Publications by authors named "Polona Umek"

20 Publications

  • Page 1 of 1

Prediction of Chronic Inflammation for Inhaled Particles: the Impact of Material Cycling and Quarantining in the Lung Epithelium.

Adv Mater 2020 Nov 19;32(47):e2003913. Epub 2020 Oct 19.

Department of Condensed Matter Physics, Jožef Stefan Institute, Ljubljana, 1000, Slovenia.

On a daily basis, people are exposed to a multitude of health-hazardous airborne particulate matter with notable deposition in the fragile alveolar region of the lungs. Hence, there is a great need for identification and prediction of material-associated diseases, currently hindered due to the lack of in-depth understanding of causal relationships, in particular between acute exposures and chronic symptoms. By applying advanced microscopies and omics to in vitro and in vivo systems, together with in silico molecular modeling, it is determined herein that the long-lasting response to a single exposure can originate from the interplay between the newly discovered nanomaterial quarantining and nanomaterial cycling between different lung cell types. This new insight finally allows prediction of the spectrum of lung inflammation associated with materials of interest using only in vitro measurements and in silico modeling, potentially relating outcomes to material properties for a large number of materials, and thus boosting safe-by-design-based material development. Because of its profound implications for animal-free predictive toxicology, this work paves the way to a more efficient and hazard-free introduction of numerous new advanced materials into our lives.
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http://dx.doi.org/10.1002/adma.202003913DOI Listing
November 2020

Bacteria Exposed to Silver Nanoparticles Synthesized by Laser Ablation in Water: Modelling Growth and Inactivation.

Materials (Basel) 2020 Feb 1;13(3). Epub 2020 Feb 1.

Faculty of Science, Department of Physics, University of Split, Ruđera Boškovića 33, 21000 Split, Croatia.

This study is aimed to better understand the bactericidal mode of action of silver nanoparticles. Here we present the production and characterization of laser-synthesized silver nanoparticles along with growth curves of bacteria treated at sub-minimal and minimal inhibitory concentrations, obtained by optical density measurements. The main effect of the treatment is the increase of the bacterial apparent lag time, which is very well described by the novel growth model as well as the entire growth curves for different concentrations. The main assumption of the model is that the treated bacteria uptake the nanoparticles and inactivate, which results in the decrease of both the nanoparticles and the bacteria concentrations. The lag assumes infinitive value for the minimal inhibitory concentration treatment. This apparent lag phase is not postponed bacterial growth. It is a dynamic state in which the bacterial growth and death rates are close in value. Our results strongly suggest that the predominant mode of antibacterial action of silver nanoparticles is the penetration inside the membrane.
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http://dx.doi.org/10.3390/ma13030653DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7040691PMC
February 2020

Photocatalytic biocidal effect of copper doped TiO2 nanotube coated surfaces under laminar flow, illuminated with UVA light on Legionella pneumophila.

PLoS One 2020 15;15(1):e0227574. Epub 2020 Jan 15.

Institute of Food Safety Feed and Environment, University of Ljubljana, Veterinary Faculty, Ljubljana, Slovenia.

Legionella pneumophila can cause a potentially fatal form of humane pneumonia (Legionnaires' disease), which is most problematic in immunocompromised and in elderly people. Legionella species is present at low concentrations in soil, natural and artificial aquatic systems and is therefore constantly entering man-made water systems. The environment temperature for it's ideal growth range is between 32 and 42°C, thus hot water pipes represent ideal environment for spread of Legionella. The bacteria are dormant below 20°C and do not survive above 60°C. The primary method used to control the risk from Legionella is therefore water temperature control. There are several other effective treatments to prevent growth of Legionella in water systems, however current disinfection methods can be applied only intermittently thus allowing Legionella to grow in between treatments. Here we present an alternative disinfection method based on antibacterial coatings with Cu-TiO2 nanotubes deposited on preformed surfaces. In the experiment the microbiocidal efficiency of submicron coatings on polystyrene to the bacterium of the genus Legionella pneumophila with a potential use in a water supply system was tested. The treatment thus constantly prevents growth of Legionella pneumophila in presence of water at room temperature. Here we show that 24-hour illumination with low power UVA light source (15 W/m2 UVA illumination) of copper doped TiO2 nanotube coated surfaces is effective in preventing growth of Legionella pneumophila. Microbiocidal effects of Cu-TiO2 nanotube coatings were dependent on the flow of the medium and the intensity of UV-A light. It was determined that tested submicron coatings have microbiocidal effects specially in a non-flow or low-flow conditions, as in higher flow rates, probably to a greater possibility of Legionella pneumophila sedimentation on the coated polystyrene surfaces, meanwhile no significant differences among bacteria reduction was noted regarding to non or low flow of medium.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227574PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6961935PMC
April 2020

Effects of physicochemical properties of TiO nanomaterials for pulmonary inflammation, acute phase response and alveolar proteinosis in intratracheally exposed mice.

