Atomic Force Microscopy Studies Research Articles

3D Generation of Multipurpose Atomic Force Microscopy Tips

In this work, 3D polymeric atomic force microscopy (AFM) tips, referred to as 3DTIPs, are manufactured with great flexibility in design and function using two‐photon polymerization. With the technology holding a great potential in developing next‐generation AFM tips, 3DTIPs prove effective in obtaining high‐resolution and high‐speed AFM images in air and liquid environments, using common AFM modes. In particular, it is shown that the 3DTIPs provide high‐resolution imaging due to their extremely low Hamaker constant, high speed scanning rates due to their low quality factor, and high durability due to their soft nature and minimal isotropic tip wear; the three important features for advancing AFM studies. It is also shown that refining the tip end of the 3DTIPs by focused ion beam etching and by carbon nanotube inclusion substantially extends their functionality in high‐resolution AFM imaging, reaching angstrom scales. Altogether, the multifunctional capabilities of 3DTIPs can bring next‐generation AFM tips to routine and advanced AFM applications, and expand the fields of high speed AFM imaging and biological force measurements.

Structural and optical properties of cubic GaN on U-grooved Si (100)

Cubic GaN epitaxy on large-area U-grooved silicon (100) dies is demonstrated by metalorganic chemical vapor deposition, and its structural and optical properties are reported. Scanning electron, atomic force, and transmission electron microscopy studies reveal that cubic GaN shows no discernible threading dislocations and a low stacking fault density of 3.27 ± 0.18 × 104 cm−1. Temperature-dependent photoluminescence studies reveal as-grown cubic GaN band edge emission internal quantum efficiency as 25.6% ± 0.9%. Selective etching of the low-temperature AlN buffer layer, SiO2 sidewalls, and hexagonal-phase GaN is demonstrated, which increases the cubic GaN band edge emission internal quantum efficiency to 31.6% ± 0.8%. This increase is attributed to the decrease in the radiative recombination lifetime via the removal of defective hexagonal-phase GaN. Overall, cubic GaN on U-grooved silicon with high structural and optical quality is reported, promising its suitability for next-generation devices.

Bivalent metal ions induce formation of α-synuclein fibril polymorphs with different cytotoxicities

α-Synuclein (α-Syn) aggregates are key components of intracellular inclusion bodies characteristic of Parkinson’s disease (PD) and other synucleinopathies. Metal ions have been considered as the important etiological factors in PD since their interactions with α-Syn alter the kinetics of fibrillation. In the present study, we have systematically explored the effects of Zn2+, Cu2+, Ca2+, and Mg2+ cations on α-Syn fibril formation. Specifically, we determined fibrillation kinetics, size, morphology, and secondary structure of the fibrils and their cytotoxic activity. While all cations accelerate fibrillation, we observed distinct effects of the different ions. For example, Zn2+ induced fibrillation by lower tlag and higher kapp and formation of shorter fibrils, while Ca2+ ions lead to formation of longer fibrils, as evidenced by dynamic light scattering and atomic force microscopy studies. Additionally, the morphology of formed fibrils was different. Circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopies revealed higher contents of β-sheets in fibrils. Interestingly, cell viability studies indicated nontoxicity of α-Syn fibrils formed in the presence of Zn2+ ions, while the fibrils formed in the presence of Cu2+, Ca2+, and Mg2+ were cytotoxic. Our results revealed that α-Syn fibrils formed in the presence of different divalent cations have distinct structural and cytotoxic features.

Human Vimentin Layers on Solid Substrates: Adsorption Kinetics and Corona Formation Investigations.

