1,232 research outputs found
On the measurement of weak repulsive and frictional colloidal forces by reflection interference contrast microscopy
terference contrast (RIC) microscopy in combination with real-time image processing. The temporal
fluctuations of the absolute sphere-to-substrate distance are determined from changes of interference
fringe pattern (Newtonian rings). Both the shape about its minimum and the absolute minimum equilibrium
distance of the interaction potential can be obtained by analyzing the distribution of distances
in terms of a Boltzmann distribution. The timeautocorrelation function of distances yields the
hydrodynamic friction. The method has been applied to the interaction of latex spheres with glass substrates
in salt solutions of different ionic strength. The results correspond to classical electrostatic double layer
theory that leads to a characteristic dependence of the mean separation distance and the mean square
displacement on the radius of the spheres. The hydrodynamic friction close to a wall exhibits the predicted
inverse proportionality to the sphere-wall distance. It is demonstrated that the method can be applied
to study the interaction between biologically relevant objects such as giant vesicles with bilayer covered
substrates
Imaging optical thicknesses and separation distances of phospholipid vesicles at solid surfaces
We present the application of reflection interference contrast microscopy (RICM) (1) to map the optical density of supported bilayers and vesicles and (2) to image the contact profile of phospholipid vesicles at surfaces. The resolution in the surface profile is 0.2 m laterally and 1 nm out of plane. The optical thickness of the membrane can be determined with 0.2 nm accuracy. We outline the theoretical basis of RICM and derive the interference intensities of adhering vesicles from first principles. An analytical expression for the decaying contrast of the intrference fringes is given. The contact contour of vesicles is determined for various substrates. We further demonstrate that deposition of a magnesium fluoride layer on the glass substrate enhances the contrast and allows the optical density of adsorbed membranes to be imaged. By contrast variation of the buffer solution, the layer thicknesses and the indices of refraction can be measured. The novel method was applied to image lipid domains of different chain lengths in a substrate supported monolayer
Dynamic Light Scattering from Semidilute Actin Solutions: A Study of Hydrodynamic Screening, Filament Bending Stiffness and the Effect of Tropomyosin/Troponin-Binding
Quasi-elastic light scattering (QELS) is applied to investigate the effect of
the tropomyosin/troponin complex (Tm/Tn) on the stiffness of actin filaments.
The importance of hydrodynamic screening in semidilute solutions is
demonstrated. A new concentration dependent expression for the dynamic
structure factor of semiflexible polymers in semidilute solutions
is used to analyze the experimental QELS data. A concentration independent
value for the bending modulus is thus obtained. It increases by 50\%
as a consequence of Tm/Tn binding in a 7:1:1 molar ratio of actin/Tm/Tn. In
addition a new expression for the initial slope of the dynamic structure factor
of a semiflexible polymer is used to determine the effective hydrodynamic
diameter of the actin filament. Our results confirm the general relevance of
the concept of (intrinsic) semiflexibility to polymer dynamics.Comment: 9 pages, RevTeX, 9 figures, all uuencoded gzipe
On Shape Transformations and Shape Fluctuations of Cellular Compartments and Vesicles
We discuss the shape formation and shape transitions of simple bilayer vesicles in context with their role in biology. In the first part several classes of shape changes of vesicles of one lipid component are described and it is shown that these can be explained in terms of the bending energy concept in particular augmented by the bilayer coupling hypothesis. In the second
part shape changes and vesicle fission of vesicles composed of membranes of lipid mixtures are reported. These are explained in terms of coupling between local curvature and phase separation
Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule-actin crosstalk
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule-actin crosstalk
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule-actin crosstalk
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule-actin crosstalk
FWN – Publicaties zonder aanstelling Universiteit Leide
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