National Institute Of Materials Physics - Romania

The work describes the development of a flexible, hydrogel embedded pH-sensor that can be integrated in inexpensive wearable and non-invasive devices at epidermal level for electrochemical quantification of H+ ions in sweat. Such a device can be useful for swift, real time diagnosis and for monitoring specific conditions. The sensors' working electrodes are flexible poly(methyl methacrylate) electrospun fibers coated with a thin gold layer and electrochemically functionalized with nanostructured palladium/palladium oxide. The response to H+ ions is investigated by cyclic voltammetry and electrochemical impedance spectroscopy while open circuit potential measurements show a sensitivity of aprox. -59 mV per pH unit. The modification of the sensing interface upon basic and acid treatment is characterized by scanning and transmission electron microscopy and the chemical composition by X-ray photoelectron spectroscopy. In order to demonstrate the functionality of the pH-sensor at epidermal level, as a wearable device, the palladium/palladium oxide working electrode and silver/silver chloride reference electrode are embedded within a pad of polyacrylamide hydrogel and measurements in artificial sweat over a broad pH range were performed. Sensitivity up to -28 mV/pH unit, response time below 30 s, temperature dependence of approx. 1 mV/degrees C as well as the minimum volume to which the sensor responses of 250 nanoliters were obtained for this device. The proposed configuration represents a viable alternative making use of low-cost and fast fabrication processes and materials.

The present work describes a new simple procedure for the direct immobilization of biomolecules on Ni electrodes using magnetic Ni nanoparticles (NiNPs) as biomolecule carriers. Ni electrodes were fabricated by electroplating, and NiNPs were chemically synthesized. The chemical composition, crystallinity, and granular size of Ni electrodes, NiNP, and NiNP-modified Ni electrodes (NiNP/Ni) were determined by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization of Ni electrodes by cyclic voltammetry and electrochemical impedance spectroscopy confirmed the existence of nickel oxides, hydroxides, and oxohydroxide films at the surface of Ni. Magnetic characterization and micromagnetic simulations were performed in order to prove that the magnetic force is responsible for the immobilization process. Further, Ni electrodes were employed as amperometric sensors for the detection of hydrogen peroxide because it is an important performance indicator for a material to be applied in biosensing. The working principle for magnetic immobilization of the enzyme-functionalized NiNP, without the use of external magnetic sources, was demonstrated for glucose oxidase (GOx) as a model enzyme. XPS results enabled to identify the presence of GOx attached to the NiNP (GOx-NiNP) on Ni electrodes. Finally, glucose detection and quantification were evaluated with the newly developed GOx-NiNP/Ni biosensor by amperometry at different potentials, and control experiments at different electrode materials in the presence and absence of NiNP demonstrated their importance in the biosensor architecture.

This study aimed at developing an antimicrobial material based on hydroxyapatite (HAp) and peppermint essential oil (P-EO) in order to stimulate the antimicrobial activity of hydroxyapatite. The molecular spectral features and morphology of the P-EO, HAp and hydroxyapatite coated with peppermint essential oil (HAp-P) were analyzed using Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The coating of the HAp with the P-EO did not affect the ellipsoidal shape of the nanoparticles. The overlapping of IR bands of P-EO and HAp in the HAp-P spectrum determined the formation of the broad molecular bands that were observed in the spectral regions of 400-1000 cm(-1) and 1000-1200 cm(-1). The antibacterial activity of the P-EO, HAp and HAp-P were also tested against different Gram-positive bacteria (methicillin-resistant Staphylococcus aureus (MRSA) 388, S. aureus ATCC 25923, S. aureus ATCC 6538, E. faecium DSM 13590), Gram-negative bacteria (Escherichia coli ATCC 25922, E. coli C5, P. aeruginosa ATCC 27853, P. aeruginosa ATCC 9027) and a fungal strain of Candida parapsilosis. The results of the present study revealed that the antimicrobial activity of HAp-P increased significantly over that of HAp.

