National Institute Of Materials Physics - Romania

A novel and disposable biosensor based on superoxide dismutase (SOD) immobilized on gold metallized polycaprolactone electrospun polymeric fibers (PCl/Au) has been developed for the determination of superoxide (O-2(center dot-)) in cell culture media. SOD biosensors were constructed employing three immobilization methods: crosslinking with EDC/NHS at a cysteine self-assembled monolayer (PCl/Au/SODCYS), biopolymer encapsulation with chitosan (PCl/Au/SODCHI) and cross-linking with glutaraldehyde (PCl/Au/SODGA). Scanning electron microscopy was performed at the three different biosensors to evaluate their surface morphologies. Biosensors were employed for the electrochemical detection of superoxide by fixed potential amperometry at different applied potentials, with two distinct enzymatic mechanisms being proposed: i) the reduction of the enzymatically generated peroxide, at -0.3 V, for which the PCl/Au/SODCHI biosensor presented the highest value of sensitivity of 40.1 mu A mM(-1) cm(-2), and ii) the regeneration of the enzyme catalytic copper centre, at +0.3 V, for which the PCl/Au/SODCYS biosensor had the highest sensitivity value of 16.1 mu A mM(-1) cm(-2). The proposed recognition mechanisms were further confirmed by cyclic voltammetric measurements, which enabled also to determine the amount of immobilized electroactive SOD, with highest value corresponding to the PCl/Au/SODCYS biosensor. The biosensors with best analytical performance, PCl/Au/SODCYS and PCl/Au/SODCHI, were further investigated for stability and selectivity, with best results for the PCl/Au/SODCYS, chosen for superoxide monitoring in cell culture media. The study is promising for future application of PCl/Au/SODCYS for the on-line superoxide monitoring of superoxide in cell cultures, grown directly on the biosensor itself.

This paper reports the synthesis and characterization of Cu2ZnSnS4 (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 degrees C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

Dextran coated cerium doped hydroxyapatite (Ca(10-x)Cex(PO4)(6)(OH)(2)), with x = 0.05 (5CeHAp-D) and x = 0.1 (10CeHAp-D) were deposited on Si substrates by radio frequency magnetron sputtering technique for the first time. The morphology, composition, and structure of the resulting coatings were examined by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), atomic force microscopy (AFM), metallographic microscopy (MM), Fourier transform infrared spectroscopy (FTIR), and glow discharge optical emission spectroscopy (GDOES), respectively. The obtained information on the surface morphologies, composition and structure was discussed. The surface morphologies of the CeHAp-D composite thin films are smooth with no granular structures. The constituent elements of the CeHAp-D target were identified. The results of the FTIR measurements highlighted the presence of peaks related to the presence of nu(1), nu(3), and nu(4) vibration modes of (PO43-) groups from the hydroxyapatite (HAp) structure, together with those specific to the dextran structure. The biocompatibility assessment of 5CeHAp-D and 10CeHAp-D composite coatings was also discussed. The human cells maintained their specific elongated morphology after 24 h of incubation, which confirmed that the behavior of gingival fibroblasts and their proliferative capacity were not disturbed in the presence of 5CeHAp-D and 10CeHAp-D composite coatings. The 5CeHAp-D and 10CeHAp-D coatings' surfaces were harmless to the human gingival fibroblasts, proving good biocompatibility.

In recent years, iron oxides-based nanostructured composite materials are of particular interest for the preparation of multifunctional thin films and membranes to be used in sustainable magnetic field adsorption and photocatalysis processes, intelligent coatings, and packing or bio-medical applications. In this paper, superparamagnetic iron oxide (core)-silica (shell) nanoparticles suitable for thin films and membrane functionalization were obtained by co-precipitation and ultrasonic-assisted sol-gel methods. The comparative/combined effect of the magnetic core co-precipitation temperature (80 and 95 degrees C) and ZnO-doping of the silica shell on the photocatalytic and nano-sorption properties of the resulted composite nanoparticles were investigated by ultraviolet-visible (UV-VIS) spectroscopy monitoring the discoloration of methylene blue (MB) solution under ultraviolet (UV) irradiation and darkness, respectively. The morphology, structure, textural, and magnetic parameters of the investigated powders were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) measurements, and saturation magnetization (vibrating sample magnetometry, VSM). The intraparticle diffusion model controlled the MB adsorption. The pseudo- and second-order kinetics described the MB photodegradation. When using SiO2-shell functionalized nanoparticles, the adsorption and photodegradation constant rates are three-four times higher than for using starting core iron oxide nanoparticles. The obtained magnetic nanoparticles (MNPs) were tested for films deposition.

For high-field power applications of high-temperature superconductors, it became obvious in recent years that nano-engineered artificial pinning centers are needed for increasing the critical current and pinning potential. As opposed to the artificial pinning centers obtained by irradiation with various particles, which is a quite expensive approach, we have studied superconducting samples having self-assembled defects, created during the sample fabrication, that act as effective pinning centers. We introduced a simple, straight-forward method of estimating the frequency-dependent critical current density by using frequency-dependent AC susceptibility measurements, in fixed temperatures and DC magnetic fields, from the positions of the maxima in the dependence of the out-of-phase susceptibility on the amplitude of AC excitation magnetic field. The results are compatible with a model that stipulates a logarithmic dependence of the pinning potential on the probing current. A mathematical derivation allowed us to estimate from the experimental data the pinning potentials in various samples, and in various DC magnetic fields. The resulted values indicate large pinning potentials, leading to very small probability of magnetic flux escaping the pinning wells, hence, leading to very high critical currents in high magnetic fields.

