(119a) Single Molecule Lamda-DNA Stretching Studied by Microfluidics and Single Particle Tracking

DNA stretching has been an intensively studied topic due to its involvement in the cellular functions. In this work, we studied DNA stretching based on microfluidics and single particle tracking techniques. Microfluidics generates well-defined flow field within microscale channels and potentially allows the incorporation of chemical and biological assays with the single molecule experiments. Single DNA molecules were tethered to the channel bottom (glass) at one end and to fluorescent microbeads at the other end. The microscale flow exerted hydrodynamic force on the microbead with a magnitude dependent on the flow rate. The force-extension curves of the single DNA molecules were obtained by localizing the fluorescent microbead with nanometer precision at different flow rates. We were able to obtain DNA force-extension curves which fit the worm-like chain model very well. Furthermore, we also observed plateaus at low forces (15~30 pN) in these curves when the hydrodynamic force was kept constant for a duration of 10 seconds at each flow rate. This indicates that stretching force with long duration may lower the activation barrier for the conformational changes of a dsDNA molecule. We expect that this approach will be useful for studying the force associated with biological events involving single DNA molecules in general.