Force spectroscopy analysis in polymer translocation

This paper reports the force spectroscopy analysis of a polymer that translocates from one side of a membrane to the other side through an extended pore, pulled by a cantilever that moves with constant velocity against the damping and the potential barrier generated by the reaction of the membrane walls. The polymer is modeled as a beads-springs chain with both excluded volume and bending contributions and moves in a stochastic three-dimensional environment described by a Langevin dynamics at fixed temperature. The force trajectories recorded at different velocities reveal two exponential regimes: The force increases when the first part of the chain enters the pore and then decreases when the first monomer reaches the trans region. The spectroscopy analysis of the force values permit the estimation of the limit force to allow the translocation, related to the free-energy barrier. The stall force to maintain the polymer fixed has been also calculated independently, and its value confirms the force spectroscopy outcomes.