Capture and Translocation of Nucleic Acids into Sub-5 nm Solid-State Nanopores - Nanopores: Sensing and Fundamental Biological Interactions - page 243

(3) The mean values of t D are nearly two orders of magnitude longer for the 4 nm
pore, suggesting that the DNA experiences slower translocation through the smaller
pores.
The last feature is of great interest for nanopore applications in DNA analysis:
while in the 8 nm pore the transport timescales approach the minimum measurable
dwell time allowed by the electrical bandwidth, in the 4 nm case, the longer dwell
times results in significantly larger total ion current flux during DNA transport, and a
proportional reduction in the measurements' shot noise [ 49 ]. This section is divided
into several parts: First, we discuss the nature of the dwell-time distribution shapes
obtained for DNA translocation through sub-5 nm pores. We then discuss in more
detail the effect of pore size, applied voltage, and temperature on the DNA transport
times. Finally, we examine some possible explanations for the observed dynamics,
and conclude with the effect of salt concentration on the transport dynamics.

10.3.1 Transport Time Distributions: The Effect
of DNA-Pore Interactions on the Distribution Shape

DNA translocation through nanopores has been a subject of numerous theoretical
studies. Lubensky and Nelson have predicted for transport of single-stranded DNA
through 1.5 nm protein pores that the first-passage time distribution, or the probabil-
ity density function for polymer translocation, is given by a non-Gaussian form for a
strongly interacting pore [ 29 ]. This form is characterized by a peak at short times
(the most probable translocation time) and a tail for longer times (Fig. 10.12a ).

Fig. 10.12 (a) Analytically-derived first-passage dwell-time distribution ( t ) (dimensioned by

L/v ) for a polymer of length L (time axis is re-dimensioned by v/L ) translocating through a small
pore ( solid line ), and a Gaussian distribution ( dashed line ) with the same mean and variance for
comparison. (Reprinted from Lubensky and Nelson [ 29 ], copyright 1999, with permission from
Elsevier.) (b) Simulated dwell-time distributions for a polymer translocating through a pore ( solid
line ), at different values of polymer-pore interactions (

c

e pm ). (Reproduced with permission from
Luo et al. [ 30 ], Copyright (2007) by the American Physical Society)