The Occurrence of Oxidative Stress Induced by Silver Nanoparticles in Chlorella vulgaris Depends on the Surface-Stabilizing Agent.

Silver nanoparticles (AgNPs) are of great interest due to their antimicrobial properties, but their reactivity and toxicity pose a significant risk to aquatic ecosystems. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by agents that affect their physicochemical properties. In this study, microalga Chlorella vulgaris was used as a model organism to evaluate the effects of AgNPs in aquatic habitats. Algae were exposed to AgNPs stabilized with citrate and cetyltrimethylammonium bromide (CTAB) agents and to AgNO3 at concentrations that allowed 75% cell survival after 72 h. To investigate algal response, silver accumulation, ROS content, damage to biomolecules (lipids, proteins, and DNA), activity of antioxidant enzymes (APX, PPX, CAT, SOD), content of non-enzymatic antioxidants (proline and GSH), and changes in ultrastructure were analyzed. The results showed that all treatments induced oxidative stress and adversely affected algal cells. AgNO3 resulted in the fastest death of algae compared to both AgNPs, but the extent of oxidative damage and antioxidant enzymatic defense was similar to AgNP-citrate. Furthermore, AgNP-CTAB showed the least toxic effect and caused the least oxidative damage. These results highlight the importance of surface-stabilizing agents in determining the phytotoxicity of AgNPs and the underlying mechanisms affecting aquatic organisms.

Development and Characterization of Cationic Nanostructured Lipid Carriers as Drug Delivery Systems for miRNA-27a.

Although miRNA-27a has been identified as a promising candidate for miRNA mimic therapy of obesity, its application is limited due to enzymatic degradation and low membrane permeation. To overcome these problems, we developed cationic nanostructured lipid carriers (cNLCs) using high-pressure homogenization and used them as non-viral carriers for the anti-adipogenic miRNA-27a. Cargo-free octadecylamine-containing NLCs and miRNA/cNLC complexes were characterized regarding particle size, size distributions, zeta potential, pH values, particle topography and morphology, and entrapment efficacy. Furthermore, the cytotoxicity and cellular uptake of the miRNA/cNLC complex in the 3T3-L1 cell line were investigated. The investigation of the biological effect of miRNA-27a on adipocyte development and an estimation of the accumulated Oil-Red-O (ORO) dye in lipid droplets in mature adipocytes were assessed with light microscopy and absorbance measurements. The obtained data show that cNLCs represent a suitable DDS for miRNAs, as miRNA/cNLC particles are rapidly formed through non-covalent complexation due to electrostatic interactions between both components. The miRNA-27a/cNLC complex induced an anti-adipogenic effect on miRNA-27a by reducing lipid droplet accumulation in mature adipocytes, indicating that this approach might be used as a new therapeutic strategy for miRNA mimic replacement therapies in the prevention or treatment of obesity and obesity-related disorders.

Dispersoids in Al-Mg-Si Alloy AA 6086 Modified by Sc and Y.

The aluminium alloy AA 6086 attains the highest room temperature strength among Al-Mg-Si alloys. This work studies the effect of Sc and Y on the formation of dispersoids in this alloy, especially L12-type ones, which can increase its high-temperature strength. A comprehensive investigation was carried out using light microscopy (LM), scanning (SEM), and transmission (TEM) electron microscopy, energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dilatometry to obtain the information regarding the mechanisms and kinetics of dispersoid formation, particularly during isothermal treatments. Sc and Y caused the formation of L12 dispersoids during heating to homogenization temperature and homogenization of the alloys, and during isothermal heat treatments of the as-cast alloys (T5 temper). The highest hardness of Sc and (Sc + Y) modified alloys was attained by heat-treating alloys in the as-cast state in the temperature range between 350 °C and 450 °C (via T5 temper).

Crack-free in situ heat-treated high-alloy tool steel processed via laser powder bed fusion: microstructure and mechanical properties.

