We report a method to optically trap and micromanipulate metallic particles using IR laser. The experiment demonstrates
the trapping of metallic particle using low NA objective lens (0.6 N.A). Unlike single beam gradient trapping of
dielectric objects, the optical trapping of metallic particles occurs due to diffraction effect. We thus provide evidence for
non-gradient forces playing a dominant role in the trapping of metallic particles, in here for the case of 3μm Fe particles,
efficient trapping occurs at off-axis position (in the side lobes) of a focused laser beam. The optical trap is characterized
by measuring the external magnetic field required to dislodge the Fe particle, and was found to be 0.03T to 0.11T for
laser power 5 to 55mW at the sample.
The composition of the cell membrane and the surrounding physiological factors determine the nature and dynamics of
membrane-cytoskeleton coupling. Mechanical strength of a cell is mainly derived from such coupling. In this article, we
investigate the effect of extra cellular cholesterol on the membrane-cytoskelaton connectivity of single cell endothelium
and consequent remodeling of its mechanical properties. Using optical tweezers as a force probe, we have measured
membrane stiffness (km), membrane microviscosity (ηeff ) and the two-dimensional shear modulus (G′(f)) as a function of
extracellular cholesterol in the range of 0.1mM to 6mM. We find that membrane stiffness and shear modulus are
dependent on cholesterol-induced membrane-cytoskeletal organization. Further, by disrupting the membranecytoskeletal
connectivity with Cytochalasin D, an actin delpolymerizing molecule, we recover pure membrane behaviour
devoid of any cytoskeleton attachment. However, behaviour of ηeff was found to be unaffected by disruption of
membrane-cytoskeleton organization. We infer that cholesterol is playing a distinct role in modulating membrane
organization and membrane-cytoskeleton connectivity independently. We further discuss implications of our approach
in characterizing cellular mechanics.
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