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.

Modulation of membrane channel currents by gap junction protein mimetic peptides: size matters

“…It is significant that the connexin and pannexin mimetic peptides are all of similar molecular size. The accessibility tests with PEGs (3,4) show that the pannexin channels could accommodate the entry of molecules in this size range, and their presence would effectively block channel currents. Thus, a mechanism involving steric block of the channel has to be considered.…”

Ion-beam sculpting at nanometre length scales

“…The dynamics and conformation of single biological nanopores with dimensions of order 2 nm or less can be studied electronically using patchclamp techniques 6 . Bio-nanopores have recently been shown to act as electronic sensors capable of identifying and characterizing single molecules in aqueous solution [7][8][9][10][11] . The incorporation of such nanoscale functionality in robust, man-made devices has far-reaching implications, but requires the manipulation of solid state materials on length scales smaller than state of the art device fabrication methods provide today.…”

Disentangling Steric and Electrostatic Factors in Nanoscale Transport Through Confined Space

“…In nanopore analytics, single molecules are detected via the passage-induced changes in ionic current. [2][3][4][5][6][7] The approach can be implemented with protein 4,[8][9][10] and solid-state nanopores [10][11][12][13][14][15][16] and has gained popularity 17 due to its simplicity, the wide range of accessible analytes, 2,13,[18][19][20] and the prospect of DNA sequencing [21][22][23] based on nucleic acid sensing. [24][25][26][27] The translocation of protein and DNA strands through protein channels is also a biologically relevant process in pathogenic bacteria and human cells.…”