National Institute Of Materials Physics - Romania

The current increasing interest in portable biosensing platforms led to their development on flexible porous substrates, such as filter paper. As these devices rely on fluid transport under capillary action, without the use of an external force, studies of the diffusion process can provide useful data for optimizing their working capabilities. We present here the results obtained by experimentally studying the radial diffusion of various fluids. The diffusion in filter paper has been recorded for six fluids with different viscosity. For each of them, the displacement of the fluid front has been measured along eight radial directions and then we investigated the possibility of describing this diffusion process using Gillespie's model.

The present work describes the electrochemical properties of ionophores immobilized at the surface of electrodes obtained from electrospun polymeric fibers, in order to develop sensors for the analysis of electrolytes. Poly(methyl methacrylate) submicrometer fibers were prepared by electrospinning, coated with a gold layer by magnetron sputtering and then transferred on polyethylene terephthalate (PET) in order to obtained flexible electrodes. The ionophores were immobilized at the surface of these electrodes by drop-casting a ionophore-Nafion mixed solution. The sensor surface was investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy in order to understand the morphology and distribution of a model Ca2+ ionophore over the electrode surface. Also, Fourier-transformed infrared spectroscopy was performed and demonstrated that the model Ca2+ ionophore can be immobilized in the nafion matrix maintaining its conformation, while cyclic voltammetry and electrochemical impedance spectroscopy demonstrated that the Ca2+ ionophore allows the diffusion of target ions through this this type of membrane. In order to prove the concept of ionophore-based sensors for the analysis of some electrolytes, Ca2+, NH4+, Cl- and H+ ionophore immobilized in a nafion matrix at the surface of these flexible electrodes were tested and the determination of the target ions performed by potentiometry in different media including artificial sweat. Finally, sensitivities, limits of detection, selectivity coefficients were determined. (C) 2020 Elsevier Ltd. All rights reserved.

The ubiquitin-proteasome system regulates the level of proteins within cells through controlled proteolysis. In some diseases, the system function is dysregulated turning the ubiquitin-proteasome complex into a target for drug development. The redox behavior of proteasome inhibitors, epoxyketone and boronated peptides carfilzomib, oprozomib and delanzomib was investigated by voltammetric methods using glassy carbon and boron doped diamond electrodes. It was showed that the oxidation of epoxyketone peptides carfilzomib and oprozomib occurred in one step at glassy carbon electrode surface while at boron doped diamond two consecutive charge transfer reactions due to different adsorption orientation at the electrode surface were observed. The moieties of these peptides, involved in the oxidation process, were morpholine for carfilzomib and thiazole for oprozomib. For the boronated peptide delanzomib, two irreversible and independent redox processes, oxidation at +0.80 V and reduction at -1.40 V were identified in neutral media at both electrodes. The oxidation reaction occurred at the amino group close to the pyridine moiety of delanzomib with the transfer of one electron and one proton whereas the reduction process takes place at pyridine ring in a two-electrons two-protons mechanism. Redox mechanisms were proposed and the implications on the proteasome inhibition discussed.

Biopolymers provide versatile platforms for designing naturally-derived wound care dressings through eco-friendly pathways. Eggshell membrane (ESM), a widely available, biocompatible biopolymer based structure features a unique 3D porous interwoven fibrous protein network. The ESM was functionalized with inorganic compounds (Ag, ZnO, CuO used either separately or combined) using a straightforward deposition technique namely radio frequency magnetron sputtering. The functionalized ESMs were characterized from morphological, structural, compositional, surface chemistry, optical, cytotoxicity and antibacterial point of view. It was emphasized that functionalization with a combination of metal oxides and exposure to visible light results in a highly efficient antibacterial activity against Escherichia coli when compared to the activity of individual metal oxide components. It is assumed that this is possible due to the fact that an axial p-n junction is created by joining the two metal oxides. This structure separates into components the charge carrier pairs promoted by visible light irradiation that further can influence the generation of reactive oxygen species which ultimately are responsible for the bactericide effect. This study proves that, by employing inexpensive and environmentally friendly materials (ESM and metal oxides) and fabrication techniques (radio frequency magnetron sputtering), affordable antibacterial materials can be developed for potential applications in chronic wound healing device area.

