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PubMed2000

In Situ Observation of Growth Process of alpha-L-Glutamic Acid with Atomic Force Microscopy.

The growth kinetics of the (111) and (001) faces of an alpha-L-glutamic acid crystal was investigated from the measurements of the growth rates, coupling with in situ surface observation using atomic force microscopy (AFM). The data of the growth rates were examined by applying the theoretical equations of the BCF and NaN models. The results indicate that the growth mechanism is not due to the screw dislocation but to the two-dimensional nucleation, i.e., the NaN model. It was confirmed by AFM observation that both the (111) and (001) faces grew with the "nucleus above nucleus" (NaN) mechanism. However, the difference of the two-dimensional nucleation behavior was observed between the faces. The growing surface of the (111) face was also observed in the presence of L-phenylaline (L-Phe) and the pinning effect by L-Phe on the growing step on the (111) face was confirmed. This result supports the mechanism of the additive effect, which was proposed previously. Copyright 2000 Academic Press.

Journal Article↗
PubMed2005

Atomic force microscopy investigation of the dependence of cellular elastic moduli on glutaraldehyde fixation.

Summary The atomic force microscope (AFM) has provided nanoscale analyses of surfaces of cells that exhibit strong adhesive and cell spreading properties. However, it is frequently reported that prior fixation is required for reliable imaging of cells with lower adhesive properties. In the present study, the AFM is used to assess the effects of fixation by glutaraldehyde on the elastic modulus of a human rhabdomyosarcoma transfectant cell line RDX2C2. Our results show a sharp increase in the elastic modulus for even mild fixation (0.5% glutaraldehyde for 60 s), accompanied by a dramatic improvement in imaging reproducibility. An even larger increase is seen in NIH-3T3 mouse fibroblasts, although in that case fixation is not typically necessary for successful imaging. In addition, our results suggest that treatment with glutaraldehyde restricts the content of the resulting images to features nearer to the cell surface.

Animals↗
PubMed2006

Components for high speed atomic force microscopy.

Many applications in materials science, life science and process control would benefit from atomic force microscopes (AFM) with higher scan speeds. To achieve this, the performance of many of the AFM components has to be increased. In this work, we focus on the cantilever sensor, the scanning unit and the data acquisition. We manufactured 10 microm wide cantilevers which combine high resonance frequencies with low spring constants (160-360 kHz with spring constants of 1-5 pN/nm). For the scanning unit, we developed a new scanner principle, based on stack piezos, which allows the construction of a scanner with 15 microm scan range while retaining high resonance frequencies (>10 kHz). To drive the AFM at high scan speeds and record the height and error signal, we implemented a fast Data Acquisition (DAQ) system based on a commercial DAQ card and a LabView user interface capable of recording 30 frames per second at 150 x 150 pixels.

Animals↗
PubMed2000

Imaging the elastic properties of coiled carbon nanotubes with atomic force microscopy

Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( >170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets.

Journal Article↗
PubMed2000

Bituminous emulsions and their characterization by atomic force microscopy

We present a new method for observing oil-in-water emulsions with a continuous water phase and a dispersed bitumen phase. The fine polydispersed bitumen micelles were adsorbed to an atomically smooth mica substrate and imaged in solution by atomic force microscopy in a liquid cell. The height of the adsorbed bitumen sheet in wet and dry states can be measured and the homogeneity of film formation by coalescence can be determined. Localization of surfactant onto and between bitumen micelles is also visualized.

Journal Article↗
PubMed2006

General theory of amplitude-modulation atomic force microscopy.

We present a general analytical theory that enables one to determine accurately the unknown tip-sample interactions from the experimental measurement of the amplitude and phase of the oscillating tip in amplitude-modulation atomic force microscopy (AM-AFM). We apply the method to the known Lennard-Jones-type forces and find excellent agreement with the reconstructed results. AM-AFM, widely used in air and liquid, is now not only an imaging tool but also a quantitative force measurement tool.

Journal Article↗
PubMed2006

Growth of ultrathin films of cadmium telluride and tellurium as studied by electrochemical atomic force microscopy.

Time dependent, cathodic electrodeposition of ultrathin CdTe and Te films has been studied in 50 mM H(2)SO(4) + 1 mM CdSO(4) + 0.1 mM TeO(2) solutions at room temperature under potential control using electrochemical atomic force microscopy (EC-AFM). The films were also characterized electrochemically and with X-ray diffraction. The growth mechanism and the composition of the films depends on the applied potentials. Island-like growth mode was observed for CdTe films when the deposition potential was -0.35 V (SHE). At a more positive deposition potential of 0.138 V (SHE), Cd was not co-deposited into the film but affected the dynamic growth mode of the deposit. At this voltage smooth Te films were obtained. Depending on the applied potential, Cd acts either as a co-deposition element for CdTe film growth, or as a mediator for layer-by-layer growth of Te films.

