Atomic Force Microscopy Force-distance Curves Research Articles

Characterization of mitochondria isolated from normal and ischemic hearts in rats utilizing atomic force microscopy

Mitochondria play critical roles in both the life and the death of cardiac myocytes. Various factors, such as the loss of ATP synthesis and increase of ATP hydrolysis, impairment in ionic homeostasis, formation of reactive oxygen species (ROS), and release of proapoptotic proteins are related to the generation of irreversible damage. It has been proposed that the release of cytochrome c is caused by a swelling of the mitochondrial matrix triggered by the apoptotic stimuli. However, there is a controversy about whether or not the mitochondria, indeed, swell during apoptosis. The major advantages of atomic force microscopy (AFM) over conventional optical and electron microscopes for bio-imaging include the fact that no special coating and vacuum are required and imaging can be done in all environments—air, vacuum or aqueous conditions. In addition, AFM force–distance curve measurements have become a fundamental tool in the fields of surface chemistry, biochemistry, and material science. In this study, we used AFM to observe the morphological and property changes in heart mitochondria that were isolated from a rat myocardial infarction model. From the shape parameters of the mitochondria in the AFM topographic image, it seemed that myocardial infarction caused the mitochondrial swelling. Also, the results of force–distance measurements showed that the adhesion force of heart mitochondria was significantly decreased by myocardial in infarction. Therefore, we suggested that myocardial infarction might be the cause of mitochondrial swelling and the changes in outer membrane of heart mitochondria.

The Degradation and Adsorption Behaviors of Enzyme on Poly(butylene succinate) Single Crystals

The enzymatic degradation behavior of poly(butylene succinate) (PBS) single crystals with a lipase from Pseudomonas cepacia (lipase PS) is monitored using atomic force microscopy (AFM) in phosphate buffer at pH 6.8 and 40 degrees C. In-situ AFM results show that enzymatic degradation of the single crystal starts from the crystal edges rather than the chain-folded surfaces and the lamellar thickness remains constant during the whole degradation process. Total internal reflection fluorescence microscopy (TIRFM) is used for the first time to study the adsorption behavior of lipase onto the PBS crystal surface. The results clearly show that the enzyme molecules preferentially adsorb on the lateral surfaces of the single crystal but not on the chain-folded surfaces. AFM force-distance curve measurements and force-volume imaging obtained using a lipase-immobilized AFM tip show that small and large adhesive forces exist in the flat-on and edge-on areas of a PBS banded spherulite, respectively, which correspond to the chain-folded surface and lateral edges of a single crystal.

Polymer nanotechnology applied to polymeric nano-soft-materials

We have been developing new techniques to evaluate polymer nano-alloys and nano-composites. This "nanotechnology" can be classified into nano-three dimensional (3D) measurement, nano-physical properties evaluation systems, and nano-spectroscopy. As for the nano-3D measurement, we developed polymer oriented energy-filtered 3D transmission electron microscopy. With this method, we can access important 3D structural and elemental information that cannot be obtainable from ordinary TEM. Nano-physical properties evaluation systems were also established by developing atomic force microscopy force-distance curve measurement. The distribution of mechanical properties such as Young's modulus and adhesive energy was quantitatively obtained on high lateral resolution. These methods give new pieces of information unobtainable by the conventional techniques on polymer nanotechnology. Several results are shown here.

Investigation of the effect of CrO 42− and MoO 42− on carbon steel corrosion using AFM and electrochemical techniques

The effect of chromate () and molybdate () ions on the corrosion of carbon steel in 0.5 M NaCl solution has been studied using electrochemical measurements and atomic force microscopy (AFM) technique. Potentiodynamic polarization data suggest that both and have inhibition effect on carbon steel corrosion, and the inhibition efficiency increases with increase in concentrations of and ; at the same concentration, the inhibition efficiency of is higher than that of . The increase in concentrations of and anions causes a shift of the breakdown potential (Eb) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. At the same concentrations, the breakdown potential of is higher than that of . Electrochemical impedance spectroscopy (EIS) tests reveal that the charge transfer resistance and passive film resistance increase with increase in concentrations of or ; at the same concentrations, as for the charge transfer resistance and passive film resistance were bigger than those of . AFM imaging technique shows that local corrosion was inhibited obviously after the addtion of or , and passive film of was much more compact than that of . AFM force–distance curves indicate that the passive film of is much stiffer than that of .

