Mode Atomic Force Microscopy Research Articles

Single-cell adhesion force mapping of a highly sticky bacterium in liquid

The sticky bacterium Acinetobacter sp. Tol 5 adheres to various material surfaces via its cell surface nanofiber protein, AtaA. This adhesiveness has only been evaluated based on the amount of cells adhering to a surface. In this study, the adhesion force mapping of a single Tol 5 cell in liquid using the quantitative imaging mode of atomic force microscopy (AFM) revealed that the adhesion of Tol 5 was near 2 nN, which was 1–2 orders of magnitude higher than that of other adhesive bacteria. The adhesion force of a cell became stronger with the increase in AtaA molecules present on the cell surface. Many fibers of peritrichate AtaA molecules simultaneously interact with a surface, strongly attaching the cell to the surface. The adhesion force of a Tol 5 cell was drastically reduced in the presence of 1% casamino acids but not in deionized water (DW), although both liquids decrease the adhesiveness of Tol 5 cells, suggesting that DW and casamino acids inhibit the cell approaching step and the subsequent direct interaction step of AtaA with surfaces, respectively. Heterologous production of AtaA provided non-adhesive Acinetobacter baylyi ADP1 cells with a strong adhesion force to AFM tip surfaces of silicon and gold.

Effect of Eigenmode Frequency on Loss Tangent Atomic Force Microscopy Measurements

Atomic Force Microscopy (AFM) is no longer used as a nanotechnology tool responsible for topography imaging. However, it is widely used in different fields to measure various types of material properties, such as mechanical, electrical, magnetic, or chemical properties. One of the recently developed characterization techniques is known as loss tangent. In loss tangent AFM, the AFM cantilever is excited, similar to amplitude modulation AFM (also known as tapping mode); however, the observable aspects are used to extract dissipative and conservative energies per cycle of oscillation. The ratio of dissipation to stored energy is defined as tanδ. This value can provide useful information about the sample under study, such as how viscoelastic or elastic the material is. One of the main advantages of the technique is the fact that it can be carried out by any AFM equipped with basic dynamic AFM characterization. However, this technique lacks some important experimental guidelines. Although there have been many studies in the past years on the effect of oscillation amplitude, tip radius, or environmental factors during the loss tangent measurements, there is still a need to investigate the effect of excitation frequency during measurements. In this paper, we studied four different sets of samples, performing loss tangent measurements with both first and second eigenmode frequencies. It is found that performing these measurements with higher eigenmode is advantageous, minimizing the tip penetration through the surface and therefore minimizing the error in loss tangent measurements due to humidity or artificial dissipations that are not dependent on the actual sample surface.

Probing the Nature of Chemical Bonds by Atomic Force Microscopy.

The nature of the chemical bond is important in all natural sciences, ranging from biology to chemistry, physics and materials science. The atomic force microscope (AFM) allows to put a single chemical bond on the test bench, probing its strength and angular dependence. We review experimental AFM data, covering precise studies of van-der-Waals-, covalent-, ionic-, metallic- and hydrogen bonds as well as bonds between artificial and natural atoms. Further, we discuss some of the density functional theory calculations that are related to the experimental studies of the chemical bonds. A description of frequency modulation AFM, the most precise AFM method, discusses some of the experimental challenges in measuring bonding forces. In frequency modulation AFM, forces between the tip of an oscillating cantilever change its frequency. Initially, cantilevers were made mainly from silicon. Most of the high precision measurements of bonding strengths by AFM became possible with a technology transfer from the quartz watch technology to AFM by using quartz-based cantilevers (“qPlus force sensors”), briefly described here.

Nanoscale morphology of thin liquid films near the advancing contact line during condensation

The extended thin-film region adjacent to the contact line is crucial in heat transfer because of its capability to enhance heat transfer and its critical role in wetting dynamics. The present investigation focused on the study of advancing contact line morphology induced by water vapor condensation. The condensation was at low rates with the advancing velocities <60 nm/s. Two modes of atomic force microscopy were utilized to measure the morphology of a liquid film with the nanometer resolution. The results indicated that the profile of the film went straight down to the apparent contact line when viewed in a sub-micron window, which is in contrast to nonvolatile cases, such as glycerol and silicon oil, which would have a convex nanobending around 20 nm from the substrate surface due to the local dynamic friction. Furthermore, a precursor nanofilm was detected beyond the contact line during condensation, and nanodroplets hundreds of nanometers in height were sitting on the nanofilm, representing the structure of the advancing contact line, and being adjacent to the condensation plays an essential role in contact line dynamics.

