and silver chloride nanoparticles by attempting to correlate the characterization of the nanoparticles with their antimicrobial activity. It was difficult to correlate the size of biogenic nanoparticles with their antimicrobial activity, since different techniques are employed for the characterization. Biogenic synthesized silver-based nanoparticles are not completely characterized, particularly the nature of capped proteins covering the nanomaterials. Moreover, the antimicrobial activity of theses nanoparticles is assayed by using different protocols and strains, which difficult the comparison among the published papers. It is important to select some bacteria as standards, by following international foundations (Pharmaceutical Microbiology Manual) and use the minimal inhibitory concentration by broth microdilution assays from Clinical and Laboratory Standards Institute, which is the most common assay used in antibiotic ones. Therefore, we conclude that to have relevant results on antimicrobial effects of biogenic silver-based nanoparticles, it is necessary to have a complete and adequate characterization of these nanostructures, followed by standard methodology in microbiology protocols.

Silver nanoparticles: A new view on mechanistic aspects on antimicrobial activity.

Silver nanoparticles are well known potent antimicrobial agents. Although significant progresses have been achieved on the elucidation of antimicrobial mechanism of silver nanoparticles, the exact mechanism of action is still not completely known. This overview incorporates a retrospective of previous reviews published and recent original contributions on the progress of research on antimicrobial mechanisms of silver nanoparticles. The main topics discussed include release of silver nanoparticles and silver ions, cell membrane damage, DNA interaction, free radical generation, bacterial resistance and the relationship of resistance to silver ions versus resistance to silver nanoparticles. The focus of the overview is to summarize the current knowledge in the field of antibacterial activity of silver nanoparticles. The possibility that pathogenic microbes may develop resistance to silver nanoparticles is also discussed. FROM THE CLINICAL EDITOR: Antibacterial effect of nanoscopic silver generated a lot of interest both in research projects and in practical applications. However, the exact mechanism is still will have to be elucidated. This overview incorporates a retrospective of previous reviews published from 2007 to 2013 and recent original contributions on the progress of research on antimicrobial mechanisms to summarize our current knowledge in the field of antibacterial activity of silver nanoparticles.

Nanotoxicity of graphene and graphene oxide.

Graphene and its derivatives are promising candidates for important biomedical applications because of their versatility. The prospective use of graphene-based materials in a biological context requires a detailed comprehension of the toxicity of these materials. Moreover, due to the expanding applications of nanotechnology, human and environmental exposures to graphene-based nanomaterials are likely to increase in the future. Because of the potential risk factors associated with the manufacture and use of graphene-related materials, the number of nanotoxicological studies of these compounds has been increasing rapidly in the past decade. These studies have researched the effects of the nanostructural/biological interactions on different organizational levels of the living system, from biomolecules to animals. This review discusses recent results based on in vitro and in vivo cytotoxicity and genotoxicity studies of graphene-related materials and critically examines the methodologies employed to evaluate their toxicities. The environmental impact from the manipulation and application of graphene materials is also reported and discussed. Finally, this review presents mechanistic aspects of graphene toxicity in biological systems. More detailed studies aiming to investigate the toxicity of graphene-based materials and to properly associate the biological phenomenon with their chemical, structural, and morphological variations that result from several synthetic and processing possibilities are needed. Knowledge about graphene-based materials could ensure the safe application of this versatile material. Consequently, the focus of this review is to provide a source of inspiration for new nanotoxicological approaches for graphene-based materials.