Antiviral efficacy of cerium oxide nanoparticles.

Nanomaterials are prospective candidates for the elimination of viruses due to their multimodal mechanisms of action. Here, we tested the antiviral potential of a largely unexplored nanoparticle of cerium dioxide (CeO2). Two nano-CeO2 with opposing surface charge, (+) and (-), were assessed for their capability to decrease the plaque forming units (PFU) of four enveloped and two non-enveloped viruses during 1-h exposure. Statistically significant antiviral activity towards enveloped coronavirus SARS-CoV-2 and influenza virus was registered already at 20 mg Ce/l. For other two enveloped viruses, transmissible gastroenteritis virus and bacteriophage φ6, antiviral activity was evidenced at 200 mg Ce/l. As expected, the sensitivity of non-enveloped viruses towards nano-CeO2 was significantly lower. EMCV picornavirus showed no decrease in PFU until the highest tested concentration, 2000 mg Ce/l and MS2 bacteriophage showed slight non-monotonic response to high concentrations of nano-CeO2(-). Parallel testing of antiviral activity of Ce3+ ions and SiO2 nanoparticles allows to conclude that nano-CeO2 activity was neither due to released Ce-ions nor nonspecific effects of nanoparticulates. Moreover, we evidenced higher antiviral efficacy of nano-CeO2 compared with Ag nanoparticles. This result along with low antibacterial activity and non-existent cytotoxicity of nano-CeO2 allow us to propose CeO2 nanoparticles for specific antiviral applications.

Preparation and Characterization of Photocatalytically Active Antibacterial Surfaces Covered with Acrylic Matrix Embedded Nano-ZnO and Nano-ZnO/Ag.

In the context of healthcare-acquired infections, microbial cross-contamination and the spread of antibiotic resistance, additional passive measures to prevent pathogen carryover are urgently needed. Antimicrobial high-touch surfaces that kill microbes on contact or prevent their adhesion could be considered to mitigate the spread. Here, we demonstrate that photocatalytic nano-ZnO- and nano-ZnO/Ag-based antibacterial surfaces with efficacy of at least a 2.7-log reduction in Escherichia coli and Staphylococcus aureus viability in 2 h can be produced by simple measures using a commercial acrylic topcoat for wood surfaces. We characterize the surfaces taking into account cyclic wear and variable environmental conditions. The light-induced antibacterial and photocatalytic activities of the surfaces are enhanced by short-term cyclic wear, indicating their potential for prolonged effectivity in long-term use. As the produced surfaces are generally more effective at higher relative air humidity and silver-containing surfaces lost their contact-killing properties in dry conditions, it is important to critically evaluate the end-use conditions of materials and surfaces to be tested and select application-appropriate methods for their efficacy assessment.

Deposition of low-density thick silica films from burning sol-gel derived alcogels.

In the current study we show that the combustion of sol-gel derived alcogels with specifically tailored composition leads to the release of silica nanoparticles from the burning alcogel in a controlled manner which enables direct deposition of the released nanoparticles into low-density silica thick films. The process has some similarities to flame spray pyrolysis but requires no aerosol generator or other sophisticated instrumental setup. By the proper choice of catalysts and mixture of silicon alkoxides for the synthesis of the alcogel, preferential hydrolysis and polycondensation of one of the alkoxides is achieved. This leads to the formation of an alcogel with volatile silica precursor trapped in the gel pores. Resulting alcogels were burned to deposit uniform porous silica films with density of ~0.1 g/cm3 and primary particle size of ~10 nm. Demonstrated method yields silanol-free silica directly, without additional treatment steps and enables straightforward control over the deposition rate and coarseness of the layer by simple adjustment of the composition of the silica alcogel. The maximum layer thickness is limited only by the deposition time (in the current work up to 134 µm). Such technique of porous oxide film preparation could potentially be extended to the preparation of porous films from other oxides by using respective metal alkoxides as precursors.

Seagrass beds reveal high abundance of microplastic in sediments: A case study in the Baltic Sea.

Microplastic (MPL) contamination in the marine environment is extensively studied yet little is known about the extent of MPL abundance in seagrass beds. The aim of this study was to evaluate MPL accumulation in coastal seagrass (Zostera marina) beds in the Baltic Sea, Estonia. Surface water was sampled by pumping using 40 µm plankton net, and sediments by trowel. MPL was extracted with NaCl, identified by microscopy and ATR-FTIR on selected samples. Surface water in the seagrass beds had 0.04-1.2 (median 0.14) MPL/L, similar to other areas of the Baltic Sea. Sediments had 0-1817 (median 208) MPL/kg (dwt), much higher than previously recorded from adjacent unvegetated and offshore sediments, thereby suggesting a strong ability of the sediments in seagrass beds to retain MPL. Of identified MPL, blue fibres were dominant in both the sampled media. Sediment characterization showed a correlation between MPL counts with poorly sorted sediments.