Toxicol Appl Pharmacol 2020 01 15;386:114830. Epub 2019 Nov 15.

National Research Centre for the Working Environment, Copenhagen Ø, Denmark; DTU Health Tech, Technical University of Denmark, Kgs. Lyngby, Denmark. Electronic address:

Nanomaterial (NM) characteristics may affect the pulmonary toxicity and inflammatory response, including specific surface area, size, shape, crystal phase or other surface characteristics. Grouping of TiO in hazard assessment might be challenging because of variation in physicochemical properties. We exposed C57BL/6 J mice to a single dose of four anatase TiO NMs with various sizes and shapes by intratracheal instillation and assessed the pulmonary toxicity 1, 3, 28, 90 or 180 days post-exposure. The quartz DQ12 was included as benchmark particle. Pulmonary responses were evaluated by histopathology, electron microscopy, bronchoalveolar lavage (BAL) fluid cell composition and acute phase response. Genotoxicity was evaluated by DNA strand break levels in BAL cells, lung and liver in the comet assay. Multiple regression analyses were applied to identify specific TiO NMs properties important for the pulmonary inflammation and acute phase response. The TiO NMs induced similar inflammatory responses when surface area was used as dose metrics, although inflammatory and acute phase response was greatest and more persistent for the TiO tube. Similar histopathological changes were observed for the TiO tube and DQ12 including pulmonary alveolar proteinosis indicating profound effects related to the tube shape. Comparison with previously published data on rutile TiO NMs indicated that rutile TiO NMs were more inflammogenic in terms of neutrophil influx than anatase TiO NMs when normalized to total deposited surface area. Overall, the results suggest that specific surface area, crystal phase and shape of TiO NMs are important predictors for the observed pulmonary effects of TiO NMs.
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http://dx.doi.org/10.1016/j.taap.2019.114830DOI Listing
January 2020

Gas Sensing with Iridium Oxide Nanoparticle Decorated Carbon Nanotubes.

Sensors (Basel) 2018 Dec 31;19(1). Epub 2018 Dec 31.

MINOS-EMaS, Universitat Rovira i Virgili, 43007 Tarragona, Spain.

The properties of multi-wall carbon nanotubes decorated with iridium oxide nanoparticles (IrO-MWCNTs) are studied to detect harmful gases such as nitrogen dioxide and ammonia. IrO nanoparticles were synthetized using a two-step method, based on a hydrolysis and acid condensation growth mechanism. The metal oxide nanoparticles obtained were employed for decorating the sidewalls of carbon nanotubes. Iridium-oxide nanoparticle decorated carbon nanotube material showed higher and more stable responses towards NH₃ and NO₂ than bare carbon nanotubes under different experimental conditions, establishing the optimal operating temperatures and estimating the limits of detection and quantification. Furthermore, the nanomaterials employed were studied using different morphological and compositional characterization techniques and a gas sensing mechanism is proposed.
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http://dx.doi.org/10.3390/s19010113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6339137PMC
December 2018

Surface deposited one-dimensional copper-doped TiO2 nanomaterials for prevention of health care acquired infections.

PLoS One 2018 26;13(7):e0201490. Epub 2018 Jul 26.

Department of Condensed Matter Physics, Jožef Stefan Institute, Ljubljana, Slovenia.

