Conventional Atomic Force Microscopy Research Articles

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

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

Deep Learning Image Recognition-Assisted Atomic Force Microscopy for Single-Cell Efficient Mechanics in Co-culture Environments.

Atomic force microscopy (AFM)-based force spectroscopy assay has become an important method for characterizing the mechanical properties of single living cells under aqueous conditions, but a disadvantage is its reliance on manual operation and experience as well as the resulting low throughput. Particularly, providing a capacity to accurately identify the type of the cell grown in co-culture environments without the need of fluorescent labeling will further facilitate the applications of AFM in life sciences. Here, we present a study of deep learning image recognition-assisted AFM, which not only enables fluorescence-independent recognition of the identity of single co-cultured cells but also allows efficient downstream AFM force measurements of the identified cells. With the use of the deep learning-based image recognition model, the viability and type of individual cells grown in co-culture environments were identified directly from the optical bright-field images, which were confirmed by the following cell growth and fluorescent labeling results. Based on the image recognition results, the positional relationship between the AFM probe and the targeted cell was automatically determined, allowing the precise movement of the AFM probe to the target cell to perform force measurements. The experimental results show that the presented method was applicable not only to the conventional (microsphere-modified) AFM probe used in AFM indentation assay for measuring the Young's modulus of single co-cultured cells but also to the single-cell probe used in AFM-based single-cell force spectroscopy (SCFS) assay for measuring the adhesion forces of single co-cultured cells. The study illustrates deep learning imaging recognition-assisted AFM as a promising approach for label-free and high-throughput detection of single-cell mechanics under co-culture conditions, which will facilitate unraveling the mechanical cues involved in cell-cell interactions in their native states at the single-cell level and will benefit the field of mechanobiology.

High-Speed AFM Observation of Electrolytic Nanobubbles Formation on HOPG

IntroductionNanobubbles (NBs) on solid surfaces are an interesting topic for surface and colloid science. Since the diameter of NBs is less than 1 μm, NBs can be morphologically measured by atomic force microscope (AFM) [1]. However, due to the slow scanning speed of conventional atomic force microscope (AFM), the nucleation and growth process is not yet known. We previously applied high-speed AFM (HS-AFM) for NBs’ evolution during water electrolysis [2]. Here, we discuss the NBs’ formation during cyclic voltammetry (CV).ExperimentalThe experimental cell was a three-electrode system at room temperature. The working electrode was highly ordered pyrolytic graphite (HOPG). The counter and reference electrodes were Pt wires. The electrolyte was a sulfuric acid solution (5 mmol L-1). CV was performed by a potentiostat. HS-AFM was operated in dynamic mode. The scanning speed was 0.5 frame s-1 and the size was 1 × 0.75 µm2.Results and discussionWhen the potential was swept to the anode from the open circuit potential, the pancake-like NBs were formed (Fig. 1). The height was ~5 nm, and the surface roughness was very small (< 1 nm). The pancake NBs grew along the step side and moved actively on the surface. They occasionally coalesced with neighboring NBs.On the other hand, when the potential was swept to the cathode, the dynamic process was the opposite. The pancake NBs dissolved. This poster will present the dynamic variation of electrolytic NBs during the CV.Reference[1] X.H. Zhang et al., Langmuir, 23, 1778 (2007).[2] M Mita, H Matsushima, M Ueda, H Ito, J. Colloid Interface Sci., 641, 389 (2022). Figure 1

Measuring mechanical properties with high-speed atomic force microscopy.

High-speed atomic force microscopy (HS-AFM) is now a widely used technique to study the dynamics of single biomolecules and complex structures. In the past, it has mainly been used to capture surface topography as structural analysis, leading to important discoveries not attainable by other methods. Similar to conventional AFM, the scope of HS-AFM was recently expanded to encompass quantities beyond topography, such as the measurement of mechanical properties. This review delves into various methodologies for assessing mechanical properties, ranging from semi-quantitative approaches to precise force measurements and their corresponding sample responses. We will focus on the application to single proteins such as bridging integrator-1, ion channels such as Piezo1, complex structures such as microtubules and supramolecular fibers. In all these examples, the unique combination of quantifiable force application and high spatiotemporal resolution allows to unravel mechanisms that cannot be investigated by conventional means.