Polycrystalline In2S3 thin films have been grown on SnO2/glass substrates by chemical bath deposition technique and irradiated at different high gamma doses 3, 7, 15 and 40 kGy. X-ray diffraction, Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Spectrophotometer, Photoluminescence and Thermoluminescence were used to investigate physical properties of In2S3 thin films induced by gamma irradiation. After being irradiated, structural properties of In2S3 thin films have shown that preferred orientation has been moved from (4 0 0) plan at 2 theta(1)=33.42 degrees to a new created orientation at 2 theta(2)=38.06 degrees for 40 kGy gamma dose. EDS analysis has shown that atomic percentage (S/In) has been strongly varied for 40 kGy which indicate significant changes in stoichiometry. Thermoluminescence of irradiated In2S3 thin films has revealed a good sensitivity toward absorbed gamma dose. After irradiation, optical transmittance of In2S3 thin films has been increased from 50% to a maximum value of 70% in the visible range for 15 kGy dose. Band gap energy E-g has been slightly decreased. Other optical parameters such absorption and extinction coefficients, refractive index and permittivity have been determined. These experimental results show that gamma radiations can be used for tuning physical properties of In2S3 thin films for photovoltaic applications.

The efficiency of the Organic Light Emitting Diode (OLED) is given either by the internal quantum efficiency of the organometallic compound or by the charge transport across OLED. IrQ(ppy)(2) is a new organometallic compound which gives green and red electroluminescence. This dual emitter compound exhibits a lower internal quantum efficiency compared with classical Ir(ppy)(3) green emitter because of a weak coupling between Ir3+ and oxygen ions which significantly reduces the charge transfer towards quinoline ligand. This lower internal quantum efficiency is compensated by the higher electron donor character of the quinoline ligand which induces better change transport in OLED structures. In the case of Ir(ppy)(3) green emitter, the efficiency can be improved by adding magnetic or metallic nanoparticles which significantly change the charge transport for the Ir(ppy)(3) based OLED structures. The metallic or magnetic nanoparticles embedded in the transparent and conductive polymer, reduce the electron injection, acting as filling traps, which directly increases the electroluminescence and the current at the same voltage.

Dextran-coated zinc-doped hydroxyapatite (ZnHApD) was synthesized by an adapted sol-gel method. The stability of ZnHApD nanoparticles in an aqueous solution was analyzed using ultrasonic measurements. The analysis of the evolution in time of the attenuation for each of the frequencies was performed. The X-ray diffraction (XRD) investigations exhibited that no impurity was found. The morphology, size and size distribution of the ZnHApD sample was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The TEM and SEM results showed that the ZnHApD particles have an ellipsoidal shape and a narrow distribution of sizes. The cell growth and toxicity of HEK-293 cells were investigated on the ZnHApD solution for four different concentrations and analyzed after 24 and 48 h. The ZnHApD solution presented a non-toxic activity against HEK-293 cells for all analyzed concentrations. The antibacterial assay revealed that all the tested microorganisms were inhibited by the ZnHApD dispersion after 24 and 48 h of incubation. It was observed that the effect of the ZnHApD solution on bacteria growth depended on the bacterial strain. The Porphyromonas gingivalis ATCC 33277 bacterial strain was the most sensitive, as a growth inhibition in the presence of 0.075 mu g/mL ZnHApD in the culture medium was observed.

The development of coenzyme Q(10) (CoQ(10)) based electrochemical sensor for the detection of oxidative stress initiators is described for the first time. The sensor relies on CoQ(10) redox properties. CoQ(10) was immobilized at the surface of glassy carbon electrodes (GCE) in combination with cyclodextrins (CD), alpha-CD or beta-CD, that ensure the formation of a well dispersed CoQ(10) film. Nanostructured thin films of CoQ(10) alone and in complexes with alpha-CD or beta-CD at the electrode surface were characterized by scanning electron microscopy (SEM) and Fourier-transformed infrared spectroscopy (FTIR), enabling to identify the morphology of the films and the interactions between the CoQ(10) and CD. Nafion (R) was used to ensure sensor stability. The optimization of the CoQ(10) sensor configuration was made by assessing CoQ(10) redox properties through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), correlated with the results obtained from SEM and FTIR characterization. Next, the sensor in the optimized configuration, GCE/alpha-CD + CoQ(10)/Nafion (R), was applied for the detection of oxidant molecules, hydrogen peroxide and the superoxide radical, through the evaluation of the CoQ(10) redox properties monitored by fixed potential chronoamperometry and square wave voltammetry (SWV). (C) 2019 Elsevier Ltd. All rights reserved.

