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At least 865 records · Page 48Linked to original sources
PubMed2004

Atomic force microscopy of emulsion droplets: probing droplet-droplet interactions.

A method has been developed for attaching oil (tetradecane) droplets to the end of an atomic force microscopy (AFM) cantilever and for immobilizing droplets on a glass substrate. This approach has permitted the monitoring of droplet-droplet interactions in aqueous solution as a function of interdroplet separation. Coating the droplet surfaces with added proteins or surfactants has allowed the production of model emulsions. We demonstrate that AFM measurements of droplet deformability are sensitive to interfacial rheology by modifying the interfacial film on a pair of droplets in situ. For droplets coated with the anionic surfactant sodium dodecyl sulfate, screening of the double layer has been found to facilitate coalescence. Direct imaging of the droplets has revealed the presence of regularly spaced concentric rings on the droplet surfaces. Careful experimental studies suggest that these structures may be imaging artifacts and are not perturbations of the droplet surface determined by the composition of the interface.

Alkanes↗
PubMed2004

Growth and disorder of macromolecular crystals: insights from atomic force microscopy and X-ray diffraction studies.

The growth processes and defect structures of protein and virus crystals have been studied in situ by atomic force microscopy (AFM), X-ray diffraction topography, and high-resolution reciprocal space scanning. Molecular mechanisms of macromolecular crystallization were visualized and fundamental kinetic and thermodynamic parameters, which govern the crystallization process of a number of macromolecular crystals, have been determined. High-resolution AFM imaging of crystal surfaces provides information on the packing of macromolecules within the unit cell and on the structure of large macromolecular assemblies. X-ray diffraction techniques provide a bulk probe with poorer spatial resolution but excellent sensitivity to mosaicity and strain. Defect structures and disorder created in macromolecular crystals during growth, seeding, and post-growth treatments including flash cooling were characterized and their impacts on the diffraction properties of macromolecular crystals have been analyzed. The diverse and dramatic effects of impurities on growth and defect formation have also been studied. Practical implications of these fundamental insights into the improvement of macromolecular crystallization protocols are discussed.

Chemistry Techniques, Analytical↗
PubMed2005

Atomic force microscopy studies on heat-induced gelation of curdlan.

Heat-induced gelation of a cold-water insoluble polysaccharide, Curdlan, was investigated using atomic force microscopy (AFM). Curdlan dissolved into NaOH aqueous solutions exhibited a spectral transition around 0.2 mol/L NaOH, which is an indicative of conformational transitions from a single helix at a lower alkali concentration to a disordered chain at a higher concentration. Nevertheless, AFM images of Curdlan solubilized in 0.01 mol/L NaOH revealed the presence of heterogeneous supramolecular assemblies of Curdlan: the majority of the molecules were in the form of microfibrils, the lengths of which were on the order of micrometers and the cross-sectional heights of which were approximately 2-3 nm, whereas single molecular chains, partially dissociated from these microfibrils, were also observed. Heating such a sol resulted in the formation of densely cross-linked microgel networks. Heat-induced gelation of Curdlan appears to be initiated by partial dissociation of single chains from supramolecular microfibrils and followed by cross-linking of microfibrils via hydrophobic interactions among these partially dissociated chains.

Gels↗
PubMed2006

Rheology of passive and adhesion-activated neutrophils probed by atomic force microscopy.

The rheology of neutrophils in their passive and activated states plays a key role in determining their function in response to inflammatory stimuli. Atomic force microscopy was used to study neutrophil rheology by measuring the complex shear modulus G*(omega) of passive nonadhered rat neutrophils on poly(HEMA) and neutrophils activated through adhesion to glass. G*(omega) was measured over three frequency decades (0.1-102.4 Hz) by indenting the cells 500 nm with a spherical tip and then applying a 50-nm amplitude multi-frequency signal. G*(omega) of both passive and adhered neutrophils increased as a power law with frequency, with a coupling between elastic (G') and loss (G'') moduli. For passive neutrophils at 1.6 Hz, G' = 380 +/- 121 Pa, whereas G'' was fourfold smaller and the power law coefficient was of x = 1.184. Adhered neutrophils were over twofold stiffer with a lower slope (x = 1.148). This behavior was adequately described by the power law structural damping model but not by liquid droplet and Kelvin models. The increase in stiffness with frequency may modulate neutrophil transit, arrest, and transmigration in vascular microcirculation.

