51, as shown in the inset LDK378 in vitro of Figure 3. Figure 3 Current blockage histograms as a function of applied voltage at medium voltages. The histograms of current amplitude are normalized by fitting

with Gaussian distribution; a linear increase of the means of current amplitude as a function of voltage can be clearly visualized in the inset. The numbers of translocation events at 300, 400, 500, and 600 mV are 102, 123, 156, and 160, respectively. Based on the volume displacement of proteins in the electrolyte solution from the pore, the transient current blockage amplitude ΔI b can be written as (2) where σ is the solution conductivity, φ is the applied voltage between the electrodes, Λ is the excluded volume of a translocation molecule inside the pore, H eff is the effective length of the nanopore, d m is the diameter and l m is the length of a particle molecule, D p is the average diameter of a cylindrical nanopore, and is a correction factor that depends primarily on the relative geometry of the molecule and the pore [47, 48]. Since the spherical-shaped protein is much smaller than the large nanopore, contributes little to the current drop. Thus, ΔI b can be simplified

as ΔI b(t) ~ Λφ, implying a linear dependence of the current blockade on the biased voltage. And the excluded volume of proteins in the pore can be calculated from the current drop. Based on the equation, the estimated volume of BSA in our experiments is about 260 nm3, which is very close to that of the native BSA structure (224 nm3) selleck chemicals llc [29]. The volume change is less than 15%; thus, the unfolding of the protein destabilized by electric field forces can be ignored in the medium voltage from 300 to 600 mV, which appears in small nanopores due to the intensive electric field inside the pore [10, 18]. Meanwhile, the transition time of proteins also has been analyzed in our experiments. The current blockage duration t d is regarded as

the dwell time of a protein from the entrance to the exit of the nanopore. Majority of proteins quickly pass through the pore with less than 5 ms, typed as short-lived events. However, there is a small amount to of blockage events with a prolonged transition time of tens of milliseconds, regarded as long-lived events, which are observed for protein translocations through small nanopores [31, 32, 47]. The distribution functions of transition times at each voltage have been analyzed in the present work. As shown in Figure 4, the histogram of dwell times shows an asymmetrical distribution, fitted by an exponential model. The mean transition times at 300, 400, 500, and 600 mV are 3.64, 2.45, 1.49, and 0.93 ms, respectively. An exponentially decaying function (t d  ~ e −v/v0) is employed to fit the dwell time dependent on the voltage, as shown in the inset of Figure 4.