Peculiar magnetism in Eu substituted BiFeO3 and its correlation with local structure.

We have systematically investigated the effects of Eu substitution on chemical pressure, bond lengths, microstrain, bond angles, octahedral tilting, vibrational modes and phase transformation, in BiFeO3. Correlation between concentration, phase, local structure and magnetism has been explained. Substitution of Eu ions with contrasting magnetic moment and dissimilar size, affects the local structure by changing bond angles and hence modifies spin structure through weakening of Dzyaloshinsky-Moriya (DM) interaction which lead to destruction of spiral spin configuration. Intriguing as well as anomalous magnetic response such as weak ferromagnetism with high coercivity, stair step like loops with significant drop in coercivity and systematic decrease in the magnetic coercivity at low temperatures has been observed as a function of Eu concentration (x). These results are explained on the basis of weakening of DM interaction, field induced melting of antiferromagnetic clusters and modification in effective magnetic anisotropy including contribution of magnetoelectric coupling, for various values of x. These results were used to generate the magnetic phase diagram.

Modification of graphene oxide film properties using KrF laser irradiation.

Modification of various properties of graphene oxide (GO) films on SiO2/Si substrate under KrF laser radiation was extensively studied. X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and the electrical resistance measurements were employed to correlate the effects of laser irradiation on structural, chemical and electrical properties of GO films under different laser fluences. Raman spectroscopy shows reduced graphene oxide patterns with increased I 2D/I G ratios in irradiated samples. X-ray photoelectron spectroscopy shows a high ratio of carbon to oxygen atoms in the reduced graphene oxide (rGO) films compared to the pristine GO films. X-ray diffraction patterns display a significant drop in the diffraction peak intensity after laser irradiation. Finally, the electrical resistance of irradiated GO films reduced by about four orders of magnitudes compared to the unirradiated GO films. Simultaneously, reduction and patterning of GO films display promising fabrication technique that can be useful for many graphene-based devices.

Regulation of Epithelial-to-Mesenchymal Transition Using Biomimetic Fibrous Scaffolds.

Epithelial-to-mesenchymal transition (EMT) is a well-studied biological process that takes place during embryogenesis, carcinogenesis, and tissue fibrosis. During EMT, the polarized epithelial cells with a cuboidal architecture adopt an elongated fibroblast-like morphology. This process is accompanied by the expression of many EMT-specific molecular markers. Although the molecular mechanism leading to EMT has been well-established, the effects of matrix topography and microstructure have not been clearly elucidated. Synthetic scaffolds mimicking the meshlike structure of the basement membrane with an average fiber diameter of 0.5 and 5 µm were produced via the electrospinning of poly(ε-caprolactone) (PCL) and were used to test the significance of fiber diameter on EMT. Cell-adhesive peptide motifs were conjugated to the fiber surface to facilitate cell attachment. Madin-Darby Canine Kidney (MDCK) cells grown on these substrates showed distinct phenotypes. On 0.5 µm substrates, cells grew as compact colonies with an epithelial phenotype. On 5 µm scaffolds, cells were more individually dispersed and appeared more fibroblastic. Upon the addition of hepatocyte growth factor (HGF), an EMT inducer, cells grown on the 0.5 µm scaffold underwent pronounced scattering, as evidenced by the alteration of cell morphology, localization of focal adhesion complex, weakening of cell-cell adhesion, and up-regulation of mesenchymal markers. In contrast, HGF did not induce a pronounced scattering of MDCK cells cultured on the 5.0 µm scaffold. Collectively, our results show that the alteration of the fiber diameter of proteins found in the basement membrane may create enough disturbances in epithelial organization and scattering that might have important implications in disease progression.

Biofunctionalization of PEDOT films with laminin-derived peptides.