Long Term Exposure to Virgin and Recycled LDPE Microplastics Induced Minor Effects in the Freshwater and Terrestrial Crustaceans Daphnia magna and Porcellio scaber.

The effects of microplastics (MP) are extensively studied, yet hazard data from long-term exposure studies are scarce. Moreover, for sustainable circular use in the future, knowledge on the biological impact of recycled plastics is essential. The aim of this study was to provide long-term toxicity data of virgin vs recycled (mechanical recycling) low density polyethylene (LDPE) for two commonly used ecotoxicity models, the freshwater crustacean Daphnia magna and the terrestrial crustacean Porcellio scaber. LDPE MP was tested as fragments of 39.8 ± 8.82 µm (virgin) and 205 ± 144 µm (recycled) at chronic exposure levels of 1-100 mg LDPE/L (D. magna) and 0.2-15 g LDPE/kg soil (P. scaber). Mortality, reproduction, body length, total lipid content, feeding and immune response were evaluated. With the exception of very low inconsistent offspring mortality at 10 mg/L and 100 mg/L of recycled LDPE, no MP exposure-related adverse effects were recorded for D. magna. For P. scaber, increased feeding on non-contaminated leaves was observed for virgin LDPE at 5 g/kg and 15 g/kg. In addition, both LDPE induced a slight immune response at 5 g/kg and 15 g/kg with more parameters altered for virgin LDPE. Our results indicated different sublethal responses upon exposure to recycled compared to virgin LDPE MP.

Surface carboxylation or PEGylation decreases CuO nanoparticles' cytotoxicity to human cells in vitro without compromising their antibacterial properties.

Clinical use of CuO nanoparticles (NPs) as antibacterials can be hampered by their toxicity to human cells. We hypothesized that certain surface functionalizations of CuO NPs may render NPs toxic to bacteria, but still be relatively harmless to human cells. To control this hypothesis, the toxicity of differently functionalized CuO NPs to bacteria Escherichia coli vs human cells (THP-1 macrophages and HACAT keratinocytes) was compared using similar conditions and end points. CuO NPs functionalized with polyethylene glycol (CuO-PEG), carboxyl (CuO-COOH, anionic), ammonium (CuO-NH4+, cationic) and unfunctionalized CuO NPs and CuSO4 (controls) were tested. In general, the toxicity of Cu compounds decreased in the following order: CuO-NH4+ > unfunctionalized CuO > CuSO4 > CuO-COOH > CuO-PEG. Positively charged unfunctionalized CuO and especially CuO-NH4+ proved most toxic (24-h EC50 = 21.7-47 mg/l) and had comparable toxicity to bacterial and mammalian cells. The multivariate analysis revealed that toxicity of these NPs was mostly attributed to their positive zeta potential, small hydrodynamic size, high Cu dissolution, and induction of reactive oxygen species (ROS) and TNF-α. In contrast, CuO-COOH and CuO-PEG NPs had lower toxicity to human cells compared to bacteria despite efficient uptake of these NPs by human cells. In addition, these NPs did not induce TNF-α and ROS. Thus, by varying the NP functionalization and Cu form (soluble salt vs NPs), it was possible to "target" the toxicity of Cu compounds, whereas carboxylation and PEGylation rendered CuO NPs that were more toxic to bacteria than to human cells envisaging their use in medical antibacterial products.

Visible light to switch-on desorption from goethite.

Switching adsorption-desorption by visible light could provide the possibility for a wide range of applications that require controlled release-on-demand. Here, we demonstrate a visible-light controlled desorption behavior in aqueous suspensions for the first time. We observed cationic dye adsorption on amphoteric goethite α-FeOOH in the dark and release during visible light exposure at a pH value slightly over the isoelectric point of goethite. During this process, the dye does not degrade. Desorption is triggered by local heating due to light absorption in narrow band gap goethite, α-FeOOH.

UVA-induced antimicrobial activity of ZnO/Ag nanocomposite covered surfaces.

