Resolution Atomic Force Microscopy Research Articles

Connexin 30 locally controls actin cytoskeleton and mechanical remodeling in motile astrocytes.

During brain maturation, astrocytes establish complex morphologies unveiling intense structural plasticity. Connexin 30 (Cx30), a gap-junction channel-forming protein expressed postnatally, dynamically regulates during development astrocyte morphological properties by controlling ramification and extension of fine processes. However, the underlying mechanisms remain unexplored. Here, we found in vitro that Cx30 interacts with the actin cytoskeleton in astrocytes and inhibits its structural reorganization and dynamics during cell migration. This translates into an alteration of local physical surface properties, as assessed by correlative imaging using stimulated emission depletion (STED) super resolution imaging and atomic force microscopy (AFM). Specifically, Cx30 impaired astrocyte cell surface topology and cortical stiffness in motile astrocytes. As Cx30 alters actin organization, dynamics, and membrane physical properties, we assessed whether it controls astrocyte migration. We found that Cx30 reduced persistence and directionality of migrating astrocytes. Altogether, these data reveal Cx30 as a brake for astrocyte structural and mechanical plasticity.

DNA Origami-Enabled Gene Localization of Repetitive Sequences.

Repetitive sequences, which make up over 50% of human DNA, have diverse applications in disease diagnosis, forensic identification, paternity testing, and population genetic analysis due to their crucial functions for gene regulation. However, representative detection technologies such as sequencing and fluorescence imaging suffer from time-consuming protocols, high cost, and inaccuracy of the position and order of repetitive sequences. Here, we develop a precise and cost-effective strategy that combines the high resolution of atomic force microscopy with the shape customizability of DNA origami for repetitive sequence-specific gene localization. "Tri-block" DNA structures were specifically designed to connect repetitive sequences to DNA origami tags, thereby revealing precise genetic information in terms of position and sequence for high-resolution and high-precision visualization of repetitive sequences. More importantly, we achieved the results of simultaneous detection of different DNA repetitive sequences on the gene template with a resolution of ∼6.5 nm (19 nt). This strategy is characterized by high efficiency, high precision, low operational complexity, and low labor/time costs, providing a powerful complement to sequencing technologies for gene localization of repetitive sequences.

Nano-positive up negative down in binary oxide ferroelectrics

Ferroelectric HfO2 and ZrO2-based materials are promising candidates for next-generation ferroelectric devices, but their characterization is challenging due to complex factors such as crystal phases, degradation mechanisms, and local inhomogeneities. In this work, we propose a novel nanosized positive-up-negative-down (PUND) method to assess the ferroelectric response of doped-HfO2. This method is based on actual current probing and is immune to most electrostatic artifacts that plague other electrical atomic force microscopy (AFM) techniques. We demonstrate the PUND method’s ability to induce ferroelectric switching in Si-doped HfO2 and investigate the distinctive PUND response obtained for individual grains. We also extract the polarization charge based on a direct estimate of the tip–sample contact area. The proposed PUND method is a significant innovation as it is a method to combine the high spatial resolution of AFM with the immunity to electrostatic artifacts of current probing. This makes it a powerful tool for studying ferroelectric materials at the nanoscale, where local inhomogeneities and other effects can have a significant impact on their behavior. The PUND method is also notable for its ability to extract polarization charge based on a direct estimate of the tip–sample contact area. This is a significant improvement over previous methods, which often relied on indirect or approximate estimates of the contact area. Overall, the PUND method is a novel and innovative technique that offers significant advantages for the characterization of ferroelectric materials at the nanoscale. It is expected to have a major impact on the research and development of next-generation ferroelectric devices.

Nanomechanical-based classification of prostate tumor using atomic force microscopy.