Visualizing Molecular Dynamics by High-Speed Atomic Force Microscopy.

Dynamic processes and structural changes of biological molecules are essential to life. While conventional atomic force microscopy (AFM) is able to visualize molecules and supramolecular assemblies at sub-nanometer resolution, it cannot capture dynamics because of its low imaging rate. The introduction of high-speed atomic force microscopy (HS-AFM) solved this problem by providing a large increase in imaging velocity. Using HS-AFM, one is able to visualize dynamic molecular events with high spatiotemporal resolution under near-to physiological conditions. This approach opened new windows as finally dynamics of biomolecules at sub-nanometer resolution could be studied. Here we describe the working principles and an operation protocol for HS-AFM imaging and characterization of biological samples in liquid.

Micromechanical characterizations and viscoelastic modeling reveal elastic and viscoelastic heterogeneities in ovarian tissue and the significant viscoelastic contribution to the apparent elastic modulus determined by AFM indentation.

Ovarian follicles develop in a highly regulated mechanical microenvironment and disruptions to the microenvironment may cause infertility. However, the viscoelastic properties of the ovarian tissue are not well studied. Here, we characterize both the elastic and viscoelastic properties of ovarian tissue from both reproductively older and younger domestic cats using atomic force microscopy (AFM) indentation and viscoelastic models of stress relaxation. Importantly, our analyses reveal the apparent elastic modulus obtained from the conventional AFM indentation measurement is significantly higher than the intrinsic elastic modulus and insignificantly different from the equivalent elastic modulus that is the summation of the intrinsic elastic modulus and the viscoelastic contribution to modulus at time 0. Interestingly, the ovarian cortex of both reproductive age groups has a higher apparent/intrinsic modulus than that of the medulla. Furthermore, two different kinetics of stress relaxation are identified with rate constants of ∼1s and ∼20-40s, respectively. Moreover, the rate constant of the slow kinetics is significantly different between the cortex and medulla in the reproductively older ovaries. Finally, these mechanical heterogeneities appear to follow the heterogeneous distribution of hyaluronic acid (HA) in the ovary. These findings may be invaluable to the development of biomimetic follicle culture for treating infertility. STATEMENT OF SIGNIFICANCE: This study investigates not only elastic but also the viscoelastic heterogeneity in both reproductively younger and older ovarian tissues for the first time. Further, by combining AFM indentation measurement and viscoelastic modeling, we show the apparent elastic modulus conventionally reported in the literature for AFM indentation measurement is the summation of the intrinsic elastic modulus and a significant viscoelastic contribution to the modulus at time 0. This is an important consideration for others who use this method to quantify biomaterial properties. In addition, the possible connection between the mechanical and compositional heterogeneities is explored. These findings may be invaluable for designing biomaterials to recapitulate the mechanical environment of the ovary and possibly many other organs for biomimetic tissue engineering.

Ultra-Large Scale Stitchless AFM: Advancing Nanoscale Characterization and Manipulation with Zero Stitching Error and High Throughput.

The atomic force microscopy (AFM) is an important tool capable of characterization, measurement, and manipulation at the nanoscale with a vertical resolution of less than 0.1nm. However, the conventional AFMs' scanning range is around 100µm, which limits their capability for processing cross-scale samples. In this study, it proposes a novel approach to overcome this limitation with an ultra-large scale stitchless AFM (ULSS-AFM) that allows for the high-throughput characterization of an area of up to 1 × 1mm2 through a synergistic integration with a compliant nano-manipulator (CNM). Specifically, the compact CNM provides planar motion with nanoscale precision and millimeter range for the sample, while the probe of the ULSS-AFM interacts with the sample. Experimental results show that the proposed ULSS-AFM performs effectively in different scanning ranges under various scanning modes, resolutions, and frequencies. Compared with the conventional AFMs, the approach enables high-throughput characterization of ultra-large scale samples without stitching or bow errors, expanding the scanning area of conventional AFMs by two orders of magnitude. This advancement opens up important avenues for cross-scale scientific research and industrial applications in nano- andmicroscale.