Adsorption kinetics of human vimentin on negatively charged substrates (mica, silica, and polymer particles) was analyzed using atomic force microscopy (AFM), quartz microbalance (QCM), and the laser doppler velocimetry (LDV) method. AFM studies realized under diffusion conditions proved that the adsorbed protein layer mainly consisted of aggregates in the form of compact tetramers and hexamers of a size equal to 11–12 nm. These results were consistent with vimentin adsorption kinetics under flow conditions investigated by QCM. It was established that vimentin aggregates efficiently adsorbed on the negatively charged silica sensor at pH 3.5 and 7.4, forming compact layers with the coverage reaching 3.5 mg m–2. Additionally, the formation of the vimentin corona at polymer particles was examined using the LDV method and interpreted in terms of the electrokinetic model. This allowed us to determine the zeta potential of the corona as a function of pH and the electrokinetic charge of aggregates, which was equal to −0.7 e nm–2 at pH 7.4 in a 10 mM NaCl solution. The anomalous adsorption of aggregates exhibiting an average negative charge on the negatively charged substrates was interpreted as a result of a heterogeneous charge distribution. These investigations confirmed that it is feasible to deposit stable vimentin layers both at planar substrates and at carrier particles with well-controlled coverage and zeta potential. They can be used for investigations of vimentin interactions with various ligands including receptors of the innate immune system, immunoglobulins, bacterial virulence factors, and spike proteins of viruses.

Atomic force microscopy application to study of the biomechanical properties of the aortic intima in the context of early atherosclerosis.

Atherosclerosis is characterized by the infiltration of macrophages, accumulation of lipids, activation of endothelial cells and synthesis of extracellular matrix by vascular smooth muscle cells. However, there have been few atomic force microscopy (AFM) studies of the aortic intima in situ in the context of atherosclerosis. By employing a customized liquid cell for AFM, we investigated the aortic intima obtained from male C57BL/6 ApoE-deficient mice (ApoE-/- ) aged 14 weeks and male C57BL/6 ApoE-sufficient mice (ApoE+/+ ) aged between 18 and 26 weeks that were fed a high-fat and high-cholesterol diet for 4 weeks and performed force spectroscopy mapping of the biomechanical properties of the intima. In the aortas of ApoE-deficient mice, the intima became stiffer than that of ApoE-sufficient mice. In addition, the cytoskeleton of endothelial cells was enlarged, and extracellular matrix accumulated. The biomechanical properties of the aortic intima are altered in early atherogenesis, which may be induced by the enlargement of the endothelial cell cytoskeleton and the increased synthesis of extracellular matrix by activated smooth muscle cells.

Interaction between active compounds from Rosa roxburghii Tratt and β-glucosidase: Characterization of complexes and binding mechanism

Understanding the molecular mechanisms underlying protein-flavonoid interactions is crucial for the application of protein-flavonoid complexes in food. The purpose of this study was to explore the factors that influence the efficient release of rutin (Rut) and isoquercitrin (Iso) from Lactobacillus acidophilus β-glucosidase (BGL) and the interaction mechanism among rutin, isoquercitrin and β-glucosidase. Spectroscopic analysis, atomic force microscopy and molecular docking studies showed that Rut or Iso quenched the intrinsic fluorescence of β-glucosidase in a static manner through the formation of a flavonoid-β-glucosidase complex. Atomic force microscopy and circular dichroism measurements confirmed that the conformation of β-glucosidase changed slightly. Molecular docking further proved that the interaction force of Rut or Iso with β-glucosidase was hydrogen bonding, hydrophobic interactions and electrostatic interactions, and the binding free energies of the interactions were −180.54 kcal mol−1 and -119.35 kcal mol−1, respectively. Substituted groups on the glycosylation of quercetin glycoside compounds are crucial for their binding to β-glucosidase. This study provides a theoretical basis for the design of natural flavonoid-protein complex functional foods.

Phospholipids and Hyaluronan: From Molecular Interactions to Nano- and Macroscale Friction

Phospholipids and hyaluronan are two key biomolecules that contribute to the excellent lubrication of articular joints. Phospholipids alone and in combination with hyaluronan have also displayed low friction forces on smooth surfaces in micro- and nanosized tribological contacts. In an effort to develop aqueous-based lubrication systems, it is highly relevant to explore if these types of molecules also are able to provide efficient lubrication of macroscopic tribological contacts involving surfaces with roughness larger than the thickness of the lubricating layer. To this end, we investigated the lubrication performance of hyaluronan, the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and mixtures of these two components using glass surfaces in a mini-traction machine. We compared our data with those obtained using flat silica surfaces in previous atomic force microscopy studies, and we also highlighted insights on hyaluronan–phospholipid interactions gained from recent simulations. Our data demonstrate that hyaluronan alone does not provide any lubricating benefit, but DPPC alone and in mixtures with hyaluronan reduces the friction force by an order of magnitude.

