Non-magnetic Nanoparticles Research Articles

A generic method to synthesise graphitic carbon coated nanoparticles in large scale and their derivative polymer nanocomposites

A versatile Rotary Chemical Vapour Deposition (RCVD) technique for the in-situ synthesis of large scale carbon-coated non-magnetic metal oxide nanoparticles (NPs) is presented, and a controllable coating thickness varying between 1–5 nm has been achieved. The technique has significantly up-scaled the traditional chemical vapour deposition (CVD) production for NPs from mg level to 10 s of grams per batch, with the potential for continuous manufacturing. The resulting smooth and uniform C-coatings sheathing the inner core metal oxide NPs are made of well-crystallised graphitic layers, as confirmed by electron microscopy imaging, electron dispersive spectrum elemental line scan, X-ray powder diffractions and Raman spectroscopy. Using nylon 12 as an example matrix, we further demonstrate that the inclusion of C-coated composite NPs into the matrix improves the thermal conductivity, from 0.205 W∙m−1∙K−1 for neat nylon 12 to 0.305 W∙m−1∙K−1 for a 4 wt% C-coated ZnO composite, in addition to a 27% improvement in tensile strength at 2 wt% addition.

Recent applications of nanomaterials in capillary electrophoresis.

Nanomaterials have found an important place in Analytical Chemistry and, in particular, in Separation Science. Among them, metal-organic frameworks, magnetic and non-magnetic nanoparticles, carbon nanotubes and graphene, as well as their combinations, are the most important nanomaterials that have been used up to now. Concerning capillary electromigration techniques, these nanomaterials have also been used as both pseudostationary phases in electrokinetic chromatography (EKC) and as stationary phases in microchip capillary electrophoresis (CE) and capillary electrochromatography (CEC), as a result of their interesting and particular properties. This review article pretends to provide a general and critical revision of the most recent applications of nanomaterials in this field (period 2010-2017).

Symmetric and Asymmetric Magnetic Tunnel Junctions with Embedded Nanoparticles: Effects of Size Distribution and Temperature on Tunneling Magnetoresistance and Spin Transfer Torque

The problem of the ballistic electron tunneling is considered in magnetic tunnel junction with embedded non-magnetic nanoparticles (NP-MTJ), which creates additional conducting middle layer. The strong temperature impact was found in the system with averaged NP diameter dav < 1.8 nm. Temperature simulation is consistent with experimental observations showing the transition between dip and classical dome-like tunneling magnetoresistance (TMR) voltage behaviors. The low temperature approach also predicts step-like TMR and quantized in-plane spin transfer torque (STT) effects. The robust asymmetric STT respond is found due to voltage sign inversion in NP-MTJs with barrier asymmetry. Furthermore, it is shown how size distribution of NPs as well as quantization rules modify the spin-current filtering properties of the nanoparticles in ballistic regime. Different quantization rules for the transverse component of the wave vector are considered to overpass the dimensional threshold (dav ≈ 1.8 nm) between quantum well and bulk-assisted states of the middle layer.

Formulation of Laccase Nanobiocatalysts Based on Ionic and Covalent Interactions for the Enhanced Oxidation of Phenolic Compounds

Oxidative biocatalysis by laccase arises as a promising alternative in the development of advanced oxidation processes for the removal of xenobiotics. The aim of this work is to develop various types of nanobiocatalysts based on laccase immobilized on different superparamagnetic and non-magnetic nanoparticles to improve the stability of the biocatalysts. Several techniques of enzyme immobilization were evaluated based on ionic exchange and covalent bonding. The highest yields of laccase immobilization were achieved for the covalent laccase nanoconjugates of silica-coated magnetic nanoparticles (2.66 U mg−1 NPs), formed by the covalent attachment of the enzyme between the aldehyde groups of the glutaraldehyde-functionalized nanoparticle and the amino groups of the enzyme. Moreover, its application in the biotransformation of phenol as a model recalcitrant compound was tested at different pH and successfully achieved at pH 6 for 24 h. A sequential batch operation was carried out, with complete recovery of the nanobiocatalyst and minimal deactivation of the enzyme after four cycles of phenol oxidation. The major drawback associated with the use of the nanoparticles relies on the energy consumption required for their production and the use of chemicals, that account for a major contribution in the normalized index of 5.28 × 10−3. The reduction of cyclohexane (used in the synthesis of silica-coated magnetic nanoparticles) led to a significant lower index (3.62 × 10−3); however, the immobilization was negatively affected, which discouraged this alternative.

Influence of a dispersion of magnetic and nonmagnetic nanoparticles on the magnetic Fredericksz transition of the liquid crystal 5CB.