Adhesiveness↗
PubMed1998

Structure of the erythrocyte membrane skeleton as observed by atomic force microscopy.

The structure of the membrane skeleton on the cytoplasmic surface of the erythrocyte plasma membrane was observed in dried human erythrocyte ghosts by atomic force microscopy (AFM), taking advantage of its high sensitivity to small height variations in surfaces. The majority of the membrane skeleton can be imaged, even on the extracellular surface of the membrane. Various fixation and drying methods were examined for preparation of ghost membrane samples for AFM observation, and it was found that freeze-drying (freezing by rapid immersion in a cryogen) of unfixed specimens was a fast and simple way to obtain consistently good results for observation without removing the membrane or extending the membrane skeleton. Observation of the membrane skeleton at the external surface of the cell was possible mainly because the bilayer portion of the membrane sank into the cell during the drying process. The average mesh size of the spectrin network observed at the extracellular and cytoplasmic surfaces of the plasma membrane was 4800 and 3000 nm2, respectively, which indicates that spectrin forms a three-dimensionally folded meshwork, and that 80% of spectrin can be observed at the extracellular surface of the plasma membrane.

Cell Fractionation↗
PubMed1995

Neurone decapping characterization by atomic force microscopy: a topological systematic analysis.

We tested a new approach to cell decapping on rat cerebellar neurones, and observed its effects on cell topography by atomic force microscopy (AFM). The results clearly demonstrate the effectiveness of our decapping approach, and also the ability of AFM to reveal fine details of the decapped cells. Specifically, varying the conditions and duration of the decapping process modifies the extent of the decapping. Such a method can be used to investigate the cytoplasm with surface sensitive techniques.

Animals↗
PubMed1995

Atomic force microscopy study of fine structures of the entire surface of red blood cells.

Glutaraldehyde-fixed red blood cells were imaged by tapping mode atomic force microscopy (TMAFM) in air at room temperature. The results show that TMAFM can visualize the morphology of the red blood cell at both cellular and nanometer scales. The scan size covers the range from several hundred nanometers to more than one hundred micrometers. TMAFM not only has a higher resolution than the optical microscope, but also can observe biological samples without precoating as required for scanning electron microscopy (SEM). The AFM images of the entire surface of an uncoated red blood cell with nanometer resolution are successfully reconstructed by 28 AFM images of the preselected subareas on the surface of the red blood cell. These images reveal directly the fine structures of the external surface of uncoated red blood cells in air. The surface exhibits a characteristic structure composed of a large number of closely-packed nanometer particles with a size ranging from a few nanometers to tens of nanometers. These "particulate" components are evenly distributed, and no jumping protrusion or depression structures were found. These particles give rise to a very smooth surface of the red blood cell as shown in a large-scan AFM image. In addition, the 28 AFM images obtained by the continuous scanning over 3 hours indicate that TMAFM can image soft biological samples such as red blood cells stably and reproducibly.

Erythrocytes↗
PubMed2004

Microscale frictional response of bovine articular cartilage from atomic force microscopy.

