Sergey V. German

Synthesis of magnetite hydrosols in inert atmosphere

A setup is described for magnetite hydrosol synthesis in inert atmosphere via coprecipitation of bi- and trivalent iron salts in the presence of a base with the formation of nanoparticles having desired sizes and chemical composition. The size of nanoparticles is estimated based on analysis of light-scattering and transmission-electron-microscopy data. The chemical composition of magnetite nanoparticles is monitored by Raman spectroscopy.

Synthesis of magnetite hydrosols and assessment of their impact on living systems at the cellular and tissue levels using MRI and morphological investigation

MRI and morphological investigations into internal organ tissues and tumors in rats with liver cancer PC-1 under the intraperitoneal administration of magnetite hydrosols have been performed. The absence of any toxic effect of magnetite nanoparticles at low concentrations (0.325 mg/mL) has been determined using neutrophil granulocytes. A technique for the synthesis of citrate-stabilized magnetite hydrosols by the coprecipitation of Fe2+ and Fe3+ salts is described. Their electrokinetic potential is −32 ± 2 mV at pH 6.5 ± 0.1. The size distribution of magnetite nanoparticles is obtained by dynamic light scattering. The average size of magnetite nanoparticles is 23 ± 6 nm. The absorption spectra of magnetite hydrosols have been measured. The dependence of the optical density on the concentration has also been obtained. Molar absorption coefficients of magnetite nanoparticles have been calculated at the following wavelengths: 532, 633, 660, and 785 nm.

Composite magnetic microcapsules based on multilayer assembly of ethanol-soluble polyimide brushes and magnetite nanoparticles: preparation and response to magnetic field gradient

Microcapsules consisting of a calcium carbonate core template surrounded by shells containing magnetite nanoparticles and ethanol-soluble polyimide brushes with polymethacrylic acid side chains were assembled using a layer-by-layer technique under nonaqueous conditions. These microcapsules represent a potential solution to the challenging problem of encapsulating water-soluble compounds, particularly low molecular weight drugs. It was possible to move these microcapsules with magnetite nanoparticles in their shells by applying a magnetic field gradient. The novel microcapsules were characterized by optical microscopy, atomic force microscopy, and scanning electron microscopy. Using the brush-like polyanions instead of linear polyanions made it possible to increase the shell thickness gain per ionic assembly cycle by a factor of ~3.

Temperature dependence of the fluorescence spectrum of ZnCdS nanoparticles

The temperature sensitivity of the spectral characteristics of ZnCdS nanoparticles both stabilized and coated with polyacrylic acid is compared. It is shown that the luminescence of the nanoparticles has two temperature-dependent parameters, namely, the intensity and the peak position. Variations in these parameters are due to the distortion of the energy states of luminescent surface defects. Aggregation of the nanoparticles does not distort obtained dependencies. Temperature sensitivity is higher for the nanoparticles coated with a layer of polyacrylic acid.

An investigation of the morphology of Langmuir films based on molecular polyimide brushes containing magnetite nanoparticles

Molecular brushes having a polyimide (PI) backbone with degree of polycondensation n = 33 and polymethylmethacrylate (PMMA) side chains with two different degrees of polymerization (m = 63 and m = 114) were synthesized by the method of controlled atom transfer radical polymerization. Hydrophobic magnetite nanoparticles of a size of 18 ± 2 nm were prepared. Langmuir monolayers on the basis of the polyimide brushes and composite monolayers, containing magnetite nanoparticles with a hydrophobic surface, were formed at the water/air interface. It is found that, in the condensed state of the monolayer at the surface pressure values from 25 to 40 mN/m, the limiting surface area A0 per side chain of a brush grows with an increase in the length of PMMA side chains of polymer brushes almost by a factor of 2: from A0 = 744 ± 64 Å2 for PI-graft-PMMA-63 to A0 = 1644 ± 50 Å2 for PI-graft-PMMA-114. Increasing the magnetite solution aliquot mixed with the polymer brush solution at the ratios from 1 : 2 and 1 : 1 to 2 : 1 leads to a rise in the limiting surface area values A0 to 1072 ± 59 Å2 for the first two ratios to 2534 ± 79 Å2 for the third one. The obtained monolayers were transferred onto mica by the Langmuir-Schaeffer method at different surface pressure values (0.5, 10, and 25 mN/m). With the use of the method of atomic force microscopy, it is shown that a four- to sixfold increase in the mean roughness of a composite film surface due to the inclusion of magnetite nanoparticles into the polymer brush monolayer is typical of all samples.

Encapsulated Magnetite Nanoparticles

Abstract Encapsulated magnetite nanoparticles (NPs) as a part of drug delivery systems have a good perspective for their tracking, navigation, and remote activation. Embedding of NPs to the drug delivery carriers can allow us to decrease the toxicity of magnetite NPs, to vary a contrast of T1 and T2 MRI imaging, and to apply the alternative magnetic field for controlled release of encapsulated bioactive substances. The efficiency and safety of magnetite NPs as a multifunctional tool for drug delivery systems have also been discussed.

Imaging and navigation of remote controlled nanostructured carriers for theranostics (Conference Presentation)

The modern medicine requires the new type of drug delivery carriers that will combine functions of in vivo navigation and visualization ability to deploy drug in controllable manner, including external triggering. This combination can be realized by multifunctional carriers produced by layer-by-layer assembly method. The carrier biodistribution can be controlled by a chosen mode of in vivo administration. Realization for chemical targeted delivery based on surface modification are not working well in vivo due to the corona effect [Kreyling W. et al., Nature Nanotech., 2015, 619]. Thus, physical targeting of drug delivery is more promising approach. It can be realized by gradient of magnetic field [Voronin D. et al., ACS App. Mater. & Interfaces, 2017, 6885], optical tweezers [Stetciura I. et al., Analyst, 2015,4981]. It was demonstrated that the sensitivity of nanostructured carriers to external influences as laser irradiation, ultrasound treatment can be changed by variation of volume fraction and chemical composition of inorganic nanoparticles in the carrier shell [Korolovych V. et al., PCCP, 2016,2389]. Same approach is applied for nanostructured carriers (NCs) imaging by MRI [German S. et al., PCCP, 2016, 32238], OCT [Genina E. et al., Biomed.Opt.Express, 2016, 2082] and photoacoustic method [Yashchenok A. et al., J. Biophotonics, 2016, 792] using magnetite and gold nanoparticles as contrast agents, respectively. Obtained NCs can be used as drug delivery systems including drug depot, combined much functionalities as navigation and visualization, in vivo monitoring of biochemical process, remote activated release of bioactive substances.