Journal Article↗
PubMed2002

Nonequilibrium statistical mechanics of mixed quantum classical ensembles: application to noncontact atomic force microscopy.

Using the nonequilibrium statistical operator method, we suggest a new general method of treating dynamics of a combined system consisting of interacting classical and quantum parts. The method is illustrated on the tip dynamics in the noncontact atomic force microscopy (NC-AFM) where a macroscopic tip interacts with a quantum microscopic system (the surface and the nanotip). The derived general equation of motion for the tip and the Fokker-Planck equation, applicable even at low temperatures, contain memory effects and a friction term which should (at least partially) be responsible for the observed energy dissipation in NC-AFM experiments.

Journal Article↗
PubMed2006

Generation of nanostructures of mica supported lysozyme molecules in aqueous solution by atomic force microscopy.

Nanostructures of lysozyme molecules adsorbed to mica were generated by the tip of an atomic force microscope in contact, tapping, and force-distance mode in aqueous solution. In contact mode at high ionic strength and adjusted lysozyme concentration a monolayer of defined pattern and orientation could be formed by the scan process of the tip. A lysozyme monolayer with minimal pattern size of about 60 nm was achieved by line scan. At larger loading forces besides a monolayer also 3D-aggregates of lysozyme molecules could be generated. In force-distance mode the volume of 3D-aggregates grows with increasing generation time, lysozyme concentration in the bulk phase, loading force, and frequency of up- and down-movement of the substrate toward the fixed cantilever. In tapping mode 3D-aggregates could be generated as well. It is postulated that reduction of electrostatic interaction between the oppositely charged lysozyme molecules and mica surface by sufficient high ionic strength is essential for monolayer formation. It is discussed that for the underlying mechanism of monolayer generation in contact mode lysozyme molecules of the bulk phase adsorb to the tip, become pulled off and attach to the mica surface by the scan process of the tip.

Aluminum Silicates↗
PubMed1993

Atomic force microscopy of mammalian sperm chromatin.

We have used the atomic force microscope (AFM) to image the surfaces of intact bull, mouse and rat sperm chromatin and partially decondensed mouse sperm chromatin attached to coverglass. High resolution AFM imaging was performed in air and saline using uncoated, unfixed and unstained chromatin. Images of the surfaces of intact chromatin from all three species and of an AFM-dissected bull sperm nucleus have revealed that the DNA is organized into large nodular subunits, which vary in diameter between 50 and 100 nm. Other images of partially decondensed mouse sperm chromatin show that the nodules are arranged along thick fibers that loop out away from the nucleus upon decondensation. These fibers appear to stretch or unravel, generating narrow smooth fibers with thicknesses equivalent to a single DNA-protamine complex. High resolution AFM images of the nodular subunits suggest that they are discrete, ellipsoid-shaped DNA packaging units possibly only one level of packaging above the protamine-DNA complex.

Animals↗
PubMed2001

Atomic Force Microscopy Study of the Adhesion of Saccharomyces cerevisiae.

An atomic force microscope (AFM) has been used to quantify directly the adhesion of metabolically active Saccharomyces cerevisiae cells at a hydrophilic mica surface, a mica surface with a hydrophobic coating, and a protein-coated mica surface in an aqueous environment. The measurements used "cell probes" constructed by immobilizing a single cell at the apex of a tipless AFM cantilever. Adhesion was quantified from force-distance data for the retraction of the cell from the surface. The data indicated stretching and sequential bond-breaking as the cell probe was retracted from all of the surfaces. Detailed studies were made for physiologically active cells, which were shown to have different adhesion properties to glutaraldehyde-treated cells. Greatest cell adhesion was measured at the hydrophobic surface. Prior adsorption of a bovine serum albumin protein layer at the hydrophilic surface did not significantly affect cell adhesion. Changes in yeast surface hydrophobicity and zeta-potential with yeast cell age were correlated with differences in adhesion. Cells from the stationary phase adhered most strongly to a mica surface. Time of surface contact was demonstrated to be important. Both the force needed to detach a cell from a hydrophilic mica surface and the length of the adhesive interaction increased after 5 min contact. The AFM cell probe technique gives unique insights into primary colonization events in biofilm formation. It will continue to aid both fundamental studies and the assessment of new procedures that are designed to lower cell adhesion at surfaces relevant to biotechnology, medicine, and dentistry Copyright 2001 Academic Press.

Journal Article↗
PubMed2006

Automated image analysis of atomic force microscopy images of rotavirus particles.

