National Institute Of Materials Physics - Romania

Spectroscopic characteristics of Pr3+ ions doped CNGG and CLNGG single crystals were investigated in order to assess their potential as laser materials for visible emission. The Judd-Ofelt intensity parameters for the f-f transitions of Pr3+ ions were used to determine spectroscopic and laser emission features. The temperature dependence of the absorption spectra for the H-3(4) -> P-3(0) transition was used to highlight the multicenter structure, different Stark levels, hot bands, and also the connection between the vibronic and electronic lines. The presence of electron-phonon interaction was also observed in the emission spectra corresponding to the P-3(0) -> H-3(4) transition under different excitation wavelengths. Based on low temperature absorption and emission spectra, partial energy level diagrams of Pr3+ ions doped in CNGG and CLNGG single crystals were obtained. The emission cross-sections for different transitions of Pr3+ ions were evaluated by the Fuchtbauer-Ladenburg formula. The fluorescence decay curve of the D-1(2) level was measured under selective excitation at different concentrations and temperatures. The concentration quenching process for the D-1(2) state was also studied. (C) 2019 Elsevier B.V. All rights reserved.

The present investigation deals with the development, characterization and application of nano-structured Pd doped Ni electrodes (Pd@Ni), which uses the electrochemical properties of Pd in synergy with the magnetic properties of Ni for biosensors development. The Pd@Ni electrodes have been characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It has been shown that palladium presented spherical assemblies ranging 150-200 nm medium diameter size that covers large areas of the electrode surface while metallic nickel, which confers magnetic properties, showed a uniform granular structure with sizes between 20 and 50 nm. Cyclic voltammetry and electrochemical impedance spectroscopy were performed to understand the electrochemical process at the Pd@Ni electrodes in neutral media. The Pd@Ni electrodes were applied for the electrochemical detection of H2O2. Finally, Ni nanoparticles (NiNP) functionalized with the model enzyme glucose oxidase (GOx-NiNP) have been attached to the Pd@Ni electrode solely through magnetic interactions, and the obtained GOx-NiNP/Pd@Ni biosensor applied for glucose determination in aqueous solutions by fixed potential amperometry at -0.05 V (vs Ag/AgCl) with reduced interferences. (C) 2019 Elsevier Ltd. All rights reserved.

The majority of eukaryotic regulated protein turnover is performed by the proteasome, a multi-catalytic enzyme. Due to the fact that proteasome enzyme abnormal functioning was observed in different malignant cells, the proteasome is becoming a target for medical treatment. In order to evaluate the mechanisms of action of pharmaceutical compounds on proteasome enzyme inhibition, detecting and characterizing its activity is essential. An electrochemical assay that allows the monitoring of the chymotrypsin-like activity and inhibition of the 20S proteasome enzyme, based on the electrochemical detection of an electroactive compound released upon proteolysis of an adequate chymotrypsin-substrate is described. By employing differential pulse voltammetric measurement, the activity of the 20S proteasome enzyme was investigated for different incubation times of 20S with oligopeptide substrate as well as for different concentrations of substrate. Enzyme kinetic parameters were determined by voltammetry and the electrochemical assay compared with fluorescence spectroscopy. Electrochemical quartz crystal microbalance and atomic force microscopy were also used to investigate substrate interaction with the 20S proteasome and their adsorption at the electrode surface. Finally, the new electrochemical assay allowed to investigate the mechanisms of two different proteasome inhibitor drugs, bortezomib and oprozomib, underlying the applicability of the assay for understanding proteasome inhibitor action.

In this work, the effect of deposition time on the structural and optical properties of ZnO films deposited by Ultrasonic Spray Mist-CVD was studied aiming the application in perovskite solar cells, as holes blocking layer. Crystallinity, surface morphology and optical properties of the ZnO films were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), conventional and Photoluminescence (PL) spectroscopies, respectively. The XRD measurement proves the existence of the hexagonal wurtzite phase and a high degree of crystallinity with [001] preferential orientation. The SEM study shows that the films possess a compact structure. Smooth and homogenous surface was confirmed also by AFM. The obtained results indicate that ZnO films deposited by a simple, safe and cost-effective method present a great potential for application in perovskite solar cells.

The influence of the Gd3+ co-dopant on the structure, morphology and up-conversion luminescence/magnetic properties of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals was investigated and compared to those of Gd-free samples. Electron microscopy has indicated an inhibiting effect of the agglomeration and collapsing process of the nanocrystals compared to the Gd-free powder samples. The surface analysis of nanocrystals have not shown oxygen-metal bonds related to the metal oxidation within the surface nanometric layer. The paramagnetic properties are related to the magnetic moment of the Gd3+ ions. The up-conversion luminescence of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals is about six times stronger than in LiYF4:Yb3+/Er3+ nanocrystals; the enhancement effect is most probably due to the lattice distortion induced by the Gd co-doping.

Up-conversion luminescence and thermoluminescence properties of LaF3 nanocrystals, with sizes of about 20 nm, were studied and discussed in relation to -size and surface related effects. XPS spectra have evidenced the presence of oxidized Er and La ions within a thin layer (of about 1 nm thickness) at the nanocrystals surface, as well as Yb ions bonded with fluorine ions. The green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion emissions of Er3+ ions are influenced by the relative dominance of Erions that reside within the thin oxidized layer. The broad thermoluminescence curves are assigned to the recombination of trap defects associated with surface states and within the oxidized surface layer. (C) 2019 Elsevier B.V. All rights reserved.

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.