Theoretical model and experimental study on environmental dissipation mechanism of tapping mode atomic force microscope.

The phase information reflects the energy dissipation of the probe and sample interactions in tapping mode atomic force microscopes (TM AFMs). In this paper, we use the method of tune test in TM AFM to study the contribution of external environment to energy dissipation by changing the probe position and ambient humidity. Finally, the theoretical and experimental quality factors of air viscous damping, squeeze film damping and liquid bridge force are obtained to characterise energy dissipation. The analytically predicted values of the model established on squeeze film damping, viscous damping and liquid bridge force comparing to the experimental results in this paper is rational. And the comparative analysis results show that the main mechanism of energy dissipation is different at different probe positions and different relative humidness. This result is of great significance for understanding the mechanism of phase imaging experimentally and theoretically.

Microstructural behavior of magnetorheological elastomer undergoing durability evaluation by stress relaxation

The widespread use of magnetorheological elastomer (MRE) materials in various applications has yet to be limited due to the fact that there are substantial deficiencies in current experimental and theoretical research on its microstructural durability behavior. In this study, MRE composed of silicon rubber (SR) and 70 wt% of micron-sized carbonyl iron particles (CIP) was prepared and subjected to stress relaxation evaluation by torsional shear load. The microstructure and particle distribution of the obtained MRE was evaluated by a field emission scanning electron microscopy (FESEM). The influence of constant low strain at 0.01% is the continuing concern within the linear viscoelastic (LVE) region of MRE. Stress relaxation plays a significant role in the life cycle of MRE and revealed that storage modulus was reduced by 8.7%, normal force has weakened by 27%, and stress performance was reduced by 6.88% along approximately 84,000 s test duration time. This time scale was the longest ever reported being undertaken in the MRE stress relaxation study. Novel micro-mechanisms that responsible for the depleted performance of MRE was obtained by microstructurally observation using FESEM and in-phase mode of atomic force microscope (AFM). Attempts have been made to correlate strain localization produced by stress relaxation, with molecular deformation in MRE amorphous matrix. Exceptional attention was focused on the development of molecular slippage, disentanglement, microplasticity, microphase separation, and shear bands. The relation between these microstructural phenomena and the viscoelastic properties of MRE was diffusely defined and discussed. The presented MRE is homogeneous with uniform distribution of CIP. The most significant recent developments of systematic correlation between the effects of microstructural deformation and durability performance of MRE under stress relaxation has been observed and evaluated.

Effect of tip radius on the nanoscale viscoelastic measurement of polymers using loss tangent method in amplitude modulation AFM

We study the influence of tip radius on the viscoelastic characterization of polymers using a recently developed loss tangent (tan δ) method operated in amplitude modulation atomic force microscopy (AM-AFM) mode. By decreasing the tip radius, we found that AM-AFM tan δ of a homogeneous polystyrene film decreased close to the bulk limit value, which can be ascribed to a reduced effect of the probe/sample adhesive interaction for a smaller tip. Decreasing the tip radius also shifted the tan δ values of nanostructured blocks in a poly(styrene-b-isoprene-b-styrene) triblock copolymer film to their bulk limits, but in different trends for glassy styrene and rubbery isoprene blocks. Besides minimizing the effect of the adhesive interaction, we demonstrate that reducing the tip radius being smaller than the characteristic size of nanostructured domains is critical to obtain their true tan δ image.

Nanomechanical properties of potato flakes using atomic force microscopy

Characterizing the nanomechanical properties of plants at the sub-cellular level is important in understanding the dynamic processes underpinning both potato plant growth and downstream effects of industrial food processing. Here, we measured nanomechanical properties and mapped the elastic properties of two types of industrial potato flakes that provide both optimal and sub-optimal results during food manufacturing by employing both amplitude-modulation and force-modulation atomic force microscopy (AFM) in air. The amplitude-modulation AFM revealed that sub-optimal potato flakes were more compliant when compared to the optimal samples. Furthermore, the elastic modulus maps demonstrated optimal potato samples to be significantly stiffer than the sub-optimal samples. Therefore, our results provide evidence that probing the elastic properties of potato flakes can be a first step in providing food industries with a quantitative differential assessment between optimal and sub-optimal samples.