Non-contact non-resonant atomic force microscopy method for measurements of highly mobile molecules and nanoparticles

Atomic force microscopy (AFM) is nowadays indispensable versatile scanning probe method widely employed for fundamental and applied research in physics, chemistry, biology as well as industrial metrology. Conventional AFM systems can operate in various environments such as ultra-high vacuum, electrolyte solutions, or controlled gas atmosphere. Measurements in ambient air are prevalent due to their technical simplicity; however, there are drawbacks such as formation of water meniscus that greatly increases attractive interaction (adhesion) between the tip and the sample, reduced spatial resolution, and too strong interactions leading to tip and/or sample modifications. Here we show how the attractive forces in AFM under ambient conditions can be used with advantage to probe surface properties in a very sensitive way even on highly mobile molecules and nanoparticles. We introduce a stable non-contact non-resonant (NCNR) AFM method which enables to reliably perform measurements in the attractive force regime even in air by controlling the tip position in the intimate surface vicinity without touching it. We demonstrate proof-of-concept results on helicene-based macrocycles, DNA on mica, and nanodiamonds on SiO2. We compare the results with other conventional AFM regimes, showing NCNR advantages such as higher spatial resolution, reduced tip contamination, and negligible sample modification. We analyze principle physical and chemical mechanisms influencing the measurements, discuss issues of stability and various possible method implementations. We explain how the NCNR method can be applied in any AFM system by a mere software modification. The method thus opens a new research field for measurements of highly sensitive and mobile nanoscale objects under air and other environments.

Unveiling localized electronic properties of ReS2 thin layers at nanoscale using Kelvin force probe microscopy combined with tip-enhanced Raman spectroscopy

Electronic properties of two-dimensional (2D) materials can be strongly modulated by localized strain. The typical spatial resolution of conventional Kelvin probe force microscopy (KPFM) is usually limited in a few hundreds of nanometers, and it is difficult to characterize localized electronic properties of 2D materials at nanoscales. Herein, tip-enhanced Raman spectroscopy (TERS) is proposed to combine with KPFM to break this restriction. TERS scan is conducted on ReS2 bubbles deposited on a rough Au thin film to obtain strain distribution by using the Raman peak shift. The localized contact potential difference (CPD) is inversely calculated with a higher spatial resolution by using strain measured by TERS and CPD-strain working curve obtained using conventional KPFM and atomic force microscopy. This method enhances the spatial resolution of CPD measurements and can be potentially used to characterize localized electronic properties of 2D materials.

Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays for High-Throughput Large-Scale Sample Inspection.

An Atomic Force Microscope(AFM) isa powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. However, due to their limited imaging throughput, AFMs have not been widely adopted for large-scale inspection purposes. Researchers have developed high-speed AFM systems to record dynamic process videos in chemical and biological reactions at tens of frames per second, at the cost of a small imaging area of up to several square micrometers. In contrast, inspecting large-scale nanofabricated structures, such as semiconductor wafers, requires nanoscale spatial resolution imaging of a static sample over hundreds of square centimeters with high productivity. Conventional AFMs use a single passive cantilever probe with an optical beam deflection system, which can only collect one pixel at a time during AFM imaging, resulting in low imaging throughput. This work utilizes an array of active cantilevers with embedded piezoresistive sensors and thermomechanical actuators, which allows simultaneous multi-cantilever operation in parallel operation for increased imaging throughput. When combined with large-range nano-positioners and proper control algorithms, each cantilever can be individually controlled to capture multiple AFM images. With data-driven post-processing algorithms, the images can be stitched together, and defect detection can be performed by comparing them to the desired geometry. This paper introduces principles of the custom AFM using the active cantilever arrays, followed by a discussion on practical experiment considerations for inspection applications. Selected example images of silicon calibration grating, highly-oriented pyrolytic graphite, and extreme ultraviolet lithography masks are captured using an array of four active cantilevers ("Quattro") with a 125 µm tip separation distance. With more engineering integration, this high-throughput, large-scale imaging tool can provide 3D metrological data for extreme ultraviolet (EUV) masks, chemical mechanical planarization (CMP) inspection, failure analysis, displays, thin-film step measurements, roughness measurement dies, and laser-engraved dry gas seal grooves.