A long time ago, Brochard and de Gennes predicted the possibility of significantly decreasing the critical magnetic field of the Fredericksz transition (the magnetic Fredericksz threshold) in a mixture of nematic liquid crystals and ferromagnetic particles, the so-called ferronematics. This phenomenon is rarely measured to be large, due to soft homeotropic anchoring induced at the nanoparticle surface. Here we present an optical study of the magnetic Fredericksz transition combined with a light scattering study of the classical nematic liquid crystal: the pentylcyanobiphenyl (5CB), doped with 6 nm diameter magnetic and nonmagnetic nanoparticles. Surprisingly, for both nanoparticles, we observe at room temperature a net decrease of the threshold field of the Fredericksz transition at low nanoparticle concentrations, which appears associated with a coating of the nanoparticles by a brush of polydimethylsiloxane copolymer chains inducing planar anchoring of the director on the nanoparticle surface. Moreover, the magnetic Fredericksz threshold exhibits nonmonotonic behavior as a function of the nanoparticle concentration for both types of nanoparticles, first decreasing down to a value from 23% to 31% below that of pure 5CB, then increasing with a further increase of nanoparticle concentration. This is interpreted as an aggregation starting at around 0.02 weight fraction that consumes more isolated nanoparticles than those introduced when the concentration is increased above c=0.05 weight fraction (volume fraction 3.5×10^{-2}). This shows the larger effect of isolated nanoparticles on the threshold with respect to aggregates. From dynamic light scattering measurements we deduced that, if the decrease of the magnetic threshold when the nanoparticle concentration increases is similar for both kinds of nanoparticles, the origin of this decrease is different for magnetic and nonmagnetic nanoparticles. For nonmagnetic nanoparticles, the behavior may be associated with a decrease of the elastic constant due to weak planar anchoring. For magnetic nanoparticles there are non-negligible local magnetic interactions between liquid crystal molecules and magnetic nanoparticles, leading to an increase of the average order parameter. This magnetic interaction thus favors an easier liquid crystal director rotation in the presence of external magnetic field, able to reorient the magnetic moments of the nanoparticles along with the molecules.

Speeding up the magnetic sedimentation of surface-modified iron-based nanoparticles

Abstract Nanoparticles with surface-modified shells are used for selective sorption of different impurities from water. Subsequent removal of nanoparticles from water can be strongly enhanced by using particles with magnetic core, providing their separation by sedimentation or filtration in magnetic field. The velocity of the magnetic sedimentation is strongly controlled by the particles aggregation which can be efficiently changed by interparticles interaction, in particular, by mixing the positively charged particles with negatively charged particles. The aggregation and sedimentation dynamics of the mixtures of the complex nanoparticles having the magnetite or the iron core, e.g., Fe 3 O 4 /SiO 2 , Fe 3 O 4 /SiO 2 NH 2 and Fe/C NH 2 in water were studied in a vertical gradient magnetic field B ≤ 0.3 T, dB/dz ≤ 0.13 T/cm. The sedimentation time t s was measured using two independent methods: by optically registered turbidity and from residual particle concentration in water by Nuclear Magnetic Resonance Relaxometry (NMRR) method. The t s reaches a minimum (7–10 min) for the (1:1) mixtures of the target Fe 3 O 4 /SiO 2 and the seed Fe 3 O 4 /SiO 2 NH 2 nanoparticles. Adding of the seed Fe/C NH 2 nanoparticles to the target Fe 3 O 4 /SiO 2 water suspension is more effective due to smaller sizes and to larger magnetic moments of the Fe-based particles. The sedimentation time of about (6−10) minutes is observed for rather small fraction (6, 15 mass%) of the added Fe/C NH 2 particles, which is important for application to reduce the residual sediment volume significantly. Preliminary exposure of the mixtures in the absence of magnetic field favors to more complete nanoparticles aggregation and, as a result, more rapid sedimentation of the nanoparticles in a vertical gradient magnetic field. The data obtained are useful for development of the methods aimed at magnetic separation of magnetic and nonmagnetic nanoparticles in water purification technologies.

Glioblastoma Targeted Gene Therapy Based on pEGFP/p53-Loaded Superparamagnetic Iron Oxide Nanoparticles.

