ChEBE Faculty Research
Laurence Brewer, Ph.D.
Single Molecule Force Spectroscopy
Laser Optical TrapThis figure (from Methods in Cell Biology, “Laser Tweezers in Cell Biology”, Michael Sheetz editor, Academic Press, 1998, pg. 3) shows the axial and lateral restoring forces caused by the refraction of light rays through a polystyrene sphere in water as the center of the sphere is displaced from the focus of the laser beam. The scattering forces due to the reflection of light from the surface of the sphere have been neglected.
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Force Measurement Using An Optical TrapThe first order restoring forces on the sphere held by the trap (shown in the previous figure) are linear with the distance the bead is displaced from the center of the trap. In this sense the sphere functions much like it is attached to a spring. Once the “spring constant” k is determined the force on the bead can be measured.
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Single Molecule Force SpectroscopyA single DNA molecule with one micrometer beads attached to both ends is moved via dual laser traps (orange) from one side of the flow cell into the side containing protamine. The optical traps serve as sensitive force transducers that allow one to measure DNA tensions with pN sensitivity.
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