Ionic Magnetic Fluids Research Articles

Hydrostatic ionic liquid-lubricated fluid film bearing for a rotational electron-beam lithography system

Rotational electron-beam mastering (REBM) systems have been studied with the aim of achieving the high data density necessary to facilitate the fabrication of next-generation optical data media, such as holographic storage. This study reports the design and testing of an ionic liquid (IL)-lubricated hydrostatic spindle system comprising an IL bearing, IL supply pump, and ionic magnetic fluid seal; and its outgassing performance under high-vacuum conditions. An inner vacuum chamber pressure of approximately 10−4 Pa was maintained during rotation of the spindle system. The outgassed products, as measured by a quadrupole mass spectrometer, were primarily generated from the air components in the lubricant IL. The non-repeatable runout in the radial direction, which is an important parameter of REBM accuracy, was 100 nm for a rotational speed of less than 130 min−1. The proposed method can be used for a 100-nm scale REBM device.

Outgassing performance of an ionic liquid-based magnetic fluid

In this study, an ionic liquid (IL)-based magnetic fluid (MF) (IMF; IL-based MF) and dispersant was synthesized to create MF seals for rotational mechanisms in high-vacuum chambers, such as those in rotational electron beam mastering systems. The synthesized dispersant dispersed magnetite nanoparticles in pyridinium ionic liquid that is stable under magnetic fields. The outgassing from the IMF was investigated using a quadrupole mass spectrometer during a sliding test under high-vacuum conditions with a pressure of 10−6 Pa. The fragmentation pattern of the outgassing from the IMF was very similar to that of the base IL. Pollution-causing fragments were not detected under vacuum conditions on the order of 10−9 Pa. On the basis of our findings, we anticipate that the IMF is suitable for use in MF seals required in clean, high-vacuum conditions.

Ionic magnetic fluids in polar solvents with tuned counter-ions

The aim of the present study is to propose a new reproducible method for preparing colloidal dispersions of electrostatically charged nanoparticles (NPs) in polar solvents with different kinds of counter-ions. Maghemite NPs are here dispersed in solvents of different dielectric constant, namely water, dimethylsulfoxide (DMSO) and an ionic liquid, ethylammonium nitrate (EAN). If the existence of a NP superficial charge happens to be necessary for the colloidal stability of the dispersions in these three solvents, the standard DLVO theory cannot be used any more to describe the colloidal stability in EAN. The structure of the dispersions and the strength of the interparticle repulsion are investigated by small angle X-ray scattering measurements, in association with Ludwig–Soret coefficient determinations. Specificities, associated to the nature of the counter-ions are identified in this work on the colloidal stability, on the interparticle repulsion and on the Ludwig–Soret coefficient.

New Magnetic Fluid Developed with Natural Organic Compounds Biocompatible

This work was developed with an aqueous suspension of maghemite nanoparticles and colloidal emulsions with nanoparticles of magnetite. The nanoparticles were synthesized by co-precipitation method. The first was the magnetic emulsion nanoparticles of maghemite dispersed in the aqueous extract obtained from the leaf embauba (Cecropia Obtusifolia), whose tree is native to Central and South America. Thereby achieving the magnetic fluid extract embauba stabilized with ionic buffer solution pH 7.4. A second emulsion was prepared with colloidal magnetite nanoparticles with surfaces previously coated with oleic acid as a means of dispersing and using the oil extracted from in nature seed Andiroba (Carapa Guianensis), tree of the Brazilian Amazon. These new magnetic fluids the nanoparticles were characterized by Photoacoustic spectroscopy (PAS) to determine the coating layer of molecules on the surfaces of nanoparticles. In aqueous ionic magnetic fluid Cecropia Obtusifolia (MFCO) chlorogenic acid contributes to the electron density in the presence of four groups alcohols, a ketone group and a carboxylic group. In magnetic fluid-based oil andiroba MFAD PAS spectra show that oleic acid molecules are tightly linked on the surface of the nanoparticles.

In vitro cytotoxicity of Selol-loaded magnetic nanocapsules against neoplastic cell lines under AC magnetic field activation

The goals of this study are to evaluate invitro compatibility of magnetic nanomaterials and their therapeutic potential against cancer cells. Highly stable ionic magnetic fluid sample (maghemite, γ-Fe2O3) and Selol were incorporated into polymeric nanocapsules by nanoprecipitation method. The cytotoxic effect of Selol-loaded magnetic nanocapsules was assessed on murine melanoma (B16-F10) and oral squamous cell carcinoma (OSCC) cell lines following AC magnetic field application. The influence of different nanocapsules on cell viability was investigated by colorimetric MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. In the absence of AC magnetic field Selol-loaded magnetic nanocapsules, containing 100 µg/mL Selol plus 5 × 1012 particle/mL, showed antitumoral activity of about 50% on B16-F10 melanoma cells while OSCC carcinoma cells demonstrated drug resistance at all concentrations of Selol and magnetic fluid (range of 100–500 µg/mL Selol and 5 × 1012−2.5 × 1013 particle/mL). On the other hand, under AC applied fields (1 MHz and 40 Oe amplitude) B16-F10 cell viability was reduced down to 40.5% (±3.33) at the highest concentration of nanoencapsulated Selol. The major effect, however, was observed on OSCC cells since the cell viability drops down to about 33.3% (±0.38) under application of AC magnetic field. These findings clearly indicate that the Selol-loaded magnetic nanocapsules present different toxic effects on neoplastic cell lines. Further, the cytotoxic effect was maximized under AC magnetic field application on OSCC, which emphasizes the effectiveness of the magnetohyperthermia approach.

Effect of Diode-Laser and AC Magnetic Field of Bovine Serum Albumin Nanospheres Loaded with Phthalocyanine and Magnetic Particles

This study reports on the development and characterization of bovine serum albumin (BSA) nanospheres containing Silicon(IV) phthalocyanine (NzPc) and/or maghemite nanoparticles (MNP), the latter introduced via ionic magnetic fluid (MF). The nanosized BSA-loaded samples were designed for synergic application while combining Photodynamic Therapy and Hyperthermia. Incorporation of MNP in the albumin-based template, allowing full control of the magnetic content, was accomplished by adding a highly-stable ionic magnetic fluid sample to the albumin suspension, following heat denaturing. The material's evaluation was performed using Zeta potential measurements and scanning electron microscopy. The samples were characterized by steady-state techniques and time-resolved fluorescence. The in vitro assay, using human fibroblasts, revealed no cytotoxic effect in all samples investigated, demonstrating the potential of the tested system as a synergistic drug delivery system.

Selol-loaded magnetic nanocapsules: A new approach for hyperthermia cancer therapy

Polylactic-co-glycolic nanocapsules, loaded with nanosized magnetic particles and Selol (a selenium-based anticancer drug), were successfully prepared by the precipitation method. Maghemite (γ-Fe2O3) nanoparticles were incorporated into the nanocapsules using a highly stable ionic magnetic fluid sample. The obtained nanocapsules presented no agglomeration, negative surface charge while revealing a narrow monomodal size distribution. All the nanocapsule formulations exhibited a good physical stability at 4 °C during 3 month storage period. The in vitro antitumoral activity of Selol-magnetic nanocapsules was assessed using a murine melanoma cell line. The influence of nanocapsules on cell viability was investigated by spectrophotometric assay. The results demonstrated that Selol-loaded magnetic nanocapsules (at 100 μg/ml/5 × 109 particle/ml) showed antitumoral activity of 50% on melanoma cells (absence of magnetic field). These results clearly indicate that the loaded nanocapsules represent a novel and promising magnetic drug delivery system suitable for cancer treatment via the active drug and magnetohyperthermia.

Ionic magnetic fluid based on cobalt ferrite nanoparticles: Influence of hydrothermal treatment on the nanoparticle size

Magnetic fluid based on cobalt ferrite nanoparticles was obtained using a hydrothermal treatment added to the Massart procedure. This treatment increases the average size of the nanoparticles from 11.9 to 18.7 nm and also improves the dispersity and crystallinity of the cobalt ferrite particles. The nanoparticles obtained after the hydrothermal treatment were dispersed in aqueous solvent by the classical procedure for ionic magnetic fluids. The ferrofluid thus obtained is stable at pH 7 and may be useful for hyperthermia applications.

Magnetic characterization of vermiculite-based magnetic nanocomposites

This study reports on the temperature dependence of hysteresis loops of magnetic nanocomposites consisting of iron oxide-based nanoparticles supported within exfoliated vermiculate. Two magnetic nanocomposite samples (IMFV and SMFV) were prepared by treating the exfoliated vermiculite with two magnetic fluid samples; an ionic magnetic fluid (IMF) and a surfacted magnetic fluid (SMF). X-ray diffraction and transmission electron microscopy of the magnetic phase powders provided the average diameter and diameter dispersity of the nanosized magnetic particles. The saturation magnetization, supported by the average nanoparticle size obtained from X-ray diffraction measurements, indicates the size-selectivity of the encapsulated nanoparticles by the hosting template. This finding is extremely interesting as it indicates the use of exfoliated vermiculite as a size-sort template for nanosized particles suspended as a colloid.

