Peter Kopcansky

Effect of Fe 3 O 4 magnetic nanoparticles on lysozyme amyloid aggregation

Peptide amyloid aggregation is a hallmark of several human pathologies termed amyloid diseases. We have investigated the effect of electrostatically stabilized magnetic nanoparticles of Fe(3)O(4) on the amyloid aggregation of lysozyme, as a prototypical amyloidogenic protein. Thioflavin T fluorescence assay and atomic force microscopy were used for monitoring the inhibiting and disassembly activity of magnetic nanoparticles of Fe(3)O(4). We have found that magnetic Fe(3)O(4) nanoparticles are able to interact with lysozyme amyloids in vitro leading to a reduction of the amyloid aggregates, thus promoting depolymerization; the studied nanoparticles also inhibit lysozyme amyloid aggregation. The ability to inhibit lysozyme amyloid formation and promote lysozyme amyloid disassembly exhibit concentration-dependent characteristics with IC50 = 0.65 mg ml(-1) and DC50 = 0.16 mg ml(-1) indicating that nanoparticles interfere with lysozyme aggregation already at stoichiometric concentrations. These features make Fe(3)O(4) nanoparticles of potential interest as therapeutic agents against amyloid diseases and their non-risk exploitation in nanomedicine and nanodiagnostics.

Depolymerization of insulin amyloid fibrils by albumin-modified magnetic fluid

Pathogenesis of amyloid-related diseases is associated with the presence of protein amyloid deposits. Insulin amyloids have been reported in a patient with diabetes undergoing treatment by injection of insulin and causes problems in the production and storage of this drug and in pplication of insulin pumps. We have studied the interference of insulin amyloid fibrils with a series of 18 albumin magnetic fluids (MFBSAs) consisting of magnetite nanoparticles modified by different amounts of bovine serum albumin (w/w BSA/Fe₃O₄ from 0.005 up to 15). We have found that MFBSAs are able to destroy amyloid fibrils in vitro. The extent of fibril depolymerization was affected by nanoparticle physical-chemical properties (hydrodynamic diameter, zeta potential and isoelectric point) determined by the BSA amount present in MFBSAs. The most effective were MFBSAs with lower BSA/Fe₃O₄ ratios (from 0.005 to 0.1) characteristic of about 90% depolymerizing activity. For the most active magnetic fluids (ratios 0.01 and 0.02) the DC50 values were determined in the range of low concentrations, indicating their ability to interfere with insulin fibrils at stoichiometric concentrations. We assume that the present findings represent a starting point for the application of the active MFBSAs as therapeutic agents targeting insulin amyloidosis.

Structure of water-based ferrofluids with sodium oleate and polyethylene glycol stabilization by small-angle neutron scattering: contrast-variation experiments

Contrast variation in small-angle neutron scattering (SANS) experiments is used to compare the structures of a water-based ferrofluid, where magnetite nanoparticles are stabilized by sodium oleate, and its mixture with biocompatible polyethylene glycol, PEG. The basic functions approach is applied, which takes into account the effects of polydispersity and magnetic scattering. Different types of stable aggregates of colloidal particles are revealed in both fluids. The addition of PEG results in a reorganization of the structure of the aggregates: the initial comparatively small and compact aggregates (about 40 nm in size) are replaced by large (more than 120 nm in size) fractal-type structures. It is postulated that these large structures are composed of single magnetite particles coated with PEG, which replaces sodium oleate. Micelle formation involving free sodium oleate is observed in both fluids. The structures of the fluids remain unchanged with increasing temperature up to 343 K. New and specific possibilities of SANS contrast variation with respect to multicomponent systems with different aggregates are considered.

Dielectric response of transformer oil based ferrofluid in low frequency range

In this article, our experimental study of the dynamic dielectric behaviour of transformer oil-based ferrofluid with magnetite nanoparticles is presented. Frequency-dependent dielectric permittivity and dissipation factor were measured within the frequency range from 20 Hz to 2 MHz by a capacitance method. The ferrofluid samples were placed in a liquid crystal cell, and experiments were carried out in an electromagnetically anechoic chamber. Two polarization processes and corresponding relaxations were revealed within the applied frequency range. Schwarz theory of electric double layer polarization is used to explain the low frequency relaxation maximum. Moreover, the shift of the maximum position towards higher frequencies is observed as the magnetic volume fraction in the ferrofluid increases. The related decrease in relaxation time due to higher counterion mobility is analysed. Reduced electric field intensity due to depolarization field, which is dependent on the particle concentration, is proposed as...

