Capture and Translocation of Nucleic Acids into Sub-5 nm Solid-State Nanopores - Nanopores: Sensing and Fundamental Biological Interactions - page 236

Fig. 10.4 Ion-current trace through a 4 nm pore, where two DNA translocation events are
observed. The transport time of the molecule is denoted as t D , whereas the time-delay between
two successive events is denoted as dt . Reproduced with permission from Wanunu et al. [ 50 ],

Copyright Nature Publishing Group

Fig. 10.5 Normalized
capture rate distributions of
2,000 bp DNA as a function
of the cis chamber KCl
concentration as indicated
([KCl] trans 1 M for all

cases). Reproduced with
permission from Wanunu
et al. [ 50 ], Copyright Nature
Publishing Group

¼

events were acquired and the distributions of their dt values evaluated. Due to the

stochastic nature of the capture process, as long as the DNA sample is sufficiently
dilute, these distributions should obey single-exponential decays, from which the
slope R c can be taken as the mean capture rate. Figure 10.5 displays a typical semi-
log time-delay distribution measured for 2,000 bp DNA, where the KCl concentra-
tion in the trans chamber was kept at 1 M, and the cis chamber KCl concentrations
were decreased to the indicated concentrations. For both symmetric and asymmetric
salt gradients, we find that the capture rate scales linearly with DNA bulk concentra-
tion, c , as shown in Fig. 10.6 [ 50 ].
The dependence of the specific capture rate on DNA length using a 4 nm solid-
state nanopore at an applied voltage of 300 mV is displayed in Fig. 10.7 . The data
clearly show two behavior regimes: For DNA molecules in the range
~400-8,000 bp, the capture rate per nM of DNA molecules increases with N ,
whereas for molecules longer than ~8,000 bp the capture rate is nearly independent
of length [ 50 ]. These results support the hypothesis that for N<

8 ; 000 bp the capture