G. Stiufiuc

SERS-active silver colloids prepared by reduction of silver nitrate with short-chain polyethylene glycol

We report a fast, one-step, facile, and green preparation method that yields very stable and biocompatible silver colloids that are highly active as surface-enhanced Raman spectroscopy (SERS) platforms that has a possible application in biomedicine. Reduction of silver nitrate has been carried out using polyethylene glycol (PEG) which acts as both reducing agent and stabilizer. It turned out that the -OH groups provided by the addition of NaOH represent a key element in the successful synthesis of PEG-coated silver nanoparticles (AgNPs). The as-obtained silver colloids have been characterized by UV-visible spectroscopy, transmission electron spectroscopy, and SERS using 532- and 633-nm laser lines on a dispersive Raman spectrometer. Several analytes as methylene blue, p-aminothiophenol, amoxicillin, and Cu(PAR)2 were used to prove SERS enhancement of the obtained silver colloid. It has been found that the PEGylated AgNPs provide SERS signals comparable to those achieved using classical hydroxylamine and citrate-reduced silver colloids, thus demonstrating the ability of this new method to prepare biocompatible silver colloids.

Critical currents of Bi:2212 doped by Fe and Ni

Abstract Measurements of the irreversible magnetization, ac susceptibility and electrical resistivity of Bi 2 Sr 2 Ca 1− x Er x (Cu 1− y M y ) 2 O 8+ d bulk are reported. Low concentrations of the doping elements increase the pinning force density and shift the magnetic irreversibility line towards higher fields. The intergranular critical current density was determined from ac susceptibility data by varying the field amplitude H ac in the range from 0.4 to 1000 A/m and from the irreversible part of magnetization using Bean’s model. The results were discussed in terms of SIS- and SNS-type models for granular superconductors.

A new class of pegylated plasmonic liposomes: Synthesis and characterization

The multifunctional nanoobjects that can be controlled, manipulated and triggered using external stimuli represent very promising candidates for nanoscale therapeutic and diagnostic applications. In this study we report the successful synthesis and characterization of a new class of very stable multifunctional nanoobjects, containing cationic liposomes decorated with PEGylated gold nanoparticles (PEGAuNPs). The multifunctional hybrid nanoobjects (mHyNp) were prepared by taking advantage of the electrostatic interactions between small unilamelar cationic liposomes and negatively charged gold nanoparticles. The mHyNps have been investigated by UV-VIS absorption spectroscopy, Dynamic Light Scattering (DLS), Zeta Potential Measurements and Transmission Electron Microscopy (TEM). The TEM images clearly revealed the attachment of individual gold nanoparticles onto the spherical outer surface of the cationic liposomes which was also confirmed by DLS and UV-VIS data. Furthermore, the plasmonic properties of the hybrid complexes have been evaluated by using the Surface Enhanced Raman Spectroscopy (SERS) technique. It is shown that PEG mediated interaction between the liposomes and the gold nanoparticles enabled the recording of the SER spectra of the liposomes in aqueous environment, thus demonstrating the plasmonic properties of the hybrids.

Effects of rare earth ion substitution for Ca in (Bi,Pb):2223 superconductors

Abstract The effect of partial replacement of Ca by Y, Er and Lu on the structural transport properties of (Bi 1.6 Pb 0.4 )(Sr 1.8 Ba 0.2 )(Ca 1− x R x ) 2 Cu 3 O y superconductors ceramics (0≤ x ≤0.03) have been investigated. The substitution of Y, Lu and Er at the Ca site induced the decrease of the volume fraction for the 2223 phase and the increase of the 2212 and 2201 phases volume fractions. In the normal state, all the samples are characterized by a linear temperature dependence of electrical resistivity and Hall concentrations. The rate of depression for the critical temperature in x =0.02 samples found to be nearly the same for all of these substitutions. The nature of T C suppression may be attributed to the increase of oxygen content in Bi 2 O 2 double layers with increasing Y, Lu and Er concentrations. The sample shows a linear dependence of intergranular temperature as a function of AC field amplitude, which is in agreement with the Muller critical state model.

SYNTHESIS, MAGNETIC AND TRANSPORT PROPERTIES OF Ru1-xSbxSr2GdCu2O8 COMPOUNDS

Polycrystalline samples with a nominal composition Ru1-xSbxSr2GdCu2O8-d were prepared by a solid state reaction technique. A mixture of RuO2, Sb2O3, Gd2O3, SrCO3 and CuO was used to obtain the samples. We performed X-ray diffraction analyses, DC susceptibility and transport measurements and the studies showed that the samples were almost pure Ru-1212 phase. We also observed that Sb doping reduce the conductivity of the system and the transition temperature decreases with increasing Sb content. This may be due to a distortion of RuO6 octahedral which is responsible for the increase of holes localization.