Layer-By-Layer Self-Assembled Dip Coating for Antifouling Functionalized Finishing of Cotton Textile.

The fouling of surfaces such as textiles is a major health challenge, and there is a continuous effort to develop materials and processes to overcome it. In consideration of this, this study regards the development of antifouling functional nanoencapsulated finishing for the cotton textile fabric by employing a layer-by-layer dip coating technique. Antifouling textile finishing was formulated by inducing the nanoencapsulation of the antifouling functional group inside the hydrophobic polymeric shell. Cotton fabric was taken as a substrate to incorporate antibacterial functionality by alternatively fabricating multilayers of antifouling polymeric formulation (APF) and polyelectrolyte solution. The surface morphology of nanoencapsulated finished textile fabric was characterized through scanning electron microscopy to confirm the uniform distribution of nanoparticles on the cotton textile fabric. Optical profilometry and atomic force microscopy studies indicated increased surface roughness in the coated textile substrate as compared to the uncoated textile. The surface thickness of the fabricated textile increased with the number of deposited bilayers on the textile substrate. Surface hydrophobicity increased with number of coating bilayers with θ values of x for single layer, up to y for 20 bilayers. The antibacterial activity of the uncoated and layer-by-layer coated finished textile was also evaluated. It was significant and exhibited a significant zone of inhibition against microbial strains Gram-positive S. aureus and Gram-negative E. coli. The bilayer coating exhibited water repellency, hydrophobicity, and antibacterial activity. Thus, the fabricated textile could be highly useful for many industrial and biomedical applications.

Influence of 8 MeV Electron Irradiation on the Properties of ZnO Nanocrystalline Thin Films for Optoelectronic Devices in the High Radiation Environment

Herein, we present the influence of 8 MeV electron beam irradiation on the structural, optical and electrical properties of sol-gel derived spin-coated ZnO films. The electron irradiation doses varied from 0 kGy to 10 kGy. We observed significant changes in the morphology, optical and electrical properties of the films upon irradiation. Structural analysis of the films revealed the preferential and dominant c-axis orientation of the crystallites along the (002) plane. The preferential growth of the films was also supported by the values of texture coefficient. Atomic Force Microscopy studies reveal the linear relationship between the surface roughness, grain size and irradiation dose. The average transmittance of the films decreased from 87% to 66% after irradiation. A slight red-shift of the optical band gap values was observed when the absorbed dose was increased from 0 kGy to 10 kGy. The Photoluminescence measurement of the films showed that the intensity of the defect-related peak increases with the electron dose. The electrical resistivity of the films decreased after irradiation and a minimum resistivity of 7.566 × 10−2 Ω m was obtained from the film irradiated with a 5 kGy electron dose. To find the performance and quality of the prepared film, the Figure of Merit was calculated and was found that the film irradiated with a 5 kGy electron dose shows the maximum value. The obtained results show that electron irradiation is a potential alternative approach to improve the performance of the ZnO films for optoelectronic devices in a high radiation environment.

Mechanical, thermal, and surface morphological properties of Musa acuminate peduncle fiber‐reinforced polymeric composite: Effect of alkalization and fiber loading

AbstractThis investigation focuses on studying the properties of treated and untreated Musa acuminate peduncle fiber (MAPF)‐reinforced epoxy composites. The effect of fiber weight fraction and alkali treatment on the mechanical, thermal, and morphological characteristics of MAPF‐reinforced epoxy composites was investigated for the first time. A considerable enhancement in the tensile, impact, and flexural characteristics was observed at 20 wt% fiber; beyond 20 wt%, the properties were found to decrease. The increase in cellulose (from 66.43 to 74.22 wt%) and decrease in lignin (from 16.85 to 7.91 wt%) and hemicellulose (from 13.72 to 8.58 wt%) in alkali‐treated fiber resulted in a more crystalline structure. This led to improved tensile (tensile strength 53.61 MPa and tensile modulus 0.561 GPa), flexural (flexural strength 64.33 MPa and flexural modulus 5.43 GPa), and impact (90.33 J/m) composite properties compared to the untreated fiber composite. After tensile testing, the composite's fractured cross‐sections were investigated using scanning electron microscopy, which revealed that the alkali‐treated MAPF‐reinforced composite had fewer voids and improved fiber bonding. Thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy studies also revealed that alkali‐treated MAPFs area promising reinforcement for the epoxy polymer matrix.

