Development of Single-Molecule Force and Torque Measurement with Application to Nucleosome Disruption

Abstract

Single-molecule force spectroscopy is a powerful method in biophysical research. The ability of detecting and manipulating single molecule finds applications in studies from DNA to cell, leads to various mechanism-based results. Among many tools in this field, optical traps is suitable for studies involving nucleic acids and its interaction with protein due to the high temporal and spatial resolution. While most experiments characterize force and displacement, the quest for manipulating and detecting torque and angular motion is increasing due to their significant role in many biological processes. This thesis mainly devotes to the development and application of an optical torque wrench which is capable of simultaneously controlling and measuring force, displacement, torque, and angular displacement of a single bio-molecule. First, angular manipulation of oblate polystyrene particles is demonstrated. Moreover, a new method for fabricating birefringent nanocylinders via nanosphere lithography is presented. Both particles are shown to provide stable angular trapping in a home-built optical torque wrench. We then apply them in measuring a single DNA molecule under force and torque. Mechanical stability of nucleosome under tension and torsion is also studied, followed by a theoretical model to elucidate the importance of torsion in such experiments. Finally, the effect of experimental parameters in a surface-based optical traps on measured kinetics of bio-molecule is detailed.