ANISOTROPIC GOLD NANOCRYSTALS: SYNTHESIS AND CHARACTERIZATION

In this letter we report on successful preparation and characterization of anisotropic gold nanocrystals bio-synthesized by reduction of aqueous chloroaurate ions in pelargonium plant extract. The nanocrystals have been characterized by means of Transmission Electron Microscopy (TEM), UV-VIS absorption spectroscopy and tapping mode atomic force microscopy (TM-AFM). Using these investigation techniques, the successful formation of anisotropic single nanocrystals with the preferential growth direction along the gold (111) plane has been confirmed. The high detail phase images could give us an explanation concerning the growth mechanism of the nanocrystals.

Origanum vulgare mediated green synthesis of biocompatible gold nanoparticles simultaneously possessing plasmonic, antioxidant and antimicrobial properties

Purpose The leaves and flowering stem of Origanum vulgare contain essential oils, flavonoids, phenolic acids and anthocyanins. We propose a new, simple, one-pot, O. vulgare extract (OVE) mediated green synthesis method of biocompatible gold nanoparticles (AuNPs) possessing improved antioxidant, antimicrobial and plasmonic properties. Materials and methods Different concentrations of OVEs were used to reduce gold ions and to synthetize biocompatible spherical AuNPs. Their morphology and physical properties have been investigated by means of transmission electron microscopy, ultraviolet–visible absorption spectroscopy, photon correlation spectroscopy and Fourier transform infrared spectroscopy, whereas their plasmonic properties have been tested using surface-enhanced Raman spectroscopy (SERS). The antioxidant properties of nanoparticles (NPs) have been evaluated by 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, and the antimicrobial tests were performed using the disk diffusion assay. Their cytotoxicity has been assessed by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Results The experimental results confirmed the successful synthesis of biocompatible, spherical, plasmonic NPs having a mean diameter of ~40 nm and an outstanding aqueous stability. This new class of NPs exhibits a very good antioxidant activity and presents interesting inhibitory effects against Staphylococcus aureus and Candida albicans. Due to their plasmonic properties, AuNPs are used as SERS substrates for the detection of a test molecule (methylene blue) up to a concentration of 10−7 M and a pharmaceutical compound (propranolol) in solution. Cytotoxicity assays revealed that AuNPs are better tolerated by normal human dermal fibroblast cells, while the melanoma cancer cells are more sensitive. Conclusion The biocompatible AuNPs synthetized using OVEs showed significant bactericidal and antimycotic activities, the most sensitive microorganisms being S. aureus and C. albicans, both commonly involved in various dermatological infections. Moreover, the significant antioxidant effect might recommend their use for protective and/or preventive effect in various skin inflammatory conditions, including the reduction in side effects in dermatological infections. Meanwhile, the as-synthesized biocompatible AuNPs can be successfully used as SERS substrates for the detection of pharmaceutical compounds in aqueous solutions.

MAGNETIC FIELD AND TEMPERATURE DEPENDENCE OF THERMALLY ACTIVATED DISSIPATION IN EPITAXIAL THIN FILMS OF YBa2 (Cu1-xZnx)3O7-d

The scaling behavior of the effective activation energy of high-quality epitaxial c-oriented YBa2(Cu1-xZnx)3O7-d thin films has been studied as a function of temperature and magnetic field. For all samples, the effective activation energy scales as U(T, μ0H) = U0(1 - T/Tc)mHn with exponent m = 1.6 ± 0.02 - 1.3 ± 0.02 and the field scaling 1/μ0H and -lnμ0H for thick films and ultrathin films, respectively. The results are discussed taking account of the influence of the Zn substitution on the flux pinning in epitaxial YBa2(Cu1-xZnx)3O7-d thin films.

ACTIVATION ENERGY OF Bi2Sr2Ca(Cu1-xFex)2O8+d THIN FILMS

The scaling behavior of the effective activation energy U(T,H) of epitaxial c-axis oriented Bi2Sr2Ca(Cu1-xFex)2O8+d thin films with 0 ≤ x ≤ 0.02 has been studied as a function of temperature and magnetic field. It has been found that the activation energy scales as U(H,T) = U0(1 - t)mHn with exponent m = 1.15 ± 0.03 and n = -1/2. The field and temperature dependence of the activation energy, as well as its overall magnitude is consistent with a model in which U(T,H) arises from plastic deformations of viscous flux liquid above the vortex-glass transition temperature.

TRANSPORT PHENOMENA IN La2-xBaxCuOy EPITAXIAL THIN FILMS

The (001) oriented thin films of La2-xBaxCuO4+d on SrAlO4 substrates with barium composition x = 0 to 2 were grown by DC sputtering and characterized by X-ray diffraction and resistivity measurement. The films with oxygen composition d=0 showed superconductivity for x between 0.055 and 0.30. For x = 0.15, the superconducting transition was maximized to 4.3 K. When the films had d>0, Tc reached 47 K. These values are higher than those for bulk samples. The depression of Tc around x =0.125 is smaller than that for the bulk samples. The compressive strain expands the c-axis and suppresses formation of the low-temperature tetragonal phase. Both effects result in an increase in the bond length between Cu and the apical oxygen, which is responsible for the enhancement of Tc. The samples with lower residual resistivity show a higher Tc, so we suppose that the Tc enhancement is caused by reduced antiferromagnetic spin fluctuation in the CuO2 planes due to the change in the Cu–O apical bond length.