The objective of this study was to compare micro- and macroscale friction coefficients of bovine articular cartilage. Microscale measurements were performed using standard atomic force microscopy (AFM) techniques, using a 5 microm spherical probe tip. Twenty-four cylindrical osteochondral plugs were harvested in pairs from adjacent positions in six fresh bovine humeral heads (4-6 months old), and divided into two groups for AFM and macroscopic friction measurements. AFM measurements of friction were observed to be time-independent, whereas macroscale measurements demonstrated the well-documented time-dependent increase from a minimum to an equilibrium value. The microscale AFM friction coefficient (mu(AFM), 0.152+/-0.079) and macroscale equilibrium friction coefficient (mu(eq), 0.138+/-0.036) exhibited no statistical differences (p=0.50), while the macroscale minimum friction coefficient (mu(min), 0.004+/-0.001) was significantly smaller than mu(eq) and mu(AFM) (p<0.0001). Variations in articular surface roughness (Rq= 462+/-216 nm) did not correlate significantly with mu(AFM), mu(eq) or mu(min). The effective compressive modulus determined from AFM indentation tests using a Hertz contact analysis was E*=45.8+/-18.8 kPa. The main finding of this study is that mu(AFM) is more representative of the macroscale equilibrium friction coefficient, which represents the frictional response in the absence of cartilage interstitial fluid pressurization. These results suggest that AFM measurements may be highly suited for exploring the role of boundary lubricants in diarthrodial joint lubrication independently of the confounding effect of fluid pressurization to provide greater insight into articular cartilage lubrication.

Animals↗
PubMed1998

The observation of the local ordering characteristics of spermidine-condensed DNA: atomic force microscopy and polarizing microscopy studies.

Condensation of DNA by multivalent cations can provide useful insights into the physical factors governing the folding and packaging of DNA in vivo. In this work, local ordered structures of spermidine-DNA complexes prepared from different DNA concentrations have been examined by using atomic force microscopy (AFM) and polarizing microscopy (PM). Two types (I and II) of DNA condensates, significantly different in sizes, were observed. It was found that for extremely dilute solutions (DNA concentrations around 1 ng/microl or below), the DNA molecules would collapse into toroidal structures with a volume equivalent to a single lambda-DNA (type I). In relatively dilute solutions (DNA concentrations between 1 and 10 ng/microll), a significantly larger structure of multimolecular toroids (circular and elliptical, type II) were formed, which were constructed by many fine particles. Measurements show that the average diameter of these fine particles was similar to the outer diameter of the monomolecular toroids observed in extremely dilute solutions, and the thickness of the multimolecular toroids had a distribution of multi-layers with height increments of 11 nm, indicating that the multimolecular toroidal structures have lamellar characteristics. Moreover, by enriching the DNA-spermidine complexes in very diluted solution, branch-like structures constructed by subunits were observed by using AFM. The analysis of the pellets in polarizing microscopy reveals a liquid-crystal-like pattern. These observations suggest that DNA-spermidine condensation could have multiple stages, which are very sensitive to the DNA and spermidine concentrations.

Bacteriophage lambda↗
PubMed2003

Structure of intracellular mature vaccinia virus visualized by in situ atomic force microscopy.

Vaccinia virus, the basis of the smallpox vaccine, is one of the largest viruses to replicate in humans. We have used in situ atomic force microscopy (AFM) to directly visualize fully hydrated, intact intracellular mature vaccinia virus (IMV) virions and chemical and enzymatic treatment products thereof. The latter included virion cores, core-enveloping coats, and core substructures. The isolated coats appeared to be composed of a highly cross-linked protein array. AFM imaging of core substructures indicated association of the linear viral DNA genome with a segmented protein sheath forming an extended approximately 16-nm-diameter filament with helical surface topography; enclosure of this filament within a 30- to 40-nm-diameter tubule which also shows helical topography; and enclosure of the folded, condensed 30- to 40-nm-diameter tubule within the core by a wall covered with peg-like projections. Proteins observed attached to the 30- to 40-nm-diameter tubules may mediate folding and/or compaction of the tubules and/or represent vestiges of the core wall and/or pegs. An accessory "satellite domain" was observed protruding from the intact core. This corresponded in size to isolated 70- to 100-nm-diameter particles that were imaged independently and might represent detached accessory domains. AFM imaging of intact virions indicated that IMV underwent a reversible shrinkage upon dehydration (as much as 2.2- to 2.5-fold in the height dimension), accompanied by topological and topographical changes, including protrusion of the satellite domain. As shown here, the chemical and enzymatic dissection of large, asymmetrical virus particles in combination with in situ AFM provides an informative complement to other structure determination techniques.

