Communications - Scientific letters of the University of Zilina, 2014
Magneto-optical effects in magnetic suspensions Numerous materials exhibit linear or circular opt... more Magneto-optical effects in magnetic suspensions Numerous materials exhibit linear or circular optical anisotropy under the influence of a magnetic field. These anisotropic media generate two effects: the magneto-optical birefringence and dichroism which introduce respectively a phase shift Δ and a difference of absorption (related to an angular parameter Ψ) between optical waves polarized along Eigen
The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been c... more The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been consisted of magnetit particles (Fe3O4) of nanometric size that were coated with oleic acid as a surfactant and dispersed in transformer oil. The DC electric and constant magnetic fields have affected on MFs simultaneously and electro-physical processes, which influence electric breakdown, were obserwed. The especial attention was devoted to pre-breakdown, breakdown and postbreakdown state in MFs. Słowa kluczowe: przebicie elektryczne, stany przedprzebiciowe, przebicia i poprzebiciowe, ciecz magnetyczna, pola elektryczne i magnetyczne, strukturalizacja cząstek magnetycznych
The effect of temperature on the magneto-dielectrics behavior was studied by dielectric spectrosc... more The effect of temperature on the magneto-dielectrics behavior was studied by dielectric spectroscopy in the transformer oil-based ferrofluid with magnetic nanoparticles upon the effect of an external magnetic field. The frequency dependence of complex permittivity and dissipation factor were measured within the frequency range from 1 mHz to 10 kHz at different temperatures by a capacitance method. The dielectrics parameters were measured as a function of the external magnetic field in the range of 0-200 mT, parallel to the direction of the electric field as a function of temperature in the range of 15-35 ¥ C. The interaction between magnetic field and magnetic moments of nanoparticles led to the aggregation of magnetic nanoparticles to new structures which had influence on dielectric parameters. The dependence of these parameters at constant magnetic field on angle between the direction of the electric and magnetic fields (anisotropy) has been measured, too.
The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electri... more The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electric and weak magnetic fields were studied by means of the attenuation of surface acoustic wave of frequency 30 MHz propagating along ferronematic liquid crystals. Three low volume concentrations (Φ = 1 × 10 −5 , 1 × 10 −4 and 1 × 10 −3) of rod-like magnetic particles were added to liquid crystal during its isotropic phase. Several measurements including the investigation of the effects of electrical and magnetic fields applied both separately and in conjunction as well as the influence of temperature on the surface acoustic wave attenuation were performed. The distinctive surface acoustic wave attenuation responses induced by both electric and magnetic fields in studied ferronematic liquid crystals have been observed suggesting both structural changes and the orientational coupling between magnetic moments of magnetic particles and the director of the liquid crystal. Obtained results confirmed the significant influence of the presence of magnetic particles on the structural properties and resulting behavior of 6CHBT liquid crystal.
The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in t... more The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in the ultralow frequency regime was investigated. A dielectric relaxation, whose relaxation time is 160 s, is observed at 303 K, and the dielectric relaxation is found to be independent of applied electric field. It is shown that the dielectric relaxation is caused by the Helmholtz double layer formed by the adsorption of impurity ions in 5CB onto the electrode surfaces of the cells, and hence the thickness of the double layer is comparable to the radius of impurity ions in 5CB. The dielectric relaxation obeys the empirical Cole‐Cole circular arc law, indicating that dielectric relaxation times are distributed. The distribution of dielectric relaxation times can be explained in terms of distributed thicknesses of the Helmholtz double layer.
Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)a... more Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)applications. Multimodal imaging as well as simultaneous control and monitoring of intracellular movements profit from the combination of these functionalities. Accordingly, several methods have been developed for the synthesis of magnetic fluorescent particles. The majority of these methods, however, require complex modification and purification steps and result in a low yield of particles. Here, we describe a straightforward and scalable method for the magnetic modification of cellulose-based fluorescent particles. The method is based on the use of microwave-synthesized magnetite nanoparticles prepared from ferrous sulfate at high pH. Magnetic modification did not change the pH sensitivity or the optical properties of the fluorescent particles, and allowed them to be manipulated by external magnetic field. Our results demonstrate the possibility of large scale, easy production of bifunctional particles. We anticipate that our method can be expanded to include other types of particles or functionalities relevant for biomedical applications.
Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. T... more Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. They appear to be a suitable carrier for the targeted drug transport, which represents a new method of cancer treatment. Advantages of targeted drugs transport are the minimizing of hurt to the organism, specific focusing on certain types of tissues, increased effect of the drug, reduced drug dose and hence side effects. The main goal of the present study was to verify the effect of bacterial magnetic nanoparticles produced by
The influence of Fe 3 O 4 nanoparticles on dielectric properties of planar oriented liquid crysta... more The influence of Fe 3 O 4 nanoparticles on dielectric properties of planar oriented liquid crystal were studied at the frequency range10 1 -10 6 Hz and in temperature interval of 292 -345 K. It was shown that the dielectric spectrum of doped liquid crystal can be divided into two areas. Parameters obtained from the dielectric spectrum for frequencies lower than 10 Hz characterize near electrode processes, and parameters obtained for frequencies more than 10 Hz characterize the bulk properties of the sample. The relaxation time and near-electrode area thickness have been estimated. It was experimentally shown that magnetic nanoparticles change the near-electrode area parameters.
Liquid crystals (LCs) composed of mesogens play important roles in various scientific and enginee... more Liquid crystals (LCs) composed of mesogens play important roles in various scientific and engineering problems. How a system with many mesogens can enter a LC state is an interesting and important problem. Using stiff and free-joint Lennard-Jones chain molecules as mesogens, we study the conditions under which the mesogens can enter various LC phases. The guideline is to eliminate the unwanted translational orders under a controlled fine-tuning procedure across a sequence of systems. Instead of monitoring the growth of order out of the disorder, we prepare a configuration of high orientation ordering and find out where it relaxes to. Such a procedure begins with a reference system, consisting of short chains of homogeneous soft spheres, in a liquid-vapor coexistence situation, at which the thermodynamic instability triggers a fast spontaneous growing process. By applying a short pulse of auxiliary field to align the dispersedly oriented clusters, followed by reducing the volume and,...
A broadband dielectric response of ferrofluids can be effectively controlled by application of an... more A broadband dielectric response of ferrofluids can be effectively controlled by application of an external magnetic field. The interaction of magnetic nanoparticles with magnetic forces and the resulting structural changes in the ferrofluids may tune their dielectric spectra. In this paper, we present an experimental study on the controllability of a dielectric spectrum of Mn-Zn ferrite transformer oil-based ferrofluid by means of a static electric field generated by a direct current (DC) bias voltage. Two experimental configurations of the DC bias voltage are applied. The spectrum of a complex permittivity measured in the frequency range from 1 mHz up to 200 kHz is firstly studied under an internal DC bias voltage applied on the electrodes of a measuring capacitor. Then, the sensitivity of the dielectric spectrum to the external DC bias voltage applied on an external pair of electrodes outside the measuring capacitor is investigated. It is found that the increasing internal DC bias...