Evaluating the Effect of an Experimental Sesame Gel on Human Enamel: Atomic Force Microscopy Study.

Every effort for increasing the calcium concentration in the saliva would be beneficial for prevention of dental caries. Regarding this issue, the natural products could be considered safer and more cost effective. Sesame is rich in calcium but the data about the effect of sesame on enamel roughness is inadequate. This study aimed to assess the effect of an experimental sesame gel on the surface roughness of human enamel by using atomic force microscopy (AFM). In the current experimental study, fifteen enamel slices with 1mm thickness were prepared. They were polished and acid etched to produce a substantial rough surface prior to the first AFM analysis. The enamel blocks were randomly divided into three groups treated with distilled water, fluoride gel, and an experimental prepared sesame gel correspondingly. The treating agent was applied for 3minutes at 0, 8, 24, and 48h intervals and washed by distilled water after each cycles. Ultimately, the final AFM micrographs were prepared. The statistical analysis was performed using paired t-test, one-way ANOVA, and Tukey Post Hoc tests (α=0.05). Statistical analysis revealed that the surface roughness was significantly reduced in both sesame and fluoride groups (p= 0.017 and 0.018, respectively) while the control group (distilled water) were not noticeably changed (p= 0.12). The control group had statistically significant difference with both the sesame and the fluoride groups (p= 0.007 and 0.007, respectively) while the there was no significance difference between sesame and fluoride groups (p= 0.997). Following demineralization by acid etched process, the sesame gel significantly reduced surface roughness of enamel and its effect was similar to fluoride gel.

Design, Synthesis and Characterization of [G10a]-Temporin SHa Dendrimers as Dual Inhibitors of Cancer and Pathogenic Microbes.

As the technologies for peptide synthesis and development continue to mature, antimicrobial peptides (AMPs) are being widely studied as significant contributors in medicinal chemistry research. Furthermore, the advancement in the synthesis of dendrimers’ design makes dendrimers wonderful nanostructures with distinguishing properties. This study foregrounds a temporin SHa analog, [G10a]-SHa, and its dendrimers as globular macromolecules possessing anticancer and antibacterial activities. These architectures of temporin SHa, named as [G10a]-SHa, its dendrimeric analogs [G10a]2-SHa and [G10a]3-SHa, and [G10a]2-SHa conjugated with a polymer molecule, i.e., Jeff-[G10a]2-SHa, were synthesized, purified on RP-HPLC and UPLC and fully characterized by mass, NMR spectroscopic techniques, circular dichroism, ultraviolet, infrared, dynamic light scattering, and atomic force microscopic studies. In pH- and temperature-dependent studies, all of the peptide dendrimers were found to be stable in the temperature range up to 40–60 °C and pH values in the range of 6–12. Biological-activity studies showed these peptide dendrimers possessed improved antibacterial activity against different strains of both Gram-positive and Gram-negative strains. Together, these dendrimers also possessed potent selective antiproliferative activity against human cancer cells originating from different organs (breast, lung, prostate, pancreas, and liver). The high hemolytic activity of [G10a]2-SHa and [G10a]3-SHa dendrimers, however, limits their use for topical treatment, such as in the case of skin infection. On the contrary, the antibacterial and anticancer activities of Jeff-[G10a]2-SHa, associated with its low hemolytic action, make it potentially suitable for systemic treatment.

