Ihab M. Obaidat

Magnetic Nanoparticles: Surface Effects and Properties Related to Biomedicine Applications

Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10–100 μm), viruses, genes, down to proteins (3–50 nm). The optimization of the nanoparticles’ size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.

Magnetic Properties of Magnetic Nanoparticles for Efficient Hyperthermia

Localized magnetic hyperthermia using magnetic nanoparticles (MNPs) under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed.

PEG coating reduces NMR relaxivity of Mn0.5Zn0.5Gd0.02Fe1.98O4 hyperthermia nanoparticles

To investigate both T1 and T2 MR relaxation enhancement of Gd substituted Zn‐Mn ferrite magnetic nanoparticles. Both uncoated and polyethylene glycol (PEG) coated particles were used.

Applications of YBCO-coated conductors: a focus on the chemical solution deposition method

High-temperature superconducting (HTSC) cables can carry much more electric current than copper wires with negligible energy losses. Many studies have been conducted on the applications of the HTSCs in electric power and energy transmission systems. The recent achievement of a critical current density of 106 A cm−2 in small samples of YBa2Cu3O7 (YBCO)-coated conductors has stimulated interest in manufacturing economic long-length YBCO-coated conductors. In the last several years, tremendous progress has been made in the scale-up of YBCO-coated conductors, but there are still several fundamental and technical issues which put limitations on the current-carrying performance of these conductors. In this article we will discuss both issues. We will discuss the fundamentals of superconductivity and the factors that limit the critical current density in HTSCs. We will present the current technology of HTSC wires. The architectures of 1G-BSCCO and the 2G-YBCO and their advantages and disadvantages will be discussed. The main preparation methods for 2G-YBCO-coated conductors will be reviewed. The main film coating methods will be discussed with a focus on the chemical solution deposition method.

Ultraviolet photodetector based on ZnO nanorods grown on a flexible PDMS substrate

A flexible, reproducible, sensitive and low-cost ultraviolet (UV) detector has been fabricated based on zinc oxide (ZnO) nanorods grown on a patterned polydimethylsiloxane (PDMS) substrate. The substrate was seeded with ZnO nanoparticles synthesised via simple low-temperature hydrothermal method using pomegranate peel extract as a reducing agent. The produced ZnO-nanorods/PDMS (ZnO-NR/PDMS) samples were tested for their UV-sensing properties. Samples were characterised using scanning electron microscopy, X-ray diffraction, I–V characteristics, UV-Vis spectroscopy and photoluminescence measurements. The UV photoresponse mechanism of prototype UV detector was analysed. The detector exhibited quite high on/off ratios between photoresponse current and dark current. With the flexible PDMS substrate, the detector photoresponse was tested with and without bending and exhibited a very slight change in the photoresponse current. The detector current–time response was also tested under various UV light intensities for three test cycles to examine the detector stability, hysteresis behaviour and performance. It is anticipated that the fabrication of ZnO-NR/PDMS UV detector may have significant potential application in flexible optoelectronic devices.

Effect of the dispersion of Eudragit S100 powder on the properties of cellulose acetate butyrate microspheres containing theophylline made by the emulsion–solvent evaporation method

The dispersion/incorporation of Eudragit S100 powder as a filler in cellulose acetate butyrate (CAB-551-0.01) microsphere containing theophylline was investigated as a means of controlling drug release. Microspheres of CAB-551-0.01 of different polymer solution concentrations/viscosities were prepared (preparations Z0, ZA, ZB and ZC) and evaluated and compared to microspheres of a constant concentration of CAB-551-0.01 containing different amounts of Eudragit S100 powder as a filler (preparations XA, XB and XC). The organic solvent acetonitrile used was capable of dissolving the matrix former CAB-551-0.01 only but not Eudragit S100 powder in the emulsion–solvent evaporation method. The CAB-551-0.01 concentration in ZA, ZB and ZC was equal to the total polymer concentration (CAB-551-0.01 and Eudragit S100 powder) in XA, XB and XC, respectively. Scanning electron microscopy (SEM) was used to identify microspheres shape and morphology. In vitro dissolution studies were carried out on the microspheres at 37°C (±0.5°C) at two successive different pH media (1.2 ± 0.2 for 2 h and 6.5 ± 0.2 for 10 h). Z preparations exhibited low rates of drug release in the acidic and the slightly neutral media. On the other hand, X preparations showed an initial rapid release in the acidic medium followed by a decrease in the release rate at the early stage of dissolution in the slightly neutral pH which could be due to some relaxation and gelation of Eudragit S100 powder to form a gel network before it dissolves completely allowing the remained drug to be released.