In the human body the protein amyloid aggregates, due to their deposition in specific tissues or ... more In the human body the protein amyloid aggregates, due to their deposition in specific tissues or organs, are associated with many serious diseases (diabetes mellitus, Alzheimer's disease, etc.). Recently, we have found that magnetite nanoparticles have ability to affect amyloid aggregatation of lysozyme and insulin [1][2]. In our study we examine effect of magnetoferritin (MFer), biocompatible magnetite nanoparticles, on lysozyme amyloid aggregates (LAA) associated with lysozyme systemic amyloidosis. The interference of LAA and MFer was investigated at ratios of LAA:MFer = 1:1 and 1:5 using small angle X-rays scattering technique (SAXS) and Thioflavin T fluorescence measurements (ThT assay). By controlled chemical synthesis magnetoferritin complexes with two loading factors (LFnumber of iron atoms per one complex) of 168 (MFer(168)) and 532 (MFer(532)) were prepared. SAXS experiments indicate that presence of MFer caused structural changes of LAAs. Analysis of data obtained for solution containing LAA with MFer(532) (LAA:MFer = 1:5) clearly indicate decreasing of the lower limit of radius of gyration from 30 nm to 20 nm compare to lysozyme fibrils alone and almost non-effected structure of MFer complexes (Fig. 1). These results suggest reduction of LAA, probably due to the truncation of the LAA by MFer. The decreasing of the amount of LAA was observed also by ThT assay. The fluorescence intensities of LAA in presence of MFer(532) and MFer(168) was significantly decreased-40% and 55% decay (ratio 1:1) and 50% and 62% decay (ratio 1:5). These data strongly support SAXS data assuming reduction of the LAA as results of their interaction with MFer. The interaction between lysozyme amyloid aggregates (LAA) and biocompatible magnetite nanoparticles (magnetoferritin, MFer) have been investigated by Thioflavin T fluorescence 1 measurements (ThT assay), small-angle X-rays scattering (SAXS) and transmission electron microscopy (TEM). The influence of concentration and degree magnetite loading (loading factors) of MFer has been examined during LAA formation (inhibition) and after LAA formation (depolymerisation) experiments. Results suggest the reduction of LAA size in the case of high concentration and LF of added magnetoferritin during depolymerisation, probably due to the truncation of the LAA by MFer. Shell structure of MFer is observed in LAA/MFer mixtures.
Control of the size and spatial distribution of materials at multiple length scales is one of the... more 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.
The electric Fredericksz transition in 8CB-based ferronematics exposed to strong magnetic field w... more The electric Fredericksz transition in 8CB-based ferronematics exposed to strong magnetic field was studied both theoretically (by means of the Burylov and Raikher's theory) and experimentally (using capacity measurements). The estimated values of anchoring energy of order WB10 À4 N/m and parameter oB124 indicate the presence of intermediate type of anchoring (between soft and rigid) in studied thermotropic ferronematic.
The structural transitions in ferronematic based on 8CB and 6CHBT, exposed to combined electric a... more The structural transitions in ferronematic based on 8CB and 6CHBT, exposed to combined electric and magnetic fields, are investigated. The influence of the presence of magnetic admixture on the Fredericksz transition threshold is studied. Using the found dependencies of critical fields on increasing magnetic particles volume concentration the type of anchoring was determined as soft with m?n in 8CB and mJn in 6CHBT-based ferronematics.
The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and th... more The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and the carrier liquid. The structural changes in magnetic fluids with different nanoparticle diameter based on transformer oils TECHNOL and MOGUL under the effect of a magnetic field and temperature were studied by acoustic spectroscopy. At a linear and jump changes of the magnetic field at various temperatures a continuous change was observed of acoustic attenuation caused by aggregation of the magnetic nanoparticles to structures. From the anisotropy of acoustic attenuation and using the Taketomi theory the basic parameters of the structures are calculated and the impact of nanoparticle diameters on the size of structures is confirmed.
Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core... more Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core diameter of about 30nm results from TEM, XRD and magnetic analysis. Specific loss power is determined from hysteresis loops, susceptibility spectra and calorimetry with ...
Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse sp... more Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse spleen ferritin (HSF) and nanoscale magnetite aqueous suspensions. The anisotropy of optical polarizability was calculated. The average magnetic dipole moment calculated assuming the Langevin model was about 20,000 and 8500μB per particle, for magnetite nanoparticle and magnetoferritin, respectively. Poor fitting results and the unphysical value of average magnetic moment
The aim of the presented work was to investigate the stability of biocompatible magnetic uid, i.e... more The aim of the presented work was to investigate the stability of biocompatible magnetic uid, i.e. water-based magnetic uid containing magnetite nanoparticles stabilized by surfactant sodium oleate and modied by bovine serum albumin (BSA) after electron irradiation. Samples with the same concentration of Fe3O4 but dierent mass ratio BSA/Fe3O4 (w/w= 0.25, 1.0 and 2.5) were studied. The electron irradiation caused about 10% reduction of the saturation magnetization in the samples with w/w BSA/Fe3O4 ratio of 0.25 and less than 5% in the samples with w/w BSA/Fe3O4 ratio of 1 and 2.5.
Peptide amyloid aggregation is a hallmark of several human pathologies termed amyloid diseases. W... more 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.
