O. N. Sorokina

Analysis of the ferromagnetic resonance spectra of aggregates of magnetite nanoparticles formed by a magnetic field

The ferromagnetic resonance (FMR) spectra of magnetite nanoparticles in aqueous solutions and solid polymer films were analyzed at different particle concentrations, matrix rigidities, temperatures, external magnetic effects, and positions of flat samples in the field of the spectrometer. The formation of linear aggregates of nanoparticles under the influence of magnetic fields is the major factor that changes the FMR spectrum shape and position. The results were analyzed in terms of phenomenological theory of FMR. The applicability of the equations of phenomenological theory was verified, and the fraction of nanoparticles in linear aggregates was evaluated.

Free-radical cross-linking of serum albumin molecules on the surface of magnetite nanoparticles in aqueous dispersion

A novel universal approach to cross-linking of protein macromolecules on the surface of magnetite nanoparticles has been developed. The approach is based on protein liability to free-radical modification, leading to the formation of intermolecular covalent cross-links. Free radicals are locally generated on the surface of nanoparticles. Stable coatings of serum albumin 3 nm thick are formed on the surface of magnetite nanoparticles. Using a set of physicochemical methods, it has been proven that stable coatings composed of protein macromolecules are formed around individual nanoparticles. The presence of reactive groups in the protein structure makes it possible to perform subsequent modification of the surface layers-in particular, to graft nonprotein drugs. The approach developed can be used to create superfine systems with desired surface properties for targeted delivery of drugs and biologically active substances.

Study of protein coatings cross-linked via the free-radical mechanism on magnetic nanoparticles by the method of spectral and fluorescent probes

Magnetite nanoparticles have been obtained with stable coatings formed from bovine and human serum albumins. The coatings are fixed by free-radical cross-linking of the proteins with the use of their ability to form interchain covalent bonds under the action of free radicals, which are generated with participation of transition metals present on nanoparticle surface. The method of spectral and fluorescent probes has been employed for the first time to describe the properties of coatings with the use of various dyes. It has been shown that, when studying the adsorption and free-radical cross-linking of proteins on nanoparticles, it is reasonable to use polymethine and squarylium dyes for estimating the functional properties of the proteins forming the coatings. It has been found that as many as 50% of molecules forming an albumin coating crosslinked via the free-radical mechanism retain their capability of bonding to a fluorescent dye. It has been concluded that the proteins occurring in the structure of the coatings retain their functional properties.

Interaction of fibrinogen with magnetite nanoparticles

The interaction between fibrinogen and magnetite nanoparticles in solution has been studied by the methods of spin labeling, ferromagnetic resonance, dynamic and Rayleigh light scattering. It is shown that protein molecules adsorb on the surface of nanoparticles to form multilayer protein covers. The number of molecules adsorbed on one nanoparticle amounts to ∼65 and the thickness of the adsorption layer amounts to ∼27 nm. Separate nanoparticles with fibrinogen covers (clusters) form aggregates due to interactions of the end D domains of fibrinogen. Under the influence of direct magnetic field, nanoparticles with adsorbed proteins form linear aggregates parallel to the force lines. It is shown that the rate of protein coagulation during the formation of fibrin gel under the action of thrombin on fibrinogen decreases ∼2 times in the presence of magnetite nanoparticles, and the magnitude of the average fiber mass/length ratio grows.

Interaction between blood plasma proteins and magnetite nanoparticles

Spin label EPR spectroscopy and dynamic and Rayleigh light scattering are employed to study the interaction between magnetite nanoparticles with a diameter of 17 nm and plasma proteins (fibrinogen and albumin). Protein molecules are shown to be adsorbed on nanoparticle surface with the formation of multilayer shells. When a buffer solution (pH 8.5) contains 0.01 vol % nanoparticles, 90–100 fibrinogen molecules are adsorbed per one particle and the thickness of an adsorbed layer is 30–40 nm. For albumin, the layer thickness is 10–15 nm. In a constant magnetic field, large linear microsized aggregates oriented parallel to field lines are formed in dispersions of nanoparticles covered with adsorbed protein molecules. The study of fibrin gel formation resulting from the action of thrombin enzyme on fibrinogen suggests that, in the presence of nanoparticles, the rate of gelation decreases by a factor of approximately two, while the ratio between the average mass and average length of fibrin polymer fibers rises.

