Visible range plasmonic effect produced by aluminium nanoparticles embedded in amorphous silicon

We present results, obtained by means of an analytic study and a numerical simulation, about the resonant condition necessary to produce a Localized Surface Plasmonic Resonance (LSPR) effect at the surface of metal nanospheres embedded in an amorphous silicon matrix. The study is based on a Lorentz dispersive model for a-Si:H permittivity and a Drude model for the metals. Considering the absorption spectra of a-Si:H, the best choice for the metal nanoparticles appears to be aluminium, indium or magnesium. No difference has been observed when considering a-SiC:H. Finite-difference time-domain (FDTD) simulation of an Al nanosphere embedded into an amorphous silicon matrix shows an increased scattering radius and the presence of LSPR induced by the metal/semiconductor interaction under green light (560 nm) illumination. Further results include the effect of the nanoparticles shape (nano-ellipsoids) in controlling the wavelength suitable to produce LSPR. It has been shown that is possible to produce LSPR in the red part of the visible spectrum (the most critical for a-Si:H solar cells applications in terms of light absorption enhancement) with aluminium nano-ellipsoids. As an additional results we may conclude that the double Lorentz-Lorenz model for the optical functions of a-Si:H is numerically stable in 3D simulations and can be used safely in the FDTD algorithm. A further simulation study is directed to determine an optimal spatial distribution of Al nanoparticles, with variable shapes, capable to enhance light absorption in the red part of the visible spectrum, exploiting light trapping and plasmonic effects. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dual-phase inkjet printed electrochromic layers based on PTA and WOX/TiO2 nanoparticles for electrochromic applications

Thesis submitted in Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa for the degree of Master in Materials Engineering

Magnetic nanoparticles for biocatalysis and bioseparation

Dissertação para obtenção do Grau de Mestre em Biotecnologia

Fabrication and characterization of transparent conductive oxide surface sensors for electrocorticography – TrECoG

Understanding how the brain works has been one of the greatest goals of mankind. This desire fuels the scientific community to pursue novel techniques able to acquire the complex information produced by the brain at any given moment. The Electrocorticography (ECoG) is one of those techniques. By placing conductive electrodes over the dura, or directly over the cortex, and measuring the electric potential variation, one can acquire information regarding the activation of those areas. In this work, transparent ECoGs, (TrECoGs) are fabricated through thin film deposition of the Transparent Conductive Oxides (TCOs) Indium-Zinc-Oxide (IZO) and Gallium-Zinc-Oxide (GZO). Five distinct devices have been fabricated via shadow masking and photolithography. The data acquired and presented in this work validates the TrECoGs fabricated as efficient devices for recording brain activity. The best results were obtained for the GZO- based TrECoG, which presented an average impedance of 36 kΩ at 1 kHz for 500 μm diameter electrodes, a transmittance close to 90% for the visible spectrum and a clear capability to detect brain signal variations. The IZO based devices also presented high transmittance levels (90%), but with higher impedances, which ranged from 40 kΩ to 100 kΩ.

Al-doped ZnO ceramic sputtering targets based on nanocrystalline powders produced by emulsion detonation synthesis – deposition and application as a transparent conductive oxide material

Transparent conducting oxides (TCOs) have been largely used in the optoelectronic industry due to their singular combination of low electrical resistivity and high optical transmittance. They are usually deposited by magnetron sputtering systems being applied in several devices, specifically thin film solar cells (TFSCs). Sputtering targets are crucial components of the sputtering process, with many of the sputtered films properties dependent on the targets characteristics. The present thesis focuses on the development of high quality conductive Al-doped ZnO (AZO) ceramic sputtering targets based on nanostructured powders produced by emulsion detonation synthesis method (EDSM), and their application as a TCO. In this sense, the influence of several processing parameters was investigated from the targets raw-materials synthesis to the application of sputtered films in optoelectronic devices. The optimized manufactured AZO targets present a final density above 99 % with controlled grain size, an homogeneous microstructure with a well dispersed ZnAl2O4 spinel phase, and electrical resistivities of ~4 × 10-4 Ωcm independently on the Al-doping level among 0.5 and 2.0 wt. % Al2O3. Sintering conditions proved to have a great influence on the properties of the targets and their performance as a sputtering target. It was demonstrated that both deposition process and final properties of the films are related with the targets characteristics, which in turn depends on the initial powder properties. In parallel, the influence of several deposition parameters in the film´s properties sputtered from these targets was investigated. The sputtered AZO TCOs showed electrical properties at room temperature that are superior to simple oxides and comparable to a reference TCO – indium tin oxide (ITO), namely low electrical resistivity of 5.45 × 10-4 Ωcm, high carrier mobility (29.4 cm2V-1s-1), and high charge carrier concentration (3.97 × 1020 cm-3), and also average transmittance in the visible region > 80 %. These superior properties allowed their successful application in different optoelectronic devices.