Surface charge density measurement of a single protein molecule with a controlled orientation by AFM

The spatial distribution of functional groups causes a charge distribution that often has a close relationship with its biofunctions. To understand them of the protein molecules, measurements of the charge distribution under physiological conditions are desired. Atomic force microscopy (AFM) has been utilized to measure the surface charge density by measuring the electric double layer (EDL) force caused by the overlap of the EDLs on the surfaces of the AFM tip and the biomolecule. Here, we demonstrated the surface charge density measurement of a single streptavidin (SA) protein molecule by the three-dimensional force mapping method based on frequency modulation AFM (FM-AFM). The SA has a strong affinity to biotin because of the electrostatic interactions between the molecules. Therefore, the surface charge density measurements of the biotin-binding sites and other surface areas of the molecule have been anticipated. However, the surface charge density of the surfaces other than the biotin-binding side has never been measured. We demonstrate the surface charge density measurement of the top surface of the single SA molecule, which is perpendicular to the biotin-binding sides, with a controlled orientation using DNA origami as a template by FM-AFM in an electrolyte solution. The surface charge density of the top surface of the SA molecule was estimated by fitting the experimental force curves to the Derjaguin-Landau-Verwey-Overbeck theory. We found that the surface charge density of the top surface of the SA molecule is comparable to those reported earlier for the biotin-binding sides of the molecule. We expect that, by using the DNA origami technology, one can control the orientation of a biomolecule attached to the substrate and measure the surface charge density of the specific surface areas of the biomolecule to obtain information that will help us to understand the relationship between their structures and functions.

The study and comparison of elastic modulus of pineapple fruit in macroscopic and microscopic modes.

According to bibliography, elastic modulus studies of agricultural produce at the macro-scale using a resistance measuring (as Magness-Taylor penetration test or compression test) by an Instron Universal Mechanical Testing Machine is often used to express this characteristic. However, the determination of the elastic properties of agricultural produce at the macro-scale result widely varying values for a particular agricultural produce. So in this study, to decrease the variability which now exists in the elastic modulus results of agricultural produce measured at the macro-scale, measuring and comparison of the elastic modulus of agricultural produce, pineapple fruit as case study, in macroscopic (by Hook's theory on the cylindrical specimen and Hertz theory in the mode of spherical indenter contact on the whole specimen) and microscopic (by atomic force microscopy) modes was investigate. There is concluded that with changing the type of theory, the behavior of the elastic modulus changes significantly at a 1% level. In microscopic mode studies, the lowest elastic modulus (0.135 MPa) was obtained by using Hertz theory in the mode of spherical indenter contact on the whole specimen while the highest elastic modulus value (0.779 MPa) was seen by using Hook's theory on the cylindrical specimen. In microscopic mode studies, the Sneddon model had the lowest elastic modulus while Hertzian model showed the highest elastic modulus value. Consequently, due to some reasons such as complex shape of most agricultural produce, assumptions required for three elastic theories of contacting bodies in macroscopic mode, complex structure and viscoelastic behavior of agricultural produce, it is found that the variability of the information can be reduced at micro-scale, or, to a lesser extent.

Heterogeneity of nanomechanical properties of the human umbilical vein endothelial cell surface

Endothelial cells, due to heterogeneity in the cell structure, can potentially form an inhomogeneous on structural and mechanical properties of the inner layer of the capillaries. Using quantitative nanomechanical mapping mode of atomic force microscopy, the parameters of the structural, elastic, and adhesive properties of the cell surface for living and glutaraldehyde-fixed human umbilical vein endothelial cells were studied. A significant difference in the studied parameters for three cell surface zones (peripheral, perinuclear, and nuclear zones) was established. The perinuclear zone appeared to be the softest zone of the endothelial cell surface. The heterogeneity of the endothelial cell mechanical properties at the nanoscale level can be an important mechanism in regulating the endothelium functions in blood vessels.

