Application Of Atomic Force Microscopy Research Articles

Amplitude response of conical multiwalled carbon nanotube probes for atomic force microscopy.

Carbon nanotubes are considered as great candidates for atomic force microscopy (AFM) probes because of their high aspect ratio and outstanding mechanical properties. In this work, we report that a conical AFM probe can be fabricated with arc discharge prepared multiwalled carbon nanotubes (MWCNTs) with an individual MWCNT at the apex by dielectrophoresis. The amplitude–displacement curve of the conical MWCNT probe demonstrates that this structure can remain stable until the force exerted on it increases to 14.0 ± 1.5 nN (nanonewton). Meanwhile, the conical MWCNT probes are able to resolve complex structure with high aspect ratio compared to commercial AFM probes, suggesting great potential for various AFM applications.

Atomic Force Microscopy in Probing Tumor Physics for Nanomedicine

Investigating the physics in tumor development and progression has been recognized as a promising way to advance both basic cancer research and clinical cancer treatment. The advent of atomic force microscopy (AFM) provides an exciting multifunctional tool for investigating the physical properties of biological systems under aqueous conditions with unprecedented spatiotemporal resolution, opening new possibilities for nanomedicine in physical oncology. In this paper, the biomedical applications of AFM to investigate the physical sciences in oncology at single-cell, single-molecule, and tissue levels are systematically reviewed, taking lymphomas as an example. First, detecting the physics of cancers at multiple scales is summarized, along with antibody-based therapy for lymphomas. Next, the principles and methods of AFM imaging and measurements are summarized. After that, utilizing AFM to probe the physics of tumors is reviewed from several facets, including topographical imaging, mechanical measurement, molecular recognition, primary cell detection, and tissue characterization. In particular, the motivations and state-of-the-art overviews of each facet are presented. Finally, the current limitations and future directions of AFM assays for cancer investigations are discussed.

A novel method and system for calibrating the spring constant of atomic force microscope cantilever based on electromagnetic actuation.

It is crucial to calibrate atomic force microscope (AFM) cantilevers for the development and further applications of AFM in precision engineering such as nanonewton force measurement. This paper presents a novel approach to calibrate the spring constant of an AFM cantilever based on electromagnetic actuation and null position measurement. According to the method, a calibration system was designed. In order to optimize the static and dynamic characteristics of the calibration system, the analytical models for the electromagnetic force and the suspension mechanism stiffness have been developed. Finite element analysis has been utilized to further investigate the precision of analytical modeling. The null position measurement method was utilized to monitor the deformation of the flexible beam, and then the deformation was compensated by the electromagnetic force. Experiments were carried out based on the developed prototype, and the results show that the electromagnetic force conversion rate is 40.08 µN/mA. Finally, a typical AFM cantilever was calibrated and the spring constant is (30.83 ± 0.24) N/m. The uncertainty of the proposed null position measurement method is better than 0.78%, which verifies the effectiveness and feasibility of the calibration method and system.

Local Photovoltaic Properties of Graphene–Silicon Heterojunctions (Phys. Status Solidi B 12/2018)

The rise of nanomaterials requires a day-to-day implementation of suitable nanoscale characterization techniques. Atomic force microscopy (AFM) has become such a one, capable of providing diverse information about the sample topography, mechanical and electrical properties with resolution down to few nanometers. The work by Otakar Frank and co-workers (article no. 1800305) shows two examples of AFM application to describe local photovoltaic properties of graphene–silicon Schottky junctions. Direct measurement of I–V curves at selected points has been employed to discriminate the effect of increased p-doping of the graphene layer. Scanning the samples in the contact mode, followed by reconstruction of I–V curves, has been utilized to evaluate the separation between the graphene layers and/or the substrate. It is imperative to stress that the standard red diode used in the deflection-type AFM provides more than enough light to generate the photocurrent, hence a great attention has to be paid whenever conductive AFM is used for the characterization of photo-active materials.