UNLABELLED: Poly(3,4-ethylenedioxythiophenes) (PEDOT) have been extensively explored as materials for biomedical implants such as biosensors, tissue engineering scaffolds and microelectronic devices. Considerable effort has been made to incorporate biologically active molecules into the conducting polymer films in order to improve their long term performance at the soft tissue interface of devices, and the development of functionalized conducting polymers that can be modified with biomolecules would offer important options for device improvement. Here we report surface modification, via straightforward protocols, of carboxylic-acid-functional PEDOT copolymer films with the nonapeptide, CDPGYIGSR, derived from the basement membrane protein laminin. Evaluation of the modified surfaces via XPS and toluidine blue O assay confirmed the presence of the peptide on the surface and electrochemical analysis demonstrated unaltered properties of the peptide-modified films. The efficacy of the peptide, along with the impact of a spacer molecule, for cell adhesion and differentiation was tested in cell culture assays employing the rat pheochromocytoma (PC12) cell line. Peptide-modified films comprising the longest poly(ethylene glycol) (PEG) spacer used in this study, a PEG with ten ethylene glycol repeats, demonstrated the best attachment and neurite outgrowth compared to films with peptides alone or those with a PEG spacer comprising three ethylene glycol units. The films with PEG10-CDPGYISGR covalently modified to the surface demonstrated 11.5% neurite expression with a mean neurite length of 90µm. This peptide immobilization technique provides an effective approach to biofunctionalize conducting polymer films. STATEMENT OF SIGNIFICANCE: For enhanced diagnosis and treatment, electronic devices that interface with living tissue with minimum shortcomings are critical. Towards these ends, conducting polymers have proven to be excellent materials for electrode-tissue interface for a variety of biomedical devices ranging from deep brain stimulators, cochlear implants, and microfabricated cortical electrodes. To improve the electrode-tissue interface, one strategy utilized by many researchers is incorporating relevant biological molecules within or on the conducting polymer thin films to provide a surface for cell attachment and/or provide biological cues for cell growth. The present study provides a facile means for generating PEDOT films grafted with a laminin peptide with or without a spacer molecule for enhanced cell attachment and neurite extension.

Study of the nanoscale morphology of polythiophene fibrils and a fullerene derivative.

Nanoscale blending of electron-donor and electron-acceptor materials in solution-processed bulk heterojunction organic photovoltaic devices is crucial for achieving high power conversion efficiency. We used a classic blend of poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) as a model to observe the nanoscale morphology of the P3HT fibrils and PCBM nanoclusters in the mixture. Energy-filtered transmission electron microscopy (EFTEM) clearly revealed a nanoscopic phase separation. Randomly connected and/or nonconnected P3HT fibrous networks and PCBM domains, revealed by 2-dimensional micrographs, were observed by collecting electron energy loss spectra in the range of 19-30 eV. From EFTEM images, the average length and the diameter of P3HT fibrils were found to be approximately 70 ± 5 and 15 ± 2 nm, respectively. Combining the EFTEM, selected area electron diffraction, and X-ray diffraction results, the number and spacing of the ordered chains in P3HT fibrils were determined. There were 18 ± 3 repeating units of P3HT perpendicular to the fibril, ∼184 layers of π-π stacking along the fibril, and ∼9 layers of interchain stacking within the fibril. These conclusive observations provide insight into the number of molecules found in one instance of ordered-plane stacking. This information is useful for the calculation of charge transport in semicrystalline polymers. Using cross-section samples prepared with a focused ion beam technique, the vertical morphology of each phase was analyzed. By collecting 30 eV energy loss images, the phase separation in the P3HT/PCBM system was distinguishable. A higher P3HT concentration was observed at the top of the cell, near Al contact, which could possibly cause loss of carriers and recombination due to a mismatch in the P3HT and Al energy bands.

Non-equilibrium cation distribution and enhanced spin disorder in hollow CoFe2O4 nanoparticles.

We present magnetic properties of hollow and solid CoFe(2)O(4) nanoparticles that were obtained by annealing of Co(33)Fe(67)/CoFe(2)O(4) (core/shell) nanoparticles. Hollow nanoparticles were polycrystalline whereas the solid nanoparticles were mostly single crystal. Electronic structure studies were performed by photoemission which revealed that particles with hollow morphology have a higher degree of inversion compared to solid nanoparticles and the bulk counterpart. Electronic structure and the magnetic measurements show that particles have uncompensated spins. Quantitative comparison of saturation magnetization (M(S )), assuming bulk Néel type spin structure with cationic distribution, calculated from quantitative XPS analysis, is presented. The thickness of uncompensated spins is calculated to be significantly large for particles with hollow morphology compared to solid nanoparticles. Both morphologies show a lack of saturation up to 7 T. Moreover magnetic irreversibility exists up to 7 T of cooling fields for the entire temperature range (10-300 K). These effects are due to the large bulk anisotropy constant of CoFe(2)O(4) which is the highest among the cubic spinel ferrites. The effect of the uncompensated spins for hollow nanoparticles was investigated by cooling the sample in large fields of up to 9 T. The magnitude of horizontal shift resulting from the unidirectional anisotropy was more than three times larger than that of solid nanoparticles. As an indication signature of uncompensated spin structure, 11% vertical shift for hollow nanoparticles is observed, whereas solid nanoparticles do not show a similar shift. Deconvolution of the hysteresis response recorded at 300 K reveals the presence of a significant paramagnetic component for particles with hollow morphology which further confirms enhanced spin disorder.