Nanostructural origins of irreversible deformation in bone revealed by an in situ atomic force microscopy study

Nanostructural origins of irreversible deformation in bone revealed by an in situ atomic force microscopy study

Broadband (NIR-Vis-UV) photoresponse of annealed SnSe films and effective oxidation passivation using Si protective layer

Tin selenide is a versatile material with superior thermoelectric properties and can compete for optoelectronics, gas sensing, etc. As the actual application of the device depends upon the stability of the material under practical conditions (like for thermoelectric application, the material must be stable up to the defined temperature at which ZT is maximum). This paper reports the material's systematic thermal and chemical stability for feasible, practical applications in optoelectronic and thermoelectric aspects. SnSe film was deposited on the soda-lime glass substrate using thermal evaporation. Annealing was carried out at different temperatures (200, 250, and 300 °C) for one hour in open-air conditions. With the increase in the annealing temperature, part of the SnSe phase was initially changed to the SnSe2 phase, and a tin dioxide layer was formed (confirmed by Raman spectroscopy). A blue shift in the direct bandgap (from 1.35 eV, for pure SnSe to 1.84 eV, for 300 °C annealed SnSe) has been observed with an increase in annealing temperature. Atomic force and scanning electron microscopic studies have been carried out. Samples annealed at 300 °C showed a broadband spectral response due to crystalline SnSe, SnSe2, and SnO2 phases. Also, the formation of three consecutive layers viz SnSe, SnSe2, and SnO2 can be used for solar cell applications. Further, deposition of Si as a protective layer on the SnSe for improved oxidation stability has been carried out, which resisted the oxidation up to 250 °C.

Lipid membrane-mediated assembly of the functional amyloid-forming peptide Somatostatin-14

Membrane-mediated assembly has been well characterised for toxic amyloid species such as the amyloid-β peptide implicated in Alzheimer's disease. However, little is known about the membrane-mediated assembly of functional-amyloid forming peptides, recently identified as a natural storage state for neuropeptide hormones in vivo. Here, we study the aggregation of somatostatin-14 (SST-14) co-incubated with model lipid membranes. Atomic force microscopy (AFM) studies confirmed that nanofibrils formed in the presence of various lipid membranes display reduced fibrillogenesis and promote the formation of non-fibrillar oligomers. Both circular dichroism (CD) and intrinsic tryptophan fluorescence studies confirmed interaction between the peptide and the lipid bilayer; this interaction appears to drive changes in membrane-mediated aggregation kinetics. We show that both the surface charge of the membrane and chain packing drive changes in the electrostatic and hydrophobic interactions between the peptide and the membrane, and hence the rate of assembly. The similarities in the effect of the lipid membrane on aggregation of functional amyloids and the more well studied toxic amyloids suggest strong aggregation modifying lipid bilayer interactions are a ubiquitous feature of all amyloid fibrils and highlight the need for further investigation as to why this leads to toxicity in some systems and not others.

Interaction of zirconia with magnesium hydride and its influence on the hydrogen storage behavior of magnesium hydride

This study demonstrates how zirconia additive transforms to zirconium hydride and substantially lowers the dehydrogenation temperature of magnesium hydride. We prepared MgH2+xZrO2 (x = 0.125 and 0.5) powder samples reacted for 15 min, 1 h, 5 h, 10 h, 15 h, 20 h and 25 h, and monitored the phase changes at each stage of the reaction. Differential scanning calorimetry (DSC) study provides the first crucial evidence regarding the chemical transformation of zirconia. Subsequently, detailed additional sample testing by X-ray diffraction (XRD), energy dispersive x-ray spectroscopy and confocal Raman microscopy provide strong supports that low temperature dehydrogenation of magnesium hydride is a result of formation of an active in situ product (zirconium hydride). This observation is validated by the negative Gibbs free energy values obtained for the formation of zirconium hydride over a broad working temperature range of 0–600 °C. Scanning electron microscopy (SEM) results prove the high dispersion of tiny nanoparticles all across the surface after the chemical interaction between MgH2 and ZrO2 and atomic force microscopy (AFM) study further proves that objects with grain sizes of ∼10 nm are abundant throughout the scanned surfaces. These observations reiterate that better metal oxide additives interact with MgH2 and results to the evolution of highly active insitu nanocatalysts.