VO2 thin films and nanoparticles for energy-saving applications in architectural elements

Vanadium dioxide (VO2) is a promising material with large interest in construction industry and architecture, due to its thermochromic properties. This material may be used to create "smart" coatings that result in improvements in the buildings energy efficiency, by reducing heat exchanges and, consequently, the need for acclimatization. In this work, VO2 thin films and coatings were produced and tested in laboratory, to apply in architectural elements, such as glass, rooftop tiles and exterior paints. Thin films were produced by RF magnetron sputtering and VO2 nanoparticles were obtained through hydrothermal synthesis, aiming to create "smart" windows and tiles, respectively. These coatings have demonstrated the capability to modulate the transmittance of infrared radiation by around 20%. The VO2 nanoparticle coatings were successfully applied on ceramic tiles. The critical temperature was reduced to around 40ºC by tungsten doping. Ultimately, two identical house models were built, in order to test the VO2 coatings, in real atmospheric conditions during one of the hottest months of the year, in Portugal – August.

Effect of acid or alkaline catalyst and of different capping agents on the optical properties of CdS nanoparticles incorporated within a diureasil hybrid matrix

CdS nanoparticles (NPs) were synthesized using colloidal methods and incorporated within a diureasil hybrid matrix. The surface capping of the CdS NPs by 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltrimethoxysilane (APTMS) organic ligands during the incorporation of the NPs within the hybrid matrix has been investigated. The matrix is based on poly(ethylene oxide)/poly(propylene oxide) chains grafted to a siliceous skeleton through urea bonds and was produced by sol–gel process. Both alkaline and acidic catalysis of the sol–gel reaction were used to evaluate the effect of each organic ligand on the optical properties of the CdS NPs. The hybrid materials were characterized by absorption, steady-state and time-resolved photoluminescence spectroscopy and High Resolution Transmission Electron Microscopy (HR-TEM). The preservation of the optical properties of the CdS NPs within the diureasil hybrids was dependent on the experimental conditions used. Both organic ligands (APTMS and MPTMS) demonstrated to be crucial in avoiding the increase of size distribution and clustering of the NPs within the hybrid matrix. The use of organic ligands was also shown to influence the level of interaction between the hybrid host and the CdS NPs. The CdS NPs showed large Stokes shifts and long average lifetimes, both in colloidal solution and in the xerogels, due to the origin of the PL emission in surface states. The CdS NPs capped with MPTMS have lower PL lifetimes compared to the other xerogel samples but still larger than the CdS NPs in the original colloidal solution. An increase in PL lifetimes of the NPs after their incorporation within the hybrid matrix is related to interaction between the NPs and the hybrid host matrix.

Fingermark detection based on the in situ growth of luminescent nanoparticles: towards a new generation of multimetal deposition

The in situ deposition of zinc oxide on gold nanoparticles in aqueous solution has been here successfully applied in the field of fingermark detection on various non-porous surfaces. In this article, we present the improvement of the multimetal deposition, an existing technique limited up to now to non-luminescent results, by obtaining luminescent fingermarks with very good contrast and details. This is seen as a major improvement in the field in terms of selectivity and sensitivity of detection, especially on black surfaces.

Stress reaction of kidney epithelial cells to inorganic solid-core nanoparticles.