PH-induced changes in adsorbed β-lactoglobulin molecules measured using atomic force microscopy

We have used atomic force microscopy (AFM) imaging and force spectroscopy to study β-lactoglobulin (β-LG) food protein molecules adsorbed onto a mica surface. In particular, we have studied the effect of in situ changes in pH on several different properties: the topographical morphology of the adsorbed β-LG molecules, adhesion of the β-LG molecules to the underlying mica substrate, and the mechanical unfolding of the β-LG molecules. In AFM images, the structure of the adsorbed protein layer was observed to change dramatically with changes in pH. This result was consistent with the mechanical unfolding of single protein molecules within the adsorbed protein layer at different pH values performed using AFM. The short rupture length (∼50 nm) measured for the fully unfolded protein at an acidic pH value of 2.5 is in good agreement with the dominant single molecule population measured previously for this pH value. Unfolding β-LG molecules from the same protein layer at a neutral value of pH = 6.8 resulted primarily in longer rupture lengths, corresponding to dimers of β-LG. AFM force–distance curves collected at pH = 9 were dominated by a large repulsion between the AFM tip and the adsorbed protein layer, which is likely due to the extended nature of the molecules because of irreversible denaturation for pH values greater than 9. This work provides a novel insight into the mechanisms of protein adsorption onto surfaces and shows that AFM force spectroscopy is a promising tool for probing in situ conformational changes in single molecules under various conditions.

SPM Characterization of Pulsed Laser Deposited Nanocrystalline CrN Hard Coatings

Nanocrystalline CrN coatings, widely required for surface engineering application covering wear and corrosion resistance, need to be investigated for atomic scale morphology, surface roughness, local stiffness, phase uniformity, and homogeneity. Evolution of these properties as a function of thickness need to be studied. In this paper, we have attempted to address these issues through use of a multimode scanning probe microscope (SPM) equipped to carry out Atomic Force Microscopy (AFM) and Atomic Force Acoustic microscopy (AFAM) of Chromium nitride films (100-500 nm thick) on Si prepared under high vacuum by pulsed Laser Ablation using Nd-YAG Q-switched laser. Prior to SPM analysis, the coatings were annealed in N2 atmosphere at 700 degrees C for 30 minutes for improving crystallanity and coating substrate adhesion. The GIXRD patterns of these annealed specimens showed formation of nanocrystalline CrN. Also signature of amorphous phases was seen. The grain size was estimated to be less than 30 nm. Contact mode AFM imaging revealed a roughness value less than 50 nm. Local stiffness values were calculated from AFM force-distance curves. Imaging of frictional force and surface flaws are being investigated by Frictional Force Microscopy (FFM), resonance spectroscopy, and AFAM, respectively. The contrast in AFAM images is seen due to variation in surface elasticity in reference and CrN samples. Stiffness constant and elastic modulus were calculated for both the samples and compared.

ADSORPTION BEHAVIOR OF DODECYLAMINE AND ITS EFFECT ON THE WETTABILITY AND CORROSION OF CARBON STEEL

The adsorption behavior of dodecylamine and its effect on the wettability and corrosion of carbon steel in hydrochloric acid solution were studied. Polarization data suggest that inhibition of carbon steel corrosion is due to geometric blocking effect of adsorbed dodecylamine molecules on the metal surface, which leads to the formation of a monolayer on the metal. Phase images measured by tapping-mode atomic force microscopy (AFM) reveal different properties of the surface with and without various concentrations of dodecylamine. AFM force–distance curves indicate that sample surface exhibits adhesion characteristic after the adsorption of dodecylamine. Contact angle measurements show that dodecylamine reduces surface wettability obviously.

Antigen Binding Forces of Single Antilysozyme Fv Fragments Explored by Atomic Force Microscopy

We used atomic force microscopy (AFM) to explore the antigen binding forces of individual Fv fragments of antilysozyme antibodies (Fv). To detect single molecular recognition events, genetically engineered histidine-tagged Fv fragments were coupled onto AFM tips modified with mixed self-assembled monolayers (SAMs) of nitrilotriacetic acid- and tri(ethylene glycol)-terminated alkanethiols while lysozyme (Lyso) was covalently immobilized onto mixed SAMs of carboxyl- and hydroxyl-terminated alkanethiols. The quality of the functionalization procedure was validated using X-ray photoelectron spectroscopy (surface chemical composition), AFM imaging (surface morphology in aqueous solution), and surface plasmon resonance (SPR, specific binding in aqueous solution). AFM force-distance curves recorded at a loading rate of 5000 pN/s between Fv- and Lyso-modified surfaces yielded a distribution of unbinding forces composed of integer multiples of an elementary force quantum of approximately 50 pN that we attribute to the rupture of a single antibody-antigen pair. Injection of a solution containing free Lyso caused a dramatic reduction of adhesion probability, indicating that the measured 50 pN unbinding forces are due to the specific antibody-antigen interaction. To investigate the dynamics of the interaction, force-distance curves were recorded at various loading rates. Plots of unbinding force vs log(loading rate) revealed two distinct linear regimes with ascending slopes, indicating multiple barriers were present in the energy landscape. The kinetic off-rate constant of dissociation (k(off) approximately = 1 x 10(-3) s(-1)) obtained by extrapolating the data of the low-strength regime to zero force was in the range of the k(off) estimated by SPR.

Force-distance curves by atomic force microscopy

Atomic force microscopy (AFM) force-distance curves have become a fundamental tool in several fields of research, such as surface science, materials engineering, biochemistry and biology. Furthermore, they have great importance for the study of surface interactions from a theoretical point of view. Force-distance curves have been employed for the study of numerous materials properties and for the characterization of all the known kinds of surface forces. Since 1989, several techniques of acquisition and analysis have arisen. An increasing number of systems, presenting new kinds of forces, have been analyzed. AFM force-distance curves are routinely used in several kinds of measurement, for the determination of elasticity. Hamaker constants, surface charge densities, and degrees of hydrophobicity. The present review is designed to indicate the theoretical background of AFM force-distance curves as well as to present the great variety of measurements that can be performed with this tool. Section 1 is a general introduction to AFM force-distance curves. In Sections 2–4 the fundamentals of the theories concerning the three regions of force-distance curves are summarized. In particular, Section 2 contains a review of the techniques employed for the characterization of the elastic properties of materials. After an overview of calibration problems (Section 5), the different forces that can be measured with AFM force-distance curves are discussed. Capillary, Coulomb, Van der Waals, double-layer, solvation, hydration, hydrophobic, specific and steric forces are considered. For each force the available theoretical aspects necessary for the comprehension of the experiments are provided. The main experiments concerning the measurements of such forces are listed, pointing out the experimental problems, the artifacts that are likely to affect the measurement, and the main established results. Experiments up to June 1998 are reviewed. Finally, in Section 7, techniques to acquire force-distance curves sequentially and to draw bidimensional maps of different parameters are listed.

Evaluation of the interactions between polymeric chains and surfaces with different structures performed by an atomic force microscope

Interactions between polymers and inorganic surfaces are present in a series of phenomena involving processes such as coagulation and deffloculation of ceramic powder and adsorption of organic macromolecules on the surface of implants, among others. In this work, Atomic Force Microscopy (AFM) was modified to allow the evaluation of interactions between polymeric chains and inorganic surfaces (silica) with different structures. Polymers (sulfonated polysulfone) were grafted onto AFM cantilevers. AFM force-distance curves were obtained for this modified tip against a series of substrates produced by depositing silica films on silicon wafers. The structure of the silica layer was modified by employing heat treatments at different temperatures. The results showed that the interactions between polymer and surfaces are dependent on the structure of the surfaces. Penetration of the polymeric chains can occur through a soft gel layer (substrates treated at low temperature, 110 °C). For surfaces with dense silica layers, the results showed that not only the concentration of hydroxy groups but also their spatial distribution along the surfaces are important in defining the magnitude of interactions between polymers and surfaces. A model involving a molecular recognition process, in which interactions are maximized for inorganic surfaces with structures that can match the chemical architecture of the polymer, was then used to explain the obtained results.