The loss of mechanical homeostasis between tumor cells and microenvironment is an important factor in tumor metastasis. In the process, mechanical forces affect cell proliferation, differentiation, migration and tissue development. Using high spatial resolution of Atomic force microscopy (AFM) technology, our study provides the direct measurement of the nanomechanical properties of prostate cancer clinical tissue specimens. AFM was used to determine the biomechanical properties of prostate tissue with different grade scores. K-means clustering method and fuzzy C-means were used to distinguish the cellular component in prostate tissue from non-cellular component based on their viscoelasticity. Futhermore, AFM measurements in vitro cells, including metastatic prostate cells (PC-3) and normal human prostate cells (PZ-HPV-7) were carried out. The Young's modulus was decreased in prostate cancer progression, and the elasticity of cellular component in prostate cancer tissue was smaller than that of normal prostate tissue. PC-3 cells were softer than PZ-HPV-7 cells. Further mechanism investigation showed that the difference in modulus between cancerous and normal prostate tissue may be associated with a greater actin cytoskeleton distribution inside the cancer cells. The results suggests that the nanomechanical properties can classify the prostate tumor, which could be used as an index for the identification and classification of cancer at cellular level.

Hippocampus of the APPNL-G-F mouse model of Alzheimer's disease exhibits region-specific tissue softening concomitant with elevated astrogliosis.

Widespread neurodegeneration, enlargement of cerebral ventricles, and atrophy of cortical and hippocampal brain structures are classic hallmarks of Alzheimer's disease (AD). Prominent macroscopic disturbances to the cytoarchitecture of the AD brain occur alongside changes in the mechanical properties of brain tissue, as reported in recent magnetic resonance elastography (MRE) measurements of human brain mechanics. Whilst MRE has many advantages, a significant shortcoming is its spatial resolution. Higher resolution "cellular scale" assessment of the mechanical alterations to brain regions involved in memory formation, such as the hippocampus, could provide fresh new insight into the etiology of AD. Characterization of brain tissue mechanics at the cellular length scale is the first stepping-stone to understanding how mechanosensitive neurons and glia are impacted by neurodegenerative disease-associated changes in their microenvironment. To provide insight into the microscale mechanics of aging brain tissue, we measured spatiotemporal changes in the mechanical properties of the hippocampus using high resolution atomic force microscopy (AFM) indentation tests on acute brain slices from young and aged wild-type mice and the APPNL-G-F mouse model. Several hippocampal regions in APPNL-G-F mice are significantly softer than age-matched wild-types, notably the dentate granule cell layer and the CA1 pyramidal cell layer. Interestingly, regional softening coincides with an increase in astrocyte reactivity, suggesting that amyloid pathology-mediated alterations to the mechanical properties of brain tissue may impact the function of mechanosensitive astrocytes. Our data also raise questions as to whether aberrant mechanotransduction signaling could impact the susceptibility of neurons to cellular stressors in their microenvironment.

Highly efficient sequestration of aqueous lead on nanostructured calcite substrates

Following defocused ion beam sputtering, large area highly corrugated and faceted nanoripples are formed on calcite (10.4) faces in a self-organized fashion. High resolution atomic force microscopy (AFM) imaging reveals that calcite ripples are defined by facets with highly kinked (11.0) and (2.12) terminations. In situ AFM imaging during the exposure of such modified calcite surfaces to PbCl2 aqueous solution reveals that the nanostructured calcite surface promotes the uptake of Pb. In addition, we observed the progressive smoothing of the highly reactive calcite facet terminations and the formation of Pb-bearing precipitates elongated in registry with the underlying nanopattern. By SEM–EDS analysis we quantified a remarkable 500% increase of the Pb uptake rate, up to 0.5 atomic weight % per hour, on the nanorippled calcite in comparison to its freshly cleaved (10.4) surfaces. These results suggest that nanostructurated calcite surfaces can be used for developing future systems for lead sequestration from polluted waters.

Are High Resolution Atomic Force Microscopy images proportional to the force gradient or the force maps?

Frequency modulation Atomic Force Microscopy using tips functionalized with carbon monoxide (also known as High Resolution AFM) shows an extraordinary resolution on molecules and it can disclose their inner structure on the frequency shift maps. When operating the microscope at low amplitudes, <1 Å, these frequency shift measurements have been traditionally interpreted as the force gradient between the probe and the sample. Here, we show that, for CO-terminated tips, this interpretation fails even for amplitudes as small as 0.2–0.3 Å. The main reason behind this failure is the very rapid variation in tip-sample interaction upon tip approach associated with the mobility of the CO probe, which deflects to reduce the Pauli repulsion with the sample. Besides, we propose a new and very simple approach for the frequency shift in terms of the force at the closest tip-sample separation. This force approximation reproduces the real frequency maps for amplitudes larger than ∼0.3 Å, independent of CO deflection.

