DNA unzipping and protein unfolding using nanopores.

We present here an overview on unfolding of biomolecular structures as DNA double strands or protein folds. After some theoretical considerations giving orders of magnitude about transport timescales through pores, forces involved in unzipping processes … we present our experiments on DNA unzipping or protein unfolding using a nanopore. We point out the difficulties that can be encountered during these experiments, such as the signal analysis problems, noise issues, or experimental limitations of such system.

Transport of long neutral polymers in the semidilute regime through a protein nanopore.

We investigate the entrance of single poly(ethylene glycol) chains into an α-hemolysin channel. We detect the frequency and duration of the current blockades induced by large neutral polymers, where chain radius is larger than pore diameter. In the semidilute regime, these chains pass only if the monomer concentration is larger than a well-defined threshold. Experiments are performed in a very large domain of concentration and molecular mass, up to 35% and 200 kDa, respectively, which was previously unexplored. The variation of the dwell time as a function of molecular mass shows that the chains are extracted from the semidilute solution in contact with the pore by a reptation mechanism.

Long-living channels of well defined radius opened in lipid bilayers by polydisperse, hydrophobically-modified polyacrylic acids.

In the presence of random amphiphilic polymers devoid of secondary structure, lipid membranes become leaky to albumin and dextran (fluorescence of giant unilamellar vesicles) and their conductance (black lipid films) shows the transient opening of channels of typical radius 1-5 nm.