Single Molecule Imaging of Protein Molecules in Nanopores

摘要

The interactions between single protein molecules andnnanoporous polycarbonate membranes were investigatednat the single molecule level. Entrapment of proteins wasnshown to be size selective and was dependent on thenmembrane pore diameter. A pore size that is only slightlynlarger than the maximum dimension of the proteins wasninadequate for intrusion into the pores. For a givennprotein, the number of molecules found at a given depthndecreased as the pore size decreased. In addition, as thendepth increased, for a given size pore, the number ofnmolecules decreased rapidly. The depth-dependent his-ntograms nicely fit a one-dimensional diffusion model.nHowever, a highly restricted motion was observed evennwhen the pore diameter was 10 times the size of thenprotein, resulting in anomalously small diffusion coef-nficients. We also demonstrated the subtle differences inndepth distribution among BSA and hemoglobin that havennearly the same molecular weight but slightly differentnmolecular shapes. These results give unique insights intonthe detailed mechanism of size-exclusion chromatographynand membrane filtration.