Profilometry and atomic force microscopy for surface characterization

<sec><strong>Aim</strong> This study aims to evaluate and compare the profilometry and atomic force microscopy (AFM) for characterization of biomaterial surfaces. </sec><sec><strong>Method</strong> The clinically commonly used titanium (Ti) was used as the specimen. Each of the specimen was prepared by different grits of sandpapers, including 2000, 1000, 800, 600, 400, 220, 180, and 100 grits. An unpolished Ti plate served as the control. Surface characterization of the Ti specimens was examined using profilometry and AFM. </sec><sec><strong>Results</strong> Both profilometry and AFM were capable of producing two-dimensional (2D) and three-dimensional (3D) topography. The scanning speed of profilometry (12 ± 5 s/image) was faster than that of AFM (250 ± 50 s/image) (<i>p</i> &lt; 0.01). The resolution of AFM was relatively higher than profilometry. AFM produced more precise value, especially at nano-scale. When the Ti surface roughness was less than 0.2 μm, the results of surface roughness measured by profilometry and AFM were similar (mean difference = 0.01 ± 0.03, <i>p</i> = 0.81). When the Ti surface roughness was more than 0.3 μm, the surface roughness measured by profilometry was slightly higher than that by AFM (mean difference = 0.43 ± 0.15, <i>p</i> = 0.04). </sec><sec><strong>Conclusion</strong> Profilometry and AFM are both useful techniques for the characterization of biomaterial surfaces. Profilometry scanned faster than the AFM but produced less detailed surface topography. Both technologies provided similar measurement when the roughness was less than 0.2 μm. When the Ti surface roughness was more than 0.3 μm, the surface roughness measured by profilometry was slightly higher than that by AFM. </sec>

Thermal annealing effects on the physical properties of GaAsBi/GaAs/GaAs:Si structure

GaAsBi is a new material called a highly mismatched alloy that has drawn attention regarding its special physical properties. The alloying of the GaAs matrix by Bi atom gives rise to a huge restructuring of the band structure. A rapid shrinkage in the bandgap energy and a splitting of the spin–orbit interaction band are noted. But the synthesis of this material requires unusual growth conditions in order to avoid the appearance of droplets on the surface and a native defects due to the non-stoichiometry. Consequently, an improvement of the physical properties is required to be used in device applications. In this perspective, we report an investigation of the effect of thermal annealing on the GaAsBi/GaAs/GaAs:Si structure. Photoreflectance, Spectroscopic ellipsometry are used to study the optical characteristics of this structure. High Resolution X-Ray Diffraction and Atomic Force Microscopy are employed as structural techniques for investigation.

A nanoscale study of the structure and electrical response of Sepia eumelanin.

Eumelanin, the brown-black member of the melanin biopigment family, is a prototype material for sustainable (green) organic electronics. Sepia eumelanin (Sepia) is a type of biosourced eumelanin extracted from the ink sac of cuttlefish. Electron microscopy and scanning probe microscopy images of Sepia show distinguishable near spherical granules with diameters of about 150-200 nm. We have recently reported on predominant electronic transport in printed films of Sepia formulated inks including the (insulating) binder Polyvinyl-butyral (PVB). In that work, we proposed that inter-granular percolative transport, observed for micrometric interelectrode distances, is promoted by the confining action of the PVB binder on the Sepia granules. Considering that inter-granular transport implies intra-granular transport, in this work we proceeded to a nanoscale study of Sepia granules by High Resolution Atomic Force Microscopy (HR-AFM) and Conductive-AFM (c-AFM). We have observed protrusions on the surface of the Sepia granules, suggesting sub-granular structures compatible with the hierarchical development of Sepia, as proposed elsewhere. For films of Sepia formulated inks deposited on gold-coated substrates, c-AFM revealed, for the very first time, a nanoscale electrical response. Nanoscale studies provide the key to structure-property relationships in biosourced materials strategic for sustainable organic electronics.

Characterization of RNA Nanoparticles and Their Dynamic Properties Using Atomic Force Microscopy.