Aluminum Silicates↗
PubMed2005

Combined study of X-ray reflectivity and atomic force microscopy on a surface-grafted phospholipid monolayer on a solid.

We investigated the detailed structure of a surface-grafted phospholipid monolayer, which was polymerized in situ onto a methacryloyl-silanized solid surface. By the combined study of X-ray reflectivity and atomic force microscopy, the in situ polymerization step of the lipid molecules are sufficiently detailed to reveal the molecular structure of lipid molecules before and after in situ polymerization. From the data of the X-ray reflectivity, we confirmed that the in situ polymerization process produces a flat lipid monolayer structure and that the lipid monolayer is substantially grafted on a silanized surface by chemical bonding. After the polymerization and washing processes, the thickness of the head group was 9 angstroms and the thickness of the tail group was 21 angstroms. The surface morphology of the polymerized phospholipid monolayer obtained by the measurements of atomic force microscopy was consistent with the results of the X-ray reflectivity. The cross-sectional analysis shows that the surface coverage of lipid molecules, which are chemically grafted onto a silanized surface, is approximately 89%.

Lysophosphatidylcholines↗
PubMed1994

Atomic force microscopy of peritoneal macrophages after particle phagocytosis.

The atomic force microscope was used to image peritoneal macrophages after phagocytosis of latex beads with 0.45 microns in diameter and of zymosan particles. The rigidity of the phagocytosed material allowed to image the live membrane at forces below 2 nN. Repeated scanning of the membrane unavoidably caused the protrusion of the beads and increased their virtual height. The influence of fixation by glutaraldehyde on the image and the corresponding force vs. distance curves were analyzed and compared. Short treatment with Triton X-100 enabled us to identify intracellular components, such as embedded latex beads, cell nucleus and cytoskeletal strands. The data demonstrate that it is possible to image living cells if they are bolstered by stiff material.

Animals↗
PubMedDate not supplied

Annealing and melting behavior of poly(l-lactic acid) single crystals as revealed by in situ atomic force microscopy.

In situ annealing and melting of folded-chain single crystals of poly(l-lactic acid) (PLLA) was examined by temperature-controlled atomic force microscopy (AFM). Prominent changes in the crystal appearance during annealing could be followed in real time by the AFM at temperatures above the original crystallization temperature. Thickening of the crystal edges could be occasionally observed, and this indicates that the crystal edges are less perfect than the central, well-ordered regions. At higher annealing temperatures, melting of the unthickened part started. The melting of the unthickened region progressed from the boundaries of the thickened portion normal to the growth face, rather than to the folding surfaces. In addition, it is suggested that melting also initiates at defective or distorted sites in the crystal as revealed by transmission electron microscopy (TEM) and AFM.

Biocompatible Materials↗
PubMed2001

Atomic force microscopy of RecA--DNA complexes using a carbon nanotube tip.

We report high resolution images of RecA-double stranded (ds) DNA complexes obtained by atomic force microscopy (AFM). When a carbon nanotube (CNT) tip was used, AFM images visualized the 10-nm pitch of RecA-dsDNA complexes and RecA filaments as three-dimensional surface topography without reconstruction analysis. The depth of the notch between two pitches was less than 1 nm. When adsorbed on a soft surface covered with proteins, naked DNA, RecA monomers, RecA hexamers, and short RecA filaments were all clearly resolved in one image. The high resolution images with a CNT tip provided valuable information on the initiation process of RecA-dsDNA complex formation.

DNA↗
PubMed2003

Characterization of crystalline drug nanoparticles using atomic force microscopy and complementary techniques.

