The translocation of a polymer through a nanopore with sandglass-like geometry

In recent years, non-uniformly geometrical nanopores, such as conical nanopores, have gained significant attention in nanopore sensing technology due to their advantages in analyte manipulation and clear output signals. This paper focuses on the polymer translocation through a sandglass-like nanopore, characterized by a double-conical geometry with a tip at the middle. We systematically investigate the effects of pore geometry on the translocation dynamics through computational simulations and theoretical analyses. The polymer translocation process is divided into three stages: approaching, threading, escaping, corresponding to the movement from the entry to the tip, through the tip, and from the tip to the exit, respectively. Our findings reveal that the duration of the approaching stage highly depends on the polymer conformations, while the durations of the threading and escaping stages are primarily influenced by the driving force associated with the pore geometry and the accompanying free energy change. Additionally, we report a relationship between the threading speed of the polymer at the tip and the combination of the driving force there and the free energy change during the threading stage.