Bacterial infections acquired in healthcare facilities including hospitals, the so called healthcare acquired or nosocomial infections, are still of great concern worldwide and represent a significant economical burden. One of the major causes of morbidity is infection with Methicillin Resistant Staphylococcus aureus (MRSA), which has been reported to survive on surfaces for several months. Bactericidal activity of copper-TiO2 thin films, which release copper ions and are deposited on glass surfaces and heated to high temperatures, is well known even when illuminated with very weak UVA light of about 10 μW/cm2. Lately, there is an increased intrerest for one-dimensional TiO2 nanomaterials, due to their unique properties, low cost, and high thermal and photochemical stability. Here we show that copper doped TiO2 nanotubes produce about five times more ·OH radicals as compared to undoped TiO2 nanotubes and that effective surface disinfection, determined by a modified ISO 22196:2011 test, can be achieved even at low intensity UVA light of 30 μW/cm2. The nanotubes can be deposited on a preformed surface at room temperature, resulting in a stable deposition resistant to multiple washings. Up to 103 microorganisms per cm2 can be inactivated in 24 hours, including resistant strains such as Methicillin-resistant Staphylococcus aureus (MRSA) and Extended-spectrum beta-lactamase Escherichia coli (E. coli ESBL). This disinfection method could provide a valuable alternative to the current surface disinfection methods.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0201490PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6062141PMC
January 2019

Nanoparticles Can Wrap Epithelial Cell Membranes and Relocate Them Across the Epithelial Cell Layer.

Nano Lett 2018 08 26;18(8):5294-5305. Epub 2018 Jul 26.

"Jožef Stefan Institute" , Jamova cesta 39 , SI-1000 Ljubljana , Slovenia.

Although the link between the inhalation of nanoparticles and cardiovascular disease is well established, the causal pathway between nanoparticle exposure and increased activity of blood coagulation factors remains unexplained. To initiate coagulation tissue factor bearing epithelial cell membranes should be exposed to blood, on the other side of the less than a micrometre thin air-blood barrier. For the inhaled nanoparticles to promote coagulation, they need to bind lung epithelial-cell membrane parts and relocate them into the blood. To assess this hypothesis, we use advanced microscopy and spectroscopy techniques to show that the nanoparticles wrap themselves with epithelial-cell membranes, leading to the membrane's disruption. The membrane-wrapped nanoparticles are then observed to freely diffuse across the damaged epithelial cell layer relocating epithelial cell membrane parts over the epithelial layer. Proteomic analysis of the protein content in the nanoparticles wraps/corona finally reveals the presence of the coagulation-initiating factors, supporting the proposed causal link between the inhalation of nanoparticles and cardiovascular disease.
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http://dx.doi.org/10.1021/acs.nanolett.8b02291DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6089500PMC
August 2018

Photocatalytic disinfection of surfaces with copper doped Ti02 nanotube coatings illuminated by ceiling mounted fluorescent light.

PLoS One 2018 16;13(5):e0197308. Epub 2018 May 16.

Jožef Stefan Institute, Ljubljana, Slovenia.

High economic burden is associated with foodborne illnesses. Different disinfection methods are therefore employed in food processing industry; such as use of ultraviolet light or usage of surfaces with copper-containing alloys. However, all the disinfection methods currently in use have some shortcomings. In this work we show that copper doped TiO2 nanotubes deposited on existing surfaces and illuminated with ceiling mounted fluorescent lights can retard the growth of Listeria Innocua by 80% in seven hours of exposure to the fluorescent lights at different places in a food processing plant or in the laboratory conditions with daily reinocuation and washing. The disinfection properties of the surfaces seem to depend mainly on the temperature difference of the surface and the dew point, where for the maximum effectiveness the difference should be about 3 degrees celsius. The TiO2 nanotubes have a potential to be employed for an economical and continuous disinfection of surfaces.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0197308PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5955584PMC
December 2018

Structural properties and thermal stability of cobalt- and chromium-doped α-MnO nanorods.

Beilstein J Nanotechnol 2017 10;8:1032-1042. Epub 2017 May 10.

Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia.

α-MnO nanorods were synthesized via the hydrothermal decomposition of KMnO in an acidic environment in the presence of Co and Cr ions. Reactions were carried out at three different temperatures: 90, 130 and 170 °C. All prepared samples exhibit a tetragonal MnO crystalline phase. SEM-EDS analysis shows that cobalt cations are incorporated to a higher degree into the MnO framework than chromium ions, and that the content of the dopant ions decreases with increasing reaction temperature. The oxidation of Co to Co during the reaction was proved by an XANES study, while EXAFS results confirm that both dopant ions substitute Mn in the center of an octahedron. The K/Mn ratio in the doped samples synthesized at 170 °C is significantly lower than in the undoped samples. Analysis of an individual cobalt-doped α-MnO nanorod with HAADF-STEM reveals that the distribution of cobalt through the cross-section of the nanorod is uniform. The course of thermal decomposition of the doped nanorods is similar to that of the undoped ones. Dopant ions do not preserve the MnO phase at higher temperatures nor do they destabilize the cryptomelane structure.
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http://dx.doi.org/10.3762/bjnano.8.104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433154PMC
May 2017

Controlling Disorder and Superconductivity in Titanium Oxynitride Nanoribbons with Anion Exchange.