PURPOSE: The purpose of this work was to image crystalline drug nanoparticles from a liquid dispersion and in a solid dosage form for the determination of size, shape, and distribution. METHODS: Crystalline drug nanoparticles were adsorbed from a colloidal dispersion on glass for atomic force microscopy (AFM) imaging. Nanoparticles that were spray coated onto a host bead were exposed by ultramicrotomy for scanning electron microscopy and AFM examination. RESULTS: The adsorbed drug nanoparticles were measured by AFM to have a mean diameter of 95 nm and an average aspect ratio of 1.3. Nanoparticles observed in the solid dosage form had a size and shape similar to drug nanoparticles in the dispersion. Particle size distribution from AFM measurement agreed well with data from field emission scanning electron microscopy, static light scattering, and X-ray powder diffraction. CONCLUSION: AFM is demonstrated to be a valuable tool in visualization and quantification of drug nanoparticle crystals in formulations. In addition to accurate size measurement, AFM readily provides shape and structural information of nanoparticles, which cannot be obtained by light scattering. Ultramicrotomy is a good sample preparation method to expose the interior of solid dosage forms with minimal structural alteration for microscopic examination.

Cellulose↗
PubMed1998

Surface analysis of the photosystem I complex by electron and atomic force microscopy.

Two-dimensional (2D) crystals of the photosystem I (PSI) reaction center from Synechococcus sp. OD24 were analyzed by electron and atomic force microscopy. Surface relief reconstructions from electron micrographs of freeze-dried unidirectionally shadowed samples and topographs recorded with the atomic force microscope (AFM) provided a precise definition of the lumenal and stromal PSI surfaces. The lumenal surface was composed of four protrusions that surrounded an indentation. One of the protrusions, the PsaF subunit, was often missing. Removal of the extrinsic proteins with the AFM stylus exposed the stromal side of the PSI core, whose surface structure could then be imaged at a resolution better than 1.4 nm. This interfacial surface between core and extrinsic subunits, had a pseudo-2-fold symmetry and protrusions that correlated with the surface helices e and e' or were at the sites of putative alpha-helix-connecting loops estimated from the 4 A map of the complex. The molecular dissection achieved with the AFM, opens new possibilities to unveil the interfaces between subunits of supramolecular assemblies.

Amino Acid Sequence↗
PubMed1999

Platelet-derived microparticles on synthetic surfaces observed by atomic force microscopy and fluorescence microscopy.

Platelet activation on a thrombogenic surface includes the release of membrane-derived microparticles that provide catalytic sites for blood coagulation factors. Here, we describe a quantitative investigation on the production and dimensions of platelet-derived microparticles observed on glass and polyethylene under aqueous conditions, using atomic force microscopy (AFM) and complementary fluorescence microscopy. The results show that contact-activated platelet microparticles are not evenly distributed over a thrombogenic surface, but in clusters in close proximity to adherent platelets. The microparticles are localized near the platelet periphery, and in some cases appear to emanate from platelet pseudopodia, suggesting that formation may result from vesiculation of the pseudopodia. The microparticles measured 125 +/- 21 nm (n = 73) in the x-y dimensions and 5.2 +/- 3.6 nm in height. The results compared closely with 125 +/- 22 nm width and 4.1 +/- 1.6 nm height obtained for control preparations of thrombin activated microparticles, that were filtered and deposited on glass. Large differences between the measured widths and heights of adsorbed microparticles suggest that platelet microparticles may undergo spreading after attachment to a surface. The adsorbed microparticles expressed platelet membrane receptor GPIIb/IIIa, and many expressed the platelet activation marker P-selectin as determined by fluorescence microscopy. The high number distribution of procoagulant microparticles per unit area of surface compared with platelets suggests that platelet-derived microparticles provide a mechanistic route for amplifying thrombus formation on a thrombogenic surface.

Biocompatible Materials↗