Hyperthermic Effect in Suspension of Magnetosomes Prepared by Various Methods

The magnetic properties and hyperthermia effect were studied in solution of magnetosomes obtained by changing conditions during biomineralization of magnetotactic bacteria Magnetospirillum sp.AMB-1. It was shown that adding a higher amount of Wolfes vitamin solution (WVS) or ferric quinate (FQ) cause increase of the mean diameter from 47 nm (normal condition) up to 52 nm and 58 nm respectively. As a consequence of this change the preparation conditions coercivity and Specific Absorption Rate (SAR) increased up to 20 Oe and 949 W/gFe for sample FQ, respectively. On the other hand the process of cultivation at the changed conditions markedly reduced the cultivation time. Also the isolated chains of magnetosome were shorter containing less amount of magnetosomes too.

Direct observation of electric field induced pattern formation and particle aggregation in ferrofluids

Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation process. Our experimental study could open future applications of ferrofluids based on insulating liquids.

On the determination of the helical structure parameters of amyloid protofilaments by small-angle neutron scattering and atomic force microscopy

The helical structure of amyloid protofilaments of hen egg white lysozyme was analyzed by small-angle neutron scattering (SANS) and atomic force microscopy (AFM). The structure of these formations in bulk solutions was adequately described by SANS in terms of a simplified model of a helix with spherical structural units. The found main helix parameters (pitch and effective diameter) are consistent with the results of AFM analysis for amyloid fibrils adsorbed on a mica surface. Both methods reveal a strong isotope effect on the structure of amyloid fibrils with respect to the substitution of heavy for light water in the solvent. Specific details responsible for the structural differences when comparing SANS and AFM data are discussed from the viewpoint of methodological aspects, the influence of different (native and adsorbed) amyloid states and sample preparation.

Multiple-length-scale patterning of magnetic nanoparticles by stamp assisted deposition.

Control of the size and spatial distribution of materials at multiple length scales is one of the most compelling issues in nanotechnology research. We report a multiple-length-scale patterning of pure magnetic particles as well as biocompatible magnetic particles based on a printing technique named micro-injection molding in capillaries. The magnetic particles were prepared by a technique of co-precipitation of ferric and ferrous salts in an alkali medium. We demonstrate that the morphology and the size of the patterning nanoparticles can be controlled by simply controlling the concentration of the solution. Our method exploits the self-organization of the nanoparticles in a solution confined between a stamp and the surfaces of a substrate, exploiting confinement and competing interactions between the adsorbate and the substrate. Our approach represents a remarkable example of an integrated top-down/bottom-up process.

RHEOLOGICAL AND MAGNETORHEOLOGICAL BEHAVIOUR OF SOME MAGNETIC FLUIDS ON POLAR AND NONPOLAR CARRIER LIQUIDS

Rheological and magnetorheological behaviour of monolayer and double layer sterically stabilized magnetic fluids, with transformer oil (UTR), diloctilsebacate (DOS), heptanol (Hept), pentanol (Pent) and water (W) as carrier liquids, were investigated. The data for volumic concentration dependence of dynamic viscosity of high colloidal stability UTR, DOS, Hept and Pent samples are particularly well fitted by the formulas given by Vand (1948) and Chow (1994). The Chow type dependence proved its universal character as the viscosity data for dilution series of various magnetic fluids are well fitted by the same curve, regardless the nonpolar or polar charcater of the sample. The magnetorheological effect measured for low and medium concentration water based magnetic fluids is much higher, due to agglomerate formation process, than the corresponding values obtained for the well stabilized UTR, DOS, Hept and Pent samples, even at very high volumic fraction of magnetic nanoparticles.

Biogenic Magnetite in Humans and New Magnetic Resonance Hazard Questions

Biogenic Magnetite in Humans and New Magnetic Resonance Hazard Questions The widespread use of magnetic resonance (MR) techniques in clinical practice, and recent discovery of biogenic ferrimagnetic substances in human tissue, open new questions regarding health hazards and MR. Current studies are restricted just to the induction of Faraday currents and consequent thermal effects, or ‘inoffensive’ interaction with static magnetic field. We outlined that magnetic energies associated with interaction of ferrimagnetic particles and MR magnetic fields can be dangerous for sensitive tissues like the human brain is. To simulate the interaction mechanism we use our. ‘Cube’ model approach, which allows more realistic calculation of the particles magnetic moments. Biogenic magnetite nanoparticles face during MR examination three principal fields: (i) main B0 field, (ii) gradient field, and (iii) B1 field. Interaction energy of biogenic magnetite nanoparticle with static magnetic field B0 exceeds the covalent bond energy 5 times for particles from 4 nm up to 150 nm. Translation energy in gradient field exceeds biochemical bond energy for particles bigger than 50 nm. Biochemical bond disruption and particle release to the tissue environment, in the presence of all MR fields, are the most critical points of this interaction. And together with relaxation processes after application of RF pulses, they make biogenic magnetite nanoparticles a potential MR health hazard issue.