In the present work, the effectiveness of vacuum deposition technique for obtaining composite thin films based on chitosan-coated magnesium-doped hydroxyapatite Ca10-xMgx(PO4)(6) (OH)(2) with x(Mg) = 0.025 (MgHApCh) was proved for the first time. The prepared samples were exposed to three doses (0, 3, and 6 Gy) of gamma irradiation. The MgHApCh composite thin films nonirradiated and irradiated were evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) studies. The biological evaluation of the samples was also presented. All the results obtained from this study showed that the vacuum deposition method allowed for obtaining uniform and homogeneous layers. Fine cracks were observed on the MgHApCh composite thin films' surface after exposure to a 6 Gy irradiation dose. Additionally, after gamma irradiation, a decrease in Ca, P, and Mg content was noticed. The MgHApCh composite thin films with doses of 0 and 3 Gy of gamma irradiation showed a cellular viability similar to that of the control. Samples with 6 Gy doses of gamma irradiation did not cause significantly higher fibroblast cell death than the control (p > 0.05). On the other hand, the homogeneous distribution of pores that appeared on the surface of coatings after 6 Gy doses of gamma irradiation did not prevent the adhesion of fibroblast cells and their spread on the coatings. In conclusion, we could say that the thin films could be suitable both for use in bone implants and for other orthopedic and dentistry applications.

Iron-oxide-doped polyaniline (PANI-IO) thin films were obtained by the polymerization of aniline monomers and iron oxide solutions in direct current glow discharge plasma in the absence of a buffer gas for the first time. The PANI-IO thin films were deposited on optical polished Si wafers in order to study surface morphology and evaluate their in vitro biocompatibility. The characterization of the coatings was accomplished using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), metallographic microscopy (MM), and X-ray photoelectron spectroscopy (XPS). In vitro biocompatibility assessments were also conducted on the PANI-IO thin films. It was observed that a uniform distribution of iron oxide particles inside the PANI layers was obtained. The constituent elements of the coatings were uniformly distributed. The Fe-O bonds were associated with magnetite in the XPS studies. The surface morphology of the PANI-IO thin films was assessed by atomic force microscopy (AFM). The AFM topographies revealed that PANI-IO exhibited the morphology of a uniformly distributed and continuous layer. The viability of Caco-2 cells cultured on the Si substrate and PANI-IO coating was not significantly modified compared to control cells. Moreover, after 24 h of incubation, we observed no increase in LDH activity in media in comparison to the control. In addition, our results revealed that the NO levels for the Si substrate and PANI-IO coating were similar to those found in the control sample.

An original photodetector system based on self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO-ZnO core-shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO-ZnO core-shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p-n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron-hole pairs at the CuO-ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO-ZnO core-shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.

The concentration of thyroxine hormone is linked to a large variety of medical conditions, where the best therapy is hormone substitution, through administration of levothyroxine (LT4) medication. Herewith, the detection of these biomolecules still lacks a simple, reliable tool, such as label-free sensors.In this work, the performances of commercial screen-printed carbon electrodes, containing different nanostructured materials (carbon nanotubes, graphene, and gold nanoparticles), used as sensors for LT4 detection, were described and compared. Electrochemical methods were used for the characterization of the nanostructure-based sensors. Several optimization steps were undertaken to achieve optimum performances for selective LT4 quantification. The redox behaviour of LT4 at sensors surface together with the interfacial changes, which occur due to the interaction between nanostructures and LT4, were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Differential pulse voltammetry (DPV) was used for LT4 detection, where best performances were obtained in the presence of carbon nanotubes, with a detection limit of 30 nM.

Single-doped [Ag, Na, iodine, naphthalene (Naph), meta-dintrobenzene (m-DNB)] and double-doped, organic-inorganic (Naph + iodine; m-DNB + iodine) benzil (Bz) crystals have been grown from melt in a Bridgman-Stockbarger configuration. All crystals have been grown in the same experimental conditions, temperature variation at the growth interface = 30 K and moving speed of the growth ampoule = 1 mm/h. These conditions have been estimated from the theoretical analysis involving the solution of the classical (conventional) Stefan problem for flat solid-liquid interface in the boundary conditions imposed by our growth system. The effect of doping on the disorder degree, photoluminescence and dielectric constant of the Bz matrix has been investigated. The disorder in the crystals increased with the increase of dopant concentration. The highest disorder was induced by the organic dopant m-DNB, whose molecules does not show an adequate geometrical similarity with Bz molecules. The position of the photoluminescence peak, both at excitation with 335 nm and 435 nm, has not been affected by the presence of dopant(s). All doped samples show Second Harmonic Generation, even those with a significant degree of disorder. The effect of the single and double-doping on the second-order ONL co-efficient was analyzed by comparison with the second-order ONL coefficient of pure Bz crystals. In the case of the double-doping, the highest second-order optical nonlinear coefficient has been evidenced in the Bz crystals simultaneously doped with m-DNB and iodine in the same concentration (1%).