The protocol described in this chapter allows for acquiring topography images of RNA-based nanoring structures and assessing their dynamic properties using atomic force microscopy (AFM) imaging. AFM is an indispensable tool for characterization of nucleic acid-based nanostructures with the exceptional capability of observing complexes in the range of a few nanometers. This method can visualize structural characteristics and evaluate differences between individual structurally different RNA nanorings. Due to the highly resolved AFM topography images, we introduce an approach that allows to distinguish the differences in the dynamic behavior of RNA nanoparticles not amenable to other experimental techniques. This protocol describes in detail the preparation procedures of RNA nanostructures, AFM imaging, and data analysis.

Areca fiber/epoxy nano-composite reinforced with amine-functionalized nano-alumina-enhancement in thermal and thermo-mechanical properties

In this study, diglycidyl ethers of bisphenol-A (DGEBA) epoxy resin and areca fiber (AF) [80:20] composite having various weight percentages (1, 2 and 3 wt%) of amine-functionalized nano-alumina (F-Al) were cured at room temperature using polyamidoamine curing agent (XY54). The F-Al acted as an adhesion promoter through its amine groups on the surface was confirmed using FT-IR. Different weight percentages of F-Al were reinforced into DGEBA/AF to improve the thermal, mechanical, and thermo-mechanical properties of DGEBA/AF epoxy nano-composite by dynamic mechanical analysis (DMA) and thermo-gravimetric analysis (TGA). The surface morphology of pristine (DGEBA) epoxy matrix, DGEBA/AF composites, and DGEBA/AF/F-Al nano-composite was studied using scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and atomic force microscopy (AFM) techniques. The 2 wt% addition of F-Al nano reinforcement found to improve the thermal, mechanical, and thermo-mechanical properties of DGEBA/AF nano-composites. • Fabrication of F-Al reinforced acrea fiber epoxy nano-composites • Enhanced mechanical and thermal properties of the F-Al/acrea fiber epoxy nano-composites • It can be used in automobile, industrial and engineering applications

Development and characterization of an amorphous curcumin-Eudragit®E100 solid dispersions with improved solubility, stability, and pharmacokinetic properties

The development of amorphous solid dispersions (ASD) is one way to overcome the bioavailability challenges of poorly water-soluble drug. Herein, Curcumin (CUR) was dispersed in the polymeric matrix of Eudragit®E100 by solvent evaporation, giving ASD, donated as CUR@Eudragit®E100. Solubility and stability of CUR were greatly enhanced. DSC and XRD analysis confirmed that the incorporated CUR was present in an amorphous state. The interaction between CUR and Eudragit®E100 was investigated through FTIR and molecular modelling studies which implied that -OH groups in CUR, and carboxyl and amino groups in Eudragit®E100 involved in the hydrogen bond formation. High resolution atomic force microscopy was employed to directly visualize the molecular morphology of Eudragit®E100 and CUR in CUR@Eudragit®E100 and the interaction between CUR and the polymer. pH influenced CUR release profile in which the sustained release pattern was revealed vs the physical mixtures. From the plasma concentration vs time profile graph, oral bioavailability of Cur@Eudragit®E100 was approximately 5-fold higher than that of native CUR. These results confirmed the potential of designing ASD to enhance the solubility and bioavailability of CUR, simultaneously deliver CUR through this alternative administration route.

Micro-nano morphology parameters and mechanical properties of soot particles sampled from high pressure jet flames of diesel from direct coal liquefaction

Diesel from direct coal liquefaction (DDCL) is a new type of engine alternative energy. In this study, a premixed constant volume combustion chamber system with soot particle sampling devices were built. High resolution transmission electron microscope (HR-TEM) and atomic force microscopy were applicated to characterize the micro-nano morphology parameters and mechanical properties of soot particles sampled from high pressure jet flames of DDCL. There were two in-house automatic processing codes were developed to process the HR-TEM images and extract the micro-nano morphology parameters of the soot particles. This study has systematically studied the effect of injection pressures on the micro-nano morphology parameters and mechanical properties of soot particles. The test results illustrated that there was a correlation between the micro-nano morphology parameters and mechanical properties of soot particles. Under the same combustion conditions, DDCL soot particles demonstrated smaller size, compacted structure, lower graphitization degree and weaker antioxidant capacity than that of diesel soot particles. The average adhesive force and energy dissipation of diesel soot particles were much higher, which indicated the diesel soot particles have stronger agglomeration performance. The average elastic modulus of DDCL soot particles was smaller than that of diesel, which caused the weaker ability to resist deformation for DDCL soot particles.

