Direct Measurement of the Transport Properties of a Single DNA Molecule

A fluorescently labeled DNA molecule is end tethered to a small magnetic bead and pulled by a calibrated magnetic force through a solution of unlabeled DNA molecules to monitor the transport coefficients of the chain. From the force velocity diagram $F-V$, we report the first direct measurement of the friction coefficient $\zeta =F/V$ of a single DNA molecule. $\zeta$ is found to be highly velocity dependent due to sharp conformational transitions for increasing velocities in agreement with a recent model by Ajdari et al. [Physica (Amsterdam) 204A, 17 (1994)].