Ablation of binary As2S3, As2Se3, GeS2, GeSe2 and GeSe3 bulk glasses and thin films with a deep ultraviolet nanosecond laser

Binary (As2S3, As2Se3, GeS2 GeSe2 and GeSe3) bulk glasses and corresponding thin films were prepared and illuminated with deep ultraviolet nanosecond (DUV ns) pulsed laser operating at 213 nm. The illumination of samples led to the reproducible crater's formation. Subsequently, the influence of the pulses number and laser fluence on their creation was studied. The ablation rate and laser-induced ablation threshold (LIAT) were determined based on these experiments. The craters with the help of digital holographic microscopy (DHM), atomic force microscopy (AFM), phase shift imaging mode of AFM, Raman scattering, scanning electron microscopy and energy-dispersive X-ray spectroscopy were characterized. As an application possibility, the formation of the diffraction gratings by laser direct writing is presented and their functionality is demonstrated.

A dynamical approach to topography estimation in atomic force microscopy based on smooth orthogonal decomposition

Atomic force microscope (AFM) is one of the most versatile and powerful devices capable of producing high-resolution images of nanomaterial. Many researchers are widely investigating to improve the scanning speed and image quality of AFM by proposing different techniques. Here, we aim to present a novel approach based on the smooth orthogonal decomposition for the estimation of the surface topography in AFM. The technique proposed in this research not only eliminates the need for a closed-loop controller but also acquires the surface three-dimensional shape (topography) very quickly and accurately. The proposed technique relies on the fact that in the tapping mode of atomic force microscopy, the tip displacements are very fast compared to the topography changes, and the surface topography as a slowly varying parameter can be estimated using the smooth orthogonal decomposition algorithm. To this aim, the state space is reconstructed based on Takens’ theorem and used only the tip displacement measurement data. According to Takens’ theorem, using the delay time and embedding dimension parameters, we are able to create a system in which dynamical behaviors are similar to the original system. The results demonstrate that the proposed estimation approach is robust to noise and does not require large data or computational resources to be implemented. Also, the performance of the proposed method is appropriate for any type of force interactions between the tip and sample.

Atomic force microscopy studies of enamel, inner enamel, dentin, and cementum in canine teeth

The main goal of the present work is to explore the three dimensional (3-D) atomic force microscopy (AFM) images of human teeth and investigating their micromorphology. For this purpose, 10 fresh and permanent canine teeth were selected from a group of 40-year-old men who were candidate for the experimental processes. Afterward, they were all applied for studying the morphology of their hard tissues. The tapping mode of AFM was used to characterize the surface micromorphology on the square areas of 1μm × 1μm (512 × 512 pts). AFM results and surface stereometric analysis indicate the relationships between the micromorphology of the surface and the structural properties of these tissues across the length scales. As can be seen, the surface of cementum has the most irregular topography (D=2.87 ± 0.01) while the most regular topography (D=2.43 ± 0.01) is found in dentin. Furthermore, the more and less regularity of the surface have been found in inner enamel (Sq=26.26 nm) and dentin (Sq=41.28 nm), respectively. Stereometric and fractal analyses give valuable information about human canine teeth via 3-D micromorphology.

Bacteria and viruses in the objective of probe microscopy

The article is devoted to the study of viruses and bacteria using a scanning probe microscope in the atomic force microscopy mode, in particular, to the question, what data can be obtained using this method and how to interpret it.

AFM force spectroscopy as a powerful tool to address material design for biomedical applications. A review

Force Spectroscopy (FS), which is one of the operating modes of Atomic Force Microscope (AFM) technique proven to be useful in many biological and medical applications, such as cancer cells recognition. Currently, many scientific institutions carry on research on the Young’s modulus of individual cancer cells in order to detect the disease at an early stage of its development. As a result of the growing interest in the use of force spectroscopy to study cells’ mechanic, this review summarizes new applications of this method to study changes in the physical and chemical properties of cells under the influence of external stimuli of different origins. The work is divided into four research areas, in which the use of AFM force spectroscopy was used to explain phenomena occurring at the early stages of intracellular organization changes. Research areas presented in this manuscript focuses on detailed description of the effect of manifold external stimuli on cells, such as: (i) cell aging, (ii) active ingredients used in the cosmetics industry to improve skin condition, (iii) nanoparticles used in biomedicine, and (iv) micro- and nano-structures of topography on the surface of substrates used for cell cultures. This review is based on a critical analysis of the latest literature reports (seven of which were created with Author’s contribution) describing the use of force spectroscopy as an effective tool to study the mechanical properties of living cells.

