M. Koneracká

Immobilization of proteins and enzymes to fine magnetic particles

In a recent study we have found that Bovine serum albumin can be covalently bound to magnetic particles without loosing its biological properties. In an extension of this study we have immobilized several clinically important proteins and enzymes and found that their activity were retained, up to 90% in certain cases. The binding of the proteins and enzymes to magnetic particles was confirmed by magnetic measurements, protein and enzyme assays, electron microscopy and FTIR spectra. We discuss in this paper the potential applications of magnetic particles in several biomedical and biotechnology fields.

Direct binding procedure of proteins and enzymes to fine magnetic particles

Several clinically important proteins and enzymes (bovine serum albumin (BSA), glucose oxidase (GOD) (EC 1.1.3.4), streptokinase (EC 3.4.99.0), chymotrypsin (EC 3.4.21.1) and dispase (EC 3.4.24.3)), respectively, have been immobilised onto fine magnetic particles using carbodiimide as a coupling agent. The coupling reactions of these substances were carried out using various ratios of magnetic particles to protein, and different values of pH to determine the optimum conditions of immobilisation. The possible applications in biomedicine and biotechnology of this method of immobilisation are discussed.

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

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.

Study of magnetic Fredericksz transition in ferronematic

Abstract The magnetic Fredericksz transition in ferronematic (thermotropic nematic liquid crystal C 7 H 15 C 6 H 4 C 6 H 4 CN combined with fine magnetite particles of size 10 nm) was studied by using simple dielectric measurements. The experimental data are discussed on the basis of theory where the finite energy of the orientation coupling between the suspended magnetic particles and the nematic liquid carrier was taken into account.

Study of the magnetic Fredericksz transition in ferronematics

Abstract The magnetic Fredericksz transition in a ferronematic (thermotropic nematic liquid crystal MBBA combined with fine magnetic particles of size 10 nm) has been studied as a function of the concentration of magnetic particles by means of simple dielectric measurements. A decrease in the threshold field is observed when the magnetic particle concentration is increased, contrary to the Burylov-Raikher theory of thermotropic ferronematics.

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.

Application of Magnetizable Complex Systems in Biomedicine

Magnetic fluids or ferrofluids as they are often called mainly consist of nano sized iron oxide particles (Fe3O4 or γ-Fe2O3) that are suspended in carrier liquid. In recent years, substantial progress has been made in developing technologies in the field of magnetic microspheres, magnetic nanospheres and ferrofluids. Techniques based on using of these biocompatible magnetizable complex systems have found application in numerous biological fields viz. diagnostics, drug targeting, molecular biology, cell isolation and purification, radio immuno assay, hyperthermia causing agents for cancer therapy, nucleic acid purification etc. Biocompatible ferrofluids normally use water as a carrier medium. In order to prevent agglomeration the magnetic nanoparticles have to be stabilized by ionic interaction, a bilayer of an appropriate agent (e.g. fatty acid), aspartic and glutamic acid or peptides. Alternatively, the coprecipitation of ferrous/ferric ions is performed in the presence of appropriate biopolymer such as dextran, polyethylen glycol or polyvinyl alcohol. It has been shown that proteins and enzymes can be bound covalently to freshly prepared magnetite in the presence of carbodiimide. Several clinically important enzymes and proteins that include bovine serum albumin, streptokinase, chymotrypsin, dispase, glucose oxidase (GOD) etc., have been immobilized based on this method. The immobilized enzymes showed about 50-80 of the original added enzyme activity. This contribution will summarize the information about the ways to synthesize biocompatible magnetic nanoparticles and complexes containing them and the application of magnetic complex systems in biomedicine at magnetic drug targeting and hyperthermia.