Magnetic Studies of Ferrofluid-Modified Microbial Cells

Microbial cells (Kluyveromyces fragilis and Chlorella vulgaris) efficiently interacted with maghemite nanoparticles stabilized as low-pH ionic magnetic fluid, leading to the formation of magnetically labeled cells. This simple procedure allows to use the prepared materials as new cheap and easy to get magnetic affinity adsorbents to the removal of water-soluble dyes from polluted water sources using magnetic separation techniques. Magnetically modified cells were investigated by means of electron spin resonance spectroscopy and conventional magnetic methods over the temperature range 4-300 K. The magnetic behavior of these materials was dominated by the superparamagnetic relaxation of isolated single domain maghemite particles although a little amount of agglomerates was also present on the cell surface. However, these agglomerates were sufficiently small to show at static conditions the superparamagnetic behavior at room temperature. Therefore, the ferrofluid-modified microbial cells represent new interesting magnetic affinity adsorbents which could be applied for large-scale magnetic separation processes.

Photoacoustic spectroscopy as a key technique in the investigation of nanosized magnetic particles for drug delivery systems

This paper describes how cubic ferrite nanoparticles, suspended as ionic or biocompatible magnetic fluids, can be used as a platform to built complex nanosized magnetic materials, more specifically magnetic drug delivery systems. In particular, the paper is addressed to the discussion of the use of the photoacoustic spectroscopy as an important technique in the investigation of key aspects related to the properties of the hosted nanosized magnetic particle. Examples of the use of the photoacoustic spectroscopy in accessing information regarding the particle size effect and the surface molecular coating of magnetic nanoparticle are included in the paper.

Magnetic resonance study of maghemite-based magnetic fluid

This study reports on the magnetic resonance (MR) data (X-band experiment) of 10.2 nm average diameter maghemite nanoparticle in the temperature range of 100–230 K. Maghemite nanoparticles were suspended as low-pH ionic magnetic fluid containing 2.3×10 17 particles/cm 3. The temperature dependence of both resonance linewidth and resonance field of the zero-field-cooled sample as well as the resonance field of the field-cooled sample (angular variation experiment) was analyzed using well-established methodology. Information regarding particle size, particle clusterization and surface magnetic anisotropy were obtained from the analysis of the MR data. The number of magnetic sites per particle from the MR data is in excellent agreement with the number provided by the transmission electron microscopy (TEM) data. The demagnetizing field value obtained from the MR data indicates cluster of particles containing on average 1.42 particles. The MR angular variation data suggest that magnetoelastic effect accounts for the non-linearity observed for the surface component of the magnetic anisotropy.

Using Mössbauer spectroscopy as key technique in the investigation of nanosized magnetic particles for drug delivery

This paper describes how cobalt ferrite nanoparticles, suspended as ionic or biocompatible magnetic fluids, can be used as a platform to built complex nanosized magnetic materials, more specifically magnetic drug delivery systems. In particular, the paper is addressed to the discussion of the use of the Mossbauer spectroscopy as an extremely useful technique in supporting the investigation of key aspects related to the properties of the hosted magnetic nanosized particle. Example of the use of the Mossbauer spectroscopy in accessing information regarding the nanoparticle modification due to the empirical process which provides long term chemical stability is included in the paper.

Aging Investigation of Cobalt Ferrite Nanoparticles in Low pH Magnetic Fluid

In this study, we report on how surface-passivated and nonpassivated cobalt ferrite nanoparticles (8 nm diameter), suspended as ionic magnetic fluids and aged under low pH conditions, revealed different behavior as far as the time evolution of the iron/cobalt cation distribution, crystal quality, coercivity, and saturation magnetization are concerned. Different techniques were used to perform a detailed study regarding the chemical stability, structural stability, and surface and magnetic properties of the suspended nanoparticles as a function of the aging time. Properties of surface-passivated and nonpassivated nanoparticles were investigated by transmission electron microscopy, X-ray diffraction, atomic absorption spectrometry, magnetic measurements, Raman spectroscopy, and Mössbauer spectroscopy. Our data showed that the employed nanoparticle surface passivation process, besides the formation of an iron-rich surface layer, modifies the nanoparticle core as well, improving the crystal quality while modifying the Fe/Co cation distribution and the nanoparticle dissolution rate profile. Magnetic data showed that the saturation magnetization increases for surface-passivated nanoparticles in comparison to the nonpassivated ones, though coercivity decreases after passivation. These two observations were associated to changes in the cation distribution among the available tetrahedral and octahedral sites.