Nanocomposite thin films, sensitive to methane at the room temperature (25-30 degrees C), have been prepared, starting from SnSe2 powder and Zn(II)-5,10,15,20-tetrakis-(4-aminophenyl)- -porphyrin (ZnTAPP) powder, that were fully characterized by XRD, UV-VIS, FT-IR, Nuclear Magnetic Resonance (H-1-NMR and C-13-NMR), Atomic Force Microscopy (AFM), SEM and Electron Paramagnetic Resonance (EPR) techniques. Film deposition was made by drop casting from a suitable solvent for the two starting materials, after mixing them in an ultrasonic bath. The thickness of these films were estimated from SEM images, and found to be around 1.3 mu m. These thin films proved to be sensitive to a threshold methane (CH4) concentration as low as 1000 ppm, at a room temperature of about 25 degrees C, without the need for heating the sensing element. The nanocomposite material has a prompt and reproducible response to methane in the case of air, with 50% relative humidity (RH) as well. A comparison of the methane sensing performances of our new nanocomposite film with that of other recently reported methane sensitive materials is provided. It is suitable for signaling gas presence before reaching the critical lower explosion limit concentration of methane at 50,000 ppm.

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures' electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.

The matrix-assisted pulsed laser evaporation (MAPLE) technique was used for depositing thin films based on a recently developed conjugated polymer, poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (DPP-DTT) and fullerene C60 blends. The targets used in the MAPLE process were obtained by freezing chloroform solutions with different DPP-DTT:C60 weight ratios, with the MAPLE deposition being carried at a low laser fluence, varying the number of laser pulses. The structural, morphological, optical, and electrical properties of the DPP-DTT:C60 blend layers deposited by MAPLE were investigated in order to emphasize the influence of the DPP-DTT:C60 weight ratio and the number of laser pulses on these features. The preservation of the chemical structure of both DPP-DTT and C60 during the MAPLE deposition process is confirmed by the presence of their vibrational fingerprints in the FTIR spectra of the organic thin films. The UV-VIS and photoluminescence spectra of the obtained organic layers reveal the absorption bands attributed to DPP-DTT and the emission bands associated with C60, respectively. The morphology of the DPP-DTT:C60 blend films consists of aggregates and fibril-like structures. Regardless the DPP-DTT:C60 weight ratio and the number of laser pulses used during the MAPLE process, the current-voltage characteristics recorded, under illumination, of all structures developed on the MAPLE deposited layers evidenced a photovoltaic cell behavior. The results proved that the MAPLE emerges as a viable technique for depositing thin films based on conjugated polymers featured by a complex structure that can be further used to develop devices for applications in the solar cell area.

Chitosan-hydroxyapatite composite layers were deposited on Si substrates in radio frequency magnetron sputtering discharges. The plasma parameters calculated from the current-voltage radio frequency-compensated Langmuir probe characteristics indicate a huge difference between the electron temperature in the plasma and at the sample holder. These findings aid in the understanding of the coagulation pattern of hydroxyapatite-chitosan macromolecules on the substrate surface. An increase in the sizes of the spherical-shape grain-like structures formed on the coating surface with the plasma electron number density was observed. The link between the chemical composition of the chitosan-hydroxyapatite composite film and the species sputtered from the target or produced by excitation/ionization mechanisms in the plasma was determined on the basis of X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and residual gas mass spectrometry analysis.

This work presents a new synthesis and characterization of Kesterite Cu2ZnSnS4 films by one step electrodeposition with free sulfurization annealing treatment at different applied potentials. This study highlights the effect of applied potential and annealing treatment on the properties of CZTS deposited films. X-ray Diffraction and Raman spectroscopy were employed to assess the structure and composition of the films elaborated at -1V, -1.1V, and -1.2V vs Saturated Calomel Electrode (SCE). The morphological and optical properties were studied using Scanning Electron microscopy and photoluminescence spectroscopy (PL), respectively. The structural properties are improved by annealing treatment, while -1.1V vs SCE was found to be the optimum applied potential to prepare the Kesterite CZTS thin film with a bandgap around 1.5 eV. (C) 2020 Elsevier B.V. All rights reserved.

Sn nanoparticles (NPs) are usually obtained by difficult chemical routes in several steps followed by thermal treatments. Here, a simple and clean method, to obtain Sn NPs directly on the substrate, is developed based on a vapor transport technique. The method is versatile, thus can be easily adjusted to obtain Sn NPs of different size, areal density and morphology, by controlling the deposition conditions. NPs are grown on Si/SiO2 substrate and characterized. Water contact angle measurements show that Sn nanoparticles increase the surface hydrophobicity by 20%. Thus, NPs cleanly obtained from a low-cost, earth-abundant, and environmentally friendly material, can be used to modulate the wettability of surfaces. (C) 2020 Elsevier B.V. All rights reserved.