Blood-brain barrier (BBB) separates the neural tissue from circulating blood because of its high selectivity. This study focused on the in vitro application of magnetic nanoparticles to deliver Tp53 as a gene of interest to glioblastoma (U87) cells across a simulated BBB model that comprised KB cells. After magnetic and non-magnetic nanoparticles were internalized by KB cells, their location in these cells was examined by transmission electron microscopy. Transfection efficiency of DNA to U87 cells was evaluated by fluorescence microscopy, real time PCR, flowcytometry, and Western immuno-blotting. When a magnetic field was applied, a large number of magnetic nanoparticles accumulated in KB cells, appearing as black dots scattered in the cytoplasm of cells. Fluorescence microscope examination showed that transfection of the DNA to U87 target cells was highest in cells treated with magnetic nanoparticles and exposed to a magnetic field. Also it was reflected in significantly increased mRNA level while the p53 protein level was decreased. It could be concluded that a significant increase in total apoptosis was induced in cells by magnetic nanoparticles, coupled with exposure to a magnetic force (p ≤0.01) as compared with cells that were not exposed to magnetism.

Ideal Magnetic Dipole Scattering

We introduce the concept of tunable ideal magnetic dipole scattering, where a nonmagnetic nanoparticle scatters light as a pure magnetic dipole. High refractive index subwavelength nanoparticles usually support both electric and magnetic dipole responses. Thus, to achieve ideal magnetic dipole scattering one has to suppress the electric dipole response. Such a possibility was recently demonstrated for the so-called anapole mode, which is associated with zero electric dipole scattering. By spectrally overlapping the magnetic dipole resonance with the anapole mode, we achieve ideal magnetic dipole scattering in the far field with tunable strong scattering resonances in the near infrared spectrum. We demonstrate that such a condition can be realized at least for two subwavelength geometries. One of them is a core-shell nanosphere consisting of a Au core and silicon shell. It can be also achieved in other geometries, including nanodisks, which are compatible with current nanofabrication technology.

Computational Modelling of Magnetic Nanoparticle Properties and In Vivo Responses.

Nanoparticles are finding many applications in medicine and other fields like photonics. Magnetic nanoparticles have additional advantages in medicine over non-magnetic hard nanoparticles, as their magnetic properties make them ideal for hyperthermic applications in therapy and for sensitive diagnostic imaging applications. I review the literature on computational models of the magnetic properties of nanoparticles specifically. Such models have the potential to accelerate the design of magnetic nanoparticles for medical applications. Much of the current literature relates to the modelling of magnetic nanoparticles for inducing hyperthermia in aberrant cells, with significant bodies of work aimed at simulating and predicting properties for medical imaging and targeted delivery of drugs and gene therapies.

Magnetically Tuning Tether Mobility of Integrin Ligand Regulates Adhesion, Spreading, and Differentiation of Stem Cells.

Cells sense and respond to the surrounding microenvironment through binding of membranous integrin to ligands such as the Arg-Gly-Asp (RGD) peptide. Previous studies show that the RGD tether properties on substrate influence cell adhesion and spreading, but few studies have reported strategies to control the tether mobility of RGD on substrate via a physical and noncontact approach. Herein, we demonstrate a novel strategy to tune the tether mobility of RGD on substrate via magnetic force. We conjugate a monolayer of RGD-bearing magnetic nanoparticles (MNPs) on a glass substrate via the flexible and coiled poly(ethylene glycol) linker of large molecular weight (PEG, average MW: 2000), and this increases the RGD tether mobility, which can be significantly reduced by applying magnetic attraction on MNPs. Our data show that high RGD tether mobility delays the early adhesion and spreading of human mesenchymal stem cells (hMSCs), leading to compromised osteogenic differentiation at later stage. In contrast, hMSCs cultured on substrate with restricted RGD tether mobility, achieved either via a shorter PEG linker (MW: 200) or magnetic force, show significantly better adhesion, spreading, and osteogenic differentiation. The control utilizing RGD-bearing nonmagnetic nanoparticles shows no such enhancing effect of magnetic field on cellular events, further supporting our conjecture of magnetic tuning of RGD tether mobility. We hypothesize that high tether mobility of RGD entails additional time and effort by the cells to fully develop traction force and mechanical feedback, thereby delaying the maturation of FAs and activation of subsequent mechanotransduction signaling. Our staining results of vinculin, a critical component of FAs, and Yes-associated protein (YAP), an important mechanosensitive transcriptional factor, support our hypothesis. We believe that our work not only sheds light on the impact of dynamic presentation of cell adhesive ligands on cellular behaviors, which should be taken into consideration for designing novel biomaterials, but also formulate an effective noncontact strategy that enables further investigation on the mechanobiological mechanisms underlying such cellular responses.

