N. Tomašovičová

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.

Capacitance changes in ferronematic liquid crystals induced by low magnetic fields

The response in capacitance to low external magnetic fields (up to 0.1 T) of suspensions of spherical magnetic nanoparticles, single-wall carbon nanotubes (SWCNT), SWCNT functionalized with carboxyl group (SWCNT-COOH) and SWCNT functionalized with Fe3O4 nanoparticles in a nematic liquid crystal has been studied experimentally. The volume concentration of nanoparticles was φ1 = 10 −4 and φ2 = 10 . Independent of the type and the volume concentration of the nanoparticles, a linear response to low magnetic fields (far below the magnetic Fréederiksz transition threshold) has been observed, which is not present in the undoped nematic. PACS numbers: 61.30.Gd, 77.84Nh, 75.50.Mm, 75.30.Gw ∗ Corresponding author; tothkatona.tibor@wigner.mta.hu

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.

Influence of the anisometry of magnetic particles on the isotropic–nematic phase transition

The influence of the shape anisotropy of magnetic particles on the isotropic–nematic phase transition was studied in ferronematics based on the nematic liquid crystal (LC) 4-(trans-4-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT). The LC was doped with spherical or rod-like magnetic particles of different size and volume concentrations. The phase transition from isotropic to nematic phase was observed by polarising microscope as well as by capacitance measurements. The influence of the concentration and the shape anisotropy of the magnetic particles on the isotropic–nematic phase transition in LC are demonstrated here. The results are in a good agreement with recent theoretical predictions.

The sensitivity of ferronematics to external magnetic fields

The stable colloidal suspensions of nematic liquid crystals with magnetic nanoparticles are called ferronematics. Their behaviour in magnetic field depends on an anchoring energy, volume concentrations of magnetic nanoparticles and sign of anisotropy of diamagnetic susceptibility of liquid crystal as well as on the initial orientation between director (n) of liquid crystal and magnetic moment (m) of magnetic nanoparticles. In this work we present structural changes in ferronematics based on two kinds of liquid crystals: 6CHBT (positive anisotropy of diamagnetic susceptibility) and ZLI1695 (negative anisotropy of diamagnetic susceptibility) exposed to high magnetic fields. In both cases the parallel initial orientation between director and magnetic moments is fulfilled. The density of anchoring energy between liquid crystal molecules and magnetic particles was determinated by Burylov and Raikhers theory. In the case of 6CHBT-based ferronematics the decrease while in the case of ZLI1695-based ferronematics the increase of the critical magnetic field were observed.

Temperature dependence of the critical magnetic field of the structural transition in MBBA-based ferronematics

We studied the structural transitions in ferronematics based on the thermotropic nematic liquid crystal MBBA (4′ -methoxybenzylidene-4-n-butylaniline) having a nematic-to-isotropic transition temperature T N–I = 48.0○C and in MBBA-based ferronematics doped with a magnetic suspension consisting of Fe3O4 particles (10 nm in diameter) coated with oleic acid as a surfactant. The ferronematic samples were prepared with different volume concentrations of magnetic particles φ =,1× 10−4, 2× 10−4 and 5×10−4. The temperature dependences of the critical magnetic fields in a bias electric field under strong applied magnetic fields are presented. We calculated the surface density of anchoring energy W at the nematic–magnetic particle boundary. Scaling of the structural transition in the MBBA and MBBA-based ferronematics with the temperature of the nematic-to-isotropic transition was observed.

Magnetically induced shift of the isotropic–nematic phase transition temperature in a mixture of bent-core and calamitic liquid crystals doped with magnetic particles

We have investigated the influence of doping with spherical magnetic nanoparticles on the mixture of a bent-core and a calamitic liquid crystal. Results showed a reduction of the critical field of the magnetic Fréedericksz transition by more than a factor of two after the doping. Moreover, we give for the first time experimental evidence of the theoretically predicted magnetically induced negative shift of the isotropic to nematic phase transition temperature.

High concentration ferronematics in low magnetic fields

Abstract We investigated experimentally the magneto-optical and dielectric properties of magnetic-nanoparticle-doped nematic liquid crystals (ferronematics). Our studies focus on the effect of the very small orienting bias magnetic field B bias , and that of the nematic director pretilt at the boundary surfaces in our systems sensitive to low magnetic fields. Based on the results we assert that B bias is not necessarily required for a detectable response to low magnetic fields, and that the initial pretilt, as well as the aggregation of the nanoparticles play an important (though not yet explored enough) role.

On the adsorption of magnetite nanoparticles on lysozyme amyloid fibrils

An adsorption of magnetic nanoparticles (MNP) from electrostatically stabilized aqueous ferrofluids on amyloid fibrils of hen egg white lysozyme (HEWL) in 2mg/mL acidic dispersions have been detected for the MNP concentration range of 0.01-0.1vol.%. The association of the MNP with amyloid fibrils has been characterized by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and magneto-optical measurements. It has been observed that the extent of adsorption is determined by the MNP concentration. When increasing the MNP concentration the formed aggregates of magnetic particles repeat the general rod-like structure of the fibrils. The effect is not observed when MNP are mixed with the solution of lysozyme monomers. The adsorption has been investigated with the aim to clarify previously found disaggregation activity of MNP in amyloid fibrils dispersions and to get deeper insight into interaction processes between amyloids and MNP. The observed effect is also discussed with respect to potential applications for ordering lysozyme amyloid fibrils in a liquid crystal phase under external magnetic fields.

Magnetic polymer nanospheres for anticancer drug targeting

Poly(D,L-lactide-co-glycolide) polymer (PLGA) nanospheres loaded with biocom-patible magnetic fluid as a magnetic carrier and anticancer drug Taxol were prepared by the modified nanoprecipitation method with size of 200–250 nm in diameter. The PLGA polymer was utilized as a capsulation material due to its biodegradability and biocompatibility. Taxol as an important anticancer drug was chosen for its significant role against a wide range of tumours. Thermal properties of the drug-polymer system were characterized using thermal analysis methods. It was determined the solubility of Taxol in PLGA nanospheres. Magnetic properties investigated using SQUID magnetometry showed superparamagnetism of the prepared magnetic polymer nanospheres.