Total Internal Reflection Peak Force Infrared Microscopy.

Total internal reflection (TIR) infrared spectroscopy is a convenient measurement tool for collecting spectra for chemical identification. However, TIR infrared microscopy lacks high spatial resolution due to the optical diffraction limit and difficulty to preserve a high-quality wave front for focus. In this article, we present the peak force infrared microscopy in the TIR geometry to achieve a 10 nm spatial resolution. Instead of optical detection, photothermal responses of the sample are collected in the peak force tapping mode of atomic force microscopy. We demonstrate the technique on two representative samples: structured polymers for soft matters and a hexagonal boron nitride flake for two-dimensional materials. As an extension of the apparatus, we also demonstrate nanoinfrared imaging with the TIR excitation for photoinduced force microscopy. The combination of TIR geometry with nanoinfrared microscopies simplifies the optical alignment, providing alternative instrument-designing principles for atomic force microscopy-based infrared microscopy.

Squeeze Film Damping Effect on Different Microcantilever Probes in Tapping Mode Atomic Force Microscope.

During the operation of tapping mode atomic force microscope (TM-AFM), the gap between the cantilever and sample surface is very small (several nanometers to micrometers). Owing to the small gap distance and high vibration frequency, squeeze film force should be considered in TM-AFM. To explore the mechanism of squeeze film damping in TM-AFM, three theoretical microcantilever simplified models are discussed innovatively herein: tip probe, ball probe, and tipless probe. Experiments and simulations are performed to validate the theoretical models. It is of great significance to improve the image quality of atomic force microscope.

Atomic Force Microscopy-Based Force Spectroscopy and Multiparametric Imaging of Biomolecular and Cellular Systems.

During the last three decades, a series of key technological improvements turned atomic force microscopy (AFM) into a nanoscopic laboratory to directly observe and chemically characterize molecular and cell biological systems under physiological conditions. Here, we review key technological improvements that have established AFM as an analytical tool to observe and quantify native biological systems from the micro- to the nanoscale. Native biological systems include living tissues, cells, and cellular components such as single or complexed proteins, nucleic acids, lipids, or sugars. We showcase the procedures to customize nanoscopic chemical laboratories by functionalizing AFM tips and outline the advantages and limitations in applying different AFM modes to chemically image, sense, and manipulate biosystems at (sub)nanometer spatial and millisecond temporal resolution. We further discuss theoretical approaches to extract the kinetic and thermodynamic parameters of specific biomolecular interactions detected by AFM for single bonds and extend the discussion to multiple bonds. Finally, we highlight the potential of combining AFM with optical microscopy and spectroscopy to address the full complexity of biological systems and to tackle fundamental challenges in life sciences.

Atomic force microscopy for nanoscale mechanical property characterization

Over the past several decades, atomic force microscopy (AFM) has advanced from a technique used primarily for surface topography imaging to one capable of characterizing a range of chemical, mechanical, electrical, and magnetic material properties with subnanometer resolution. In this review, we focus on AFM as a nanoscale mechanical property characterization tool and examine various AFM contact and intermittent contact modes that add mechanical contrast to an imaged surface. Through detailed analysis of the tip-sample contact mechanics, this contrast can be converted into quantitative measurements of various nanomechanical properties including elastic modulus, shear modulus, wear rate, adhesion, and viscoelasticity. Different AFM modes that provide such measurements are compared and contrasted in this work on a wide range of materials including ceramics, metals, semiconductors, polymers, and biomaterials. In the last few years, considerable improvements have been made in terms of fast imaging capabilities, tip preservation, and quantitative mechanics for multifrequency measurements as well as well-known AFM modes like amplitude modulation and peak-force tapping. In line with these developments, a major highlight of this review is the discussion of the operation and capabilities of one such mode, namely, intermittent contact resonance AFM (ICR-AFM). The applications of ICR-AFM to nanoscale surface and subsurface quantitative mechanical characterizations are reviewed with specific examples provided for thin polymeric films and patterned nanostructures of organosilicate dielectric materials. The combination of AFM-based mechanical characterization with AFM-based chemical spectroscopy to allow nanoscale structure-property characterization is also discussed and demonstrated for the analysis of low-k dielectric/copper nanoelectronic interconnect structures and further highlights synergistic advances in the AFM field.