Model Developed To Describe Polymer Passing Through Nanopore Process

In 1994 and 1996 two papers were released both on the topic of polymers transporting through nanopores. Since then the quite niche filed has been very active with over forty different theoretical and experimental papers being written on the subject. This is because the concept of a large chemical chain fitting through an enclosed space has acute relevance in biology as well as medicine. Almost all of these studies have been based on using an electric field to drive the movement of the polymers. A break through was made with the development of the tension propagation theory. This is where the driving force acting towards the trans side of the membrane causes mechanical tension to develop in the polymer. This produces mobile and immobile parts of the polymer as some parts are acting under the force and some have yet to experience it, see the diagram below:

Figure 1
Diagram of tension propagation taken from the paper of interest itself. The blue dotted line is the tension front; the inequality is to show that the strong stretching regime applies; and the value of l+s is the number of polymer components, called beads, which have experienced the tension.

Later this theory was improved with aspects like pore friction and thermal fluctuations being taken into account. One of the assumptions made in these theories is that the friction from the trans side of the membrane can be ignored, a fact only true if the polymers are fully flexible. This is not true in many practical examples such as DNA strands have a persistence length (distance that thermal fluctuations require to bend it) of 500 angstroms. As a result this study has modelled the behaviour of semi flexible polymers with assigned persistence lengths. It was found that when the inflexibility was calculated and the resultant friction factored in; the current theories predicting the process remained accurate with good correlation with the already collected experimental data.

Paper links: Driven translocation of a semi-flexible polymer through a nanopore


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