Elucidating the Dynamics of Polymer Transport through Nanopores using Asymmetric Salt Concentrations



While notable progress has been made in recent years both experimentally and theoretically in understanding the highly complex dynamics of polymer capture and transport through nanopores, there remains significant disagreement between experimental observation and theoretical prediction that needs to be resolved. Asymmetric salt concentrations, where the concentrations of ions on each side of the membrane are different, can be used to enhance capture rates and prolong translocation times of polymers translocating through a nanopore from the low salt concentration reservoir, which are both attractive features for single-molecule analysis. However, since asymmetric salt concentrations affect the electrophoretic pull inside and outside the pore differently, it also offers a useful control parameter to elucidate the otherwise inseparable physics of the capture and translocation process. In this work, we attempt to paint a complete picture of the dynamics of polymer capture and translocation in both symmetric and asymmetric salt concentration conditions by reporting the dependence of multiple translocation metrics on voltage, polymer length, and salt concentration gradient. Using asymmetric salt concentration conditions, we experimentally observe the predictions of tension propagation theory and verify the significant impact of the electric field gradient on pre-stretching polymers on approach to the pore.


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Supplementary material

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Supporting Information Document
Additional information regarding the three-resistor model and its resulting conductance, potential and electric fields in ASC conditions, the non-linearity of salt-concentration and conductivity, the regime-dependent capture enhancement viewed through the dependence of capture rate on salt gradients if linear DNA and DNA nanostructures, the different fits of translocation time and DNA length scaling, the mechanisms responsible for translocation time modulation, the DNA-length dependence of higher order translocation time statistics, the folding statistics, IV stabilization when going from SSC to ASC conditions, and regarding the methods for extracting the standard deviation of translocation times