Counting polymers moving through a single ion channel

Nature. 1994 Jul 28;370(6487):279-81. doi: 10.1038/370279a0.


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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alamethicin*
  • Diffusion
  • Ion Channels / metabolism*
  • Lipid Bilayers
  • Particle Size
  • Polymers*


  • Ion Channels
  • Lipid Bilayers
  • Polymers
  • Alamethicin