Hence, there are some interactions of protein-protein and protein-pore involved in the protein transition. Figure 4 Current blockage histograms as a function of applied voltage at medium voltages. The histograms of time duration are fitted by exponential distribution. An exponential function of dwell time versus voltage is defined in the inset. As mentioned above, the current blockage signals reveal the information of the size, conformation, ABT199 and interactions of proteins passing through the nanopore. According to both t d and I b, different types of discrete current blockades are characterized

in Figure 5. For type I, the current signal has a typical spike shape with a deep intensity and a short dwell time. For type II, the current blockage turns to be rectangle with a similar amplitude but a long transition time. For type III, a distinct asymmetric and retarded current signal is observed with an even longer transition time. Usually, the negatively charged protein will flash past the nanopore driven by the strong electric force within the nanopore, giving the short-lived event as type I. However, given a protein with a high content of charged residues, a variety of electrostatic and hydrophobic interactions are involved in the liquid–solid interface RG7204 mw between the protein

and nanopore [31]. Once the protein is absorbed in the pore wall, the current signal will be blocked persistently, and it recovers till the protein is desorbed and impelled out the nanopore, showing as the long-lived events of types II and III. The type II event shows an abrupt restore, implying a very fast release of absorption. In contrast, the type III event shows a triangle-shaped signal and a longer restore period, implying a gradual release of absorption. Since the electric field (and thus the main driving force) within the nanopore is much stronger than that around the mouths of the nanopore (see Figure 2), it is reasonable to speculate that the absorption in the type II case is within the pore this website while that

in type III is near the pore mouths. Owing to the decaying electric field in the pore mouth, there is a complicated equilibrium of adsorption and desorption involved between the protein and nanopore in type III. The absorption of protein to the nanopore wall also slows down the velocity of protein translocation, which accounts for the smaller diffusion constant D of proteins in the pore. In contrast with the prolonged dwell time from hundreds of milliseconds to several minutes obtained by small nanopores, the protein adsorption time is shortened and the frequency of the long-lived events is also decreased in larger nanopores. Especially, with the increase of the voltage, the adsorption phenomenon is gradually weakened by the enhanced driving force, and the velocity of protein transition is also speeded up.