Comparative study on Newtonian/non-Newtonian base fluids with magnetic/non-magnetic nanoparticles over a flat plate with uniform heat flux

Abstract In this study comparison between the magnetohydrodynamic flow and heat transfer of Newtonian/non-Newtonian base fluids with magnetic/non-magnetic nanoparticles is investigated for the first time. To analyze the flow and heat transfer, velocity slip boundary conditions are considered. Water and Sodium alginate are considered as the Newtonian and non-Newtonian base fluids respectively and then magnetite and aluminium oxide as magnetic and non-magnetic nanoparticles are added to it. Similarity transformations are employed to transform the governing partial differential equations into a system of ordinary differential equations. The transformed equations are then solved numerically by means of robust Runge-Kutta method of fourth order with shooting technique. Graphs are presented to demonstrate the effect of several emerging parameters on velocity, temperature profiles along with the local skin friction coefficient and Nusselt number, which clearly describe the flow characteristics. Compared with non-magnetic nanoparticles, magnetic nanoparticles have an increased effect by magnetic field. It is also observed that non-Newtonian based nanofluids have higher skin friction and Nusselt numbers than Newtonian based nanofluids.

Finite element study of three dimensional radiative nano-plasma flow subject to Hall and ion slip currents

Abstract In this article, we developed a computer code of Galerikan Finite Element method (GFEM) for three dimensional flow equations of nano-plasma fluid (blood) in the presence of uniform applied magnetic field when Hall and ion slip current are significant. Lorentz force is calculated through generalized Ohm’s law with Maxwell equations. A series of numerical simulations are carried out to search η max and algebraic equations are solved by Gauss-Seidel method with simulation tolerance 10 - 8 . Simulated results for special case have an excellent agreement with the already published results. Velocity components and temperature of the nano-plasma (blood) are influenced significantly by the inclusion of nano-particles of Copper (Cu) and Silver (Ag). Heat enhancement is observed when copper and silver nonmagnetic nanoparticles are used instead of simple base fluid (conventional fluid). Radiative nature of nano-plasma in the presence of magnetic field causes a decrease in the temperature due to the transfer of heat by the electromagnetic waves. In contrast to this, due to heat dissipated by Joule heating and viscous dissipation phenomena, temperature of nano-plasmaincreases as thermal radiation parameter is increased. Thermal boundary layer thickness can be controlled by using radiative fluid instead of non-radiative fluid. Momentum boundary layer thickness can be reduced by increasing the intensity of the applied magnetic field. Temperature of plasma in the presence magnetic field is higher than the plasma in the absence of magnetic field.

Enhancement of Ferromagnetism in Nonmagnetic Metal Oxide Nanoparticles by Facet Engineering.

Ferromagnetism in semiconducting metal oxide nanoparticles has been intensively investigated due to their potential applications in spintronics, information storage, and biomedicine. Ferromagnetism can be produced in nonmagnetic metal oxide nanoparticles by a variety of methods or factors, but the saturated magnetization is typically of the order of 10-4 emu g-1 and too small to be useful in practice. In this work, it is demonstrated theoretically and experimentally that stronger ferromagnetism can be achieved in undoped nonmagnetic metal oxide semiconductors by exposing some specific polar crystal facets with carvings of special bonds via the interaction with underlying vacancies. In2 O3 microcubes with completely enclosed {001} polar facets show two orders of magnitude enhancement at room temperature compared to nanoparticles with an irregular morphology. The surface magnetic domains on the {001} facets account for the significantly enhanced ferromagnetism. The technique and concept described here can be extended to other types of metal oxide nanostructures to spur their application to spintronics.

Exceptionally large magneto-optical response in dispersions of plate-like nanocrystallites and magnetic nanoparticles

We introduce a binary colloidal system with an exceptionally strong magneto-optical response. Its induced optical birefringence at even low magnetic fields (in the mT range) reaches a value with the same order of magnitude as that of nematic liquid crystals. This system is based on a binary mixture of plate-like, non-magnetic pigment nanoparticles and a small volume fraction (<1v%) of spherical magnetic nanoparticles. In the field-free state, the suspension is isotropic. Birefringence is caused by an alignment of the pigment platelets, commanded by shape-anisotropic agglomerates of the magnetic nanoparticles in an external magnetic field. We give a semiquantitative discussion about this.

