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PubMedDate not supplied

Morphology of modified regenerated model cellulose II surfaces studied by atomic force microscopy: effect of carboxymethylation and heat treatment.

Model cellulose II surfaces with different surface charge have been prepared from carboxymethylated wood pulp. AFM tapping-mode imaging in air showed that the introduction of charged groups into the film does not appreciably change the surface morphology. However, after a mild heat treatment (heating at 105 degrees C for 6 h), an irreversible surface structure change, from near spherical-type aggregates to a fibrillar structure, was observed. This might be attributed to the formation of strong hydrogen bonds in the crystalline region of the films while the amorphous regions shrank upon drying. The suitability of these charged cellulose films for surface forces studies was also investigated. At pH below the pK(a) of the carboxyl groups present in the film, the interaction force could be fit by a van der Waals force interaction. At higher pH, the interaction was of a purely electrostatic nature with no van der Waals component observable due to the swelling of the surfaces.

Carboxymethylcellulose Sodium↗
PubMed2004

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.

Animals↗
PubMed2004

Electron and atomic force microscopy of the trimeric ammonium transporter AmtB.

Escherichia coli AmtB is an archetypal member of the ammonium transporter (Amt) family, a family of proteins that are conserved in all domains of life. Reconstitution of AmtB in the presence of lipids produced large, ordered two-dimensional crystals. From these, a 12 A resolution projection map was determined by cryoelectron microscopy, and high-resolution topographs were acquired using atomic force microscopy. Both techniques showed the trimeric structure of AmtB in which each monomer seems to have a pseudo-two-fold symmetry. This arrangement is likely to represent the in vivo structure. This work provides the first views of the structure of any member of the Amt family.

Cation Transport Proteins↗
PubMed2000

Effects of ethanol and acetaldehyde on isolated nerve ending membranes: study by atomic-forced microscopy.

A new method of fixation of native synaptosomes and synaptosomal membranes from rat striatum was applied for their visualization by atomic-force microscopy. A scheme for examination of the surface of biological material was developed, which helps to distinguish intact synaptosomes from washed synaptic membranes and evaluate damage to synaptic membrane surface caused by ethanol (25 mM) and acetaldehyde (50 microM). The proposed method can be used for evaluation of the damaging effects of ethanol and acetaldehyde on neurons.

Acetaldehyde↗
PubMedDate not supplied

Integrins and regulation of the microcirculation: from arterioles to molecular studies using atomic force microscopy.

Integrins are an important class of receptors for extracellular matrix proteins that can mediate both force transmission, by virtue of their connections with the cell matrix and cytoskeleton; and signal transduction, resulting from the assemblages of signaling proteins that associate with focal contacts. Consequently, integrins have been proposed to be the mechanosensor in vascular smooth muscle and endothelial cells and to play a central role in mechanotransduction. In this regard, mechanical force is an important stimulus for many vascular functions, including contractile and relaxation processes,proliferation, migration, attachment, and cell phenotype determination. Collectively, these functions define physiological properties of the vasculature such as control of blood flow, capillary pressure,permeability, and peripheral vascular resistance, and play a role in pathophysiological processes like hypertension, diabetes, and arteriosclerosis. Our knowledge concerning how integrins sense and transduce physical forces into cellular signals and which integrins are involved is incomplete. Compared to other cell surface receptors, integrins have a relatively low affinity for their binding sites on the extracellular matrix and their affinity can be regulated. These characteristics of integrin-ligand interaction may facilitate dynamic processes such as cell migration, cell remodeling, and contractile activation in response to external forces. Important questions remain concerning the nature and origin of integrin-mediated signaling in the vascular wall.

Animals↗
PubMed1993

In vitro activation of human platelets triggered and probed by atomic force microscopy.

We report on the activation of human platelets probed by atomic force microscopy under nearly physiological conditions. We could image native platelets in different stages of activation at a resolution of about 100 nm. Intracellular structures within the platelets could be resolved without staining. Furthermore we could trigger and follow the activation process of individual platelets, demonstrating that the platelets are still intact and are not destroyed or severely harmed by this novel imaging process.

Blood Platelets↗
PubMed2000

Soft-contact Atomic Force Microscopy Imaging of Adsorbed Surfactant and Polymer Layers.

The technique of atomic force microscopy (AFM) soft-imaging is outlined with respect to characterizing the adsorption of surfactants and polymers at the solid/liquid interface. This method utilizes the electrostatic and steric repulsion forces between the scanning probe and the sample to allow sensitive placement of the imaging probe near to the delicate surface layer. Specifically, the mixed adsorption of sodium dodecylsulfate (SDS) and poly(vinyl pyrrolidone) (PVP) on graphite is examined. Unlike the adsorbed layer in a solution of either component, the adsorbed layer in the mixture does not cover the substrate uniformly until equilibrium is reached (often hours later). The interesting kinetic and coverage effects observed are significant to the many applications reliant on adsorption from polymer-surfactant mixtures, especially to the flocculation of dispersions.

Journal Article↗
PubMed2000

Aspects of the physical chemistry of polymers, biomaterials and mineralised tissues investigated with atomic force microscopy (AFM).

Beyond being merely a tool for measuring surface topography, atomic force microscopy (AFM) has made significant contributions to various scientific areas dealing with physical chemistry processes. This paper presents aspects of the physical chemistry at surfaces and interfaces of polymers, biomaterials and tissues investigated with AFM. Selected examples presented include surface induced self-assembly of polymer blends, copolymer interfacial reinforcement of immiscible homopolymers, protein adsorption on biomaterials and erosion of mineralised human tissues. In these areas, AFM is a useful and versatile tool to study structural or dynamic sample properties including thermodynamically driven surface evolution of polymer surfaces, lateral surface composition of interfaces, adsorption processes, and the metrology of demineralisation phenomena.

Journal Article↗
PubMed2005

Atomic force microscopy: a powerful tool for high-resolution imaging of spermatozoa.

Atomic force microscopy (AFM) has emerged as the only technique capable of real-time imaging of the surface of a living cell at nano-resolution. Since AFM provides the advantage of directly observing living biological cells in their native environment, this technique has found many applications in pharmacology, biotechnology, microbiology, structural and molecular biology, genetics and other biology-related fields. AFM has also proved to be a valuable tool for reproductive biologists. An exhaustive review on the various applications of AFM to sperm cells is presented. AFM has been extensively applied for determining the structural and topological features of spermatozoa. Unstained, unfixed spermatozoa in their natural physiological surroundings can be imaged by this technique which provides valuable information about the morphological and pathological defects in sperm cells as three-dimensional images with precise topographical details. Sperm head defects and the acrosome at the tip of the head responsible for fertilization, can be examined and correlated with the lack of functional integrity of the cell. Considerable amount of work is reported on the structural details of the highly condensed chromatin in sperm head using AFM. Detailed information on 3D topographical images of spermatozoa acquired by AFM is expected to provide a better understanding of various reproductive pathways which, in turn, can facilitate improved infertility management and/or contraceptive development.

Journal Article↗
PubMed1993

Humidity effects on atomic force microscopy of gold-labeled DNA on mica.

Recent work in atomic force microscopy (AFM) of deoxyribonucleic acid (DNA) has relied on immobilizing DNA molecules by drying a small volume of buffered DNA solution onto cleaved mica. When imaging in air, relative humidity has been known to affect both the resolution and measured height of the DNA strands. We present data of measured height versus humidity for DNA and attached gold labels, and we propose a model for this data based on swelling of coadsorbed buffer salts upon exposure to moisture. In this model, small particles (e.g., DNA) stay near the top of the swelling salt layer, whereas larger particles (e.g., gold spheres) tend to be anchored down to the substrate until a moderate humidity is reached. At high humidity (around 65%), the salt layer becomes fluid-like and susceptible to tip-induced motion; the salts are either removed from the scan area or aggregate into island structures, depending on initial salt concentration on the surface.

Aluminum Silicates↗
PubMed2003

Atomic force microscopy as a tool for biomedical and biotechnological studies.

This work presents different applications in progress with the aid of the atomic force microscopy (AFM) technique for biomedical and biotechnological applications, comprising both the acquisition of three-dimensional images and spectroscopic force measurements, in the following systems: first, low-density lipoprotein (LDL)-glycosaminoglycans; second, lectins-polysaccharides; third, mycobacterium leprae cellular wall and Vesicular Stomatites Virus (VSV) with fibronectin laminin, and lipidic membranes; fourth, DNA-complex; and fifth, actin, as well as the development of surface functionalizing protocols and image restoration by means of mathematical techniques.

Biomedical Technology↗
PubMed2005

Conformation of microcontact-printed proteins by atomic force microscopy molecular sizing.

We investigated the structural changes occurring in proteins patterned via microcontact printing. This was done by molecular sizing using atomic force microscopy to observe the structure of printed individual metalloprotein molecules in the unlabeled and untreated states. We observed that the size of the printed proteins were more than 2-fold smaller than the native shape, which indicates that some deformations take place upon the contact-assisted adsorption on silanized silicon dioxide. This can be attributed to simultaneously occurring effects, and particularly to the sandwiching between surfaces of very different hydrophilic/hydrophobic properties during contact lithography.

Adsorption↗
PubMed2003

Relationship between the local stiffness of the outer hair cell along the cell axis and its ultrastructure observed by atomic force microscopy.

As electromotility may arise from a conformational change of the molecules' 'protein motors', which might be distributed along the outer hair cell (OHC) lateral wall, the force generated by the OHC electromotility would be related not only to the conformational change of the protein motors but also to the mechanical properties of the lateral wall. Therefore, a detailed understanding of the mechanical properties of the OHC lateral wall is important. In our previous reports, to understand the difference in the stiffness along the cell axis, the local deformation of the OHC in response to hypotonic stimulation was analyzed by measuring the displacement of microspheres attached randomly to the cell lateral wall, and the distribution of Young's modulus along the cell axis was obtained using the contact mode of an atomic force microscope (AFM). These investigations revealed that the stiffness of the cell in the apical region was greater than that in other regions where the stiffness is constant. In this study, the ultrastructure of the OHC lateral wall was investigated with the oscillation imaging mode of the AFM (Tapping Mode), and the relationship between the stiffness along the cell axis and the ultrastructure that was observed by the AFM imaging was analyzed. From the analysis, it was concluded that the circumferential filaments observed in the tapping mode AFM are actins which are part of the cortical lattice, and that the difference between the intervals of the circumferential filaments in the apical region and those in other regions is one factor that causes the high stiffness in the apical region.

Actin Cytoskeleton↗
PubMed1995

Atomic force microscopy of cholera toxin B-oligomers bound to bilayers of biologically relevant lipids.

Cholera toxin B-oligomer was imaged by atomic force microscopy (AFM) on biologically relevant model membranes, such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and egg yolk phosphatidylcholine at room temperature in solution at a resolution in the range of 1 to 2 nm. In addition, two-dimensional arrays were grown directly on these model membranes without any special treatment, and were also imaged by AFM. These results demonstrate the ability of AFM for imaging membrane proteins at high resolution without the need of chemical cross-linking, either within the membrane or to the substratum.

Cholera Toxin↗
PubMedDate not supplied

Nanotribological effects of silicone type, silicone deposition level, and surfactant type on human hair using atomic force microscopy.

The atomic/friction force microscope (AFM/FFM) has recently become an important tool for studying the micro/nanoscale structure and tribological properties of human hair. Of particular interest to hair and beauty care science is how common hair-care materials, such as conditioner, deposit onto and change hair's tribological properties, since these properties are closely tied to product performance. Since a conditioner is a complex network of many different ingredients (including silicones for lubrication and cationic surfactants for static control and gel network formulation), studying the effects of these individual components can give insight into the significance each has on hair properties. In this study, AFM/FFM is used to conduct nanotribological studies of surface roughness, friction force, and adhesive forces as a function of silicone type, silicone deposition level, and cationic surfactant type. Changes in the coefficient of friction as a result of soaking hair in de-ionized water are also discussed.

Adhesiveness↗
PubMed2001

Visualizing detergent resistant domains in model membranes with atomic force microscopy.

Evidence is accumulating that in cell membranes microdomains exist, also referred to as rafts or detergent resistant membranes. In this study, atomic force microscopy is used to study supported lipid bilayers, consisting of a fluid phosphatidylcholine, sphingomyelin and cholesterol. Domains were visualized of which the morphology and size depended on the cholesterol concentration. The presence of cholesterol was found to induce bilayer coupling. At 30 mol% cholesterol, a change in percolation phase was observed, and at 50 mol%, when both fluid lipids and solid lipids are saturated with cholesterol, phase separation was still observed. In addition, we were able to directly visualize the resistance of domains against non-ionic detergent.

Animals↗
PubMed2002

Characterization of Gorleben groundwater colloids by atomic force microscopy.

Groundwater colloids from the Gorleben site (Lower Saxony, Germany) are characterized in the presence of Eu(III) by tapping-mode atomic force microscopy (AFM) with phase contrast imaging. Using a liquid cell the method allows investigations of samples being in contact with aqueous solution. This ensures that complex structures are kept in their native hydrated state. Different types of colloids and aggregates are found by AFM, e.g., spherical particles, fibrous structures, and structures which appear to be hollow. A partial coating of the edges of clay particles with humic colloids can be assumed from phase contrast images. Therefore, aquatic colloids and their aggregates found in Gorleben groundwater can be characterized as a complex mixture of components, which may influence the migration of groundwater contaminants in different processes.

Colloids↗