ESR line shape of paramagnetic particles in a magnetic liquid. Theory and experiment

A basic model has been proposed to describe the resonance spectra of the paramagnetic sensor particles in dispersions of magnetic nanoparticles aggregated in chains. A theory of the line shape of low-mobility sensors has been developed in the case of chains of a sufficiently homogeneous length. A specific line shift has been shown to appear in such systems and the spectrum may be asymmetric. The ESR spectra of a magnetite-based magnetic liquid have been measured and the main parameters of the chains have been determined.

High-gradient magnetic separation of microparticles on membrane separation unit

A simple design of a magnetic separator based on a membrane made of a laser-perforated ferromagnetic foil has been proposed. The separator is primarily intended for analytical and research purposes. The developed magnetic separator of the proposed design has been tested in the separation of a composite aqueous suspension of magnetite nanoparticles adsorbed on hydroxyapatite microparticles. Separation efficiency has been determined via measuring the magnetic moment by the ferromagnetic resonance method; the suspension particle size has been found by dynamic light scattering before and after the separation process. It has been shown that all the particles with a diameter of more than 500 nm are retained during separation; the magnetization of the fraction decreases twofold after passing through the membrane.

Electronic excitation energy transfer between molecules of cyanine dyes in a complex with protein and in systems of magnetic nanoparticles with protein coatings

Electronic excitation energy transfer (EEET) between molecules of carbocyanine dyes bound noncovalently with human serum albumin (HSA) has been studied. 3,3′-Di-(gamma-sulfopropyl)-9-methylcarbocyanine betaine has been used as an electronic excitation energy donor and 3,3′-di-(gamma-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine, as an acceptor dye. EEET has been studied both in samples of HSA solutions and in systems containing protein-coated magnetic nanoparticles. Stable coatings of magnetic nanoparticles, consisting of a mixture of HSA and bovine serum albumin, have been formed by the method of free radical linking of protein molecules adsorbed on the surface of the particles. The effect of HSA denaturation on the spectral and fluorescent properties of the dyes and EEET has been studied, and the data on donor fluorescence quenching by the acceptor have been obtained. It has been concluded that HSA retains its functional properties in the linked coating, thereby providing evidence for biocompatibility of the coatings obtained by free-radical oxidative protein modification.

Study of protein coatings on magnetic nanoparticles by the method of spectral and fluorescent probes

268 Creation of biocompatible coatings on the surface of magnetic nanoparticles (MNP) opens up the pros pects for their use in medicine [1, 2]. Of particular interest is creation of stable coatings based on pro teins. The novel free radical method of creation of sta ble protein coatings on the surface of individual MNP, which is based on the ability of proteins to undergo modification with formation of interchain covalent bonds under the action of free radicals generated on the surface of MNP by the Fenton reaction [3], per mits overcoming the problems conventionally appear ing upon creation of protein coatings on the surface of MNP: the formation of a polydisperse ensemble of particles, nonselective linking of proteins leading to crosslinking of macromolecules in solution, and des orption of coatings [4, 5]. Recently [6] the free radical method has been realized for serum albumin. The coatings obtained were formed on individual nanopar ticles and were characterized by high stability. To date, different approaches have been developed to study the processes of protein adsorption on nanoobjects and functional properties of proteins with the use of IR spectroscopy, UV spectrophotometry, ESR spectros copy of spin labels, and other techniques [6, 7]. These approaches are of limited use as regards studying the functional properties of proteins adsorbed on MNP. The aim of this communication is to develop a spectral and fluorescent method for studying the adsorption processes of proteins and their functional properties in MNP coatings linked by the free radical mechanism.

The application of the spin label method for studying the adsorption of macromolecules on magnetic nanoparticles

A procedure for using spin-label EPR spectroscopy in studies of the adsorption of macromolecular systems on magnetic nanoparticles and quantitative characterization of adsorption layers was developed. The procedure was based on measurements of the intensity of EPR signals of stable nitroxide radical labels covalently bound with macromolecules. The adsorption of spin-labeled macromolecules on the surface of nanoparticles caused broadening of EPR lines as a result of the dipole interaction of unpaired radical electrons with the magnetic moment of particles, which decreased signal intensity. Multilayer adsorption in aqueous media of biological fibrinogen molecules and synthetic polymer (polyethyleneimine) on magnetite particles with a mean diameter of 17 nm was studied. The method was shown to be applicable to the estimation of the amount of adsorbed macromolecules in multilayer coatings up to ∼40 nm thick.