title: Counting polymers moving through a single ion channel.
abstract: The change in conductance of a small electrolyte-filled capillary owing to the passage of sub-micrometre-sized particles has long been used for particle counting and sizing. A commercial device for such measurements, the Coulter counter, is able to detect particles of sizes down to several tenths of a micrometre. Nuclepore technology (in which pores are etched particle tracks) has extended the lower limit of size detection to 60-nm particles by using a capillary of diameter 0.45 micron (ref. 4). Here we show that natural channel-forming peptides incorporated into a bilayer lipid membrane can be used to detect the passage of single molecules with gyration radii as small as 5-15 A. From our experiments with alamethicin pores we infer both the average number and the diffusion coefficients of poly(ethylene glycol) molecules in the pore. Our approach provides a means of observing the statistics and mechanics of flexible polymers moving within the confines of precisely defined single-molecule structures.
authors.affiliation: Division of Intramural Research, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: S M
authors.initials: SM
authors.lastname: Bezrukov
authors.forename: I
authors.initials: I
authors.lastname: Vodyanoy
authors.forename: V A
authors.initials: VA
authors.lastname: Parsegian
mesh_terms: D000408:Alamethicin; D004058:Diffusion; D007473:Ion Channels / Q000378:metabolism*; D008051:Lipid Bilayers; D010316:Particle Size; D011108:Polymers
chemical_list: D007473:Ion Channels; D008051:Lipid Bilayers; D011108:Polymers; D000408:Alamethicin