The determination of the amount and composition of artificial polymer microparticles in ponds requires the preparation of representative water samples. A new method has been proposed in this work for magnetic separation of polyethylene microparticles (PEMPs, 10–200 μm), with the method implying their aggregation with magnetic nanoparticles. Composite magnetic nanoparticles containing magnetite cores and silica shells functionalized with amino groups (Fe3O4@SiO2–NH2, dhydr = 200 nm) have been synthesized and characterized. Due to electrostatic interactions, these nanoparticles can form aggregates with polyethylene particles and be separated from water under the action of a gradient magnetic field. The effects of added salts (NaCl, Na2SO4, NaH2PO4, and CaCl2) and a surfactant, sodium dodecyl sulfate (SDS), on the separation conditions of PEMPs from water have been studied. It has been shown that the addition of the magnetic particles in concentration c = 0.01 g/L to aqueous suspensions containing NaCl and NaH2PO4 (c = 10 mM), and SDS (c = 3 mM) provides an efficiency of magnetic separation of PEMPs equal to, at least, 98

A procedure for determining lithium concentration in formation waters by NMR relaxometry is proposed. The method makes it possible to quickly determine the lithium content for concentrations of industrial interest. The experiments have shown good agreement between the data obtained by the proposed method and the data obtained by the induction coupled plasma (ICP) method.

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T 2 by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T 2 , wich makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T 2 on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry. Keywords: porous media, fluid flow, NMR-relaxometry, magnetic nanoparticles.

A procedure has been proposed for determining the concentration of lithium in formation waters using NMR relaxometry. The method allows to determine quickly lithium content at concentrations of industrial interest. Experiments showed good agreement of the proposed method with the inductively coupled plasma (ICP) method.

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T2 by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T2, with makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T2 on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry. V.V.Maikov, S.V.Zhakov, I.V.Byzov, A.A.Mysik

Micro- and nanofragments resulting from the decomposition of disposable plastic items might be dangerous for the environment and humans. A new approach based on a “green” environmental technology of microplastic particles removal by magnetic sedimentation is suggested. In order to remove polyethylene (PE, 10–200 µm) and polyethylene terephthalate (PET, 5–30 µm) particles from model aqueous suspensions (starting concentration of 0.1 mg/l), the composite magnetic Fe–C–NH2 particles (4–8 nm) were added, afterward, the magnetic sedimentation of the formed heteroaggregates in a gradient magnetic field produced by permanent magnets was conducted. Magnetic nanoseeds were synthesized by the gas condensation method and characterized by magnetization measurements. The conditions for the heteroaggregation and for the magnetic sedimentation of the heteroaggregates have been investigated. For this, the dynamic light scattering analysis, SEM, optical microscopy, XRD and UV-visible spectrophotometry were used. The amount of the added magnetic nanoparticles (0.005 g/l) is less for the PET compared to the PE microparticles, which can be caused by a combination of several factors, in particular, by a higher hydrophilicity of PET particles which promotes a more active attachment of magnetic nanoparticles. For a more efficient removal of both plastic and magnetic particles from water, an increased up to 3–5 h time exposure for the heteroaggregation is recommended. At the magnetic field gradients up to dB/dz = 90 T/m, a 100-fold reduction in the plastics concentration in water after 15 min was achieved.

In vitro systems serve as compact and manipulate models to investigate interactions between different cell types. A homogeneous population of cells predictably and uniformly responds to external factors. In a heterogeneous cell population, the effect of external growth factors is perceived in the context of intercellular interactions. Indirect cell co-cultivation allows one to observe the paracrine effects of cells and separately analyze cell populations. The article describes an application of custom-made cell co-cultivation systems based on protein membranes separated from the bottom of the vessel by the 3d printed holder or kept afloat by a magnetic field. Using the proposed co-cultivation system, we analyzed the interaction of A549 cells and fibroblasts, in the presence and absence of growth factors. During co-cultivation of cells, the expression of genes of the activation for epithelial and mesenchymal transitions decreases. The article proposes the application of a newly available system for the co-cultivation of different cell types.

The dynamics of magnetic separation of TiO2 nanoparticles (25 nm) from water by adding composite magnetic Fe-C-COOH nanoparticles (15 nm) and subsequent magnetic sedimentation or magnetic filtration has been studied. Magnetic sedimentation was carried out in a gradient magnetic field (H-max = 0.3 T, (gradH)(max) = 0.13 T/m), and magnetic filtration (H-max = 0.5 T, (gradH)(max) similar to 10(5)T / m) was carried out in a column bench filter with a steel wool magnetic matrix. The applied methods of spectrophotometry using the PLS algorithm and nuclear relaxometry made it possible to determine the partial concentrations of the target TiO2 particles and of the magnetic seeds in water. Oppositely charged target TiO2 nanoparticles and magnetic Fe-C-COOH nanoparticles formed heteroaggregates in water, the size of which depended on the pH of the aqueous medium, on the ratio of their concentrations, and on the concentration of the solid phase in water. The maximum efficiency of TiO2 separation from water by both methods was observed at pH = 6, at which the electric charge of the aggregates was minimal. The largest heteroaggregates (with d(h) - 3 mu m) are formed at initial concentrations of TiO2 nanoparticles of 0.1-0.5 g/l and at the 2:1 mass ratio of the nonmagnetic and magnetic components. Magnetic filtration is a more efficient separation process than magnetic sedimentation due to higher magnetic field gradients applied. It was found that by adding Fe-C-COOH magnetic nanoseeds, the magnetic filtration at a flow rate of 7 * 10(-3) m/s through a filter of the 50 cm length, leads to the reduction of the TiO2 concentration in water from 0.5 g/l to 3 * 10(-4) g/l for 10 min. The results obtained can serve as a basis for designing a magnetic separation unit in photocatalytic reactors for water purification.

Two variants of automatic correction of temperature variations of a constant magnetic field in the system of a permanent magnet NMR relaxometer are described. In the first version, the magnetic flux correction in the magnetic circuit of the system is used with a magnetic shunt, which is moved by a stepping motor. In the second version, the field is corrected by the current in the coils placed on the magnetic circuit of the magnetic system. Correction of the field is carried out automatically during the tuning of the resonant frequency of the device. The proposed methods make it possible to correct the relative change in the magnetic field within 1%, which covers possible temperature variations of the magnetic field in the entire range of room temperatures when using magnets based on neodymium–iron–boron and samarium–cobalt alloys (NdFeB and SmCo).

Magnetic iron nanoparticles (MNPs) encapsulated in a carbon shells and containing sulfo groups on the surface (Fe@C-SO3H) were synthesized. The aggregative stability of aqueous suspensions of the Fe@C-SO3H nanoparticles was studied in solutions of bovine serum albumin and calcium chloride and in phosphate-buffered saline, which simulate blood plasma. It is shown that the Fe@C-SO3H particles practically do not aggregate in the phosphate buffer saline for a long time (several days). On the contrary, MNPs encapsulated in a protein shells using ultrasonic treatment form aggregates up to 110–120 nm in size under these conditions. Suspensions of the Fe@C-SO3H particles are stable in aqueous solutions of calcium chloride in the range of the solid phase concentration between 0.05 and 0.10 g L−1. The results obtained indicate the possibility of using the functionalized Fe@C-SO3H nanoparticles in vitro experiments in biological media.

Gd2O3, SiO2-Gd2O3 and SiO2-MnO2 nanoparticles w.re produced by the method of pulsed electron evaporation of oxide targets with condensation of the vapors in a vacuum. These materials are considered as probable contrast agents for magnetic resonance imaging (MRI). The Gd2O3 nanoparticles exhibit a rather high r1 and r2 relaxivities. These results point to the potential of using nanocrystals for MRI diagnosis. The mesoporous nanostructures SiO2-Gd2O3 and SiO2-MnO2 could be considered as multimodal theranostic agents.

Core–shell CoFe@C and NiFe@C nanocomposites were prepared by gas-condensation synthesis. CoFe@C and NiFe@C particles had bcc and fcc cores, respectively. The treatment of these nanocomposites with hydrochloric acid revealed that they are more chemically stable than Fe@C composites. The maximum specific magnetization of CoFe@C and NiFe@C nanocomposites at room temperature in the field with a strength of 27 kOe was 125 and 58 G cm 3 /g, respectively. The processes of longitudinal and transverse relaxation of nuclear proton spins of aqueous suspensions of nanocomposites in various magnetic fields (0.5, 1, and 2 kOe) were studied. NiFe@C and CoFe@C nanocomposites have high transverse relaxivity values and can be used as magnetic markers for detection of low concentrations of bioobjects by NMR relaxometry.

The possibility of using the transverse relaxation time T2 of protons in aqueous media for quantitative measurement of the capture of magnetic nanoparticles by cells has been studied and demonstrated. The measurement of T2 was performed on a portable original NMR relaxometer with a measuring cell for a standard well of a biological plate. The novelty of the approach is that quantitative measurements of the capture kinetics were carried out using measurements of the proton relaxation time of the nutrient medium, which is determined by the remaining number of magnetic particles (not captured by the cells) in the medium. To study the kinetics of capture, two types of magnetic nanoparticles were synthesized: magnetite particles Fe3O4 and composite particles Fe@C with an iron-carbon shell structure. The surface of the particles was functionalized with amine-and carboxyl groups. The capture of aminated particles of Fe@C cells is established by microscopy and NMR-relaxometry by measuring the time T2. It is shown that the proposed method makes it possible to register very small concentrations of trapped magnetic nanoparticles equal to tens of pg/cell.

The method for determination of the component partial concentrations in mixed two-component water suspension from the UV spectrophotometry by applying the PLS algorithm is suggested. This quantitative method does not require special probe preparations, it is convenient and inexpensive and it can be realized for water quality monitoring by using portable devices. As an example, the water suspensions of TiO2 and Fe3O4—coated by SiO2 nanoparticles were analyzed. The concentration range for the simultaneous determination of nanoparticles is 0.5–10 mg/l. The relative standard errors for single components determination are 1.8% for TiO2 and 3.9% for Fe3O4-coated by SiO2. The processes of nanoparticles aggregation in the studied mixed suspensions are reversible and do not distort significantly the results of the partial concentrations determination. The method suggested can be used for detection of the residual partial concentrations of titanium oxides and iron-containing nanoparticles in water treatment technologies.

A comparative analysis of the structure and magnetic properties of nanoparticles of Fe-Ni and Fe-Co alloys without carbon and encapsulated in carbon obtained by gas-condensation synthesis is carried out. Particular attention is paid to the study of the formation of a solid solution in nanoparticles with carbon. X-ray analysis and magnetic properties convincingly demonstrate that a disordered supersaturated solid solution of carbon in FeNi@C and FeCo@C nanoparticles is formed. (C) 2019 Elsevier B.V. All rights reserved.

H1 NMR relaxometry is a method that is extremely sensitive to the presence of magnetic nanoparticles, which significantly affect the transverse relaxation time of the water proton. Accordingly, the use of magnetic nanoparticles as labels allows detection of even extremely small amounts of the test substance. This paper analyzes the prospects for applying the method of solid-phase NMR-relaxometric determination of biologically active molecules. The nitrocellulose membranes are chosen as a solid phase and nanoparticles based on iron core with a carbon shell are used as magnetic labels. The possibility of detecting small concentrations of magnetic particles in porous medium is demonstrated. Finally, the ability to detect extremely low concentrations of an analyte, in this case, streptavidin protein (0.5 ng/ml to 100 ng/ml), which is actively used in various fields of biology and medicine, is demonstrated.

— Nanopowders Ni@C synthesized by gas condensation have a core-shell structure. The size of the core is 2–10 nm and the thickness of the shell is 1–3 nm. The changes in the magnetic properties and the structure of these particles upon annealing in the 100–1100°C temperature range are investigated in this work. Analysis of changes in the magnetic properties, the structure, and the chemical stability shows that the core of the particles in the initial state after synthesis is a supersaturated solid solution of carbon in nickel, which decomposes into nickel and carbon upon high-temperature annealing. Rather slow cooling of nickel particles causes the carbon shell to form. The shell ensures their chemical stability.