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

High Energy Density and Temperature Stability in PVDF/PMMA via In Situ Polymerization Blending.

Dielectrics with improved energy density have long-standing demand for miniature and lightweight energy storage capacitors for electrical and electronic systems. Recently, polyvinylidene fluoride (PVDF)-based ferroelectric polymers have shown attractive energy storage performance, such as high dielectric permittivity and high breakdown strength, and are regarded as one of the most promising candidates. However, the non-negligible energy loss and inferior temperature stability of PVDF-based polymers deteriorated the energy storage performance or even the thermal runaway, which could be ascribed to vulnerable amorphous regions at elevated temperatures. Herein, a new strategy was proposed to achieve high energy density and high temperature stability simultaneously of PVDF/PMMA blends by in situ polymerization. The rigidity of the amorphous region was ideally strengthened by in situ polymerization of methyl methacrylate (MMA) monomers in a PVDF matrix to obtain PVDF/PMMA blends. The atomic force microscopic study of the microstructure of etched films showed the ultra-homogenous distribution of PMMA with high glass transition temperature in the PVDF matrix. Consequently, the temperature variation was remarkably decreased, while the high polarization response was maintained. Accordingly, the high energy density of ∼8 J/cm3 with ∼80% efficiency was achieved between 30 and 90 °C in PVDF/PMMA films with 39–62% PMMA content, outperforming most of the dielectric polymers. Our work could provide a general solution to substantially optimize the temperature stability of dielectric polymers for energy storage applications and other associated functions.

Atomic Force Microscope Study of Friction at the Submicron-Scale During Tribotests With Self-Mated Steel

Abstract Friction at the microscale during reciprocal sliding tribotests was studied for the first time with self-mated steel (100Cr6/AISI 52100) taking advantage of an atomic force microscope (AFM). To this aim, microsized steel particles were glued to the AFM-cantilever and employed as colloidal tips to perform tribotests on a steel disc. The torsion of the cantilever, which correlates with the friction force, was measured during the tests. Due to the irregular shape of the test particles and their wear, it is not possible to calibrate the torsional response of the cantilever and absolute quantification of the friction force cannot be achieved. Nevertheless, the model system used in the presented measurements is more representative of the tribology of real mechanical tribo-elements than already studied systems, in which for example only one tribopartner is worn. Few tests with the same load did not yield any wear and show that the load and adhesion contributions to friction stay constant when the shape of the test particle does not change. Most of the presented tribotests engendered wear. For those tests, the increase of friction during the tribotests was detected and was attributed to the emerging plowing contribution. Furthermore, analysis of both torsion and local slope experienced by the cantilever during the tests gives information on the creation of wear particles and their influence on friction.

Calendula flower extract loaded collagen film exhibits superior wound healing potential: Preparation, evaluation, in-vitro &in-vivo wound healing study

The present study was aimed to prepare Calendula flower extract loaded collagen film as a safe and effective wound dressing. Collagen film was prepared by solvent casting method and characterized for physicochemical properties like water absorption capacity, total phenolic content, total flavonoid content, antioxidant activity, infrared spectra, biodegradation, moisture content, differential scanning calorimetry, and sterility. The triple helical structure of collagen in the formulation was confirmed by gel electrophoresis and atomic force microscopy study. The safety and efficacy of developed formulation were investigated by in-vitro cell culture experiments including MTT assay, scratch assay on 3T3 Swiss albino cell line, In-vitro hemolysis study and In-vivo wound healing animal study on Wistar rats. In-vitro cell cytotoxicity test showed that the developed film was non-cytotoxic. In-vivo animal study on Wistar rats showed rapid wound healing compared to non-treated and placebo-treated group. The rate of wound contraction was significantly (p < 0.001) high in CFE loaded collagen film treated wounds (92.18 ± 1.2%) when compared to the control group (56.25 ± 4.1%), placebo-treated group (62.5 ± 5.1%) and marketed product treated group (68.75 ± 6.1%) on day 21. The prepared biodegradable collagen film incorporated with calendula flower extract was safe, stable, and effective as a wound healing dressing.