A Nanopore with an Internal Cavity to Selectively Translocate Polymers of a Specific Length

In the majority of experimental and simulation studies of polymer translocation through a nanopore, the scaling of the translocation time, $\tau$, with polymer length, $N$, is well described by a single exponent: $\tau \sim N^\alpha$. Hence, an increase in $N$ always yields an increase in $\tau$. I will present a nanopore geometry in which there is a large central cavity between narrow nanopores at both the $cis$ entrance and the $trans$ exit. Results from simulations of this system reveal a complex dependence of $\tau$ on $N$. Most notably, the translocation time is now non-monotonic in polymer length such that $\tau$ is a minimum for polymers of an intermediate length with both longer and shorter polymers taking a longer time to cross across the membrane. A simple yet effective model for predicting this critical length as a function of the size of the cavity and the magnitude of the external field will be presented. The pore thus can be designed to be optimized for particular lengths – with some dynamic tuning being possible by varying the strength of the external field. These results suggest new applications for nanopore-based devices such as the ability to select DNA strands of a specific length from a sample containing both shorter and longer strands.