REU student James Kath, under the supervision of Professor John Marko has constructed a magnetic tweezer system which allows force-extension and twisting experiments to be carried out on single DNA molecules. The primary application of this instrument will be to the study of protein-DNA interactions.
This system uses a 100X microscope objective to image beads of size between 0.5 and 3 microns using reflection microscopy. The use of objective (reflective) illumination permits magnets to be positioned close to the other side of the sample without causing problems for imaging, allowing a simple instrument design. The objective is mounted on a piezoelectric positioner to allow one to hold “surface beads” in fixed focus, and to monitor the position of DNA-tethered beads.
Preliminary studies have verified that the new instrument can carry out rapid acquisition of extensions of DNA molecules, via particle-tracking and out-of-focus bead image analysis. This simple instrument can monitor motions of paramagnetic colloidal particles attached to DNA molecules in three dimensions.
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