Water desorption in Kelvin-probe force microscopy: a generic model

Nanoparticles or similar, nanoscale objects such as proteins or biological fibrils usually have to be deposited from aqueous suspension onto a solid support surface for further characterization by atomic force microscopy (AFM) and related methods such as Kelvin-probe force microscopy (KFM). Here we show, on the examples of functionalized nanoparticles and collagen fibrils, that water desorption after sample preparation affects their electrostatic potential determined by KFM in a predictable manner. We explain this effect with a simple, analytical model based on the capacitance of the partially dielectric-filled tip-sample system. We also propose practical measures to avoid false interpretation of electrical AFM-based experiments. As the phenomenon is very generic it may have significant implications in the application of AFM to nanoparticles and other nanostructures including biological ones.

Exploring mechanism of xanthate adsorption on chalcopyrite surface: An atomic force microscopy study

In this work, adsorption of the potassium amyl xanthate collector on the pure chalcopyrite surface was studied by applying atomic force microscopy (AFM). The adsorption experiments were carried out at different concentrations of the collector and at diverse pH values in the presence or absence of exterior ions. The changes occurring in the surface morphology of chalcopyrite due to the collector adsorption were evaluated by measuring the contact angle of the collector and its surface coating. According to the 3D images obtained by AFM, an increase in the pH value from 7.5 to 9.5 at two concentrations of 25*10-3 and 50*10-3 g/ton of the collector would increase the number of particles adsorbed on the surface, improve the adsorption morphology, and reduce the contact angle. Moreover, at a constant pH value, increasing the collector would result in the proliferation of contact angles as well as a relative increase in the number of particles. By comparing the morphological surface changes in the tap and distilled water samples, applying tap water, owing to the presence of Cu2+ ions and activation of the surface through the production of CuS, the quality and quantity of adsorption would be increased. The use of tap water not only can account for an appropriate coating by the collector but also causes to reduce the consumption of collector for at least 50%.

Direct Quantification of Trace Amounts of a Chronic Myeloid Leukemia Biomarker Using Locked Nucleic Acid Capture Probes.

Molecular monitoring is indispensable for the clinical management of chronic myeloid leukemia (CML) patients. Real-time quantitative polymerase chain reaction (RT-qPCR) is the gold standard for the quantitative assessment of BCR-ABL transcript levels, which are critical in clinical decision-making. However, the frequent recurrence of the disease after drug discontinuation for 60% of patients has necessitated more sensitive and specific techniques to detect residual BCR-ABL transcripts. Here, we describe a quantification method for the detection of BCR-ABL targets at very low concentrations (<10 copies/sample) in the presence of a million copies of normal BCR and ABL genes. In this method, a fully modified locked nucleic acid (LNA) and a LNA/DNA chimera were used as capture probes, and the quantitative imaging mode of atomic force microscopy (AFM) was employed. Targets with one of the major breakpoints (found in more than 95% of CML patients), b3a2 and b2a2, were quantified. The BCR-ABL target captured on a miniaturized LNA-probe spot was scanned at nanometric resolution, and the samples containing one to ten copies of the BCR-ABL genes were examined. It was observed that the highest sensitivity, i.e., the detection of a single copy of the target gene, could be achieved through multiple runs, and the observed cluster number was well correlative (adjusted R2 = 0.999) to the target copy number in the sample solution. This observation clearly demonstrates that the LNA-based platform is effective in quantifying BCR-ABL targets with extremely low copy numbers, highlighting the potential applicability of AFM for use in the direct quantification of such targets without amplification or labeling.

AFM of tissue sections is a useful complementary tool as a biomedical marker

The aim of the study was to demonstrate a good diagnostic potential of atomic force microscopy (AFM) in tracking morphological changes in the extracellular matrix (ECM) of connective tissue due to pathological processes. Here we summarize our experience in AFM application in a number of biomedical studies on the connective tissue disease, both for research and clinical purposes. AFM has been shown to reveal visible deviations from the normal morphology of the extracellular matrix in diseased tissues. We found that AFM and related techniques are capable of tracking disease-related changes at different levels of collagen organization in the ECM. AFM may also monitor a ratio between collagen and non-fibrous material of the ECM, for example, in inflammatory and neoplastic processes. The FNS parameters provide quantification of the morphological changes visualized by AFM. The PeakForce QNM and nanoindentation studies give a further insight into the state of ECM via tracking changes in the local mechanical and adhesive properties. All our AFM studies appeared in a good agreement with the histological findings and generally had a superior sensitivity to the ECM pathological changes. AFM may serve as a valuable complementary diagnostic tool for tracking pathological changes in the connective tissue.