Heat transfer in ferrofluid with cylindrical shape nanoparticles past a vertical plate with ramped wall temperature embedded in a porous medium

This paper studies magnetogydrodynamic (MHD) and porosity effects on ferrofluid over an oscillating plate with time dependent wall temperature. Nanoparticles of cylindrical shape are contained inside the base fluids. Kerosene oil is chosen as conventional base fluids. Two types of nanoparticles, magnetite (Fe3O4) and non-magnetic (Al2O3) are added to the base fluid. The flow is unsteady and the ferrofluid is considered as an electrically conducting due to a uniform magnetic field applied in a perpendicular direction to the plate. The problem is modelled in terms of partial differential equation with some physical conditions and solved by using the Laplace transform technique. Exact solutions are obtained for velocity and temperature for both cases of time dependent and isothermal wall temperatures. Graphs of velocity and temperature for time dependent and isothermal wall temperatures are plotted and compared. It is found that under time dependent wall temperature condition, velocity and temperature are smaller in magnitudes than those obtained under isothermal wall temperature condition. Moreover, effects of porosity and Hartmann number are studied graphically and discussed. A comparison is also made between magnetite (Fe3O4) and non-magnetic (Al2O3) nanoparticles. Expressions for skin-friction and Nusselt number are computed in tables. Excellent agreement of the present results is found with existing results in the literature. In this work, cylindrical nanoparticles are chosen because of their abundant applications in biology and medicine. For instance, cylindrical nanoparticles are seven times more deadly than traditional spherical nanoparticles when delivering drugs to breast cancer cells.

Attosecond and femtosecond forces exerted on gold nanoparticles induced by swift electrons

We report time-dependent calculations of attosecond and femtosecond forces imposed by a kilovolt swift electron during passage near a nanometer-sized metal particle. Contrary to expectations based on dielectric theory, which suggest that the forces should always be attractive, we find that for very close approaches, attosecond forces are repulsive, and are caused by interaction of the magnetic field of the relativistic electron with currents within even nominally nonmagnetic nanoparticles. These results suggest an explanation for the observation of both attractive and repulsive nanoparticle movement during the first use of \AA{}ngstrom-sized electron beams in electron microscopy.

Numerical study of homogeneous–heterogeneous reactions on stagnation point flow of ferrofluid with non-linear slip condition

This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous–heterogeneous reactions. Three kinds of ferroparticles, namely, magnetite (Fe3O4), cobalt ferrite (CoFe2O4) and manganese zinc ferrite (Mn–ZnFe2O4) are taken into account with water and kerosene as conventional base fluids. The developed model of homogeneous–heterogeneous reactions in boundary layer flow with equal and unequal diffusivities for reactant and autocatalysis is considered. The governing partial differential equations are converted into system of non-linear ordinary differential equations by mean of similarity transformations. These ordinary differential equations are integrated numerically using shooting method. The effects of pertinent parameters on velocity and concentration profiles are presented graphically and discussed. We found that in the presence of Fe3O4–kerosene and CoFe2O4–kerosene, velocity profiles increase for large values of α and β whereas there is a decrement in concentration profiles with increasing values of K and Ks. Furthermore, the comparison between non-magnetic (Al2O3) and magnetic Fe3O4 nanoparticles is given in tabular form.

Pinning Behaviour of Nano Nonmagnetic CuO, SnO2 and Magnetic Mn3O4 Substitutions in YBCO Bulk Superconductors

Nanoparticles were doped into YBCO samples as pinning centres by chemical solid-state reaction. High magnetic moment nanoparticles Mn3O4 and nonmagnetic nanoparticles SnO2 and CuO were prepared with a concentration of 0.1, 0.2, 0.3, 0.4 and 0.5 mass-%, respectively by a co-precipitation method. The microstructure and electrical properties of the doped YBCO samples was investigated. Increasing SnO2 in the YBCO samples from 0.1 mass-% to 0.5 mass-% tended together at one point through the sample and appeared as a defect that affects the lattice parameters of the YBCO crystal, which in turn led to degradation of the critical temperature Tc, which did not differ much from the CuO effect, which was added in the same proportions, but it was distributed through the samples. On the contrary, Mn3O4 acted as nano-pinning centre through the sample, which in turn initially led to an improvement of the critical temperature Tc. Further increase of Mn3O4 content, Tc began to decay which is due to the distortion of the lattice parameters of the YBCO crystal.

Calculation of Tunnel Magnetoresistance in Magnetic Tunnel Junctions With Particle Size Dispersion

Simulation results are given for electron tunneling through the insulating layer of a magnetic tunnel junction with embedded nonmagnetic nanoparticles (NPs). The size dispersion of the NPs was an important part of the solution for tunnel magnetoresistance, which was calculated on the basis of the double-barrier model. Theoretical agreement with experimental data was achieved by adjusting the NP dispersion and quantization. A step-like quantization related to the initial distribution of the electrons over quantum-well states was considered for different size NPs.

Anomalous Tunnel Magnetoresistance and Spin Transfer Torque in Magnetic Tunnel Junctions with Embedded Nanoparticles.

The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature.