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Results for “atomic force microscopy”

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At least 703 records · Page 39Linked to original sources
PubMed2001

Comparative studies of bacteria with an atomic force microscopy operating in different modes.

Escherichia coli bacterial cells of two strains JM109 and K12 J62 were imaged with atomic force microscopy (AFM) in different environmental conditions. The AFM results show that the two strains have considerable difference in the surface morphology. At the same time after rehydration both strains show the loss of the topographic features and increase in lateral and vertical dimensions. Results obtained in different AFM modes (contact, tapping, MAC) were compared. Imaging in culture medium was applied for direct observation of the surface degradation effect of lysozyme. The treatment of the cells with the enzyme in the culture medium lead to the loss of surface rigidity and eventually to dramatic changes of the bacteria shape.

Air Microbiology↗
PubMed1998

Tapping mode atomic force microscopy of hyaluronan: extended and intramolecularly interacting chains.

The extracellular matrix polysaccharide hyaluronan has been examined by tapping mode atomic force microscopy. High molecular weight hyaluronan was deposited on mica from dilute aqueous solution and imaged in air. Long unbranched chains could be observed and were found to be compatible with the known covalent structure of hyaluronan. In addition, chains with evidence of intramolecular association were observed. In the simplest cases, the association took the form of loops stabilized by antiparallel double-stranded (probably double-helical) segments. In other cases, the polarity of the associated regions could not be determined. Extensive intramolecular association in long hyaluronan chains resulted in a fenestrated structure of the same type as that formed by intermolecular association at higher concentrations.

Animals↗
PubMedDate not supplied

Atomic force microscopy of liposomes bearing fibrinogen.

Extruded liposomes formed from dipalmitoylphosphatidylcholine and cholesterol, with and without fibrinogen, were examined by atomic force microscopy (AFM). The sequence of events involved in the transition from attached liposomes to bilayer patches on mica supports was viewed by tapping mode in liquid. After adhesion to the mica surface, both liposomes without fibrinogen and liposomes with attached fibrinogen collapsed into patches. The fibrinogen layer attached to the liposomes was 2.6 nm thick. This implied that the protein was spread over the entire liposome and the protein characteristic trinodular structure disappeared. To check the type of bond between fibrinogen and liposome, sequential images were taken after the incubation of fibrinogen with liposomes with and without a chemical group for attaching the protein. The results clearly confirmed that fibrinogen bound covalently to liposomes.

Fibrinogen↗
PubMed2006

SEBS aggregate patterning at a surface studied by atomic force microscopy.

The morphologies of films spin coated from dilute block copolymer solution onto a mica substrate were studied by atomic force microscopy (AFM). Variables of interest were the polymer concentration, solvent, heating temperature, aging, and ultrasonic effect. It is shown that the solution concentration is the predominant factor in determining the shape of the aggregates displayed from spheres and rods to irregular patches with increasing concentration. The solubility parameter of the solvent plays an important role in modifying the distribution and the size of clusters at the surface. The structures of the aggregates at the surface are metastable, which could evolve with temperature from rodlike aggregates into regular stripes when annealed at a temperature higher than the order-disorder transition temperature of SEBS, whereas those in solution could evolve with aging and ultrasonic treatment into a more stable network structure.

Aluminum Silicates↗
PubMedDate not supplied

Cooperativity and intermediate structures of single-stranded DNA binding-assisted RecA-single-stranded DNA complex formation studied by atomic force microscopy.

The formation of a complex between RecA protein and single-stranded (ss) DNA was studied systematically by atomic force microscopy (AFM) by varying incubation time and the molecular ratio of RecA protein to single-stranded DNA binding (SSB) protein. New intermediate structures, such as small circular, tangled, and protruded structures in the absence of SSB and sharply turned structures in the presence of SSB, were clearly identified at the early stage of complex formation. These structures have probably resulted from competitive binding of RecA and SSB to DNA. After long incubation, only fully covered RecA-ssDNA and totally RecA-free SSB-ssDNA complexes were present regardless of RecA concentrations. Together with intermediate structures which consisted of only two parts, that is, ssDNA covered by SSB and by RecA proteins, the observation suggested strong neighbor cooperative binding of RecA to ssDNA assisted by SSB.

Allosteric Regulation↗
PubMed1996

Conformational change of the hexagonally packed intermediate layer of Deinococcus radiodurans monitored by atomic force microscopy.

Both surfaces of the hexagonally packed intermediate (HPI) layer of Deinococcus radiodurans were imaged in buffer solution by atomic force microscopy. When adsorbed to freshly cleaved mica, the hydrophilic outer surface of the HPI layer was attached to the substrate and the hydrophobic inner surface was exposed to the stylus. The height of a single HPI layer was 7.0 nm, while overlapping edges of adjacent single layers adsorbed to mica had a height of 14.7 nm. However, double-layered stacks with inner surfaces facing each other exhibited a height of 17.4 nm. These stacks exposed the outer surface to the stylus. The different heights of overlapping layers and stacks are attributed to differences in the interaction between inner and outer surfaces. At high resolution, the inner surface revealed a protruding core with a central pore connected by six emanating arms. The pores exhibited two conformations, one with and the other without a central plug. Individual pores were observed to switch from one state to the other.

Bacterial Proteins↗
PubMed2005

Refractive index of thin, aqueous films between hydrophobic surfaces studied using evanescent wave atomic force microscopy.

We have studied the refractive index of a thin aqueous film between microscopic hydrophobic surfaces using evanescent wave atomic force microscopy (EW-AFM). An evanescent wave, generated at a solid-liquid interface, is scattered by AFM tips or glass particles attached to AFM cantilevers. The scattering of this wave is used to determine the refractive index as a function of separation between these surfaces. Measurements were performed on surfaces that were rendered hydrophobic with octadecyltrichlorosilane, which produces solid-water contact angles in excess of 90 degrees. For AFM tips, the average refractive index in the thin film was always equal to that of water when the film was thicker than approximately 100 nm. At smaller separations, the refractive index was always greater than or equal to that of water. This is inconsistent with the formation of air or vapor films and consistent with a small amount of organic material between the surfaces. For colloidal spheres (R approximately 10 microm), we were not able to detect changes in the refractive index of the thin film between the sphere and plate.

Microscopy, Atomic Force↗
PubMed2005

Application of atomic force microscopy in blood research.

AIM: To find suitable solutions having lesser granules and keeping erythrocytes in normal shapes under atomic force microscopy (AFM). METHODS: Eight kinds of solutions, 1% formaldehyde, PBS buffer (pH7.2), citrate buffer (pH 6.0), 0.9% NaCl, 5% dextrose, TAE, 1640 medium and 5% EDTA-K2, were selected from commonly used laboratory solutions, and venous blood from a healthy human volunteer was drawn and anticoagulated with EDTA-K2. Before scanned by AFM (NanoScopeIIIa SPM, Digital Instruments, Santa Barbara, CA), a kind of intermixture was deposited on freshly cleaved mica and then dried in the constant temperature cabinet (37 degrees). RESULTS: One percent formaldehyde, citrate buffer, 5% dextrose, TAE, were found to keep human erythrocytes in normal shape with few particles. Processed by these solutions, fine structures of human erythrocyte membrane were obtained. CONCLUSION: One percent formaldehyde, citrate buffer, 5% dextrose and TAE may be applied to dispose erythrocytes in AFM. The results may offer meaningful data for clinical diagnosis of blood by AFM.

Buffers↗
PubMed2004

Study on biological effect of La3+ on Escherichia coli by atomic force microscopy.

The biological effects of rare-earth metal ions on the organism have been studied using La3+ as a probe ion and Escherichia coli cell as a target organism. Atomic force microscopy (AFM) studies reveal that La3+ substantially changes the structure of the outer cell membrane responsible for the cell permeability. Significant damages of the outer cell membrane are observed using scanning electron microscopy (SEM) after the introduction of La3+. In result, the cell becomes easily attacked by lysozyme. Moreover, inductively coupled plasma-mass spectrometry (ICP-MS) measurements show considerable amount of Ca2+ and Mg2+ in the supernatant from the La3+ exposed cells. It is proposed that La3+ can replace Ca2+ from the binding sites because of their close ionic radii and similar ligand specificities. Lipopolysaccharide (LPS), which forms the outer membrane of Gram-negative bacteria, could not serve as the cellular envelope steadily after Ca2+ and Mg2+ released from their binding sites on the LPS patches.

Calcium↗
PubMed2001

Direct measurement of conformational changes on DNA molecule intercalating with a fluorescence dye in an electrophoretic buffer solution by means of atomic force microscopy.

By means of atomic force microscopy (AFM), we performed the direct imaging of DNA molecules (200, 500, 1000 bp) in a Tris-borate buffer solution, and measured the contour length and the end-to-end distance of DNA. Processing the data according to the worm-like chain model, we calculated the persistence length of the double-stranded DNA. Based on the analysis of the contour length and the persistence length, we discussed the interactions between DNA and an intercalating fluorescence dye (YO-PRO-1). YO-PRO-1 stacks between the base pairs and extends the contour length of DNA, changing the electric charge and the persistence length of DNA. From AFM measurement, we investigated directly the relationship between the persistence length and the number of the YO-PRO-1 intercalating to DNA. We will discuss on the relationship between the effect of an intercalating dye on the electrophoretic behavior and the conformational changes of DNA with an intercalating dye.

Benzoxazoles↗
PubMed2005

Organization of polyhydroxyalkanoate synthase for in vitro polymerization as revealed by atomic force microscopy.

Individual polyhydroxyalkanoate synthase molecules from Ralstonia eutropha (PhaCRe) were directly visualized on highly oriented pyrolytic graphite (HOPG) by atomic force microscopy (AFM). PhaCRe molecule was observed as a spherical particle of 2.9 +/- 0.4 nm in height and 28 +/- 4 nm in width. In vitro polymerization reaction on HOPG was carried out for 5 min by reacting the PhaCRe molecules with (R)-3-hydroxybutyryl-CoA monomers. The reaction product was then observed after the removal of water solution. Several PhaCRe molecules associated with each other to form an assembly, which was attached to a fibrillar structure of ca. 0.2-0.3 nm in height. The fibrillar structure that elongated from the PhaCRe assembly was interpreted as the poly[(R)-3-hydroxybutyrate] polymer chain. High resolution AFM suggested that the PhaCRe assembly was composed of 3-4 subunits of PhaCRe molecules. This was further supported by SDS-PAGE analysis of the cross-linked PhaCRe enzyme. These results suggest that more than two subunits of PhaCRe are necessary for the in vitro polymerization of PHB molecular chains.

Acyltransferases↗
PubMed2005

Quantification of the kinetics and thermodynamics of protein adsorption using atomic force microscopy.

Both in situ and ex situ methods for quantifying area fraction coverage of protein on a surface using atomic force microscopy were developed. The in situ method used a continuous fluid flow system to observe the kinetics of adsorption in real time. The ex situ method required immersing the sample in solution, drying the sample, and imaging in an ambient environment to obtain kinetic and isothermal data. These methods were developed using the plasma protein fibrinogen in a phosphate-buffered saline solution on grade IV muscovite mica and highly ordered pyrolytic graphite (HOPG) substrates. Kinetic and quasiisothermal data were obtained and a Langmuir model was fit to the data. An adsorption rate constant of 2.2 x 10(-4) mL . microg(-1)s(-1) and a desorption rate constant of 8.3 x 10(-5) s(-1) were found on an HOPG surface. Completely irreversible adsorption was found on the mica surface with an adsorption rate constant of 2.7 x 10(-4) mL . microg(-1)s(-1). Additionally, protein conformation and assembly orientation on these surfaces were documented where fibrinogen on HOPG formed a network-like structure, whereas fibrinogen on mica was more random. Also, nano-topographical factors (ledges) were seen as sites of preferential adsorption.

Aluminum Silicates↗