ACS Nano 2015 Oct 14;9(10):10133-41. Epub 2015 Sep 14.

Jožef Stefan Institute , Jamova cesta 39, SI-1000 Ljubljana, Slovenia.

In recent years, conversion chemical reactions, which are driven by ion diffusion, emerged as an important concept for formation of nanoparticles. Here we demonstrate that the slow anion diffusion in anion exchange reactions can be efficiently used to tune the disorder strength and the related electronic properties of nanoparticles. This paradigm is applied to high-temperature formation of titanium oxynitride nanoribbons, Ti(O,N), transformed from hydrogen titanate nanoribbons in an ammonia atmosphere. The nitrogen content, which determines the chemical disorder through random O/N occupancy and ion vacancies in the Ti(O,N) composition, increases with the reaction time. The presence of disorder has paramount effects on resistivity of Ti(O,N) nanoribbons. Atypically for metals, the resistivity increases with decreasing temperature due to the weak localization effects. From this state, superconductivity develops below considerably or completely suppressed critical temperatures, depending on the disorder strength. Our results thus establish the remarkable versatility of anion exchange for tuning of the electronic properties of Ti(O,N) nanoribbons and suggest that similar strategies may be applied to a vast number of nanostructures.
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http://dx.doi.org/10.1021/acsnano.5b03742DOI Listing
October 2015

Protein Corona Prevents TiO2 Phototoxicity.

PLoS One 2015 17;10(6):e0129577. Epub 2015 Jun 17.

Jožef Stefan Institute, Ljubljana, Slovenia; NAMASTE Center of Excellence, Ljubljana, Slovenia.

Background & Aim: TiO2 nanoparticles have generally low toxicity in the in vitro systems although some toxicity is expected to originate in the TiO2-associated photo-generated radical production, which can however be modulated by the radical trapping ability of the serum proteins. To explore the role of serum proteins in the phototoxicity of the TiO2 nanoparticles we measure viability of the exposed cells depending on the nanoparticle and serum protein concentrations.

Methods & Results: Fluorescence and spin trapping EPR spectroscopy reveal that the ratio between the nanoparticle and protein concentrations determines the amount of the nanoparticles' surface which is not covered by the serum proteins and is proportional to the amount of photo-induced radicals. Phototoxicity thus becomes substantial only at the protein concentration being too low to completely coat the nanotubes' surface.

Conclusion: These results imply that TiO2 nanoparticles should be applied with ligands such as proteins when phototoxic effects are not desired - for example in cosmetics industry. On the other hand, the nanoparticles should be used in serum free medium or any other ligand free medium, when phototoxic effects are desired - as for efficient photodynamic cancer therapy.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0129577PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470505PMC
March 2016

Transformation of hydrogen titanate nanoribbons to TiO2 nanoribbons and the influence of the transformation strategies on the photocatalytic performance.

Beilstein J Nanotechnol 2015 27;6:831-44. Epub 2015 Mar 27.

Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia.

The influence of the reaction conditions during the transformation of hydrogen titanate nanoribbons to TiO2 nanoribbons on the phase composition, the morphology, the appearance of the nanoribbon surfaces and their optical properties was investigated. The transformations were performed (i) through a heat treatment in oxidative and reductive atmospheres in the temperature range of 400-650 °C, (ii) through a hydrothermal treatment in neutral and basic environments at 160 °C, and (iii) through a microwave-assisted hydrothermal treatment in a neutral environment at 200 °C. Scanning electron microscopy investigations showed that the hydrothermal processing significantly affected the nanoribbon surfaces, which became rougher, while the transformations based on calcination in either oxidative or reductive atmospheres had no effect on the morphology or on the surface appearance of the nanoribbons. The transformations performed in the reductive atmosphere, an NH3(g)/Ar(g) flow, and in the ammonia solution led to nitrogen doping. The nitrogen content increased with an increasing calcination temperature, as was determined by X-ray photoelectron spectroscopy. According to electron paramagnetic resonance measurements the calcination in the reductive atmosphere also resulted in a partial reduction of Ti(4+) to Ti(3+). The photocatalytic performance of the derived TiO2 NRs was estimated on the basis of the photocatalytic oxidation of isopropanol. After calcinating in air, the photocatalytic performance of the investigated TiO2 NRs increased with an increased content of anatase. In contrast, the photocatalytic performance of the N-doped TiO2 NRs showed no dependence on the calcination temperature. An additional comparison showed that the N-doping significantly suppressed the photocatalytic performance of the TiO2 NRs, i.e., by 3 to almost 10 times, in comparison with the TiO2 NRs derived by calcination in air. On the other hand, the photocatalytic performance of the hydrothermally derived TiO2 NRs was additionally improved by a subsequent heat treatment in air.
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http://dx.doi.org/10.3762/bjnano.6.86DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4419672PMC
May 2015

Aerosol-assisted CVD-grown WO₃ nanoneedles decorated with copper oxide nanoparticles for the selective and humidity-resilient detection of H₂S.

ACS Appl Mater Interfaces 2015 Apr 23;7(12):6842-51. Epub 2015 Mar 23.

†Research Centre on the Engineering of Materials and micro/nano Systems, Universitat Rovira i Virgili Països Catalans 26, 43007 Tarragona, Spain.

A gas-sensitive hybrid material consisting of Cu2O nanoparticle-decorated WO3 nanoneedles is successfully grown for the first time in a single step via aerosol-assisted chemical vapor deposition. Morphological, structural, and composition analyses show that our method is effective for growing single-crystalline, n-type WO3 nanoneedles decorated with p-type Cu2O nanoparticles at moderate temperatures (i.e., 380 °C), with cost effectiveness and short fabrication times, directly onto microhot plate transducer arrays with the view of obtaining gas sensors. The gas-sensing studies performed show that this hybrid nanomaterial has excellent sensitivity and selectivity to hydrogen sulfide (7-fold increase in response compared with that of pristine WO3 nanoneedles) and a low detection limit (below 300 ppb of H2S), together with unprecedented fast response times (2 s) and high immunity to changes in the background humidity. These superior properties arise because of the multiple p-n heterojunctions created at the nanoscale in our hybrid nanomaterial.
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http://dx.doi.org/10.1021/acsami.5b00411DOI Listing
April 2015

Single-step co-deposition of nanostructured tungsten oxide supported gold nanoparticles using a gold-phosphine cluster complex as the gold precursor.

Sci Technol Adv Mater 2014 Dec 9;15(6):065004. Epub 2014 Dec 9.

Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ London, UK.

The use of a molecular gold organometallic cluster in chemical vapour deposition is reported, and it is utilized, together with a tungsten oxide precursor, for the single-step co-deposition of (nanostructured) tungsten oxide supported gold nanoparticles (NPs). The deposited gold-NP and tungsten oxide supported gold-NP are highly active catalysts for benzyl alcohol oxidation; both show higher activity than SiO supported gold-NP synthesized via a solution-phase method, and tungsten oxide supported gold-NP show excellent selectivity for conversion to benzaldehyde.
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http://dx.doi.org/10.1088/1468-6996/15/6/065004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090393PMC
December 2014

Stabilisation of 2D colloidal assemblies by polymerisation of liquid crystalline matrices for photonic applications.

Soft Matter 2014 Aug 30;10(31):5797-803. Epub 2014 Jun 30.

Soft Matter Materials Lab, Solid State Physics Department, Jožef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia.

Colloidal crystals in anisotropic matrices are extremely stable and versatile, but disassemble as soon as the anisotropy of the matrix disappears. We present an approach to first custom-assemble colloidal structures and subsequently stabilize them through photo-polymerisation of the liquid crystalline matrix. The resulting 2D colloidal assemblies are stable at high temperatures and can even be obtained as free-standing films without a decrease in the degree of organization. This approach could be used to stabilize and extract recently proposed soft-matter photonic microcircuits based on liquid crystal optical microresonators, microlasers and microfibers, and opens up routes towards real soft matter photonic devices that are stable over extended time and temperatures.
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http://dx.doi.org/10.1039/c4sm00358fDOI Listing
August 2014

Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray-absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations.

Beilstein J Nanotechnol 2012 23;3:789-97. Epub 2012 Nov 23.

ChIPS, University of Mons, B-7000, Mons, Belgium.

Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS-TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/ΔE = 10(4) and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS-TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs.
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http://dx.doi.org/10.3762/bjnano.3.88DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3512128PMC
December 2012

Au nanoparticle-functionalised WO3 nanoneedles and their application in high sensitivity gas sensor devices.

Chem Commun (Camb) 2011 Jan 19;47(1):565-7. Epub 2010 Nov 19.

Departament d'Enginyeria Electrònica, Universitat Rovira i Virgili, Països Catalans 26, 43007 Tarragona, Spain.

A new method of synthesising nanoparticle-functionalised nanostructured materials via Aerosol Assisted Chemical Vapour Deposition (AACVD) has been developed. Co-deposition of Au nanoparticles with WO(3) nanoneedles has been used to deposit a sensing layer directly onto gas sensor substrates providing devices with a six-fold increase in response to low concentrations of a test analyte (ethanol).
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http://dx.doi.org/10.1039/c0cc02398aDOI Listing
January 2011

Micropatterning of light-sensitive liquid-crystal elastomers.

Phys Rev E Stat Nonlin Soft Matter Phys 2009 Nov 24;80(5 Pt 1):050701. Epub 2009 Nov 24.

J. Stefan Institute, Jamova 39, SI 1001 Ljubljana, Slovenia.

We demonstrate that photoisomerizable liquid-crystal elastomer soft films can be used as tunable holographic gratings. Optomechanical mechanism of imprinting one-dimensional grating structure into the soft matrix by two-beam uv laser interference can be clearly resolved from the time dependence of the reading beam diffraction patterns. We analyze the observed response in terms of cis-trans isomerization-controlled modulation of the grating profile. The grating period can be tuned reversibly by stretching or contraction of the specimen, either thermomechanically or by applying external stress. Temperature-induced modifications of the grating parameters in the vicinity of the nematic-paranematic phase transition are also examined.
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http://dx.doi.org/10.1103/PhysRevE.80.050701DOI Listing
November 2009

The influence of the reaction temperature on the morphology of sodium titanate 1D nanostructures and their thermal stability.

J Nanosci Nanotechnol 2007 Oct;7(10):3502-8

Institute Jo2ef Stefan, Jamova 39, SI-1000 Ljubljana, Slovenia.

We have synthesized large quantities of sodium-titanate-based nanotubes and nanoribbons with high yields under hydrothermal conditions from anatase powder in an aqueous NaOH solution. The reaction temperatures were from 95 to 195 degrees C, in steps of 20 degrees C. We observed that the morphology of the nanomaterials, which is reflected in their specific surface areas, depends strongly on the reaction temperature. For the materials synthesized in the range 95-135 degrees C and above 155 degrees C only a single morphology type was observed for the nanostructures, i.e., nanotubes and nanoribbons, respectively. In contrast, when the reaction was carried out at 155 degreesC, both nanotubes and nanoribbons were found in the product. SEM, TEM, and XRD techniques were used to determine the materials' morphological and structural properties, and the thermal stability of the materials was investigated with TGA and DSC. The largest weight loss, of approximately 25%, was observed in a temperature range from 25 up to 600 degrees C for the product obtained at 95 degrees C, probably due to the presence of unrolled titanate sheets.
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http://dx.doi.org/10.1166/jnn.2007.838DOI Listing
October 2007

Synthesis and characterization of Mo6S4.5I4.5 nanowires.

J Nanosci Nanotechnol 2007 Mar;7(3):982-5

Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, 1000 Ljubljana, Slovenia.

We report on the synthesis and characterization of new a nano-wire-like material with chemical formula Mo6S4.5I4.5. The material can be synthesized in a single step reaction from elements in bulk quantities. The material has a fur-like appearance and is composed of nanowires that are weakly bound in bundles. Bundles itself can be dispersed using an ultrasonic bath in various organic solvents and water. Elemental analysis, X-ray diffraction, thermal analysis (TG, DTA), and electron microscopy were used to characterize the new material in the shape of nanowires. Due to their monodisperse and metallic nature, molybdenum-sulphur-iodine nanowires are an interesting alternative to carbon nanotubes for some applications.
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http://dx.doi.org/10.1166/jnn.2007.213DOI Listing
March 2007