Atomic Force Microscopy Methods Research Articles

Studying the structure and function of nucleosomes by atomic force microscopy

Chromatin is an epigenetic platform for the implementation of DNA-dependent processes. The nucleosome, as the basic level of chromatin compaction, largely determines its properties and structure. When studying the structure and functions of nucleosomes, physicochemical tools are actively used, such as magnetic and optical “tweezers,” “DNA curtains,” nuclear magnetic resonance, X-ray diffraction analysis and cryoelectron microscopy, as well as optical methods based on FRET. Despite the fact that these approaches make it possible to determine a wide range of structural and functional characteristics of chromatin and nucleosomes with high spatial and temporal resolution, atomic-force microscopy (AFM) complements the capabilities of these methods. This review presents the results of structural studies of nucleosomes in view of the development of the AFM method. The capabilities of AFM are considered in the context of the use of other physicochemical approaches.

Structural features of skeletal muscle titin aggregates

Titin is a multidomain protein of striated and smooth muscles of vertebrates. The protein consists of repeating immunoglobulin-like (Ig) and fibronectin-like (FnIII) domains, which are β-sandwiches with a predominant β-structure, and also contains disordered regions. In this work, the methods of atomic force microscopy (AFM), X-ray diffraction and Fourier transform infrared spectroscopy were used to study the morphology and structure of aggregates of rabbit skeletal muscle titin obtained in two different solutions: 0.15 M glycine-KOH, pH 7.0 and 200 mM KCl, 10 mM imidazole, pH 7.0. According to AFM data, skeletal muscle titin formed amorphous aggregates of different morphology in the above two solutions. Amorphous aggregates of titin formed in a solution containing glycine consisted of much larger particles than aggregates of this protein formed in a solution containing KCl. The “KCl-aggregates” according to AFM data had the form of a “sponge”-like structure, while amorphous “glycine-aggregates” of titin formed “branching” structures. Spectrofluorometry revealed the ability of titin “glycine aggregates” to bind to the dye thioflavin T (TT), and X-ray diffraction revealed the presence of one of the elements of the amyloid cross β-structure, a reflection of ~4.6 Å, in these aggregates. These data indicate that the “glycine-aggregates” of titin are amyloid or amyloid-like. No similar structural features were found in titin “KCl-aggregates”; they also did not show the ability to bind to thioflavin T, indicating the non-amyloid nature of these titin aggregates. Fourier transform infrared spectroscopy revealed differences in the secondary structure of the two types of titin aggregates. The data obtained demonstrate the features of structural changes during the formation of intermolecular bonds between molecules of the giant titin protein during its aggregation. The data expand the understanding of the process of amyloid protein aggregation.

Optimized-selenization preparation and laser Q-switching characteristics of layered PtSe2

Abstract PtSe2 has high carrier mobility, excellent electrical and optical properties, and high potential in the field of optoelectronic devices. In this paper, the conventional selenization method is optimized and a single-temperature zone preparation is used to prepare large-area and homogeneous PtSe2 thin-film materials on sapphire substrates in a shorter time and at a lower temperature. The prepared sample is characterized by optical microscopy, atomic force microscopy, Raman spectroscopy and Z-scan method. The saturable absorption properties of layered PtSe2 as a passive Q-switched are investigated in a solid-state laser. The results show that the PtSe2 thin film material is synthesized at 400 °C for 1 h to cover the entire one-inch sapphire wafer with a thickness of about 25 nm and the surface roughness is 13.1 nm. The modulation at 1064 nm yielded an output pulse with a maximum repetition frequency of 688.47 kHz, corresponding to a pulse width of 202.5 ns, a peak power of 7.35 W, a single-pulse energy of 1.51 μJ, and a stable pulse train.