An Integrated, Exchangeable Three-Electrode Electrochemical Setup for AFM-Based Scanning Electrochemical Microscopy.

Scanning electrochemical microscopy (SECM) is a versatile scanning probe technique that allows monitoring of a plethora of electrochemical reactions on a highly resolved local scale. SECM in combination with atomic force microscopy (AFM) is particularly well suited to acquire electrochemical data correlated to sample topography, elasticity, and adhesion, respectively. The resolution achievable in SECM depends critically on the properties of the probe acting as an electrochemical sensor, i.e., the working electrode, which is scanned over the sample. Hence, the development of SECM probes received much attention in recent years. However, for the operation and performance of SECM, the fluid cell and the three-electrode setup are also of paramount importance. These two aspects received much less attention so far. Here, we present a novel approach to the universal implementation of a three-electrode setup for SECM in practically any fluid cell. The integration of all three electrodes (working, counter, and reference) near the cantilever provides many advantages, such as the usage of conventional AFM fluid cells also for SECM or enables the measurement in liquid drops. Moreover, the other electrodes become easily exchangeable as they are combined with the cantilever substrate. Thereby, the handling is improved significantly. We demonstrated that high-resolution SECM, i.e., resolving features smaller than 250 nm in the electrochemical signal, could be achieved with the new setup and that the electrochemical performance was equivalent to the one obtained with macroscopic electrodes.

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review.

Hard dental tissues possess a complex hierarchical structure that is particularly evident in enamel, the most mineralised substance in the human body. Its complex and interlinked organisation at the Ångstrom (crystal lattice), nano-, micro-, and macro-scales is the result of evolutionary optimisation for mechanical and functional performance: hardness and stiffness, fracture toughness, thermal, and chemical resistance. Understanding the physical-chemical-structural relationships at each scale requires the application of appropriately sensitive and resolving probes. Synchrotron X-ray techniques offer the possibility to progress significantly beyond the capabilities of conventional laboratory instruments, i.e., X-ray diffractometers, and electron and atomic force microscopes. The last few decades have witnessed the accumulation of results obtained from X-ray scattering (diffraction), spectroscopy (including polarisation analysis), and imaging (including ptychography and tomography). The current article presents a multi-disciplinary review of nearly 40 years of discoveries and advancements, primarily pertaining to the study of enamel and its demineralisation (caries), but also linked to the investigations of other mineralised tissues such as dentine, bone, etc. The modelling approaches informed by these observations are also overviewed. The strategic aim of the present review was to identify and evaluate prospective avenues for analysing dental tissues and developing treatments and prophylaxis for improved dental health.

Enhancing the precision of 3D sidewall measurements of photoresist using atomic force microscopy with a tip-tilting technique

A key issue associated with advanced lithography techniques for semiconductor-device manufacturing is the reduction in the sidewall roughness of photoresist line patterns, known as line-edge roughness (LER). We have developed a technique for measuring the sidewall of the resist pattern using atomic force microscopy (AFM) that enables three-dimensional (3D), high-resolution, low-noise, and nondestructive measurements. Conventional LER measurement technology using scanning electron microscopy (SEM) causes shrinkage of the resist pattern due to electron-beam (EB) exposure, whereas our new AFM technique can in principle avoid EB-induced shrinkage. This AFM technology is capable of 3D measurements because it employs a tip-tilting mechanism that enables the sharp AFM tip to scan the vertical sidewalls, which is difficult for a conventional AFM technique. In addition, laser interferometers are equipped for the measurement of the AFM tip displacement, which yields high-resolution, high-accuracy, and low-noise results. This technology overcomes issues such as low resolution, noise, and destructive measurements that afflict conventional SEM measurements. In addition, it enables observations and quantitative analyses of the 3D sidewall roughness. For example, in the present experiment, we observed that grain shapes (several tens of nm in size) were formed randomly on the resist sidewall and that there were almost no footing shapes. By analyzing the sidewall profiles with a height resolution of 1 nm, we obtain the roughness (self-affine fractal) parameters at each height. This AFM-based resist sidewall measurement technique can, thus, provide important insights into resist patterning and related process technologies for next-generation semiconductor-device manufacturing.

Accurate Electrostatic Force Measurements by Atomic Force Microscopy Using Proper Distance Control

Electrostatic force microscopy (EFM) enables us to examine the local electrostatic force between an AFM tip and sample surface, from which an electrical capacitance between them and surface potential can be evaluated, by applying direct current (DC) and alternating current (AC) voltages. From the dependences of the electrostatic force on the DC voltage and on the frequency of AC voltage in EFM, carrier density, carrier type, and deep level states in a semiconductor can also be investigated. Since EFM is basically operated as an atomic force microscopy (AFM), special care should be taken in an effect of the electrostatic force on a distance control between the tip and sample, and robust distance control is necessary even under the strong electrostatic force in order to realize proper measurements of both topography and electrostatic force. In this paper, we have examined the effectiveness of the usage of the oscillation amplitude of a cantilever as a feedback target for the distance control, which is referred to as Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> -mode operation, while the cantilever oscillation frequency is always kept at its primary resonance, like the conventional frequency modulation AFM (FM-AFM) which uses a resonant frequency shift as the feedback target. First, we have verified that a distance change due to the strong electrostatic force was significantly reduced compared with FM-AFM. Secondly, we have confirmed that the Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> -mode operation in EFM realized proper measurements of the dependance of a tip-sample capacitance including a surface depletion capacitance on the DC voltage and on the frequency of AC voltage, indicating good robustness of the method against the strong electrostatic force.

Control of interaction force in constant-height contact mode atomic force microscopy

Contact mode is a versatile and widely used technique for imaging samples using the Atomic Force Microscope (AFM). When contact mode imaging is performed in constant-height mode, it enables linear and faster response but leads to uncontrolled tip-sample forces. Here, a control strategy based on magnetic actuation is proposed to achieve high-bandwidth control of the tip-sample forces in constant-height contact mode AFM. A magnetic particle attached to the AFM probe is actuated by an external solenoid and employed for force regulation. A quasi-static model has been proposed and employed to develop the control strategy. Likewise, the contact natural-frequency, which decides the limit of achievable speed, has been shown to be significantly higher relative to the free probe and to be relatively insensitive to the particle size. Subsequently, a setup is developed to validate the control strategy and demonstrate reduction of tip-sample force variation by over a factor of 12 compared to conventional constant-height mode operation. Likewise, in comparison with conventional contact mode AFM, an improvement of linearity by over a factor of 9 and improvement in response speed by a factor of 100 have been demonstrated while imaging hard samples. The system has been shown to image topography at speeds of 2.44 frames per second while regulating the interaction force. Finally, the stiffness of a sample has also been characterized using the developed system and simultaneous estimation of topography has also been demonstrated. They are shown to agree well with theoretical expectations.

Effective Stiffness of Hydrated Atomic Force Microscopy Tips.

When generating force curves with atomic force microscopy (AFM), the conventional assumption is that the silicon tip's apex is infinitely stiffer than the force gradient acting between the apex and test object. Although true for measurements in vacuum or at long distances, we show this assumption fails badly at short distances in aqueous environments. In this case, the effective apex is an adsorbed water molecule, bound by a weak O-H···O-H H-bond. At short distances, the magnitude of the force gradient exceeds the stiffness of this bond. This causes conventional AFM measurements to be dominated by the mechanical H-bond stiffness, instead of the force gradient. Here, we introduce a new multifrequency technique that is able to measure the surface force gradient independently from the H-bond. We compare our results to conventional FM-AFM and show that due to the H-bond, FM-AFM can give extremely erroneous measurements and even the wrong force polarity.

Integrated optical waveguide atomic force microscopy system with a differential splitter readout

There is an urgent need for high-speed atomic force microscopy (AFM) systems, and chip-AFM on an integrated optical waveguide provides a perfect solution. A differential splitter of double waveguides is introduced as a readout method of an integrated optical waveguide AFM to overcome the non-linear response of a conventional optical waveguide AFM. Results show that an optical waveguide AFM with a 190 nm width and 1 μm height nano-tip shows a good monotonic dependence on the cantilever deflection within a range of ± 0.4 μm using a differential splitter readout method.

Atomic resolution with high-eigenmode tapping mode atomic force microscopy

Atomic surface structure imaging is instrumental for the understanding of surface-related phenomena. Here, we show that conventional tapping mode atomic force microscopy with high cantilever eigenmodes and subnanometer amplitudes allow routine atomic imaging at atmospheric pressures. We identify the reasons for failure of atomic resolution imaging employing low eigenmodes. Strong tip-surface interactions cause significant differences between the oscillatory behaviors of the inclination of the cantilever as detected by conventional instruments and of the vertical position of the tip, which prevents correct functioning of instrumental feedback control loops. However, high effective spring constants of high eigenmodes make it possible to overcome the problem. Furthermore, the combination of high effective elastic constants of high cantilever eigenmodes with the high flexibility of the cantilever substantially enhances the imaging stability, thereby universally allowing atomic imaging of solid surfaces in gaseous environments and at elevated temperatures. Demonstrated imaging examples include single sulfur vacancies at the surface of ${\mathrm{MoS}}_{2}$ crystals imaged at temperatures ranging from room temperature to 250\ifmmode^\circ\else\textdegree\fi{}C and potassium ions on hydrophilic and highly adhesive muscovite mica surfaces. Moreover, the high imaging stability allows knocking atoms off the ${\mathrm{MoS}}_{2}$ surface by hard tapping, indicating the potential for ultrahigh resolution lithography.

Analysis of the extranucleolar ribonucleoprotein particles of Cycas revoluta Thunb. (Cycadaceae) and Ceratozamia mexicana Brongn. (Zamiaceae)

Background: Nuclear ribonucleoprotein particles play a key role in RNA processing and in the gene expression pathway. Interchromatin granules (GICs) involved in the metabolism of pre-messenger RNA (pre-mRNA) were described in Allium cepa and Chiranthodendron pentadactylon . Other particles as Lacandonia granules (LGs) were found in Lacandonia schismatica as well as Ginkgo biloba and Welwitschia mirabilis . LGs are structures equivalent to perichromatin granules (PCGs) described in mammals and to Balbiani ring granules (BRGs) described in the midge Chironomus tentans . PCGs and BRGs are involved in the metabolism of messenger RNA (mRNA). Here, we analyze the extranucleolar particles from Cycas revoluta and Ceratozamia mexicana and compare them to GICs and LGs using conventional electron microscopy and atomic force microscopy.&#x0D; Species study: Cycas revoluta (Cycadaceae) and Ceratozamia mexicana (Zamiaceae)&#x0D; Hypothesis: The extranucleolar ribonucleoprotein particles in the nuclei of C. revoluta and C. mexicana are equivalent to GICs or GLs.&#x0D; Methods: Fragments of young leaves of C. revoluta and C. mexicana were processed for standard transmission electron microscopy. Thin sections were stained with the EDTA technique preferential for ribonucleoproteins and osmium amine specific for DNA. From the semithin sections the samples were studied with the AFM and images of them were obtained.&#x0D; Results: Ribonucleoprotein particles 32 nm in diameter are present in the interchromatin and perichromatin space in C. revoluta and C. mexicana .&#x0D; Conclusion: Ribonucleoprotein particles present in the cell nuclei of C. mexicana and C. revoluta are ultrastructurally equivalent to LGs .&#x0D; &#x0D; &#x0D; Translate&#x0D; stop&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; Translate&#x0D; stop&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; Translate&#x0D; stop&#x0D; &#x0D; &#x0D;

Exploring electrostatic properties of biomolecules by a combination of soft-lithography and Kelvin force microscopy

Electrostatic properties of biomolecules play an important role in a vast myriad of fundamental biological processes. Despite of the great importance of this matter, techniques to directly determine these properties are quite scarce and are still facing technical limitations. To date, Kelvin force microscopy (KFM), a variation of conventional atomic force microscopy which is generally used to study surface potential in semiconductors, is capturing attention due to its capability of mapping electrostatic properties of biomolecules with great sensitivity and spatial resolution at sub-micrometer scale.