Effects of Ag nanoparticles on survival and oxygen consumption of zebra fish embryos, Danio rerio.

Ultrafine silver (Ag) particles, defined as having one dimension in 1-100 nanometer (nm) size range, pose a unique threat to aquatic ecosystems due to their wide use in the healthcare and commercial industries. Previous studies have demonstrated some consequences of nanosilver exposure for earlier life stages of aquatic organisms, but few focus on the effects on metabolic processes such as oxygen consumption. Additionally, few authors have tackled the issue of how size, shape and composition of nanosilver particles are important in determining their level of bioactivity and biodistribution in the aquatic environment. In this study, embryos of the zebra fish, Danio rerio, (n = 2373) were exposed to varying concentrations of two Ag particle sizes, 12 and 21 nm, at time points 24 and 48 h after fertilization. The 12 nm particles were found to be more bioactive with a lethal dose 50 (LD(50)) concentration of 15.8 µg/mL compared to 50.1 µg/mL for 21 nm particles. The effective dose level (ED) was measured as 12.6 µg/mL for the 12 nm particles and 5.0 µg/mL for the 21 nm particles. Using survival curves, we found that in terms of number of particles in suspension, 21 nm particles have a greater impact on survival than 12 nm particles. Our measured respiration rates for 24 and 48 h embryos (n = 528) exposed to 0 0.02-0.14 mg/mL Ag showed no active upregulation of an energetically expensive detoxification pathway at this early point in development. Results from this study illustrate that advancements in the development of environmentally friendly nanoparticles can only occur if there is continued research to identify the most bioactive characteristics of these metallic particles.

Orientation-dependent magnetic behavior in aligned nanoparticle arrays constructed by coaxial electrospinning.

A modified electrospinning process has been utilized to align magnetite (Fe(3)O(4)) nanoparticles inside highly oriented poly(ethylene oxide) nanofibers. The structural characterization of the fiber encapsulated nanoparticle arrays via electron microscopy has been detailed, and the magnetic behavior has been studied using vibrating sample magnetometry. The fiber encapsulated nanoparticle arrays exhibit orientation-dependent magnetic behavior with respect to the applied magnetic field. A strong anisotropy along orthogonal axes is obtained for aligned arrays and is manifested as a notable increase in the coercivity and remanence magnetization in the parallel field configuration. The magnetic behavior of isotropic fibers is also examined as a reference and no orientation dependence is observed. The results were found to corroborate theoretical predictions from the chain-of-spheres model. Such hybrid nanoparticle arrays may find relevance in applications requiring an orientation-dependent physical response and in the directional transfer of signals.

Interplay of dopant, defects and electronic structure in driving ferromagnetism in Co-doped oxides: TiO(2), CeO(2) and ZnO.

A comprehensive study of the defects and impurity (Co)-driven ferromagnetism is undertaken in the oxide semiconductors: TiO(2), ZnO and CeO(2). The effect of magnetic (Co(2+)) and non-magnetic (Cu(2+)) impurities in conjunction with defects, such as oxygen vacancies (V(o)), have been thoroughly investigated. Analyses of the x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) data reveal the incorporation of cobalt in the lattice, with no signature of cobalt segregation. It is shown that oxygen vacancies are necessary for the ferromagnetic coupling in the Co-doped oxides mentioned above. The possible exchange mechanisms responsible for the ferromagnetism are discussed in light of the energy levels of dopants in the host oxides. In addition, Co and Cu co-doped TiO(2) samples are studied in order to understand the role of point defects in establishing room temperature ferromagnetism. The parameters calculated from the bound magnetic polaron (BMP) and Jorgensen's optical electronegativity models offer a satisfactory explanation of the defect-driven ferromagnetism in the doped/co-doped samples.

Reactive gas condensation synthesis of aluminum nitride nanoparticles.

Aluminum Nitride (AIN) nanoparticles were synthesized using a Reactive Gas Condensation (RGC) technique in which a mixture of ammonia (NH3) and nitrogen (N2) gases were used for the nitridation of aluminum. NH3 served as the reactive gas, while N2 served as both a carrier gas and the inert source for particle condensation. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that at reactive gas compositions greater than 10% NH3 in N2, samples were composed entirely of hexagonal AIN nanoparticles. Electron diffraction patterns showed single crystal hexagonal AIN structure. The particle size was controlled by varying the pressure of the gas mixture. AIN nanoparticles were dispersed in a liquid matrix to enhance thermal conductivity. Results showed that a minimal addition of AIN increased the thermal conductivity of hydrocarbon pump oil by approximately 27%. The thermal conductivity became constant after reaching a maximum above 0.01 wt% AIN. Temporal stability of AIN was studied by XRD. Samples exposed to air for extended periods of time and analyzed by XRD show no degradation of crystalline AIN nanoparticles.

Effect of reducing atmosphere on the magnetism of Zn(1-x)Co(x)O (0≤x≤0.10) nanoparticles.

We report the crystal structure and magnetic properties of Zn(1-x)Co(x)O (0≤x≤0.10) nanoparticles synthesized by heating metal acetates in organic solvent. The nanoparticles were crystallized in the wurtzite ZnO structure after annealing in air and in a forming gas (Ar95% + H5%). The x-ray diffraction and x-ray photoemission spectroscopy (XPS) data for different Co content show clear evidence for the Co(2+) ions in tetrahedral symmetry, indicating the substitution of Co(2+) in the ZnO lattice. However, samples with x = 0.08 and higher cobalt content also indicate the presence of Co metal clusters. Only those samples annealed in the reducing atmosphere of the forming gas, that showed the presence of oxygen vacancies, exhibited ferromagnetism at room temperature. The air annealed samples remained non-magnetic down to 77 K. The essential ingredient in achieving room temperature ferromagnetism in these Zn(1-x)Co(x)O nanoparticles was found to be the presence of additional carriers generated by the presence of the oxygen vacancies.

Effect of cobalt doping on the phase transformation of TiO2 nanoparticles.

Co-doped TiO2 nanoparticles containing 0.0085, 0.017, 0.0255, 0.034, and 0.085 mol % Co(III) ion dopant were synthesized via sol-gel and dip-coating techniques. The effects of metal ion doping on the transformation of anatase to the rutile phase have been investigated. Several analytical tools, such as X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray analysis (EDAX) were used to investigate the nanoparticle structure, size distribution, and composition. Results obtained revealed that the rutile to anatase concentration ratio increases with increase of the cobalt dopant concentration and annealing temperature. The typical composition of Co-doped TiO2 was Ti(1-x)Co(x)O2, where x values ranged from 0.0085 to 0.085. The activation energy for the phase transformation from anatase to rutile was measured to be 229, 222, 211, and 195 kJ/mole for 0.0085, 0.017, 0.0255, and 0.034 mol % Co in TiO2, respectively.

Synthesis and antibacterial properties of silver nanoparticles.

Nanometer sized silver particles were synthesized by inert gas condensation and co-condensation techniques. Both techniques are based on the evaporation of a metal into an inert atmosphere with the subsequent cooling for the nucleation and growth of the nanoparticles. The antibacterial efficiency of the nanoparticles was investigated by introducing the particles into a media containing Escherichia coli. The antibacterial investigations were performed in solution and on petri dishes. The silver nanoparticles were found to exhibit antibacterial effects at low concentrations. The antibacterial properties were related to the total surface area of the nanoparticles. Smaller particles with a larger surface to volume ratio provided a more efficient means for antibacterial activity. The nanoparticles were found to be completely cytotoxic to E. coli for surface concentrations as low as 8 microg of Ag/cm2.