Cellular Biology: Electrons & Ions - same difference

March 30, 2016 | 12:00
Cellular Biology: Electrons & Ions - same difference © lben.epfl.ch
Cellular Biology: Electrons & Ions - same difference © lben.epfl.ch
Cell membranes have tiny channels called ionic canals, because they assist the passage at high speed of certain ions.  Their role is central notably in the workings of neurons, muscle cells or heart cells.  But their complexity is such that numerous questions remain. How do these canals choose the ions? How can we explain the strong conductivity of these passages, which allow ions to travel at such high speeds?

Researchers from Biology Labs and of electronics at nanometer scale at the EFP at Lausanne have shown that the transport of ions is similar to that of electrons. For this they have created an artificial ionic canal by making a a tiny hole of less than a nanometer in a two­‑dimensional material called Molybdenum disulphide.   They then placed this material between two electrodes with an ionized liquid on both sides.  Applying a voltage allowed variations in current between the two chambers to be measured.  In a traditional system, where the hole is larger (>1nm) the flow of ions never stops entirely.  With their system, the researchers observed “energy gaps” proving that the ions were first retained, before transiting from one side to the other of the tiny hole when the voltage became sufficient.

The way that the ions are transported conforms to known laws of physics for the transport of electrons, the Coulomb Blockade, observed in electronics, in particular in the tiny “wells” for semi-conductor electrons called “quantum dots”, capable of retaining electrons.  The number of electrons that may be received by these “Islands” is restricted, in that some must leave to make way for new arrivals.

Predicted by theory, this phenomenon has thus been observed for the first time thanks to these nanostructures. This experience has paved the way for new experiments on the transport of ions at the mesoscopic scale.

Source : Feng J, Liu K, Graf M, Dumcenco D, Kis A, Di Ventra M, & Radenovic A., Observation of Ionic Coulomb Blockade in Nanopores, Nature Materials

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