A route of accumulation and elimination of therapeutic engineered nanoparticles (NPs) may be the kidney. Therefore, the interactions of different solid-core inorganic NPs (titanium-, silica-, and iron oxide-based NPs) were studied in vitro with the MDCK and LLC-PK epithelial cells as representative cells of the renal epithelia. Following cell exposure to the NPs, observations include cytotoxicity for oleic acid-coated iron oxide NPs, the production of reactive oxygen species for titanium dioxide NPs, and cell depletion of thiols for uncoated iron oxide NPs, whereas for silica NPs an apparent rapid and short-lived increase of thiol levels in both cell lines was observed. Following cell exposure to metallic NPs, the expression of the tranferrin receptor/CD71 was decreased in both cells by iron oxide NPs, but only in MDCK cells by titanium dioxide NPs. The tight association, then subsequent release of NPs by MDCK and LLC-PK kidney epithelial cells, showed that following exposure to the NPs, only MDCK cells could release iron oxide NPs, whereas both cells released titanium dioxide NPs. No transfer of any solid-core NPs across the cell layers was observed.

Induction of oxidative stress, lysosome activation and autophagy by nanoparticles in human brain-derived endothelial cells.

Different types of NPs (nanoparticles) are currently under development for diagnostic and therapeutic applications in the biomedical field, yet our knowledge about their possible effects and fate in living cells is still limited. In the present study, we examined the cellular response of human brain-derived endothelial cells to NPs of different size and structure: uncoated and oleic acid-coated iron oxide NPs (8-9 nm core), fluorescent 25 and 50 nm silica NPs, TiO2 NPs (21 nm mean core diameter) and PLGA [poly(lactic-co-glycolic acid)]-PEO [poly(ethylene oxide)] polymeric NPs (150 nm). We evaluated their uptake by the cells, and their localization, generation of oxidative stress and DNA-damaging effects in exposed cells. We show that NPs are internalized by human brain-derived endothelial cells; however, the extent of their intracellular uptake is dependent on the characteristics of the NPs. After their uptake by human brain-derived endothelial cells NPs are transported into the lysosomes of these cells, where they enhance the activation of lysosomal proteases. In brain-derived endothelial cells, NPs induce the production of an oxidative stress after exposure to iron oxide and TiO2 NPs, which is correlated with an increase in DNA strand breaks and defensive mechanisms that ultimately induce an autophagy process in the cells.

Differentiated chemical reactivity of nanoparticles toward DTT

RATIONALE: Induction of oxidative stress and impairment of the antioxidant defense are considered important biological responses following nanoparticle (NP) exposure. The acellular in vitro dithiothreitol (DTT) assay is proposed to measure the oxidative potential of NP. In addition, DTT can be considered as a model compound of sulfur containing antioxidants. The objective of this work is to evaluate the surface reactivity in solution of a NP panel toward DTT. METHOD: The NP panel was composed of four carbonaceous particles, six types of metal oxides and silver with primary size ranged from 7 to 300 nm. Suspensions were prepared in surfactant solution with 30 min sonication. DTT was used as reductant to evaluate the oxidative properties of the different NP. The determination of the NP ability to catalyze electron transfer from DTT to oxygen was carried out as described in Sauvain et al., Nanotoxicology, 2008, 2:3, 121−129. RESULTS: All the carbonaceous NP catalyzed the oxidation of DTT by oxygen following the mass based order: carbon black > diesel exhaust particle > nanotubes > fullerene. A contrasting reactivity was observed for the metallic NP. Except for nickel oxide and metallic silver, which reacted similarly to the carbonaceous NP, all other metal oxides hindered the oxidation of DTT by oxygen, with ZnO being the most effective one. CONCLUSIONS : DTT was stabilized against oxidation in the presence of metal oxide NP in the solution. This suggests that different chemical interactions take place compared with carbonaceous NP. To explain these differences, we hypothesize that DTT could form complexes with the metal oxide surface (or dissolved metal ions), rendering it less susceptible to oxidation. By analogy, such a process could be thought to apply in biological systems with sulfur−containing antioxidants, reducing their buffer capacity. Such NP could thus contribute to oxidative stress by an alternative mechanism.

Si3N4 single-crystal nanowires grown from silicon micro- and nanoparticles near the threshold of passive oxidation

A simple and most promising oxide-assisted catalyst-free method is used to prepare silicon nitride nanowires that give rise to high yield in a short time. After a brief analysis of the state of the art, we reveal the crucial role played by the oxygen partial pressure: when oxygen partial pressure is slightly below the threshold of passive oxidation, a high yield inhibiting the formation of any silica layer covering the nanowires occurs and thanks to the synthesis temperature one can control nanowire dimensions

Mechanisms of interaction of therapeutic nanoparticles with cells

Nanoparticles (NPs) have gained a lot of interest in recent years due to their huge potential for applications in industry and medicine. Their unique properties offer a large number of attractive possibilities in the biomedical field, providing innovative tools for diagnosis of diseases and for novel therapies. Nevertheless, a deep understanding of their interactions with living tissues and the knowledge about their possible effects in the human body are necessary for the safe use of nanoparticulate formulations. The aim of this PhD project was to study in detail the interactions of therapeutic NPs with living cells, including cellular uptake and release, cellular localization and transport across the cell layers. Moreover, the effects of NPs on the cellular metabolic processes were determined using adapted in vitro assays. We evaluated the biological effect of several NPs potentially used in the biomedical field, including titanium dioxide (Ti02) NPs, 2-sized fluorescent silica NPs, ultrasmall superparamagnetic iron oxide (USPIO) NPs, either uncoated or coated with oleic acid or with polyvinylamine (aminoPVA) and poly(lactic-co-glycolic acid) - polyethylene-oxide (PLGA-PEO) NPs. We have found that the NPs were internalized by the cells, depending on their size, chemical composition, surface coating and also depending on the cell line considered. The uptake of aminoPVA-coated USPIO NPs by endothelial cells was enhanced in the presence of an external magnetic field. None of the tested USPIO NPs and silica NPs was transported across confluent kidney cell layers or brain endothelial cell layers, even in the presence of a magnetic field. However, in an original endothelium-glioblastoma barrier model which was developed, uncoated USPIO NPs were directly transferred from endothelial cells to glioblastoma cells. Following uptake, Ti02 NPs and uncoated USPIO NPs were released by the kidney cells, but not by the endothelial cells. Furthermore, these NPs induced an oxidative stress and autophagy in brain endothelial cells, possibly associated with their enhanced agglomeration in cell medium. A significant DNA damage was found in brain endothelial cells after their exposure to TiO2NPs. Altogether these results extend the existing knowledge about the effects of NPs on living cells with regard to their physicochemical characteristics and provide interesting tools for further investigation. The development of the in vitro toxicological assays with a special consideration for risk evaluation aims to reduce the use of animal experiments. -Les nanoparticules (NPs) présentent beaucoup d'intérêt dans le domaine biomédical et industriel. Leurs propriétés uniques offrent un grand nombre de possibilités de solutions innovantes pour le diagnostique et la thérapie. Cependant, pour un usage sûr des NPs il est nécessaire d'acquérir une connaissance approfondie des mécanismes d'interactions des NPs avec les tissus vivants et de leur effets sur le corps humain. Le but de ce projet de thèse était d'étudier en détail les mécanismes d'interactions de NPs thérapeutiques avec des cellules vivantes, en particulier les mécanismes d'internalisation cellulaire et leur subséquente sécrétion par les cellules, leur localisation cellulaire, leur transport à travers des couches cellulaires, et l'évaluation des effets de NPs sur le métabolisme cellulaire, en adaptant les méthodes existante d'évaluation cyto-toxico logique s in vitro. Pour ces expériences, les effets biologiques de nanoparticules d'intérêt thérapeutique, telles que des NPs d'oxyde de titane (TiO2), des NPs fluorescents de silicate de 2 tailles différentes, des NPs, d'oxyde de fer super-para-magnétiques ultra-petites (USPIO), soit non- enrobées soit enrobées d'acide oléique ou de polyvinylamine (aminoPVA), et des NPs d'acide poly(lactique-co-glycolique)-polyethylene-oxide (PLGA-PEO) ont été évalués. Les résultats ont démontré que les NPs sont internalisées par les cellules en fonction de leur taille, composition chimique, enrobage de surface, et également du type de cellules utilisées. L'internalisation cellulaire des USPIO NPs a été augmentée en présence d'un aimant externe. Aucune des NPs de fer et de silicate n'a été transportée à travers des couches de cellules épithéliales du rein ou endothéliales du cerveau, même en présence d'un aimant. Cependant, en développant un modèle original de barrière endothélium-glioblastome, un transfert direct de NPs d'oxyde de fer de cellule endothéliale à cellule de glioblastome a été démontré. A la suite de leur internalisation les NPs d'oxyde de fer et de titane sont relâchées par des cellules épithéliales du rein, mais pas des cellules endothéliales du cerveau. Dans les cellules endothéliales du cerveau ces NPs induisent en fonction de leur état d'agglomération un stress oxydatif et des mécanismes d'autophagie, ainsi que des dommages à l'ADN des cellules exposées aux NPs d'oxyde de titane. En conclusion, les résultats obtenus élargissent les connaissances sur les effets exercés par des NPs sur des cellules vivantes et ont permis de développer les outils expérimentaux pour étudier ces effets in vitro, réduisant ainsi le recours à des expériences sur animaux.