Communications - Scientific letters of the University of Zilina, 2014
Magneto-optical effects in magnetic suspensions Numerous materials exhibit linear or circular opt... more Magneto-optical effects in magnetic suspensions Numerous materials exhibit linear or circular optical anisotropy under the influence of a magnetic field. These anisotropic media generate two effects: the magneto-optical birefringence and dichroism which introduce respectively a phase shift Δ and a difference of absorption (related to an angular parameter Ψ) between optical waves polarized along Eigen
The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been c... more The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been consisted of magnetit particles (Fe3O4) of nanometric size that were coated with oleic acid as a surfactant and dispersed in transformer oil. The DC electric and constant magnetic fields have affected on MFs simultaneously and electro-physical processes, which influence electric breakdown, were obserwed. The especial attention was devoted to pre-breakdown, breakdown and postbreakdown state in MFs. Słowa kluczowe: przebicie elektryczne, stany przedprzebiciowe, przebicia i poprzebiciowe, ciecz magnetyczna, pola elektryczne i magnetyczne, strukturalizacja cząstek magnetycznych
The effect of temperature on the magneto-dielectrics behavior was studied by dielectric spectrosc... more The effect of temperature on the magneto-dielectrics behavior was studied by dielectric spectroscopy in the transformer oil-based ferrofluid with magnetic nanoparticles upon the effect of an external magnetic field. The frequency dependence of complex permittivity and dissipation factor were measured within the frequency range from 1 mHz to 10 kHz at different temperatures by a capacitance method. The dielectrics parameters were measured as a function of the external magnetic field in the range of 0-200 mT, parallel to the direction of the electric field as a function of temperature in the range of 15-35 ¥ C. The interaction between magnetic field and magnetic moments of nanoparticles led to the aggregation of magnetic nanoparticles to new structures which had influence on dielectric parameters. The dependence of these parameters at constant magnetic field on angle between the direction of the electric and magnetic fields (anisotropy) has been measured, too.
The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electri... more The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electric and weak magnetic fields were studied by means of the attenuation of surface acoustic wave of frequency 30 MHz propagating along ferronematic liquid crystals. Three low volume concentrations (Φ = 1 × 10 −5 , 1 × 10 −4 and 1 × 10 −3) of rod-like magnetic particles were added to liquid crystal during its isotropic phase. Several measurements including the investigation of the effects of electrical and magnetic fields applied both separately and in conjunction as well as the influence of temperature on the surface acoustic wave attenuation were performed. The distinctive surface acoustic wave attenuation responses induced by both electric and magnetic fields in studied ferronematic liquid crystals have been observed suggesting both structural changes and the orientational coupling between magnetic moments of magnetic particles and the director of the liquid crystal. Obtained results confirmed the significant influence of the presence of magnetic particles on the structural properties and resulting behavior of 6CHBT liquid crystal.
The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in t... more The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in the ultralow frequency regime was investigated. A dielectric relaxation, whose relaxation time is 160 s, is observed at 303 K, and the dielectric relaxation is found to be independent of applied electric field. It is shown that the dielectric relaxation is caused by the Helmholtz double layer formed by the adsorption of impurity ions in 5CB onto the electrode surfaces of the cells, and hence the thickness of the double layer is comparable to the radius of impurity ions in 5CB. The dielectric relaxation obeys the empirical Cole‐Cole circular arc law, indicating that dielectric relaxation times are distributed. The distribution of dielectric relaxation times can be explained in terms of distributed thicknesses of the Helmholtz double layer.
Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)a... more Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)applications. Multimodal imaging as well as simultaneous control and monitoring of intracellular movements profit from the combination of these functionalities. Accordingly, several methods have been developed for the synthesis of magnetic fluorescent particles. The majority of these methods, however, require complex modification and purification steps and result in a low yield of particles. Here, we describe a straightforward and scalable method for the magnetic modification of cellulose-based fluorescent particles. The method is based on the use of microwave-synthesized magnetite nanoparticles prepared from ferrous sulfate at high pH. Magnetic modification did not change the pH sensitivity or the optical properties of the fluorescent particles, and allowed them to be manipulated by external magnetic field. Our results demonstrate the possibility of large scale, easy production of bifunctional particles. We anticipate that our method can be expanded to include other types of particles or functionalities relevant for biomedical applications.
Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. T... more Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. They appear to be a suitable carrier for the targeted drug transport, which represents a new method of cancer treatment. Advantages of targeted drugs transport are the minimizing of hurt to the organism, specific focusing on certain types of tissues, increased effect of the drug, reduced drug dose and hence side effects. The main goal of the present study was to verify the effect of bacterial magnetic nanoparticles produced by
The influence of Fe 3 O 4 nanoparticles on dielectric properties of planar oriented liquid crysta... more The influence of Fe 3 O 4 nanoparticles on dielectric properties of planar oriented liquid crystal were studied at the frequency range10 1 -10 6 Hz and in temperature interval of 292 -345 K. It was shown that the dielectric spectrum of doped liquid crystal can be divided into two areas. Parameters obtained from the dielectric spectrum for frequencies lower than 10 Hz characterize near electrode processes, and parameters obtained for frequencies more than 10 Hz characterize the bulk properties of the sample. The relaxation time and near-electrode area thickness have been estimated. It was experimentally shown that magnetic nanoparticles change the near-electrode area parameters.
Liquid crystals (LCs) composed of mesogens play important roles in various scientific and enginee... more Liquid crystals (LCs) composed of mesogens play important roles in various scientific and engineering problems. How a system with many mesogens can enter a LC state is an interesting and important problem. Using stiff and free-joint Lennard-Jones chain molecules as mesogens, we study the conditions under which the mesogens can enter various LC phases. The guideline is to eliminate the unwanted translational orders under a controlled fine-tuning procedure across a sequence of systems. Instead of monitoring the growth of order out of the disorder, we prepare a configuration of high orientation ordering and find out where it relaxes to. Such a procedure begins with a reference system, consisting of short chains of homogeneous soft spheres, in a liquid-vapor coexistence situation, at which the thermodynamic instability triggers a fast spontaneous growing process. By applying a short pulse of auxiliary field to align the dispersedly oriented clusters, followed by reducing the volume and,...
A broadband dielectric response of ferrofluids can be effectively controlled by application of an... more A broadband dielectric response of ferrofluids can be effectively controlled by application of an external magnetic field. The interaction of magnetic nanoparticles with magnetic forces and the resulting structural changes in the ferrofluids may tune their dielectric spectra. In this paper, we present an experimental study on the controllability of a dielectric spectrum of Mn-Zn ferrite transformer oil-based ferrofluid by means of a static electric field generated by a direct current (DC) bias voltage. Two experimental configurations of the DC bias voltage are applied. The spectrum of a complex permittivity measured in the frequency range from 1 mHz up to 200 kHz is firstly studied under an internal DC bias voltage applied on the electrodes of a measuring capacitor. Then, the sensitivity of the dielectric spectrum to the external DC bias voltage applied on an external pair of electrodes outside the measuring capacitor is investigated. It is found that the increasing internal DC bias...