Optimization of tip-enhanced Raman spectroscopy for probing the chemical structure of DNA

Tip-enhanced Raman (TER) spectroscopy combines the nanometric spatial resolution of atomic force microscopy (AFM) and the chemical sensitivity of Raman spectroscopy. Thus, it provides a unique possibility to obtain spectroscopic information on individual, nanometre-size molecules. The enhancement of Raman scattering cross-section requires modification of the AFM tip apex with a plasmonic nanostructure. Despite numerous advances of TERS research, attaining good reproducibility and stable enhancement is still challenging mainly due to the lack of optimized probes and sample preparation procedures. Moreover, current nanospectroscopic standard samples - carbon nanotubes (CNTs) have relatively simple chemical structure, and therefore, they are far from real-life analytes, especially biological samples. In this work we focus on the optimization of TERS technique for efficient DNA measurements, including: a preparation of atomically-flat gold substrates, fixative free deposition of DNA and optimization of TERS probe preparation. Here we demonstrate a comprehensive comparison of the efficacy of several types of TERS probes. Applying the systematic approach, we obtained reliable and reproducible TER spectra of DNA. Thus, we provide preparation procedures of a new standard TERS sample, TERS substrates and TERS probes. Our research provides a solid foundation for further research on DNA and its interaction with other biomolecules upon biologically significant processes such as DNA damage and repair.

Measurements and Modeling of Atomic‐Scale Sidewall Roughness and Losses in Integrated Photonic Devices

AbstractAtomic‐level imperfections play an increasingly critical role in nanophotonic device performance. However, it remains challenging to accurately characterize the sidewall roughness with sub‐nanometer resolution and directly correlate this roughness with device performance. A method that allows to measure the sidewall roughness of waveguides made of any material (including dielectrics) using the high resolution of atomic force microscopy is developed. This method is illustrated by measuring state‐of‐the‐art photonic devices made of silicon nitride. The roughness of devices fabricated using both deep ultraviolet (DUV) photo‐lithography and electron‐beam lithography for two different etch processes is compared. To correlate roughness with device performance, a new Payne–Lacey Bending model is described, which adds a correction factor to the widely used Payne–Lacey model so that losses in resonators and waveguides with bends can be accurately predicted given the sidewall roughness, waveguide width and bending radii. Having a better way to measure roughness and use it to predict device performance can allow researchers and engineers to optimize fabrication for state‐of‐the‐art photonics using many materials.

Unbalanced bidirectional radial stiffness gradients within the organ of Corti promoted by TRIOBP

Hearing depends on intricate morphologies and mechanical properties of diverse inner ear cell types. The individual contributions of various inner ear cell types into mechanical properties of the organ of Corti and the mechanisms of their integration are yet largely unknown. Using sub-100-nm spatial resolution atomic force microscopy (AFM), we mapped the Young's modulus (stiffness) of the apical surface of the different cells of the freshly dissected P5-P6 cochlear epithelium from wild-type and mice lacking either Trio and F-actin binding protein (TRIOBP) isoforms 4 and 5 or isoform 5 only. Variants of TRIOBP are associated with deafness in human and in Triobp mutant mouse models. Remarkably, nanoscale AFM mapping revealed unrecognized bidirectional radial stiffness gradients of different magnitudes and opposite orientations between rows of wild-type supporting cells and sensory hair cells. Moreover, the observed bidirectional radial stiffness gradients are unbalanced, with sensory cells being stiffer overall compared to neighboring supporting cells. Deafness-associated TRIOBP deficiencies significantly disrupted the magnitude and orientation of these bidirectional radial stiffness gradients. In addition, serial sectioning with focused ion beam and backscatter scanning electron microscopy shows that a TRIOBP deficiency results in ultrastructural changes of supporting cell apical phalangeal microfilaments and bundled cortical F-actin of hair cell cuticular plates, correlating with messenger RNA and protein expression levels and AFM stiffness measurements that exposed a softening of the apical surface of the sensory epithelium in mutant mice. Altogether, this additional complexity in the mechanical properties of the sensory epithelium is hypothesized to be an essential contributor to frequency selectivity and sensitivity of mammalian hearing.