Suitability of human and mammalian cells of different origin for the assessment of genotoxicity of metal and polymeric engineered nanoparticles.

Nanogenotoxicity is a crucial endpoint in safety testing of nanomaterials as it addresses potential mutagenicity, which has implications for risks of both genetic disease and carcinogenesis. Within the NanoTEST project, we investigated the genotoxic potential of well-characterised nanoparticles (NPs): titanium dioxide (TiO2) NPs of nominal size 20 nm, iron oxide (8 nm) both uncoated (U-Fe3O4) and oleic acid coated (OC-Fe3O4), rhodamine-labelled amorphous silica 25 (Fl-25 SiO2) and 50 nm (Fl-50 SiO) and polylactic glycolic acid polyethylene oxide polymeric NPs - as well as Endorem® as a negative control for detection of strand breaks and oxidised DNA lesions with the alkaline comet assay. Using primary cells and cell lines derived from blood (human lymphocytes and lymphoblastoid TK6 cells), vascular/central nervous system (human endothelial human cerebral endothelial cells), liver (rat hepatocytes and Kupffer cells), kidney (monkey Cos-1 and human HEK293 cells), lung (human bronchial 16HBE14o cells) and placenta (human BeWo b30), we were interested in which in vitro cell model is sufficient to detect positive (genotoxic) and negative (non-genotoxic) responses. All in vitro studies were harmonized, i.e. NPs from the same batch, and identical dispersion protocols (for TiO2 NPs, two dispersions were used), exposure time, concentration range, culture conditions and time-courses were used. The results from the statistical evaluation show that OC-Fe3O4 and TiO2 NPs are genotoxic in the experimental conditions used. When all NPs were included in the analysis, no differences were seen among cell lines - demonstrating the usefulness of the assay in all cells to identify genotoxic and non-genotoxic NPs. The TK6 cells, human lymphocytes, BeWo b30 and kidney cells seem to be the most reliable for detecting a dose-response.

pH effect on the synthesis of magnetite nanoparticles by the chemical reduction-precipitation method

This work aimed at putting in evidence the influence of the pH on the chemical nature and properties of the synthesized magnetic nanocomposites. Saturation magnetization measurements evidenced a marked difference of the magnetic behavior of samples, depending on the final pH of the solution after reaction. Magnetite and maghemite in different proportions were the main magnetic iron oxides actually identified. Synthesis with final pH between 9.7-10.6 produced nearly pure magnetite with little or no other associated iron oxide. Under other synthetic conditions, goethite also appears in proportions that depended upon the pH of the synthesis medium.