Investigations of reconstruction of passivation layer on stainless steel surface using AFM-based techniques

Abstract Continuous development of stainless steel technology forced by the increase in the growing demands on the operating parameters of various stainless steel alloys, is the motivation for implementation of research for understanding the complexity of electrochemical processes ongoing on the surface of a material during various technological processes and during exploitation of the finished components. In this paper, the use of atomic force microscopy (AFM) is presented as a tool for observation of reconstruction process of passivation layers on the surface of previously electropolished stainless steel. For this purpose, a technique called nanoscratching was used, in which scratches are made on the surface of a material by means of diamond scanning probe, which violates the continuity of the passivation layer. Then, the dynamics of the process of reconstruction of that layer was assessed using continuous imaging of the scratched area in AFM semicontact mode. Studies of this type can be used to evaluate the impact of various factors on the spontaneous reconstruction of the passivation layer as well as possible susceptibility of the material on the course of corrosion processes initiated as a result of mechanical defects arising during operation of the material. By using the AFM, it was possible to observe changes in the depth of scratches with a subnanometer resolution. Obtained results proved that the presented AFM application allowed observation of the dynamics of passivation layer reconstruction process in a quantitative fashion, therefore it seems to be a very useful tool in the investigation of the impact of various conditions on this phenomenon. The results showed that changes in surface modification were occurring in a continuous manner. Changing dynamics of said process was presented. It should be underlined that no such experiments have been reported so far.

Surface optical phonon – Plasmon interaction in nanodimensional CdTe thin films

Structural and optical properties of CdTe thin films were investigated applying atomic force microscopy (AFM), XRD powder technique, Raman spectroscopy and far–infrared spectroscopy. CdTe thin films were prepared by using thermal evaporation technique. In the analysis of the far – infrared reflection spectra, numerical model for calculating the reflectivity coefficient for system which includes films and substrate has been applied. Effective permittivity of film mixture (CdTe and air) was modeled by Maxwell – Garnet approximation. We reveal the existence of surface optical phonon (SOP) mode and coupled plasmon-SOP modes (CPSOPM).

Nanoscale characterization of dynamic cellular viscoelasticity by atomic force microscopy with varying measurement parameters.

Cell mechanics plays an important role in regulating the physiological activities of cells. The advent of atomic force microscopy (AFM) provides a novel powerful instrument for quantifying the mechanics of single cells at the nanoscale. The applications of AFM in single-cell mechanical assays in the past decade have significantly contributed to the field of cell and molecular biology. However, current AFM-based cellular mechanical studies are commonly carried out with fixed measurement parameters, which provides limited information about the dynamic cellular mechanical behaviors in response to the variable external stimuli. In this work, we utilized AFM to investigate cellular viscoelasticity (portrayed as relaxation time) with varying measurement parameters, including ramp rate and surface dwell time, on both cell lines and primary cells. The experimental results show that the obtained cellular relaxation times are remarkably dependent on the parameter surface dwell time and ramp rate during measurements. Besides, the dependencies to the measurement parameters are variable for different types of cells, which can be potentially used to indicate cell states. The research improves our understanding of single-cell dynamic rheology and provides a novel idea for discriminating different types of cells by AFM-based cellular viscoelastic assays with varying measurement parameters.

Atomic force microscopy characterisation of alkali-silica reaction products to reveal their nanostructure and formation mechanism

Microscopic studies on alkali-silica reaction (ASR) products revealed two distinct forms of solid ASR products. However, their chemical and morphological aspects have not been adequately understood. This study provides a new insight into the nanostructure of ASR products as examined by atomic force microscopy (AFM). Results reveals that the surface microscale morphology of the rosette-like ASR product is associated with the loss of surface water, and the granular ASR product is formed by the accumulation of nanoscale particles with a typical size of around thirty nanometers. Moreover, the application of AFM provides evidence for the fluid nature of the granular ASR product at high moisture content.

Supported Lipid Bilayers for Atomic Force Microscopy Studies.

