Figure 3 presents the scatter plots of the event residence time t d versus blockade current amplitude ∆I for different experiment conditions. Once a DNA strand enters the nanopore, it will block the ions in and out the nanopore and cause ionic current reduction. The amplitude of the blocked ionic current can be expressed with Kowalczyk’s

model [31], (2) where V is the applied bias voltage, and is the effective diameter of the nanopore with DNA in the pore. According to formula (2), the blocked ionic current amplitude (∆I) is linearly proportional to σ for the nanopore with the same diameter. Therefore, the amplitude of the blockade ionic current for DNA translocation through the nanopore in MgCl2 solution is expected to

be larger than that in the KCl buy BGB324 solution with the same molar concentration because the former has a high electrolytic conductivity. Unfortunately, Trichostatin A purchase the results as shown in Figure 3 do not meet such prediction. The 20-nm diameter nanopore produced a little difference in the amplitude of the blocked ionic current in the three salt solutions (1 M KCl, 0.5 M KCl + 0.5 M MgCl2, and 1 M MgCl2). As shown in Figure 3, the red solid circle points denote the events for the 48.5 kbp λ-DNA translocation through the nanopore in 1 M KCl solution. The green solid triangle points stand for the events that occurred in 0.5 M KCl + 0.5 M MgCl2 solution, and the black open rectangle symbols stand for the events in 1 M MgCl2 solution. The three symbols almost overlap with the black open rectangle symbols which are located a little higher. This result tells us that the electrolyte conductivity is only one of the factors that affect the blockade ionic currents. Figure 3 Scatter plot of the event residence time versus its blocked ionic current amplitude. In Figure 3, some outliers we call as ‘trapped events’ have

been observed in 1 M MgCl2 experiments. Although the probability is small, the duration time of these events is 22 ms, about PLEKHB2 17 times of the other events in 1 M MgCl2 experiments. As we know, Si3N4 surface in aqueous solution at pH 8.0 is negatively charged. The correlations between Mg2+ ions on both the negatively charged DNA and the Si3N4 surface can generate a net attraction force and then help stick the DNA into the nanopore, but the phenomenon only obviously occurred for the 7-nm diameter nanopore experiments. This is because the gap between the DNA and the inner surface of the nanopore is also increased with the increasing nanopore diameter. With the increase of the gap, the net attraction force is not strong enough to stick the DNA, which leads to the trapped events unremarkable in the 22-nm diameter nanopore. From Figure 3, we find not only the blockade current amplitude and duration time but also the event point dispersion degree increase with the increasing Mg2+ ion concentration.