P. Kopčanský

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.

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

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.

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.

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.

The effect of self-diffraction in magnetic fluids

Abstract The effect of optical self-diffraction occurs when an intensive interference field is created in a nonlinear optical medium. The aim of this work was to study the self-diffraction effect in magnetic fluids, i.e. generation of an optical grating by laser interference field due to the thermal diffusion phenomenon known as Soret effect. For the experiment we have used magnetic fluids with fine Fe 3 O 4 particles with various carrier base (water, kerosene, mineral oil). The proof of self-diffraction was evident from the observation of diffraction patterns. In our experiments we have observed the Soret effect with negative Soret constant.

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.