ABSTRACT
The prospect of creating ferroelectric or high permittivity nanomaterials provides motivation for investigating complex transition metal oxides of the form Ba(Ti, MV)O3, where M = Nb or Ta. Solid state processing typically produces mixtures of crystalline phases, rarely beyond minimally doped Nb/Ta. Using a modified sol-gel method, we prepared single phase nanocrystals of Ba(Ti, M)O3. Compositional and elemental analysis puts the empirical formulas close to BaTi0.5Nb0.5O3-δ and BaTi0.5Ta0.5O3-δ. For both materials, a reversible temperature dependent phase transition (non-centrosymmetric to symmetric) is observed in the Raman spectrum in the region 533-583 K (260-310 °C); for Ba(Ti, Nb)O3, the onset is at 543 K (270 °C); and for Ba(Ti, Ta)O3, the onset is at 533 K (260 °C), which are comparable with 390-393 K (117-120 °C) for bulk BaTiO3. The crystal structure was resolved by examination of the powder x-ray diffraction and atomic pair distribution function (PDF) analysis of synchrotron total scattering data. It was postulated whether the structure adopted at the nanoscale was single or double perovskite. Double perovskites (A2B'Bâ³O6) are characterized by the type and extent of cation ordering, which gives rise to higher symmetry crystal structures. PDF analysis was used to examine all likely candidate structures and to look for evidence of higher symmetry. The feasible phase space that evolves includes the ordered double perovskite structure Ba2(Ti, MV)O6 (M = Nb, Ta) Fm-3m, a disordered cubic structure, as a suitable high temperature analog, Ba(Ti, MV)O3Pm-3m, and an orthorhombic Ba(Ti, MV)O3Amm2, a room temperature structure that presents an unusually high level of lattice displacement, possibly due to octahedral tilting, and indication of a highly polarized crystal.
ABSTRACT
A selection of 36 commercial probiotic fermented dairy products from UK and Europe markets were evaluated for the numbers, types, and viability of Lactobacillus strains against the stated information on their packages. A comparative study was carried out on selectivity of MRS-Clindamycin, MRS-Sorbitol, and MRS-IM Maltose, to select the right medium for enumeration of probiotic Lactobacillus. Based on selectivity of medium for recovery of the targeted lactobacilli, and also simplicity of preparation, MRS-Clindamycin was chosen as the best medium for enumeration of probiotic Lactobacillus in fermented milks. The results of enumeration of lactobacilli showed that 22 out of a total 36 tested products contained more than 106 colony-forming units/g at the end of their shelf life, which comply with the recommended minimum therapeutic level for probiotics. Rep-PCR using primer GTG-5 was applied for initial discrimination of isolated strains, and isolates, which presented different band profile, were placed in different groups. The isolated Lactobacillus spp. were identified mainly as Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus paracasei by analysis of partial sequences of the 16S ribosomal RNA and rpoA genes.
ABSTRACT
Cerenkov imaging provides an opportunity to expand the application of approved radiotracers and therapeutic agents by utilizing them for optical approaches, which opens new avenues for nuclear imaging. The dominating Cerenkov radiation is in the UV/blue region, where it is readily absorbed by human tissue, reducing its utility in vivo. To solve this problem, we propose a strategy to shift Cerenkov light to the more penetrative red-light region through the use of a fluorescent down-conversion technique, based upon europium oxide nanoparticles. We synthesized square-shape ultrasmall Eu2O3 nanoparticles, functionalized with polyethylene glycol and chelate-free radiolabeled for intravenous injection into mice to visualize the lymph node and tumor. By adding trimethylamine N-oxide during the synthesis, we significantly increased the brightness of the particle and synthesized the (to-date) smallest radiolabeled europium-based nanoparticle. These features allow for the exploration of Eu2O3 nanoparticles as a preclinical cancer diagnosis platform with multimodal imaging capability.
Subject(s)
Europium , Nanoparticles , Animals , Mice , Multimodal ImagingABSTRACT
We report nanoscale Eu0.5Ba0.5TiO3, a multiferroic in the bulk and candidate in the search to quantify the electric dipole moment of the electron. Eu0.5Ba0.5TiO3, in the form of nanoparticles and other nanostructures is interesting for nanocomposite integration, biomedical imaging and fundamental research, based upon the prospect of polarizability, f-orbital magnetism and tunable optical/radio luminescence. We developed a [non-hydrolytic]sol-[H2O-activated]gel route, derived from in-house metallic Ba(s)/Eu(s) alkoxide precursors and Ti{(OCH(CH3)2}4. Two distinct nanoscale compounds of Ba:Ti:Eu with the parent perovskite crystal structure were produced, with variable dielectric, magnetic and optical properties, based on altering the oxidizing/reducing conditions. Eu0.5Ba0.5TiO3 prepared under air/O2 atmospheres produced a spherical core-shell nanostructure (30-35 nm), with perovskite Eu0.5Ba0.5TiO3 nanocrystal core-insulating oxide shell layer (â¼3 nm), presumed a pre-pyrochlore layer abundant with Eu3+. Fluorescence spectroscopy shows a high intensity 5D0â7F2 transition at 622 nm and strong red fluorescence. The core/shell structure demonstrated excellent capacitive properties: assembly into dielectric thin films gave low conductivity (2133 GΩ mm-1) and an extremely stable, low loss permittivity of εeffâ¼25 over a wide frequency range (tan δ < 0.01, 100 kHz-2 MHz). Eu0.5Ba0.5TiO3 prepared under H2/argon produced more irregular shaped nanocrystals (20-25) nm, with a thin film permittivity around 4 times greater (εeff 101, tan δ < 0.05, 10 kHz-2 MHz, σâ¼59.54 kΩ mm-1). Field-cooled magnetization values of 0.025 emu g-1 for EBTO-Air and 0.84 emu g-1 for EBTO-Argon were observed. X-ray photoelectron spectroscopy analysis reveals a complex interplay of EuII/III/TiIII/IV configurations which contribute to the observed ferroic and fluorescence behavior.
