Translocation of a heterogeneous polymer
Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA.The Journal of Chemical Physics (Impact Factor: 2.95). 08/2012; 137(6):064904. DOI: 10.1063/1.4742970
We present results on the sequence dependence of translocation kinetics for a partially charged heteropolymer moving through a very thin pore using theoretical tools and Langevin dynamics simulational techniques. The chain is composed of two types of monomers of differing frictional interaction with the pore and charge. We present exact analytical expressions for passage probability, mean first passage time, and mean successful passage times for both reflecting/absorbing and absorbing/absorbing boundary conditions, showing rich and unexpected dependence of translocation behavior on charge fraction, distribution along the chain, and electric field configuration. We find excellent qualitative and good quantitative agreement between theoretical and simulation results. Surprisingly, there emerges a threshold charge fraction of a diblock copolymer beyond which the success rate of translocation is independent of charge fraction. Also, the mean successful translocation time of a diblock copolymer displays non-monotonic behavior with increasing length of the charged block; there is an optimum length of the charged block where the mean translocation rate is the slowest; and there can be a substantial range of higher charge fractions which make the translocation slower than even a minimally charged chain. Additionally, we find for a fixed total charge on the chain, finer distribution along the backbone significantly decreases mean translocation time.
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ABSTRACT: Polymer translocation into adsorbing nanopores is studied by using the Fokker-Planck equation of chain diffusion along the energy landscape calculated with Monte Carlo simulations using the incremental gauge cell method. The free energy profile of a translocating chain was found by combining two independent sub-chains, one free but tethered to a hard wall, and the other tethered inside an adsorbing pore. Translocation dynamics were revealed by application of the Fokker-Planck equation for normal diffusion. Adsorption of polymer chains into nanopores involves a competition of attractive adsorption and repulsive steric hindrance contributions to the free energy. Translocation times fell into two regimes depending on the strength of the adsorbing pore. In addition, we found a non-monotonic dependence of translocation times with increasing adsorption strength, with sharp peak associated with local free energy minima along the translocation coordinate.
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ABSTRACT: A study was conducted to demonstrate disease detection and management through single nanopore-based sensors. The goal of the study was to mimic the general principle of analyte detection by channels and refine it with a simpler measurement design. Investigations revealed that the interaction of a single analyte and the channel pore caused relatively long-lived conductance changes. It was assumed that the analyte reduced the conductance, but it was conceivable that a charged analyte bound to the pore mouth and modulated the conductance up or down by a field effect. Increasing the analyte concentration was found to increase the frequency of analyte-induced conductance changes and the mean time the pore was occupied by the analyte. The analyte concentration was measured directly from the mean channel current, assuming that the reaction stoichiometry was 1:1.
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