Structural and morphological features of magnetron nanofilms of TaN with different thicknesses

Purpose of research. Study of morphological and phase changes in the structure of tantalum nitride nanofilms formed by magnetron reactive sputtering on a silicon substrate.Methods. Magnetron sputtering on a silicon substrate was performed using the MVU TM-Magna T setup with the sputtering time parameter changing from 300 to 900 sec, and also with constant power parameters of 500 W and working gas pressure of Ar 0,5 Pa. The morphological and phase changes in the structure of tantalum nitride nanofilms were studied using atomic force microscopy and X-ray phase analysis. The fractal dimension was determined using the cube counting method. X-ray diffractometric analysis in the in situ measurement mode with discrete heating (in 100 °C increments) in air up to 1000 °C using the PAAR HTK-16 high-temperature attachment.Results. Using atomic force microscopy methods, it was found that the granulometric distribution of nanoclusters in the studied TaN nanofilms was Gaussian and an increase in the lateral size of particles was observed with an increase in the deposition time. The nanofilm with a deposition time of 300 s had minimal roughness. The statistical fractal dimension was calculated, the value of which corresponded to their three-dimensionality. According to the X-ray phase analysis data, the sizes of the coherence region, texturing, microdeformations and interplanar deformation distortions were determined, and a mixed Stranski-Krastanov mechanism of nanofilm formation was established.Conclusion. The surface roughness of nitride nanofilms formed at a constant power (500 W) depends significantly on the magnetron sputtering time and N2 concentration. In all studied nanofilm structures, the dominant growth mechanism was the mixed Stranski–Krastanov mechanism.

Morphological study of remineralization of the eroded enamel lesions by tyrosine-rich amelogenin peptide

BackgroundTyrosine-rich amelogenin peptide (TRAP) is the main amelogenin digestion product in the developmental enamel matrix. It has been shown to promote remineralization of demineralized enamel in our previous study. However, direct evidence of the effect of TRAP on the morphology and nanostructure of crystal growth on an enamel surface has not been reported. This study aimed to examine the effect of TRAP on the morphology of calcium phosphate crystals grown on early enamel erosion using a pH-cycling model.MethodsEroded lesions were produced in human premolars by 30-second immersion in 37% phosphoric acid. Forty-five samples of eroded human premolar enamel blocks were selected and randomly divided into 3 groups: deionized water (DDW, negative control); 100 µg/mL TRAP, and 2 ppm sodium fluoride (NaF, positive control group). For 14 days, the specimens were exposed to a pH-cycling model. Using scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods, the surface morphology, calcium-phosphorus ratio, and enamel surface roughness were examined. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to assess crystal characteristics.ResultsAfter pH-cycling, compared to the two control groups, the surface of the eroded enamel of the peptide TRAP group shows a large number of new, densely arranged rod-like crystals, parallel to each other, regularly arranged, forming an ordered structure, with crystal morphology similar to that of natural enamel. The crystals are mostly hydroxyapatite (HA).ConclusionThis study demonstrates that the peptide TRAP modulates the formation of hydroxyapatite in eroded enamel and that the newly formed crystals resemble natural enamel crystals and promote the remineralization of enamel, providing a promising biomaterial for remineralization treatment of enamel lesions.

Role of the magnetic layer interface, roughness, and thickness in the temperature-dependent magnetic properties of Al2O3/Co/CoO thin films deposited by magnetron sputtering

Using the methods of atomic force and electron microscopy and the magneto-optical Kerr effect, the role of the interface, roughness, and thickness of the magnetic layer in the temperature-dependent magnetic properties of thin Al2O3–Co films with a naturally oxidized cobalt surface was studied. The layers were deposited by magnetron sputtering. The thickness of the cobalt layer varied from 2 to 100 nm. For the first time, the dependences of coercive forces and exchange displacements on the thickness of the cobalt film in the temperature range from 80 to 300 K were obtained and analyzed. The contribution to the coercive force and exchange displacement from the oxidized cobalt surface increases as the temperature decreases below 160 K. The magnitude of the contribution depends on the base material on which the cobalt film is deposited and is maximum for a cobalt film with a thickness of ∼20 nm in the Al2O3/Co structure. A weakly magnetic layer was found at the Al2O3/Co interface. The behavior of the exchange bias in this layer is similar to the behavior of a ferromagnetic Co core with a naturally oxidized CoO shell. The thickness of this layer depends on the speed and order of deposition of the layers. When the order of deposition of layers (Co/Al2O3) changes, the behavior of the exchange displacement of the interface becomes similar to that observed in the ferromagnet/antiferromagnet system. That is, when the deposition order changes, the value of the exchange shift changes sign when the cobalt layer thickness is below 10 nm.

How to achieve nanometer flat surfaces: Pulsed electrochemical machining of bulk metallic glass

The Bulk Metallic Glass (BMG) Vitreloy 105 (Zr52.5Ti5Ni14.6Cu17.9Al10) as well as two crystalline reference materials of the same composition were machined with Pulsed Electrochemical Machining (PECM). One reference material was nano crystalline with an average grain size of 11 nm and the second one was a fine grain crystalline sample with an average grainsize of 110 nm. The goal was to achieve maximum surface quality in terms of roughness by utilizing a readily available industrial process. Samples were characterized by tactile profilometer, atomic force microscopy and electron microscopy methods. The results show superior surface quality of the amorphous samples over the reference materials with an average roughness depth as low as 1 nm. The observed dissolution mechanism of the BMG differs from the reference materials -as in contrast to the crystalline alloys that show a passive layer formation - no such surface layer other than the native oxide could be observed. The PECM procedure is found to be a promising post-processing step for BMGs with a resulting surface that can face even the most challenging surface quality requirements.

Hypoxic extracellular vesicles from hiPSCs protect cardiomyocytes from oxidative damage by transferring antioxidant proteins and enhancing Akt/Erk/NRF2 signaling

BackgroundStem cell-derived extracellular vesicles (EVs) are an emerging class of therapeutics with excellent biocompatibility, bioactivity and pro-regenerative capacity. One of the potential targets for EV-based medicines are cardiovascular diseases (CVD). In this work we used EVs derived from human induced pluripotent stem cells (hiPSCs; hiPS-EVs) cultured under different oxygen concentrations (21, 5 and 3% O2) to dissect the molecular mechanisms responsible for cardioprotection.MethodsEVs were isolated by ultrafiltration combined with size exclusion chromatography (UF + SEC), followed by characterization by nanoparticle tracking analysis, atomic force microscopy (AFM) and Western blot methods. Liquid chromatography and tandem mass spectrometry coupled with bioinformatic analyses were used to identify differentially enriched proteins in various oxygen conditions. We directly compared the cardioprotective effects of these EVs in an oxygen-glucose deprivation/reoxygenation (OGD/R) model of cardiomyocyte (CM) injury. Using advanced molecular biology, fluorescence microscopy, atomic force spectroscopy and bioinformatics techniques, we investigated intracellular signaling pathways involved in the regulation of cell survival, apoptosis and antioxidant response. The direct effect of EVs on NRF2-regulated signaling was evaluated in CMs following NRF2 inhibition with ML385.ResultsWe demonstrate that hiPS-EVs derived from physiological hypoxia at 5% O2 (EV-H5) exert enhanced cytoprotective function towards damaged CMs compared to EVs derived from other tested oxygen conditions (normoxia; EV-N and hypoxia 3% O2; EV-H3). This resulted from higher phosphorylation rates of Akt kinase in the recipient cells after transfer, modulation of AMPK activity and reduced apoptosis. Furthermore, we provide direct evidence for improved calcium signaling and sustained contractility in CMs treated with EV-H5 using AFM measurements. Mechanistically, our mass spectrometry and bioinformatics analyses revealed differentially enriched proteins in EV-H5 associated with the antioxidant pathway regulated by NRF2. In this regard, EV-H5 increased the nuclear translocation of NRF2 protein and enhanced its transcription in CMs upon OGD/R. In contrast, inhibition of NRF2 with ML385 abolished the protective effect of EVs on CMs.ConclusionsIn this work, we demonstrate a superior cardioprotective function of EV-H5 compared to EV-N and EV-H3. Such EVs were most effective in restoring redox balance in stressed CMs, preserving their contractile function and preventing cell death. Our data support the potential use of hiPS-EVs derived from physiological hypoxia, as cell-free therapeutics with regenerative properties for the treatment of cardiac diseases.

Synthesis and evaluation of Schiff base as corrosion inhibitor for carbon steel in 1 M HCl solution

PurposeThe main purpose of the present study is to introduce new Schiff bases as corrosion inhibitor for carbon steel in 1 M HCl. The inhibitory activity of Schiff base was also assessed.Design/methodology/approach2,2′-((1Z,1′Z)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))diphenol was synthesized and it’s performance as an inhibitor was then investigated in 1 M HCl. The inhibition of this compound was studied and evaluated by the chemical methods of electrochemical impedance spectroscopy, electrochemical potential dynamic polarization and Atomic Force microscopy (AFM) method. The thermodynamics parameters were investigated for corrosion of carbon steel in both the absence and presence of Schiff base.FindingsThe results of the tests showed that this compound has a good performance as an inhibitor and the percentage of inhibition on steel corrosion will increase with increasing concentration and it will reach 70% in the presence of 2 × 10−3 M of this inhibitor. Polarization tests indicated that this compound will act as a mixed inhibitor. Nyquist curves showed that the addition of this substance to the solution increased the charge transfer resistance and decreased the capacity of the double layer. The absorption of the new Schiff base on steel follows Langmuir adsorption isotherm, and the amount of free energy of adsorption indicates the spontaneous adsorption of this inhibitor. Using AFM investigations, the results of electrochemical methods were confirmed.Originality/valueIncorporation of a new Schiff base into 1 M HCl is a promising approach for protecting the carbon steel against corrosive solution.

Scratching of metallized polymer films by Vickers indenter as a method for controlled production of SERS-active metasurfaces

The opportunities of a system of parallel microscratches drowed on a PET film metallized with silver and copper using a Vickers indenter as an active Surface-enhanced Raman spectroscopy (SERS) or Photoluminescence-enhanced surface have been investigated. It is shown that the enhancement of the SERS signal for rhodomine is proportional to the total length of microscratches in the laser spot and increases after their application due to the relaxation of the polymer backing. The results of the microscratch geometry analysis by an atomic force microscopy and scanning electron microscopy methods indicate the probability of the location of “hot points” along the “dumps” of metal along the shores of scratches, as well as on nanoroughnesses along their inner walls.© 2017 Elsevier Inc. All rights reserved.

Tuning the Topo-Morphological properties of ITO Films using Al-Ag interlayer for Low-Resistance Optoelectronics Devices

Indium tin oxide (ITO) is recently attracting intense attention for application as transparent conducting electrode in different optoelectronic devices including solar cells, liquid crystal displays and organic light emitting diodes. This is attributed to their high optical transmittance in the visible region and good electrical conductivity. In this work, surface topological-morphological (topo-morphological) and electrical properties of ITO based multilayer films with aluminum-silver (Al-Ag) metal interlayer (ITO/Al-Ag/ITO) are investigated after post annealing treatment at 300-500oC by atomic force microscopic (AFM), field emission scanning electron microscopy (FESEM), four-point probe and hall-effect techniques respectively. The ITO/Al-Ag/ITO films are deposited by direct current and radio frequency magnetron sputtering techniques on p-type Si at room temperature. The results showed a smooth surface topology by as-deposited film with films smoothness improving after post annealing treatment as analyzed by AFM method. Sharp crystallites peaks were obtained by all the films with smaller peaks diffusing and recombining to form larger films with increasing post-annealing temperature. The films root means square roughness increased as the temperature increases with film annealed at 500oC showing a superior and enhanced microstructure. Compared to as-deposited film, careful observation shows that surface morphology smoothness increased with increase in temperature with films annealed at 400oC and 500oC showing highest increasing surface smoothness pattern as determined by FESEM technique. Similarly, higher grain sizes are observed especially by films annealed at 400oC and 500oC due to the heat absorption which causes the particles to expand thereby narrowing the grain boundaries and subsequently improve the surface smoothness. These FESEM findings are consistent with AFM measurements confirming the high surface property and enhanced grain size with increasing post annealing temperature. The films exhibit decreased electrical resistivity and sheet resistance while carrier concentration and Hall mobility increased with increasing post annealing treatment indicating highest corresponding values of...

In Ukrainian

The paper discusses the results of saponite research from the Tashkiv deposit of Ukraine. X-ray structural analysis proved the necessity of preliminary cleaning of saponites from mineral impurities. The study of the morphology, nanoprofile and topography of the surface of saponite by the methods of SEM-microscopy and Atomic Force Microscopy revealed that the mineral is represented by aggregates of nano- and microparticles of a pyramidal shape. Its characteristic feature is the heterogeneity of isomorphic substitutions of ions in the tetrahedral and octahedral sheets of the structural elementary package. According to X-ray fluorescence analysis, saponite contains a significant amount of Fe3+, which isomorphically replaces magnesium Mg2+ and, accordingly, is located mastly in the octahedral sheet of the structural package with a charge from +0.37 to +0.35. The number and mechanism of isomorphic substitutions determine the presence of a total negative charge of the crystal lattice (from –0.38 to –0.3), the value of which ensures intensive interaction with water molecules of the interpacket space with the formation of surface OH groups. Accordingly, both acidic and alkaline Lewis and Brønsted centers are present on the surface with a predominance of acidic ones, so the acidity function is 5.82, and the point of zero proton charge is pH = 5.5. During dispersion in water, a part of the alkaline centers of the side surface are transformed into Brønsted acid centers as a result of their protonation, which causes an increase in the pH of the dispersion medium to pH = 8–8.6. Accordingly, the isoionic state is reached at pH = 7.5. The difference in pH values characterizing the isoionic state of the surface and the point of zero net proton charge (PZNPC) indicates the presence of weak acid-alkaline centers on the surface. The study of the adsorption of acid-alkaline dyes showed the adsorption of alkaline (pK = 1¸3) and acid (pK = 7¸14) dyes on saponites. The latter is significantly reduced due to the preliminary hydration of the solid surface - mainly the lateral edges of the particles. Acidic dyes are not adsorbed from a dispersion medium with pH < 5.5 (PZNPC), and basic dyes are adsorbed at pH > 5,5( PZNPC).

Shear viscosity of a near-critical binary system analyzed with variable-temperature atomic force microscopy

Variation in shear viscous drag in a near-critical binary mixture was measured between a hydrophilic probe sphere and a hydrophilic substrate down to a distance range comparable to or smaller than the correlation length ξ using a magnetic excitation method of atomic force microscopy at temperatures T=Tc−∆T with ∆T varying from 0.1 to 0.7 K. As the temperature approached the Tc, the increase in the drag coefficient toward the zero distance was observed to be less pronounced in the distance range below ca. 100 nm. The data was discussed as arising from suppression in a concentration gradient in the intersurface region due to the overlap of the affected layers on similar surfaces.

A hydrometallurgical process flowsheet for recovering MoO3 from Molybdenite

In this study, a comprehensive hydrometallurgical processing of molybdenite (MoS2) concentrate was investigated. This investigation involved a novel approach combining mechanical activation, leaching, and polyelectrolyte extraction methods. The integrated method effectively addressed the challenge of low leaching rate of molybdenite, resulting in the successful production of high-purity molybdenum trioxide. Milled molybdenite samples were analyzed by different methods of X-ray diffraction, atomic force and electron microscopy, and BET. The increasing trend of the specific surface area during milling was determined by a model fitting which was useful for optimization of milling time. Several leaching reagents were studied to achieve high molybdenum dissolution. The most promising results were achieved through a two-hour process, yielding an impressive leaching efficiency of 80% and a resulting Mo concentration of 6700 mg/L. Molybdenum recovery was efficiently carried out through polyelectrolyte extraction, as confirmed by ICP and CHNS analyses, demonstrating selective precipitation of molybdenum from the solution. The subsequent calcination of the precipitated molybdenum(VI) compound resulted in the production of high-purity molybdenum trioxide. Furthermore, a conceptual hydrometallurgical treatment process for molybdenite concentrate was proposed, aiming to recover molybdenum, sulfuric acid, and copper. This proposed process presents a promising avenue for further exploration in pilot plant studies within the molybdenum industry.

Pluronic P123/DMSO Lyotropic Liquid Crystal for Incorporating Bioactive Substances for Topical Application.

Lyotropic liquid crystals (LLCs) have attracted considerably growing interest in drug delivery applications over the last years. The structure of LLC matrices is complementary to cell membranes and provides an efficient, controlled, and selective release of drugs. In this work, a complex of experimental methods was used to characterize binary LLCs Pluronic P123/DMSO and triple LLC systems Pluronic P123/DMSO/Ibuprofen, which are interesting as transdermal drug delivery systems. Liquid crystalline, thermal, and rheological properties of LLCs were studied. Concentration and temperature areas of the lyomesophase existence were found, and phase transition enthalpies were evaluated. Intermolecular interactions among the components were studied by infrared (IR) spectroscopy. In vitro studies of Ibuprofen (Ibu) release from various LLCs allow differentiation of its release depending on the polymer content. Atomic force microscopy and contact angle methods were used to characterize the surface morphology of the hydrophobic membrane, which was used as a stratum corneum model, and also evaluate the adhesion work of the LLCs. A complex analysis of the results provided by these experimental methods allowed revealing correlations between the phase behavior and rheological characteristics of the LLCs and release kinetics of ibuprofen. The proposed biocompatible systems have considerable potential for a transdermal delivery of bioactive substances.

Enhancing biocompatibility and osseointegration of medical implants using ti based nanocomposite coatings

The surface of the replacement medical implant can be coated, which is one of the most basic and effective ways to develop and strengthen bones and increase their compatibility for the human body to solve problems with bone defects, such as the problem of releasing ions from some elements of the body Medical alloy implants are one of the major drawbacks in bone fracture surgery, and biocompatible implants are new ways to ensure that these implants work well. These implants play a major role in accelerating osseointegration processes, but at the same time they suffer from the problem of releasing niobium and zirconium ions, which may cause serious diseases to human health. To stop these toxic ions from releasing, a bioceramic nanolayer coating was put on the alloy's surface. This made it more biocompatible and stopped the toxic ions from escaping. Among several types of coatings, the best nanocomposite coating was selected. Three criteria and levels were used: voltage, time, and cocentartion. A Takeuchi statistical program was used to collect data on all the tests (thickness, adhesion, contact angle, and roughness) in order to find the best coated sample. The study then used atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) methods.

Study of the Fenton Oxidative Reaction on a Culture of Human Fibroblast Cells Incubated with Ablated CeO<sub>2</sub> Particles

Purpose. Study of the bioprotective properties of ablated cerium dioxide nanoparticles in relation to immortalized human fibroblasts under conditions of oxidative stress caused by the Fenton reaction.Methods. Cerium dioxide nanoparticles with pronounced antioxidant properties were obtained using laser ablation. The average maximum sizes of ablated particles of oxidized cerium in non-centrifuged and centrifuged at a speed of 1000 rpm nanodispersed aqueous solutions were revealed using the method of atomic force microscopy. The spectrophotometric method revealed that ablated cerium dioxide nanoparticles exhibit antioxidant properties and prevent the degradation of the methylene blue dye during the Fenton reaction. Cell culture samples were mapped using scanning electron microscopy using an energy-dispersive attachment after their incubation with ablated cerium dioxide nanoparticles. Using MTT analysis, the effect of ablated cerium dioxide nanoparticles on the survival of BJ TERT cell culture in the Fenton reaction was studied. Non-centrifuged and centrifuged at a speed of 1000 rpm nanodispersed solutions of oxidized cerium were used. The antioxidant activity of cerium dioxide nanoparticles after 6- and 24-hour incubation was studied.Results. The average limiting sizes of ablated cerium dioxide nanoparticles have been established, the values of which are (61,95±0,1) nm for a non-centrifuged aqueous solution and (56,59±0,1) nm for an aqueous solution centrifuged at a microcentrifuge speed of 1000 rpm. It was revealed that in the presence of ablated cerium dioxide nanoparticles, the degree of oxidative degradation of methylene blue during the Fenton reaction was significantly reduced. It was found that with an increase in the concentration of ablated cerium dioxide nanoparticles from 20 to 1000 mg/l, their antioxidant effect increased. From the obtained SEM images of cell cultures with ablated cerium dioxide nanoparticles, it follows that the nanoparticles are captured by cells during incubation and can have a significant effect on oxidative processes during the Fenton reaction. Statistical analysis based on the results of the MTT assay showed that 6-hour and 24-hour incubation with ablated cerium dioxide nanoparticles had a pronounced protective effect on the BJ TERT cell line.Conclusion. This work shows that during the Fenton reaction, cerium dioxide nanoparticles prevent the oxidative degradation of the methylene blue dye. When immortalized human fibroblasts are incubated, ablated cerium oxide nanoparticles are taken up by the cells and have a significant protective effect on them in the oxidative reaction. The high antioxidant activity of nanoparticles is determined by the high content of functional defects on the surface of nanoparticles obtained under sharply nonequilibrium conditions of laser ablation.

Compressed sensing reconstruction of cell mechanical images obtained from atomic force microscopy

Compressed sensing (CS), a technique in signal processing that reconstructs sparse signals from a limited sampling number, has been valuable in topographic images obtained from atomic force microscopy (AFM). However, how CS is effective in reconstructing AFM mechanical images remains unclear. We investigated the reconstruction of topographic and mechanical images of living cells, such as developing embryos obtained from AFM mapping experiments using CS. The results showed that both topographic and mechanical images of embryonic cells in the different developmental stages were well reconstructed at a spatial resolution higher than the original AFM images. These results suggested that the CS approach enabled the cell mechanical properties, together with cell surface morphology, using AFM mapping measurements to be faster than the conventional AFM methods without reducing the spatial resolution.

Studying Structure and Functions of Nucleosomes with Atomic Force Microscopy.

Chromatin is an epigenetic platform for implementation of DNA-dependent processes. Nucleosome, as a basic level of chromatin compaction, largely determines its properties and structure. In the study of nucleosomes structure and functions physicochemical tools are actively used, such as magnetic and optical "tweezers", "DNA curtains", nuclear magnetic resonance, X-ray crystallography, and cryogenic electron microscopy, as well as optical methods based on Förster resonance energy transfer. Despite the fact that these approaches make it possible to determine a wide range of structural and functional characteristics of chromatin and nucleosomes with high spatial and time resolution, atomic force microscopy (AFM) complements the capabilities of these methods. The results of structural studies of nucleosome focusing on the AFM method development are presented in this review. The possibilities of AFM are considered in the context of application of other physicochemical approaches.

Microstructure and Properties of Thin-Film Submicrostructures Obtained by Rapid Thermal Treatment of Nickel Films on Silicon

Nickel films of 40 nm thickness were obtained by means of magnetron sputtering on a single-crystalline silicon substrate. The films were subjected to rapid thermal treatment (RTT) for 7 s until the temperature increased from 200 to 550 °C. By means of the X-ray diffraction method, the structural-phase composition of nickel films before and after RTT was explored. The atomic force microscopy method due to direct contact with the surface under study, made it possible to accurately define the microstructure, roughness, specific surface energy and grain size of the nickel films before and after RTT, as well as to establish the relationship of these parameters with the phase composition and electrical properties of the films. Surface specific resistance was measured using the four-probe method. Based on XRD results, formation of Ni2Si and NiSi phases in the film was ascertained after RTT at 300 °C. At RTT 350–550 °C, only the NiSi phase was formed in the film. The microstructure and grain size significantly depend on the phase composition of the films. A correlation has been established between specific surface energy and resistivity with the average grain size after RTT at 350–550 °C, which is associated with the formation and constant restructuring of the crystal structure of the NiSi phase.