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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

difficult to imagine a physical mechanism by which mass would be the decisive molecular property determining the depth of block. Here, we show that it is, indeed, possible to achieve high-fidelity discrimination between leucine or isoleucine (MW=131 g/mol) linked to the C-terminus of a heptarginine carrier. We show that single-passage discrimination between these two isomers can be made to exceed 95% using optimized low-noise recording conditions and careful analysis of the complex resistive pulses characteristic of the aerolysin pore. Notably, we identify a low-frequency component of added current noise as the limiting factor in peptide discrimination and show that this may be significantly reduced by substitution of NO3-for Cl-in the recording electrolyte. (1)

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.