We used electrical recording to detect the passage of single polymer molecules: a single 2 nm a-hemolysin pore is allowed to assemble into a lipid bilayer separating two chambers filled with a conductive solution at different voltages. During the passage of one single polymer molecules, the ion current flowing through the channel is mostly blocked, indicating the presence of polymer inside the channel. The analysis of these blockades gives us informations on the dynamics and the structure of the various polymers.
Firstly, we studied the translocation of large neutral polymers (PEG with gyration radius from 5 to 20 nm well above the 2 nm pore size), which is possible only if the monomer concentration (in the semi-dilute range) is larger than a well-defined threshold. The dynamic of translocation appeared to be modified, suggesting a reptation mechanism. Similarly, the passage of charged polymers is only possible if the ionic strength of the solution is high enough. In both cases, the correlation length or screening length of the bulk polymer solution has to be smaller than the pore diameter to allow the polymer passage.
Secondly, the structure of the polymer can also be discriminated by this technique; we will present some new results on diblock copolymers.
Eventually, as demonstrated by Bayley, we will show how to decrease the size of the pore with a molecular adapter. It allowed us to increase the electrical resolution and then to observe the translocation of small chains of polymers (malto-triose) which cannot be detected with the large ionic a-hemolysin channel.
I will discuss also the translocation of protein.
Université d’Evry