Nanoimaging methods, atomic force microscopy (AFM) in particular, are widely used to study the interaction of biological molecules with the supported lipid bilayer (SLB), which itself is a traditional model for cellular membranes. Success in these studies is based on the availability of a stable SLB for the required observation period, which can extend several hours. The application of AFM requires that the SLB have a smooth morphology, thus enabling visualization of proteins and other molecules on its surface. Herein, we describe protocols for SLB assembly by using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) on a mica support. Our methodology enables us to assemble defect-free POPC and POPS SLBs that remain stable for at least 8h. The application of such smooth and stable surfaces is illustrated by monitoring of the on-surface aggregation of amyloid proteins with the use of time-lapse AFM.

Fidelity Measurement on Signal Detection Algorithms With Application to AFM Imaging

Many signal processing and decision making algorithms reported in contemporary literature characterize the performance of the proposed methods utilizing decision error rates. However there is significant need for strategies that provide quantitative assessment of the fidelity of decisions made by the algorithms. This paper develops novel techniques utilizing which fidelity measures can be assigned quantitatively on some prevalent signal detection algorithms. The developed fidelity measurement methods with the detection algorithms are employed for topography imaging utilizing dynamic mode atomic force microscope (AFM). The AFM is a versatile metrology tool for interrogating material at the nano-scale. In spite of its remarkable achievements, a key issue that remains largely unaddressed is the assessment of fidelity of the measurement data. The developed paradigm facilitates user specific priority for either detection of sample features with high decision confidence or on not missing detection of true features. The fidelity measures presented here are suitable for real-time implementation. A detailed comparative study is presented to characterize the proposed signal detection algorithms and fidelity measurement techniques under practical AFM applications. Comprehensive simulation and experimental data corroborate the effectiveness of proposed methods.

Force Spectroscopy with 9-μs Resolution and Sub-pN Stability by Tailoring AFM Cantilever Geometry

Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) is a powerful yet accessible means to characterize the unfolding/refolding dynamics of individual molecules and resolve closely spaced, transiently occupied folding intermediates. On a modern commercial AFM, these applications and others are now limited by the mechanical properties of the cantilever. Specifically, AFM-based SMFS data quality is degraded by a commercial cantilever’s limited combination of temporal resolution, force precision, and force stability. Recently, we modified commercial cantilevers with a focused ion beam to optimize their properties for SMFS. Here, we extend this capability by modifying a 40 × 18 μm2 cantilever into one terminated with a gold-coated, 4 × 4 μm2 reflective region connected to an uncoated 2-μm-wide central shaft. This “Warhammer” geometry achieved 8.5-μs resolution coupled with improved force precision and sub-pN stability over 100 s when measured on a commercial AFM. We highlighted this cantilever’s biological utility by first resolving a calmodulin unfolding intermediate previously undetected by AFM and then measuring the stabilization of calmodulin by myosin light chain kinase at dramatically higher unfolding velocities than in previous AFM studies. More generally, enhancing data quality via an improved combination of time resolution, force precision, and force stability will broadly benefit biological applications of AFM.

Application of atomic force microscopy (AFM) to study bacterial biofilms

Because of the nanometre resolution, piconewton force sensitivity, label-free technique and the ability to operate in liquid environments, atomic force microscopy (AFM) has emerged as a powerful tool to explore the biofilm development processes. AFM provides three-dimensional topography and structural details of biofilm surfaces under in-situ conditions. It also helps to generate key information on the mechanical properties of biofilm surfaces, such as elasticity and stickiness. Additionally, single-molecule and single-cell force spectroscopies can be applied to measure the strength of adhesion, attraction, and repulsion forces between cell-solid and cell-cell surfaces. This paper outlined the basic principle of AFM technique and introduced recent advances in the application of AFM for the investigation of ultra-morphological, mechanical and interactive properties of biofilms. Furthermore, the existing problems and future prospects were discussed.