Featuring exfoliated 2D stacks into fractal-like patterns in WS2/carboxy methyl cellulose nanocomposites

We report on the formation of fractal-like structures with 2D layer support derived from exfoliated WS2 stacks in cellulose environment (NaCMC, sodium carboxymethyl cellulose). Morphological features and surface topography are studied on 1–4 wt.% WS2/NaCMC nanocomposite films by employing high resolution scanning electron microscopy (HR-SEM) and atomic force microscopy (AFM) employed in semi-contact mode. The development of termite-like, fractal patterns in the nanocomposites can be visualized from the micrographs. Using a box-count method, we predict bi- and tri-modal fractals in the background of 2D, giving out asymmetric shapes in the dimension vs. frequency curves. While typical fractal dimension reduces from 1.98 to 1.6 with increasing WS2 content, the AFM images exhibited an evenly spread rough units while giving a root mean square (RMS) roughness of σ = 66.5 nm, for 4 wt.% specimen. Moreover, Raman analysis exhibited an augmented in-plane (E12g ∼350 cm−1) to out-of-plane (A1g ∼418 cm−1) intensity ratio with an increase in WS2 loading. Also, the intensities of individual Raman modes were found to vary nonlinearly with an increase in concentration of WS2(1-16%) being dispersed in cellulose-based polymer. Furthermore, the force constants are estimated using vibrational frequencies observed in the fourier transform infrared (FTIR) spectra which predict several orders of higher strength in W−S relative to S−S, depending on stretching or bending vibrations. The hexagonal, 2H phase of WS2 system with prominent (002) diffraction plane along the c-axis representing crystalline nature in the composites can be seen from the XRD patterns. Association of fractal-like textural patterns in 2D is expected to draw implications in advanced sensing, antifouling, photo-catalysis, energy storage etc.

Photothermal AFM-IR spectroscopy and imaging: Status, challenges, and trends

This article focuses on the atomic force microscopy-infrared (AFM-IR) technique and its recent technological developments. Based on the detection of the photothermal sample expansion signal, AFM-IR combines the high spatial resolution of atomic force microscopy with the chemical identification capability of infrared spectroscopy to achieve submicrometric physico-chemical analyses. Since the first publication in 2005, technological improvements have dramatically advanced the capabilities of AFM-IR in terms of spatial and spectral resolution, sensitivity, and fields of applications. The goal of this paper is to provide an overview of these developments and ongoing limitations. We summarize recent progress in AFM-IR implementations based on the major AFM contact, tapping, and peak force tapping modes. Additionally, three new trends are presented, namely, AFM-IR applied to mineral samples, in fluid and a novel, purely surface sensitive AFM-IR configuration, to probe top layers. These trends demonstrate the immense potential of the technique and offer a good insight into the scope of AFM-IR.

Room temperature ethanol sensing by chemically reduced graphene oxide film

Herein, we report the synthesis and fabrication of a low-cost sensor using thin film of chemically reduced graphene oxide (rGO) that can detect ethanol at room temperature with high sensitivity. X-ray Diffraction (XRD) confirmed the reduction of graphene oxide whereas high resolution electron microscopies and atomic force microscopy revealed existence of multiple (>20) layers within the rGO sheets. Optical band gap of rGO was estimated to be ∼ 1.7 eV from the UV–vis absorbance data whereas Raman spectrum confirmed the multilayered structure of rGO sheets. Thin films of rGO deposited on glass substrate showed sharp increase in current when exposed to ethanol vapor and exhibited response as high as 297 at room temperature against 100 ppm of ethanol. The rGO film sensor also showed fast response and recovery times of 2 s and 17 s, respectively and good repeatability over several cycles. The selectivity of the sensor to ethanol was also good as the response exhibited by it was much lower for other alcoholic vapors and almost nil to non-alcoholic VOCs and gases like CO and NO2. Upon co-exposure to standard humid air of 50% relative humidity, the sensor response to ethanol did not change suggesting its suitability for practical applications.