Preparation, Characterization and in vitro Toxicity Test of Magnetic Nanoparticle-Based Drug Delivery System to Hyperthermia of Biological Tissues

The goals of this study were first to prepare and second to test albumin-based beads containing maghemite nanoparticles dispersed on them. Incorporation of maghemite nanoparticles in the albumin-based template, allowing full control of the magnetic content, was accomplished by adding ionic magnetic fluid to the albumin suspension, following heat denaturation. The material evaluation was performed using Zeta potential measurements and scanning electron microscopy from one side and by investigating the cell activity on the other hand.

Cell Toxicity Studies of Albumin-Based Nanosized Magnetic Beads

The aim of this study was to prepare bovine serum albumin-based beads containing maghemite nanoparticles incorporated via ionic magnetic fluid and to evaluate the cell toxicity of this biocompatible system using the J774-A1 cell line. Transmission electron micrographs obtained from the magnetic fluid sample were used to estimate the average particle diameter around 7.6 nm and diameter dispersion of 0.22. The BSA-based magnetic beads were prepared using the heat protein denaturation route. The nanoparticle concentration in the magnetic fluid sample used for the synthesis of the magnetic beads was in the range of 1.2 x 10(16) to 2.3 x 10(17) particle/ml. The methodology used to investigate the cell toxicity of the magnetic beads was the classical MTT assay. Our observation showed that the toxicity against the J774-A1 cell line depends upon the amount of magnetic material incorporated into the magnetic nanobeads and was found to be 14, 11, 9, 5, and 3% for 2.3 x 10(17), 1.2 x 10(17), 4.6 x 10(16), 2.3 x 10(16), and 1.2 x 10(16) particle/ml, respectively.

What Tunes the Structural Anisotropy of Magnetic Fluids under a Magnetic Field?

In the present study, the structure of monophasic ionic magnetic fluids under a static magnetic field is explored. In these aqueous electrostatically stabilized ferrofluids, we vary both the isotropic interparticle interactions and the anisotropic dipolar magnetic interaction by tuning the ionic strength and the size of the nanoparticles. Small angle neutron scattering measurements carried out on nanoparticles dispersed in light water exhibit miscellaneous 2D nuclear patterns under a magnetic field with various q-dependent anisotropies. In this nondeuterated solvent where the magnetic scattering is negligible, this anisotropy originates from an anisotropy of the structure of the dispersions. Both the low q region and the peak of the structure factor can be anisotropic. On the scale of the interparticle distance, the structure is better defined in the direction perpendicular to the field. In the thermodynamic limit (q-->0), the model previously described in ref 10 matches the data without any fitting parameters: the interparticle interaction is more repulsive in the direction parallel to the magnetic field. At low q, the amplitude of the anisotropy of the pattern is governed by the ratio of two interaction parameters: the reduced parameter of the anisotropic magnetic dipolar interaction, gamma/Phi, over the isotropic interaction parameter, , in zero field, which is proportional to the second virial coefficient.

Birefringence of maghemite-based magnetic fluid in the highly concentrated regime

The transmitted light intensity of a series of ionic magnetic fluid samples based on maghemite nanoparticles was investigated using the typical birefringence experimental setup. The field dependence of the transmitted light intensity evolves from a peak-like profile to a typical second-order Langevin profile as the nanoparticle volume fraction reduces from 2.4% to 0.9% volume fraction. The onset of the peak-like profile as the nanoparticle volume fraction increases is accounted for by two points, namely the transmitted light first scales with a sine function and second the birefringence signal appears in the argument of the sine function. The observed negative differential transmitted light is explained as one brings the above-mentioned sine dependence into the nowadays used model for the analysis of birefringence in magnetic fluids.

Magneto‐optical properties of ionic magnetic fluids: The effect of the nanoparticle surface passivation

In this study the influence of the empirical passivation process of cobalt ferrite nanoparticles upon magneto-optical properties of magnetic fluid samples is investigated. The protective character of this process was evaluated for nanoparticles peptized in two perchloric acid concentrations (0.25M and 0.75M). In addition samples aged to different times (20 and 110 days) were also investigated. The results show that all samples present an increment in the number of particle aggregates due to passivation and aging time. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of anisotropy in cadmium ferrite-based ionic magnetic fluid using magnetic resonance

Magnetic resonance was used to investigate a magnetic fluid sample containing a bimodal particle size distribution of CdFe 2O 4. The angular variation data was explained considering the external, the exchange, and the anisotropy fields. The isotropic structure around g = 2 was associated to the 7.4 nm particles whereas the signal around g = 4 , assigned to the 4.8 nm particles, is highly anisotropic. The resonance field versus temperature of the anisotropic component indicates that the anisotropy surface component dominates the magnetic behavior of very small particles.