Liquid–Liquid Interfacial Imaging Using Atomic Force Microscopy

Nanoscale imaging of a liquid/liquid interface by atomic force microscopy (AFM) is achieved through the self‐assembly of interfacial layers of either polymers, lipids, or nanoparticles. Stabilization of the interface through spreading of a thin film of polystyrene‐b‐poly(methyl‐methacrylate) block copolymer or 1,2‐dioleoyl‐sn‐glycero‐3‐phosphoethanolamine lipids or adsorption of monolayers of silica nanoparticles allows reproducible imaging of these soft materials at an oil/water interface with nanoscale resolution on a timescale of 10 s. Amplitude modulation AFM is employed and requires that the subphase of water is below a critical depth of 100 µm to prevent excitation of gravity waves at the interface. The amplitude of these vertical oscillations is of the order of 1 nm but increases with the water layer depth. Below this critical water layer depth, force measurements show a linear compliance of the water/heptane and water/octane interfaces to be close to 10−2 N m−1. This study discusses in detail the experimental setup, sample preparation procedures, and AFM parameters necessary to achieve nanoscale resolution at the extremely soft and dynamic liquid interface. This expands the application of AFM to structural and dynamic nanoscale measurements for soft matter, biological, and nanomaterials away from solid supports.

Evaluation of bio-binder modified asphalt’s adhesion behavior using sessile drop device and atomic force microscopy

Bio-binder is a renewable material which can be derived from natural resources. Applications of bio-binder in enhancing asphalt’s properties have gained profound progresses in past several years. However, limitation still exists in our knowledge on adhesion property of asphalt blended with bio-binder. This study aims to characterize adhesion behavior of bio-binder modified asphalt using sessile drop device (SDD) and atomic force microscopy (AFM). Relationship between the two test results is also investigated. It is shown that addition of bio-binder would introduce different impacts on surface properties for different base asphalts (Pen30 and Pen70 asphalts in this paper), which may be attributed to distinct compatibilities between bio-binder and different asphalts. And the work of adhesion data demonstrates that the bio-binder enhances the interaction between basalt and bio-binder modified Pen70 asphalt binders while depress the interaction between basalt and bio-binder modified Pen30 asphalt binders. It is also found that AFM adhesive force is tip-dependent which may be interpreted using different contact mechanics. In this paper, the high coefficient of variation in soft tip’s data may result from the capillary force and contamination during scanning. Interestingly, dispersive surface free energy and AFM results show some reasonable agreements for modified Pen70 asphalts, though there is still a gap between these two methods’ results. It is speculated that the variations between surface free energy method and AFM measurement can be attributed to the differences in probe substance, test scale and measured components. Findings in this paper not only promote the development of bio-binder modified asphalt, but also shed lights of the application of AFM in characterization of asphalt’s adhesion property.

Ultrahigh-resolution imaging of water networks by atomic force microscopy

Local defects in water layers growing on metal surfaces have a key influence on the wetting process at the surfaces; however, such minor structures are undetectable by macroscopic methods. Here, we demonstrate ultrahigh-resolution imaging of single water layers on a copper(110) surface by using non-contact atomic force microscopy (AFM) with molecular functionalized tips at 4.8 K. AFM with a probe tip terminated by carbon monoxide predominantly images oxygen atoms, whereas the contribution of hydrogen atoms is modest. Oxygen skeletons in the AFM images reveal that the water networks containing local defects and edges are composed of pentagonal and hexagonal rings. The results reinforce the applicability of AFM to characterize atomic structures of weakly bonded molecular assemblies.

Hybrid AFM for Nanoscale Physicochemical Characterization: Recent Development and Emerging Applications.

Atomic force microscopy (AFM) has evolved to be one of the most powerful tools for the characterization of material surfaces especially at the nanoscale. Recent development of AFM has incorporated a suite of analytical techniques including surface-enhanced Raman scattering (SERS) technique and infrared (IR) spectroscopy to further reveal chemical composition and map the chemical distribution. This incorporation not only elevates the functionality of AFM but also increases the resolution limitation of conventional IR and Raman spectroscopy. Despite the rapid development of such hybrid AFM techniques, many unique features, principles, applications, potential pitfalls or artifacts are not well known to the community. This review systematically summarizes the recent relevant literature on hybrid AFM principles and applications. It focuses specially on AFM-IR and AFM-Raman techniques. Various applications in different research fields are critically reviewed and discussed, highlighting the potentials of these hybrid AFM techniques. Here, the major drawbacks and limitations of these two hybrid AFM techniques are presented. The intentions of this article are to shed new light on the future research and achieve improvements in stability and reliability of the measurements.