In this study, high-alloy tool steel S390 was processed crack-free and dense for the first time using laser powder bed fusion (LPBF). The resulting mechanical properties and microstructure of the LPBF steel parts were investigated. High-alloy tool steels, such as high-performance high-speed Boehler S390 steel (containing 1.64 wt% C and W, Mo, V, Co, and Cr in the ratio 10:2:5:8:5 wt%), are prone to cracking when processed using LPBF because these steels have high carbon and carbide-forming alloying elements content. Cracks are induced by thermal stresses and solid-phase transformation, combined with weak grain boundaries caused by segregated primary carbides. Substrate plate heating reduces thermal stresses and enables in situ heat treatment, thus modulating solid-phase transformation and carbide precipitation and preventing cracking during cooling. The resulting microstructure, precipitations, and mechanical properties of the as-built LPBF specimens, which were in situ heat-treated at 800 °C, and the conventionally post-heat-treated specimens were assessed using optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, X-ray diffraction, hardness testing, bending testing, and density measurement. In situ heat treatment impacts microstructure, precipitation behavior, and solid-phase transformation, causing a change in the microstructure of the material along the build direction due to different thermal histories. The as-built specimens exhibit a hardness gradient along the build direction of 500 HV1 to 800 HV1 in the top layer. The average bending strength is 2500 MPa, measured from the tensile stresses on the harder side and the compressive stresses on the softer side. Conventional post-heat treatment yields a mean hardness of 610 HV1 and a mean bending strength of 2800 MPa.

Lactoferricins impair the cytosolic membrane of Escherichia coli within a few seconds and accumulate inside the cell.

We report the real-time response of Escherichia coli to lactoferricin-derived antimicrobial peptides (AMPs) on length scales bridging microscopic cell sizes to nanoscopic lipid packing using millisecond time-resolved synchrotron small-angle X-ray scattering. Coupling a multiscale scattering data analysis to biophysical assays for peptide partitioning revealed that the AMPs rapidly permeabilize the cytosolic membrane within less than 3 s-much faster than previously considered. Final intracellular AMP concentrations of ∼80-100 mM suggest an efficient obstruction of physiologically important processes as the primary cause of bacterial killing. On the other hand, damage of the cell envelope and leakage occurred also at sublethal peptide concentrations, thus emerging as a collateral effect of AMP activity that does not kill the bacteria. This implies that the impairment of the membrane barrier is a necessary but not sufficient condition for microbial killing by lactoferricins. The most efficient AMP studied exceeds others in both speed of permeabilizing membranes and lowest intracellular peptide concentration needed to inhibit bacterial growth.

Competing magnetic states andM-Hloop splitting in core-shell NiO nanoparticles.

Magnetic relaxation in a nanoparticles system depends on the intra-particle interactions, reversal mechanism, the anisotropy field, easy axis distribution, particle volume, lattice defects, surface defects, materials composite, etc. Here we report the competing magnetic states between superparamagnetic blocking and Néel transition states in 14 nm core-shell NiO nanoparticles. A crossover temperature of 50 K was observed for both these states from the zero field cooled/field cooled magnetization curves taken at different fields. At crossover temperature, an interestingM-Hloop splitting is observed which is attributed to the slow spin relaxation. This anomalousM-Hloop splitting behaviour was found to be particle size dependent and suppressed for diameters above and below 14 nm which indicates a critical size for these competing magnetic states. Additional neutron diffraction experiments confirmed this observation. This experimental study provides a new insight for the understanding of intra-particle interactions in fine antiferromagnetic nanoparticles and obtained results are an important step towards deeper understanding of the competing/non-competing modes between superparamagnetic blocked and Néel transition states.

Ultrastructure of spherites in the midgut diverticula and Malpighian tubules of the harvestman Amilenus aurantiacus during the winter diapause.

Amilenus aurantiacus overwinter in diapause, a natural starvation period, in hypogean habitats. The structure of spherites in the midgut diverticula (MD) and Malpighian tubules (MT) has been studied comparatively by light microscopy and TEM to detect eventual differences in mineral consumption in the beginning and at the end of the starvation period in these organs (MD and MT) associated with digestive processes. The chemical composition of spherites was examined by combining energy-dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy-filtered TEM (EFTEM). The structure of the spherites changed during overwintering in both organs. At the beginning of overwintering, the spherites were composed of densely packed concentric layers of electron-dense and electron-lucent material. In the middle and at the end of overwintering, the electron-lucent layers between the layers of material indicated the loss of some material. The chemical composition of the spherites changed only in the MD; at the beginning of overwintering, these contained Si, O, C and Fe, while later there was no more Fe. In contrast, spherites in the MT were composed of Si, O, C and Ca throughout overwintering. A less intensive exploitation of the MD spherites was probably due to complete cessation of digestive and other cell activity in this organ during the winter diapause; activity of the MT slowed, but continued removing the cell metabolites.

A novel nZVI-bentonite nanocomposite to remove trichloroethene (TCE) from solution.

Nanoscale zero-valent iron (nZVI) based (nano)composites supported by clay mineral substrates are a promising technology for the in-situ remediation of groundwater and (sub)soils contaminated with chlorinated hydrocarbons, such as trichloroethene (TCE). However, the physicochemical processes and interaction mechanisms between nZVI particles, clay minerals and TCE are poorly understood, yet. We immobilized nZVI particles on a commercial bentonite substrate to prepare a novel nZVI-B nanocomposite and tested its performance for TCE removal from solution against pure nZVI in batch reactors. The nZVI-B exhibited a higher reactivity (2.2·10-3 L h-1·m-2) and efficiency (94%) for TCE removal than nZVI (2.2·10-4 L h-1·m-2; 45%). Sorption of TCE onto the clay surfaces and reductive de-chlorination in "micro-reactors" developing within the nZVI-B controlled the kinetics and the magnitude of TCE loss from solution. Contrary to pure nZVI, no signs of nZVI particle agglomeration or inactivation due to oxide shell formation were found in nZVI-B. We attribute this to the uptake of dissolved Fe species that are liberated via progressing nZVI particle corrosion by the bentonite substrate to form Fe-smectite (nontronite domains), which prevented from a deterioration of the properties and reactivity of the nZVI-B. The use of nZVI-B in permeable reactive barriers at contaminated field sites could be feasible, where a system-inherent reduction of the soil-bearing capacity has to be minimized.

High-Fidelity 3D Nanoprinting of Plasmonic Gold Nanoantennas.

The direct-write fabrication of freestanding nanoantennas for plasmonic applications is a challenging task, as demands for overall morphologies, nanoscale features, and material qualities are very high. Within the small pool of capable technologies, three-dimensional (3D) nanoprinting via focused electron beam-induced deposition (FEBID) is a promising candidate due to its design flexibility. As FEBID materials notoriously suffer from high carbon contents, the chemical postgrowth transfer into pure metals is indispensably needed, which can severely harm or even destroy FEBID-based 3D nanoarchitectures. Following this challenge, we first dissect FEBID growth characteristics and then combine individual advantages by an advanced patterning approach. This allows the direct-write fabrication of high-fidelity shapes with nanoscale features in the sub-10 nm range, which allow a shape-stable chemical transfer into plasmonically active Au nanoantennas. The here-introduced strategy is a generic approach toward more complex 3D architectures for future applications in the field of 3D plasmonics.

Alkaline Ethanol Oxidation Reaction on Carbon Supported Ternary PdNiBi Nanocatalyst using Modified Instant Reduction Synthesis Method.

Direct ethanol fuel cells (DEFC) still lack active and efficient electrocatalysts for the alkaline ethanol oxidation reaction (EOR). In this work, a new instant reduction synthesis method was developed to prepare carbon supported ternary PdNiBi nanocatalysts with improved EOR activity. Synthesized catalysts were characterized with a variety of structural and compositional analysis techniques in order to correlate their morphology and surface chemistry with electrochemical performance. The modified instant reduction synthesis results in well-dispersed, spherical Pd85Ni10Bi5 nanoparticles on Vulcan XC72R support (Pd85Ni10Bi5/C(II-III)), with sizes ranging from 3.7 ± 0.8 to 4.7 ± 0.7 nm. On the other hand, the common instant reduction synthesis method leads to significantly agglomerated nanoparticles (Pd85Ni10Bi5/C(I)). EOR activity and stability of these three different carbon supported PdNiBi anode catalysts with a nominal atomic ratio of 85:10:5 were probed via cyclic voltammetry and chronoamperometry using the rotating disk electrode method. Pd85Ni10Bi5/C(II) showed the highest electrocatalytic activity (150 mA⋅cm-2; 2678 mA⋅mg-1) with low onset potential (0.207 V) for EOR in alkaline medium, as compared to a commercial Pd/C and to the other synthesized ternary nanocatalysts Pd85Ni10Bi5/C(I) and Pd85Ni10Bi5/C(III). This new synthesis approach provides a new avenue to developing efficient, carbon supported ternary nanocatalysts for future energy conversion devices. Graphical AbstractThe modified instant reduction method for synthesis of ternary Pd85Ni10Bi5/C(II) nanocatalyst using Vulcan XC72R as carbon support initiates an agglomeration reduction, provides low average particle size, and enables enhanced activity for the alkaline ethanol oxidation reaction (EOR) compared to the common instant reduction method and to a commercial Pd/C catalyst.

Magnetic homogeneity in Fe-Mn co-doped NiO nanoparticles.

The effect of Fe and Mn co-doping on the magnetic properties of the antiferromagnetic (AFM) NiO nanoparticles which offer large potential for different magnetic applications have been studied. The Rietveld refinement fitting of powder x-ray diffractometry (XRD) patterns confirmed the phase formation of face-centred cubic crystal structure of NiO and average crystallite size lies in the short range of 32-38 nm. The cavity and broadband ferromagnetic resonance (FMR) measurements taken at room temperature demonstrate the smaller local magnetic inhomogeneity for 4%Mn-4%Fe co-doped NiO nanoparticles as compared to undoped, single doped and co-doped with different concentration NiO nanoparticles. The M-H loops revealed the room temperature ferromagnetism-like behaviour for higher Fe doping concentration and lower Mn doping concentration. This can be attributed to the double exchange interaction. The zero field cooled (ZFC) and field cooled (FC) dc magnetization curves showed a small surface freezing peak (at[Formula: see text] at low temperatures and a blocking peak (at [Formula: see text] at higher temperatures. For samples with 4%Mn-4%Fe and 2%Mn-6%Fe, the blocking peak was found at a relatively high temperature in comparison to other samples. This can be attributed to the presence of magnetic exchange interactions which block the magnetic spins against a thermal increase. The ZFC AC-susceptibility showed three peaks; a surface freezing peak at Tf, a blocking peak at TB peak and an anomalous peak at Tx in between [Formula: see text] and [Formula: see text], which was found to be most prominent for the 4%Mn-4%Fe co-doped nanoparticles. The neutron diffraction pattern confirmed the AFM order of the core of the 4%Mn-4%Fe co-doped nanoparticles, which indicates an AFM coupling between the Fe2+ and Mn2+ ions and the Ni2+ ions through super-exchange interaction. Therefore, the origin of TX peak can be attributed to the ferromagnetic coupling between the Fe2+ and Mn2+ ions which has a maximum strength at equal concentration. Thus, small and equal doping concentration of Fe and Mn in NiO nanoparticles increase the magnetic homogeneity which makes them attractive for magnetic applications.

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

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

Magainin 2 and PGLa in Bacterial Membrane Mimics II: Membrane Fusion and Sponge Phase Formation.