NMR relaxation in systems with magnetic nanoparticles: A temperature study

To measure and model nuclear magnetic resonance (NMR) relaxation enhancement due to the presence of gadolinium (Gd)‐substituted Zn‐Mn ferrite magnetic nanoparticles (MNP) at different temperatures.

Temperature Dependence of Saturation Magnetization and Coercivity in Mn0.5Zn0.5Gd0.02Fe1.98O4 Ferrite Nanoparticles

The influence of temperature on coercivity, Hc and saturation magnetization, Ms were investigated experimentally in Mn0.5Zn0.5Gd0.02Fe1.98O4 ferrite nanoparticles (average size 35 nm). Isothermal magnetization curves M (H) were obtained in the field range from -5 kOe to +5 kOe at different temperatures after the zero field cooling (ZFC) process. The temperature dependence of the coercivity, Hc(T) deviated slightly from the classical Knellers law. The temperature dependence of saturation magnetization, Ms(T) was found to have an excellent agreement with the Blochs law. These results are discussed in terms of several factors such as the size and size distribution of the particles, inter-particle interactions and the surface spin.

Investigating Exchange Bias and Coercivity in Fe3O4–γ-Fe2O3 Core–Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses

We have carried out extensive measurements on novel Fe3O4–γ-Fe2O3 core–shell nanoparticles of nearly similar core diameter (8 nm) and of various shell thicknesses of 1 nm (sample S1), 3 nm (sample S2), and 5 nm (sample S3). The structure and morphology of the samples were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The direct current (DC) magnetic measurements were carried out using a superconducting quantum interference device (SQUID). Exchange bias and coercivity were investigated at several temperatures where the applied field was varied between 3 and −3 T. Several key results are obtained, such as: (a) the complete absence of exchange bias effect in sample S3; (b) the occurrence of nonconventional exchange bias effect in samples S2 and S1; (c) the sign-change of exchange bias field in sample S2; (d) the monotonic increase of coercivity with temperature above 100 K in all samples; (e) the existence of a critical temperature (100 K) at which the coercivity is minimum; (f) the surprising suppression of coercivity upon field-cooling; and (g) the observation of coercivity at all temperatures, even at 300 K. The results are discussed and attributed to the existence of spin glass clusters at the core–shell interface.

INSIGHTS ON THE BOUND STATES IN THE STRAINED CdSe–ZnSe SINGLE-QUANTUM WELLS

The bound states in the (CdSe)Nw–ZnSe(001) single quantum well are investigated versus the well width (Nw monolayers) and the valence-band offset (VBO). The calculation, based on the sp3s* tight-binding method which includes the spin-orbit interactions, is employed to calculate the band-gap energy (Eg), quantum-confinement energy (EQ), and band structures. It is found that the studied systems possess a vanishing valence-band offset (VBO ≃ 0) in consistency with the common-anion rule, and a large conduction band offset of about (CBO ≃ 1 eV); both of which made the electronic confinement become predominant. The bi-axial strain, on the other hand, remains to control the hole states. Namely, the two highest (spin-degenerate) hole states are found to localize at the two interfaces due to the formation of two similar strain-induced potential dips at these interfaces, each of depth equal to the strain energy ~35 meV. More importantly, the ultrathin CdSe wells (with Nw ≤ 4 monolayers) are found to contain only a single (spin-degenerate) bound state; but by increasing the well width further, a new (spin-degenerate) bound state falls into the well every time Nw hits a multiple of 4 monolayers (more specifically, for 4n+1 ≤ Nw ≤ 4 (n+1), the number of bound states is (n+1), where n is an integer). The rule governing the variation of the quantum-confinement energy EQ versus the well width Nw has been derived. Our theoretical results are in excellent agreement with the available experimental photoluminescence data.