A variety of biological samples can be imaged by the atomic force microscope (AFM) under environments that range from vacuum to ambient to liquid. Generally imaging is pursued to evaluate structural features of the sample or perhaps identify some structural changes in the sample that are induced by the investigator. In many cases, AFM images of sample features and induced structural changes are interpreted in general qualitative terms such as markedly smaller or larger, rougher, highly irregular, or smooth. Various manual tools can be used to analyze images and extract more quantitative data, but this is usually a cumbersome process. To facilitate quantitative AFM imaging, automated image analysis routines are being developed. Viral particles imaged in water were used as a test case to develop an algorithm that automatically extracts average dimensional information from a large set of individual particles. The extracted information allows statistical analyses of the dimensional characteristics of the particles and facilitates interpretation related to the binding of the particles to the surface. This algorithm is being extended for analysis of other biological samples and physical objects that are imaged by AFM.

Algorithms↗
PubMed1998

Microminiaturized immunoassays using atomic force microscopy and compositionally patterned antigen arrays.

This paper combines the topographic imaging capability of the atomic force microscope (AFM) with a compositionally patterned array of immobilized antigenic rabbit IgG on gold as an approach to performing immunoassays. The substrates are composed of micrometer-sized domains of IgG that are covalently linked to a photolithographically patterned array of a monolayer-based coupling agent. The immobilized coupling agent, which is prepared by the chemisorption of dithiobis(succinimidyl undecanoate) on gold, is separated by micrometer-sized grids of a monolayer formed from octadecanethiol (ODT). The strong hydrophobicity of the ODT adlayer, combined with the addition of the surfactant Tween 80 to the buffer solution that is used in forming the antibody-antigen pairs, minimizes the nonspecific adsorption of proteinaceous materials to the grid regions. This minimization allows the grids to function as a reference plane for the AFM detection of the height increase when a complementary antibody-antigen pair is formed. The advantageous features of this strategy, which include ease of sample preparation, an internal reference plane for the detection of topographic changes, and the potential for regeneration and reuse, are demonstrated using rabbit IgG as an immobilized antigen and goat anti-rabbit IgG as the complementary antibody. The prospects for further miniaturization are discussed.

Animals↗
PubMedDate not supplied

Atomic force microscopy in biology: technology and techniques.

In this review, I describe the biological applications of the atomic force microscope (AFM). The historical background and the development of the microscope are described. The AFM can operate in many different modes relevant to biological systems including topography, chemical analysis, and forces relevant at the biological length scale (single cell to DNA dimensions and pico to nano Newton forces). A limited number of examples from the literature are described to illustrate some of the many capabilities of this microscope. The aim is to give an introduction of the technique to the inexperienced in this rapidly growing field.

Animals↗
PubMed2005

Structural characterization of self-assembled monolayers of neoglycoconjugates using atomic force microscopy.

Thiolated self-assembled monolayers of carbohydrates may serve as useful polyvalent tools to mimic the organized presentation of such molecules at the cell surface. SAMs presenting the disaccharide maltose as a neoglycoconjugate were produced, and the structure was studied by high resolution atomic force microscopy. The molecules form highly ordered structures on a gold (111) surface, with lattice parameters determined by the linker moiety rather than the headgroup.

Journal Article↗
PubMed1994

Granula motion and membrane spreading during activation of human platelets imaged by atomic force microscopy.

The redistribution of platelet constituents during activation is essential for their physiological function of maintaining hemostasis. We report here about real time investigations of the activation of native human platelets under physiological conditions from the initial formation of filopodia to the fully spread form by atomic force microscopy. We followed the trafficking of granules and their interaction with the plasma membrane within single cells. Our results show movement of certain granula towards the lamellipodia. Analysis of this rearrangement and the subsequent enlargement of the platelet surface reveals details of the membrane spreading process. Images of living cells are presented that show the distribution of cytoskeletal components and membrane-bound filaments at a resolution of better than 50 nm. The local minimum forces between the tip and the platelets were estimated to be smaller than 60 pN. A model for the elastic contributions of the glycocalix to the tip/membrane interaction was developed using the theory of grafted polymers.

Biophysical Phenomena↗
PubMed2000

Atomic force microscopy analysis of wool fibre surfaces in air and under water

Wool fibre surfaces have been treated by solvent cleaning which leaves the native covalently bound surface lipid layer intact, and by alcoholic alkali which removes the lipid layer. The resultant surfaces have been analysed by atomic force microscopy (AFM), with particular emphasis on force-distance (F-d) methods. Methodologies were developed for investigation in situ in water of both the surface topography and the characteristics of the lipid layer. Longitudinal surface texturing was resolved in images of wool fibre surfaces in air; the texturing remained prominent after exposure to water. High resolution F-d curves revealed features associated with the lipid layer. A simple formalism was used to show that the layer had a thickness of a few nm, and an effective stiffness of some 0. 12+/-0.01N/m. Strong adhesive interactions, equivalent to a pressure of 0.1MPa, acted on the tip at the tip-to-substrate interface. The methodology and formalism are likely to be relevant in the broad field of thin-film analysis and for fibre technology.

Journal Article↗