We studied the synergistic mechanism of equimolar mixtures of magainin 2 (MG2a) and PGLa in phosphatidylethanolamine/phosphatidylglycerol mimics of Gram-negative cytoplasmic membranes. In a preceding article of this series, we reported on the early onset of parallel heterodimer formation of the two antimicrobial peptides already at low concentrations and the resulting defect formation in the membranes. Here, we focus on the structures of the peptide-lipid aggregates occurring in the synergistic regime at elevated peptide concentrations. Using a combination of calorimetric, scattering, electron microscopic, and in silico techniques, we demonstrate that the two peptides, even if applied individually, transform originally large unilamellar vesicles into multilamellar vesicles with a collapsed interbilayer spacing resulting from peptide-induced adhesion. Interestingly, the adhesion does not lead to a peptide-induced lipid separation of charged and charge-neutral species. In addition to this behavior, equimolar mixtures of MG2a and PGLa formed surface-aligned fibril-like structures, which induced adhesion zones between the membranes and the formation of transient fusion stalks in molecular dynamics simulations and a coexisting sponge phase observed by small-angle x-ray scattering. The previously reported increased leakage of lipid vesicles of identical composition in the presence of MG2a/PGLa mixtures is therefore related to a peptide-induced cross-linking of bilayers.

Comparative proteomic study of phytotoxic effects of silver nanoparticles and silver ions on tobacco plants.

Widespread application of silver nanoparticles (AgNPs), due to their antibacterial and antifungal properties, increases their release into the environment and potential detrimental impact on living organisms. Plants may serve as a potential pathway for AgNPs bioaccumulation and a route into the food chain, hence investigation of AgNP phytotoxic effects are of particular importance. Since proteins are directly involved in stress response, studies of their abundance changes can help elucidate the mechanism of the AgNP-mediated phytotoxicity. In this study, we investigated proteomic changes in tobacco (Nicotiana tabacum) exposed to AgNPs and ionic silver (AgNO3). A high overlap of differently abundant proteins was found in root after exposure to both treatments, while in leaf, almost a half of the proteins exhibited different abundance level between treatments, indicating tissue-specific responses. Majority of the identified proteins were down-regulated in both tissues after exposure to either AgNPs or AgNO3; in roots, the most affected proteins were those involved in response to abiotic and biotic stimuli and oxidative stress, while in leaf, both treatments had the most prominent effect on photosynthesis-related proteins. However, since AgNPs induced higher suppression of protein abundance than AgNO3, we conclude that AgNP effects can, at least partially, be attributed to nanoparticle form.

Thermoreversible Surface Polymer Patches: A Cryogenic Transmission Electron Microscopy Investigation.

Hybrid core-shell type nanoparticles from gold nanoparticle cores and poly( N-isopropylacrylamide) shells were investigated with regard to their structural plasticity. Reversible addition-fragmentation chain transfer polymerization was used to synthesize well-defined polymers that can be readily anchored onto the gold nanoparticle surface. The polymer shell morphologies were directly visualized in their native solution state at high resolution by cryogenic transmission electron microscopy, and the microscopic results were further corroborated by dynamic light scattering. Different environmental conditions and brush architectures are covered by our experiments, which leads to distinct thermally induced responses. These responses include constrained dewetting of the nanoparticle surface at temperatures above the lower critical solution temperature of poly( N-isopropylacrylamide), leading to surface polymer patches. This effect provides a novel approach toward breaking the symmetry of nanoparticle interactions, and we show first evidence for its impact on the formation of colloidal superstructures.

Physiological, ultrastructural and proteomic responses of tobacco seedlings exposed to silver nanoparticles and silver nitrate.

Since silver nanoparticles (AgNPs) are a dominant nanomaterial in consumer products, there is growing concern about their impact on the environment. Although numerous studies on the effects of AgNPs on living organisms have been conducted, the interaction of AgNPs with plants has not been fully clarified. To reveal the plant mechanisms activated after exposure to AgNPs and to differentiate between effects specific to nanoparticles and ionic silver, we investigated the physiological, ultrastructural and proteomic changes in seedlings of tobacco (Nicotiana tabacum) exposed to commercial AgNPs and ionic silver (AgNO3) from the seed stage. A higher Ag content was measured in seedlings exposed to AgNPs than in those exposed to the same concentration of AgNO3. However, the results on oxidative stress parameters obtained revealed that, in general, higher toxicity was recorded in AgNO3-treated seedlings than in those exposed to nanosilver. Ultrastructural analysis of root cells confirmed the presence of silver in the form of nanoparticles, which may explain the lower toxicity of AgNPs. However, the ultrastructural changes of chloroplasts as well as proteomic study showed that both AgNPs and AgNO3 can affect photosynthesis. Moreover, the majority of the proteins involved in the primary metabolism were up-regulated after both types of treatments, indicating that enhanced energy production, which can be used to reinforce defensive mechanisms, enables plants to cope with silver-induced toxicity.

Inter-Backbone Charge Transfer as Prerequisite for Long-Range Conductivity in Perylene Bisimide Hydrogels.

Hydrogelation, the self-assembly of molecules into soft, water-loaded networks, is one way to bridge the structural gap between single molecules and functional materials. The potential of hydrogels, such as those based on perylene bisimides, lies in their chemical, physical, optical, and electronic properties, which are governed by the supramolecular structure of the gel. However, the structural motifs and their precise role for long-range conductivity are yet to be explored. Here, we present a comprehensive structural picture of a perylene bisimide hydrogel, suggesting that its long-range conductivity is limited by charge transfer between electronic backbones. We reveal nanocrystalline ribbon-like structures as the electronic and structural backbone units between which charge transfer is mediated by polar solvent bridges. We exemplify this effect with sensing, where exposure to polar vapor enhances conductivity by 5 orders of magnitude, emphasizing the crucial role of the interplay between structural motif and surrounding medium for the rational design of devices based on nanocrystalline hydrogels.

Intrinsic Curvature-Mediated Transbilayer Coupling in Asymmetric Lipid Vesicles.

We measured the effect of intrinsic lipid curvature, J0, on structural properties of asymmetric vesicles made of palmitoyl-oleoyl-phosphatidylethanolamine (POPE; J0<0) and palmitoyl-oleoyl-phosphatidylcholine (POPC; J0∼0). Electron microscopy and dynamic light scattering were used to determine vesicle size and morphology, and x-ray and neutron scattering, combined with calorimetric experiments and solution NMR, yielded insights into leaflet-specific lipid packing and melting processes. Below the lipid melting temperature we observed strong interleaflet coupling in asymmetric vesicles with POPE inner bilayer leaflets and outer leaflets enriched in POPC. This lipid arrangement manifested itself by lipids melting cooperatively in both leaflets, and a rearrangement of lipid packing in both monolayers. On the other hand, no coupling was observed in vesicles with POPC inner bilayer leaflets and outer leaflets enriched in POPE. In this case, the leaflets melted independently and did not affect each other's acyl chain packing. Furthermore, we found no evidence for transbilayer structural coupling above the melting temperature of either sample preparation. Our results are consistent with the energetically preferred location of POPE residing in the inner leaflet, where it also resides in natural membranes, most likely causing the coupling of both leaflets. The loss of this coupling in the fluid bilayers is most likely the result of entropic contributions.

Phytotoxic effects of silver nanoparticles in tobacco plants.

The small size of nanoparticles (NPs), with dimensions between 1 and 100 nm, results in unique chemical and physical characteristics, which is why they are implemented in various consumer products. Therefore, an important concern is the potential detrimental impact of NPs on the environment. As plants are a vital part of ecosystem, investigation of the phytotoxic effects of NPs is particularly interesting. This study investigated the potential phytotoxicity of silver nanoparticles (AgNPs) on tobacco (Nicotiana tabacum) plants and compared it with the effects of the same AgNO3 concentrations. Accumulation of silver in roots and leaves was equally efficient after both AgNP and AgNO3 treatment, with predominant Ag levels found in the roots. Exposure to AgNPs did not result in elevated values of oxidative stress parameters either in roots or in leaves, while AgNO3 induced oxidative stress in both plant tissues. In the presence of both AgNPs and AgNO3, root meristem cells became highly vacuolated, which indicates that vacuoles might be the primary storage target for accumulated Ag. Direct AgNP uptake by root cells was confirmed. Leaf ultrastructural studies revealed changes mainly in the size of chloroplasts of AgNP-treated and AgNO3-treated plants. All of these findings indicate that nano form of silver is less toxic to tobacco plants than silver ions.