In the human body the protein amyloid aggregates, due to their deposition in specific tissues or ... more In the human body the protein amyloid aggregates, due to their deposition in specific tissues or organs, are associated with many serious diseases (diabetes mellitus, Alzheimer's disease, etc.). Recently, we have found that magnetite nanoparticles have ability to affect amyloid aggregatation of lysozyme and insulin [1][2]. In our study we examine effect of magnetoferritin (MFer), biocompatible magnetite nanoparticles, on lysozyme amyloid aggregates (LAA) associated with lysozyme systemic amyloidosis. The interference of LAA and MFer was investigated at ratios of LAA:MFer = 1:1 and 1:5 using small angle X-rays scattering technique (SAXS) and Thioflavin T fluorescence measurements (ThT assay). By controlled chemical synthesis magnetoferritin complexes with two loading factors (LFnumber of iron atoms per one complex) of 168 (MFer(168)) and 532 (MFer(532)) were prepared. SAXS experiments indicate that presence of MFer caused structural changes of LAAs. Analysis of data obtained for solution containing LAA with MFer(532) (LAA:MFer = 1:5) clearly indicate decreasing of the lower limit of radius of gyration from 30 nm to 20 nm compare to lysozyme fibrils alone and almost non-effected structure of MFer complexes (Fig. 1). These results suggest reduction of LAA, probably due to the truncation of the LAA by MFer. The decreasing of the amount of LAA was observed also by ThT assay. The fluorescence intensities of LAA in presence of MFer(532) and MFer(168) was significantly decreased-40% and 55% decay (ratio 1:1) and 50% and 62% decay (ratio 1:5). These data strongly support SAXS data assuming reduction of the LAA as results of their interaction with MFer. The interaction between lysozyme amyloid aggregates (LAA) and biocompatible magnetite nanoparticles (magnetoferritin, MFer) have been investigated by Thioflavin T fluorescence 1 measurements (ThT assay), small-angle X-rays scattering (SAXS) and transmission electron microscopy (TEM). The influence of concentration and degree magnetite loading (loading factors) of MFer has been examined during LAA formation (inhibition) and after LAA formation (depolymerisation) experiments. Results suggest the reduction of LAA size in the case of high concentration and LF of added magnetoferritin during depolymerisation, probably due to the truncation of the LAA by MFer. Shell structure of MFer is observed in LAA/MFer mixtures.
Control of the size and spatial distribution of materials at multiple length scales is one of the... more 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.
The electric Fredericksz transition in 8CB-based ferronematics exposed to strong magnetic field w... more The electric Fredericksz transition in 8CB-based ferronematics exposed to strong magnetic field was studied both theoretically (by means of the Burylov and Raikher's theory) and experimentally (using capacity measurements). The estimated values of anchoring energy of order WB10 À4 N/m and parameter oB124 indicate the presence of intermediate type of anchoring (between soft and rigid) in studied thermotropic ferronematic.
The structural transitions in ferronematic based on 8CB and 6CHBT, exposed to combined electric a... more The structural transitions in ferronematic based on 8CB and 6CHBT, exposed to combined electric and magnetic fields, are investigated. The influence of the presence of magnetic admixture on the Fredericksz transition threshold is studied. Using the found dependencies of critical fields on increasing magnetic particles volume concentration the type of anchoring was determined as soft with m?n in 8CB and mJn in 6CHBT-based ferronematics.
The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and th... more The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and the carrier liquid. The structural changes in magnetic fluids with different nanoparticle diameter based on transformer oils TECHNOL and MOGUL under the effect of a magnetic field and temperature were studied by acoustic spectroscopy. At a linear and jump changes of the magnetic field at various temperatures a continuous change was observed of acoustic attenuation caused by aggregation of the magnetic nanoparticles to structures. From the anisotropy of acoustic attenuation and using the Taketomi theory the basic parameters of the structures are calculated and the impact of nanoparticle diameters on the size of structures is confirmed.
Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core... more Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core diameter of about 30nm results from TEM, XRD and magnetic analysis. Specific loss power is determined from hysteresis loops, susceptibility spectra and calorimetry with ...
Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse sp... more Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse spleen ferritin (HSF) and nanoscale magnetite aqueous suspensions. The anisotropy of optical polarizability was calculated. The average magnetic dipole moment calculated assuming the Langevin model was about 20,000 and 8500μB per particle, for magnetite nanoparticle and magnetoferritin, respectively. Poor fitting results and the unphysical value of average magnetic moment
The aim of the presented work was to investigate the stability of biocompatible magnetic uid, i.e... more The aim of the presented work was to investigate the stability of biocompatible magnetic uid, i.e. water-based magnetic uid containing magnetite nanoparticles stabilized by surfactant sodium oleate and modied by bovine serum albumin (BSA) after electron irradiation. Samples with the same concentration of Fe3O4 but dierent mass ratio BSA/Fe3O4 (w/w= 0.25, 1.0 and 2.5) were studied. The electron irradiation caused about 10% reduction of the saturation magnetization in the samples with w/w BSA/Fe3O4 ratio of 0.25 and less than 5% in the samples with w/w BSA/Fe3O4 ratio of 1 and 2.5.
Peptide amyloid aggregation is a hallmark of several human pathologies termed amyloid diseases. W... more 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.
Uploads
Papers by Milan Timko