ZnO-CuxO core-shell radial heterojunction nanowire arrays were fabricated by a straightforward approach which combine two simple, cost effective and large-scale preparation methods: (i) thermal oxidation in air of a zinc foil for obtaining ZnO nanowire arrays and (ii) radio frequency magnetron sputtering for covering the surface of the ZnO nanowires with a CuxO thin film. The structural, compositional, morphological and optical properties of the high aspect ratio ZnO-CuxO core-shell nanowire arrays were investigated. Individual ZnO-CuxO core-shell nanowires were contacted with Pt electrodes by means of electron beam lithography technique, diode behaviour being demonstrated. Further it was found that these n-p radial heterojunction diodes based on single ZnO-CuxO nanowires exhibit a change in the current under UV light illumination and therefore behaving as photodetectors.

This study proves that the new developed zinc-doped hydroxyapatite (ZnHAp) colloids by an adapted sol-gel method can be widely used in the pharmaceutical, medical, and environmental industries. ZnHAp nanoparticles were stabilized in an aqueous solution, and their colloidal dispersions have been characterized by different techniques. Scanning Electron Microscopy (SEM) was used to get information on the morphology and composition of the investigated samples. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the elemental compositions of ZnHAp colloidal dispersions. The homogeneous and uniform distribution of constituent elements (zinc, calcium, phosphorus, oxygen) was highlighted by the obtained elemental mapping results. The X-ray diffraction (XRD) results of the obtained samples showed a single phase corresponding to the hexagonal hydroxyapatite. The characteristic bands of the hydroxyapatite structure were also evidenced by Fourier-transform infrared spectroscopy (FTIR) analysis. For a stability assessment of the colloidal system, -potential for the ZnHAp dispersions was estimated. Dynamic light scattering (DLS) was used to determine particles dispersion and hydrodynamic diameter (D-HYD). The goal of this study was to provide for the first time information on the stability of ZnHAp particles in solutions evaluated by non-destructive ultrasound-based technique. In this work, the influence of the ZnHAp colloidal solutions stability on the development of bacteria, such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), was also established for the first time. The antimicrobial activity of ZnHAp solutions was strongly influenced by both the stability of the solutions and the amount of Zn.

Laser melting deposition is a 3D printing method usually studied for the manufacturing of machine parts in the industry. However, for the medical sector, although feasible, applications and actual products taking advantage of this technique are only scarcely reported. Therefore, in this study, Ti6Al4V orthopedic implants in the form of plates were 3D printed by laser melting deposition. Tuning of the laser power, scanning speed and powder feed rate was conducted, in order to obtain a continuous deposition after a single laser pass and to diminish unwanted blown powder, stuck in the vicinity of the printed elements. The fabrication of bone plates is presented in detail, putting emphasis on the scanning direction, which had a decisive role in the 3D printing resolution. The printed material was investigated by optical microscopy and was found to be dense, with no visible pores or cracks. The metallographic investigations and X-ray diffraction data exposed an unusual biphasic alpha+beta structure. The energy dispersive X-ray spectroscopy revealed a composition very similar to the one of the starting powder material. The mapping of the surface showed a uniform distribution of elements, with no segregations or areas with deficient elemental distribution. The in vitro tests performed on the 3D printed Ti6Al4V samples in osteoblast-like cell cultures up to 7 days showed that the material deposited by laser melting is cytocompatible.