Application of efficient antimicrobial surfaces has been estimated to decrease both, the healthcare-associated infections and the spread of antibiotic-resistant bacteria. In this paper, we prepared ZnO and ZnO/Ag nanoparticle covered surfaces and evaluated their antimicrobial efficacy towards a Gram-negative bacterial model (Escherichia coli), a Gram-positive bacterial model (Staphylococcus aureus) and a fungal model (Candida albicans) in the dark and under UVA illumination. The surfaces were prepared by spin coating aliquots of ZnO and ZnO/Ag nanoparticle suspensions onto glass substrates. Surfaces contained 2 or 20 µg Zn/cm2 and 0-0.02 µg Ag/cm2. No significant antimicrobial activity of the surfaces, except of those with the highest Ag or Zn content was observed in the dark. On the other hand, UVA illuminated surfaces containing 20 µg Zn/cm2 and 2 µg Zn plus 0.02 µg Ag/cm2 caused >3 log decrease in the viable counts of E. coli and S. aureus in 30 min. As proven by brilliant blue FCF dye degradation and elemental analysis of the surfaces, this remarkable antimicrobial activity was a combined result of photocatalytic effect and release of Zn and Ag ions from surfaces. Surfaces retained significant antibacterial and photocatalytic properties after several usage cycles. Compared to bacteria, yeast C. albicans was significantly less sensitive to the prepared surfaces and only about 1 log reduction of viable count was observed after 60 min UVA illumination. In conclusion, the developed ZnO/Ag surfaces exhibit not only high antibacterial activity but also some antifungal activity.

Uptake and transcytosis of functionalized superparamagnetic iron oxide nanoparticles in an in vitro blood brain barrier model.

Two major hurdles in nanomedicine are the limited strategies for synthesizing stealth nanoparticles and the poor efficacy of the nanoparticles in translocating across the blood brain barrier (BBB). Here we examined the uptake and transcytosis of iron oxide nanoparticles (IONPs) grafted with biomimetic phosphorylcholine (PC) brushes in an in vitro BBB model system, and compared them with bare, PEG or PC-PEG mixture grafted IONPs. Hyperspectral imaging indicated IONP co-localization with cells. Quantitative analysis with total reflection X-ray fluorescence spectrometry showed that after 24 h, 78% of PC grafted, 68-69% of PEG or PC-PEG grafted, and 30% of bare IONPs were taken up by the BBB. Transcytosis of IONPs was time-dependent and after 24 h, 16-17% of PC or PC-PEG mixture grafted IONPs had passed the BBB model, significantly more than PEG grafted or bare IONPs. These findings point out that grafting of IONPs with PC is a viable strategy for improving the uptake and transcytosis of nanoparticles.

Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate.

Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2 nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.

Bacterial polysaccharide levan as stabilizing, non-toxic and functional coating material for microelement-nanoparticles.

Levan, fructose-composed biopolymer of bacterial origin, has potential in biotechnology due to its prebiotic and immunostimulatory properties. In this study levan synthesized by levansucrase from Pseudomonas syringae was thoroughly characterized and used as multifunctional biocompatible coating material for microelement-nanoparticles (NPs) of selenium, iron and cobalt. Transmission electron microscopy (TEM), hydrodynamic size measurements (DLS) and X-ray photoelectron spectroscopy (XPS) showed the interaction of levan with NPs. Levan stabilized the dispersions of NPs, decreased their toxicity and had protective effect on human intestinal cells Caco-2. In addition, levan attached to cobalt NPs remained accessible as a substrate for the colon bacteria Bacteroides thetaiotaomicron. We suggest that the combination of levan and nutritionally important microelements in the form of NPs serves as a first step towards a novel "2 in 1" approach for food supplements to provide safe and efficient delivery of microelements for humans and support beneficial gut microbiota with nutritional oligosaccharides.

Toxicity of 11 Metal Oxide Nanoparticles to Three Mammalian Cell Types In Vitro.

The knowledge on potential harmful effects of metallic nanomaterials lags behind their increased use in consumer products and therefore, the safety data on various nanomaterials applicable for risk assessment are urgently needed. In this study, 11 metal oxide nanoparticles (MeOx NPs) prepared using flame pyrolysis method were analyzed for their toxicity against human alveolar epithelial cells A549, human epithelial colorectal cells Caco2 and murine fibroblast cell line Balb/c 3T3. The cell lines were exposed for 24 h to suspensions of 3-100 µg/mL MeOx NPs and cellular viability was evaluated using. Neutral Red Uptake (NRU) assay. In parallel to NPs, toxicity of soluble salts of respective metals was analyzed, to reveal the possible cellular effects of metal ions shedding from the NPs. The potency of MeOx to produce reactive oxygen species was evaluated in the cell-free assay. The used three cell lines showed comparable toxicity responses to NPs and their metal ion counterparts in the current test setting. Six MeOx NPs (Al2O3, Fe3O4, MgO, SiO2, TiO2, WO3) did not show toxic effects below 100 µg/mL. For five MeOx NPs, the averaged 24 h IC50 values for the three mammalian cell lines were 16.4 µg/mL for CuO, 22.4 µg/mL for ZnO, 57.3 µg/mL for Sb2O3, 132.3 µg/mL for Mn3O4 and 129 µg/mL for Co3O4. Comparison of the dissolution level of MeOx and the toxicity of soluble salts allowed to conclude that the toxicity of CuO, ZnO and Sb2O3 NPs was driven by release of metal ions. The toxic effects of Mn3O4 and Co3O4 could be attributed to the ROS-inducing ability of these NPs. All the NPs were internalized by the cells according to light microscopy studies but also proven by TEM, and internalization of Co3O4 NPs seemed to be most prominent in this aspect. In conclusion, this work provides valuable toxicological data for a library of 11 MeOx NPs. Combining the knowledge on toxic or non-toxic nature of nanomaterials may be used for safe-by-design approach.

Photocatalytic antibacterial activity of nano-TiO2 (anatase)-based thin films: effects on Escherichia coli cells and fatty acids.

Titanium dioxide is a photocatalyst with well-known ability to oxidise a wide range of organic contaminants as well as to destroy microbial cells. In the present work TiO2 nanoparticles with high specific surface area (150m(2)/g) were used to prepare nanostructured films. The TiO2 nanoparticle-based film in combination with UV-A illumination with intensity (22W/m(2)) comparable to that of the sunlight in the UV-A region was used to demonstrate light-induced antibacterial effects. Fast and effective inactivation of Escherichia coli cells on the prepared thin films was observed. Visualization of bacterial cells under scanning electron microscopy (SEM) showed enlargement of the cells, distortion of cellular membrane and possible leakage of cytoplasm after 10min of exposure to photoactivated TiO2. According to the plate counts there were no viable cells as early as after 20min of exposure to UV-A activated TiO2. In parallel to effects on bacterial cell viability and morphology, changes in saturated and unsaturated fatty acids - important components of bacterial cell membrane-were studied. Fast decomposition of saturated fatty acids and changes in chemical structure of unsaturated fatty acids were detected. Thus, we suggest that peroxidation and decomposition of membrane fatty acids could be one of the factors contributing to the morphological changes of bacteria observed under SEM, and ultimately, cell death.

Size-dependent toxicity of silver nanoparticles to bacteria, yeast, algae, crustaceans and mammalian cells in vitro.

The concept of nanotechnologies is based on size-dependent properties of particles in the 1-100 nm range. However, the relation between the particle size and biological effects is still unclear. The aim of the current paper was to generate and analyse a homogenous set of experimental toxicity data on Ag nanoparticles (Ag NPs) of similar coating (citrate) but of 5 different primary sizes (10, 20, 40, 60 and 80 nm) to different types of organisms/cells commonly used in toxicity assays: bacterial, yeast and algal cells, crustaceans and mammalian cells in vitro. When possible, the assays were conducted in ultrapure water to minimise the effect of medium components on silver speciation. The toxic effects of NPs to different organisms varied about two orders of magnitude, being the lowest (∼0.1 mg Ag/L) for crustaceans and algae and the highest (∼26 mg Ag/L) for mammalian cells. To quantify the role of Ag ions in the toxicity of Ag NPs, we normalized the EC50 values to Ag ions that dissolved from the NPs. The analysis showed that the toxicity of 20-80 nm Ag NPs could fully be explained by released Ag ions whereas 10 nm Ag NPs proved more toxic than predicted. Using E. coli Ag-biosensor, we demonstrated that 10 nm Ag NPs were more bioavailable to E. coli than silver salt (AgNO3). Thus, one may infer that 10 nm Ag NPs had more efficient cell-particle contact resulting in higher intracellular bioavailability of silver than in case of bigger NPs. Although the latter conclusion is initially based on one test organism, it may lead to an explanation for "size-dependent" biological effects of silver NPs. This study, for the first time, investigated the size-dependent toxic effects of a well-characterized library of Ag NPs to several microbial species, protozoans, algae, crustaceans and mammalian cells in vitro.

Dissolution of silver nanowires and nanospheres dictates their toxicity to Escherichia coli.

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of 100 × 6100 nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag(+) ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ~80-100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles.