Detection of magnetic-labeled antibody specific recognition events by combined atomic force and magnetic force microscopy

Atomic force (AFM) and magnetic force microscopy (MFM) were developed to detect biomolecular specific interaction. Goat anti-mouse immunoglobulin (anti-IgG) was covalently attached onto gold substrate modified by a self-assembly monolayer of thioctic acid via 1-ethyl-3-[3-(dimethylamino) propyl] carbodiimide (EDC) activation. Magnetic-labeled IgG then specifically adsorbed onto anti-IgG surface. The morphological variation was identified by AFM. MFM was proved to be a fine assistant tool to distinguish the immunorecognized nanocomposites from the impurities by detection of the magnetic signal from magnetic-labeled IgG. It would enhance the understanding of biomolecular recognition process.     

Surface structure investigations using noncontact atomic force microscopy

Surfaces of several A_IIIB_V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination.     

Thermomechanical properties of polymer nanolithography using atomic force microscopy

The temperature-dependent mechanical properties of polyethylene terephthalate (PET) polymers are investigated using force-distance curves, adhesion force, and atomic force microscope (AFM) nanolithography combined the heating techniques. The results show that the width of grooves on the polymers at 20-60 °C were in the range of 14-363 nm. The wear depth of the polymers increased with increasing heating temperature. A volume of 251.85-2422.66 μm(3) at a load of 30-50 nN with heating to 30-60 °C was removed, as compared to that of 26.60-70.30 μm(3) obtained at room temperature. The contact forces of PET started increasing at 9 nN, whereas the size of the holes was average at a pressure. The results may be of importance in explaining the heating relationship among adhesion force, volume removal rate, and pressure.     

Tarantula hemocyanins imaged by atomic force microscopy

Individual 4 x 6-meric tarantula hemocyanins and dissociation products were imaged by AFM in the non-contact mode. Although the resolution was low, the hexamers and topological arrangement within the oligomers can be seen. However, the relative humidity seems to affect the height profiles.     

Compliance profile of the human cornea as measured by atomic force microscopy

The ability to accurately determine the elastic modulus of each layer of the human cornea is a crucial step in the design of better corneal prosthetics. In addition, knowledge of the elastic modulus will allow design of substrates with relevant mechanical properties for in vitro investigations of cellular behavior. Previously, we have reported elastic modulus values for the anterior basement membrane and Descemet's membrane of the human cornea, the surfaces in contact with the epithelial and endothelial cells, respectively. We have completed the compliance profile of the stromal elements of the human cornea by obtaining elastic modulus values for Bowman's layer and the anterior stroma. Atomic force microscopy (AFM) was used to determine the elastic modulus, which is a measure of the tissue stiffness and is inversely proportional to the compliance. The elastic response of the tissue allows analysis with the Hertz equation, a model that provides a relationship between the indentation force and depth and is a function of the tip radius and the modulus of the substrate. The elastic modulus values for each layer of the cornea are: 7.5±4.2 kPa (anterior basement membrane), 109.8±13.2 kPa (Bowman's layer), 33.1±6.1 kPa (anterior stroma), and 50±17.8 kPa (Descemet's membrane). These results indicate that the biophysical properties, including elastic modulus, of each layer of the human cornea are unique and may play a role in the maintenance of homeostasis as well as in the response to therapeutic agents and disease states. The data will also inform the design and fabrication of improved corneal prosthetics.     

Three-dimensional molecular imaging using mass spectrometry and atomic force microscopy

We combine imaging ToF-SIMS depth profiling and wide area atomic force microscopy to analyze a test structure consisting of a 300 nm trehalose film deposited on a Si substrate and pre-structured by means of a focused 15-keV Ga⁺ ion beam. Depth profiling is performed using a 40-keV C₆₀⁺ cluster ion beam for erosion and mass spectral data acquisition. A generic protocol for depth axis calibration is described which takes into account both lateral and in-depth variations of the erosion rate. By extrapolation towards zero analyzed lateral area, an “intrinsic” depth resolution of about 8 nm is found which appears to be characteristic of the cluster-surface interaction process.     

Measurement of nanomechanical properties of biomolecules using atomic force microscopy

The capabilities of atomic force microscopy (AFM) have been rapidly expanding beyond topographical imaging to now allow for the analysis of a wide range of properties of diverse materials. The technique of nanoindentation, traditionally performed via dedicated indenters can now be reliably achieved using AFM instrumentation, enabling mechanical property determination at the nanoscale using the high spatial and force resolutions of the AFM. In the study of biological systems, from biomolecules to complexes, this technique provides insight into how mesoscale properties and functions may arise from a myriad of single biomolecules. In vivo and in situ analyses of native structures under physiological conditions as well as the rapid analysis of molecular species under a variety of experimental treatments are made possible with this technique. As a result, AFM nanoindentation has emerged as a critical tool for the study of biological systems in their natural state, further contributing to both biomaterial design and pharmacological research. In this review, we detail the theory and progression of AFM-based nanoindentation, and present several applications of this technique as it has been used to probe biomolecules and biological nanostructures from single proteins to complex assemblies. We further detail the many challenges associated with mechanical models and required assumptions for model validity. AFM nanoindentation capabilities have provided an excellent improvement over conventional nanomechanical tools and by integration of topographical data from imaging, enabled the rapid extraction and presentation of mechanical data for biological samples.     

Observation of single- and double-stranded DNA using non-contact atomic force microscopy

Non-contact atomic force microscopy (NC-AFM) has been applied to observe single- and double-stranded DNA. For the wet processes used to prepare the sample, a strong adhesion force at the surface is observed even in vacuum conditions. Despite the presence of this adhesion force, single- and double-stranded DNA images can be obtained by NC-AFM. Because of the high sensitivity of the tip-sample interaction, NC-AFM images provide stronger contrast than tapping mode (TM)-AFM images. NC-AFM images reveal detailed structures of single- and double-stranded DNA which are not revealed by TM-AFM. In addition, several NC-AFM images show contrast artifacts, which might provide information on the detailed structure of DNA.     

Determination of silicone coating Young's modulus using atomic force microscopy

The polymerisation degree of thin polymer coatings was checked by following the variation of their local mechanical properties. Atomic force microscope (AFM) was used in an indentation mode to investigate the mechanical characteristics of silicone coatings on polycarbonate substrates. The evolution of Young's modulus of the silicone coatings was determined as a function of the polymer annealing time. We have used a relative method to measure Young's moduli, which involves a calibration step with a set of reference polymers. No variation was observed for the modulus of silicone coatings annealed during more than 40 min at 130 °C. This result indicates that over-heating does not modify the mechanical properties of the coating.     

Characterization of electrodeposited nickel film surfaces using atomic force microscopy

Microstructures of nickel surfaces electrodeposited on indium tin oxides coated glasses are investigated using atomic force microscopy. The fractal dimension D and Hurst exponent H of the nickel surface images are determined from a frequency analysis method proposed by Aguilar et al. [J. Microsc. 172 (1993) 233] and from Hurst rescaled range analysis. The two methods are found to give the same value of the fractal dimension D∼2.0. The roughness exponent α and growth exponent β that characterize scaling behaviors of the surface growth in electrodeposition are calculated using the height-difference correlation function and interface width in Fourier space. The exponents of α∼1.0 and β∼0.8 show that the surface growth does not belong to the universality classes theoretically predicted by statistical growth models.     

Quantitative determination of contact stiffness using atomic force acoustic microscopy

Atomic force acoustic microscopy is a near-field technique which combines the ability of ultrasonics to image elastic properties with the high lateral resolution of scanning probe microscopes. We present a technique to measure the contact stiffness and the Young's modulus of sample surfaces quantitatively, with a resolution of approximately 20 nm, exploiting the contact resonance frequencies of standard cantilevers used in atomic force microscopy. The Young's modulus of nanocrystalline ferrite films has been measured as a function of oxidation temperature. Furthermore, images showing the domain structure of piezoelectric lead zirconate titanate ceramics have been taken.     

Topographical observation of silane-treated inorganic surface using atomic force microscopy

The topography of the silane-treated layer on an inorganic surface was observed using an atomic force microscope. For this purpose, the cleaved mica plate was treated with some silane coupling agent at varying conditions. The silanes having aminopropyl or methacryloxypropyl group as organofunctional groups with di- or trialkoxyl structures were used. Three different solvents for silane solution — 2-propanol, 2-propanol/water mixture and water — were used. The pH of the aqueous solution was controlled. As a result, the most suitable solvent and pH in order to obtain smooth silane layer was clarified. The solubility of silane molecules in the solution, the wettability of silane molecule onto inorganic surface, and prevention of the mutual condensation of silane molecules in the solution were found to be important parameters for this purpose.     

Membrane deformation of unfixed erythrocytes in air with time lapse investigated by tapping mode atomic force microscopy

Estimation of the time of death is one of the most important problems for forensic medicine and law. Physical and chemical postmortem changes are evaluated together while estimating the time of death. The pattern analysis of antemortem and postmortem bloodstains is one of the important parameters for forensic science, and cellular changes of blood cells can be useful for the quantitative assessment of the time of death. In this study, by successively investigating erythrocytes exposed in air on mica for 5 days using tapping mode atomic force microscopy (TM-AFM), we observed deformation of whole cell and membrane surface of unfixed erythrocytes with time lapse. We found that the time-dependent cellular changes occurred after exposure of erythrocytes in air for several days. At 0.5 days of exposure, fissures and cell shrinkage were observed. At 2.5 days of exposure, the emergence of nanometer-scale protuberances were observed and these protuberances increased in number with increasing time. The changes of cell shape and cell membrane surface ultrastructure can be used to estimate the time of death. Futhermore, smear-induced abnormal erythrocytes and immunostained erythrocytes were observed here. The need for more precise research is indicated, such as the correlation of membrane changes to intervals of less than 0.5 day of air exposure, and use of various substrates in addition to mica, including glass, metals, fabrics, among others, on which the bloodstains appear in crime scenes. The results of this research demonstrate the efficacy of AFM as a potentially powerful analytical tool in forensic science.     

Single-shell carbon nanotubes imaged by atomic force microscopy

Single-shell carbon nanotubes, approximately 1 nm in diameter, have been imaged for the first time by atomic force microscopy operating in both the contact and tapping modes. For the contact mode, the height of the imaged nanotubes has been calibrated using the atomic steps of the silicon substrate on which the nanotubes were deposited. For the tapping mode, the calibration was performed using an industry-standard grating. The paper discusses substrate and sample preparation methods for the characterization by scanning probe microscopy of nanotubes deposited on a substrate.     

Water-solid interfaces probed by high-resolution atomic force microscopy

Water-solid interfaces play important roles across a broad range of scientific and application fields. In the past decades, atomic force microscopy (AFM) has significantly deepened our understanding of water-solid interfaces at molecular scale. In this review, we describe the recent progresses on probing water-solid interfaces by noncontact AFM, highlighting the imaging of interfacial water with ultrahigh spatial resolution. In particular, the recent development of qPlus-based AFM with functionalized tips has made it possible to directly image the H-bonding skeleton of interfacial water under UHV environment. Based on high-order electrostatic forces, such a technique even enables submolecular-level imaging of weakly bonded water structures with negligible disturbance. In addition, the three-dimensional (3D) AFM using low-noise cantilever deflection sensors can achieve atomic resolution imaging at liquid/solid interfaces, which opens up the possibility of probing the hydration layer structures under realistic conditions. We then discuss the application of those AFM techniques to various interfacial water systems, including water clusters, ion hydrates, water chains, water monolayers/multilayers and bulk water/ice on different surfaces under UHV or ambient environments. Some important issues will be addressed, including the H-bonding topology, ice nucleation and growth, ion hydration and transport, dielectric properties of water, etc. In the end, we present an outlook on the directions of future AFM studies of water at interfaces and the challenges faced by this field, as well as the development of new AFM techniques.     

Study of the ferroelectric properties of BaTiO3 films grown on an iron sublayer using atomic force microscopy

The article demonstrates the feasibility of the formation of ultra-thin (2?C15 nm) BaTiO@3 ferroelectric films on an Fe sublayer by pulsed laser deposition. The measured data obtained by piezoresponse force microscopy evidence that the grown BaTiO₃ films are a functional ferroelectric material and possess high polarization stability. An efficient piezomodule for BaTiO₃ layers of various thicknesses is 8?C10 pm/V.     

Time-frequency modeling of atomic force microscopy

Atomic force microscopy is modeled in the time-frequency phase space. In this phase space it is equivalent to a succession of temporal lenses and free spaces which includes a temporal fractional Fourier device. Then, the Wigner transform and its second order moments are introduced to model the atomic force microscopy as a detector of ultrafast electrical signals.     

Thermal transitions of polymers measured by atomic force microscopy

A new method has been developed to measure thermal transitions by atomic force microscopy in the non-contact mode, using it as a dynamic mechanical analyser on a local scale. In this method the cantilever is oscillating above the polymer surface and the resonance frequency is measured as a function of the temperature. Thermal transitions of a polymer are clearly visible as a change in the characteristic-frequency behaviour of the cantilever. This paper introduces a simple model to explain the response of the cantilever caused by the transitions in the polymer and the related form of the frequency/temperature curves. This new technique adds a new dimension to the standard thermal analysis techniques, with which the thermal transitions of different polymer phases can be resolved individually for polymer blends or copolymers, for example in structured multiphase polymers. Received: 1 November 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002     

Observation of the mica surface by atomic force microscopy

Freshly cleaved mica and a mica surface treated with pure water and dilute-salt solution have been investigated by Atomic Force Microscopy (AFM). On the bare mica surface (after repeated scanning), small dots and islands were observed. The disappearance of these dots and islands has also been captured by AFM. We believe these structures to be condensed water. The water meniscus between AFM tip and mica surface is considered as the source of this water structure. On the mica surface treated with pure water and dilute-salt solution, network structures are frequently observed by AFM.