Ion Transport By The Thermally Rectified Brownian Ratchet

Abstract

The Brownian ratchet is a mechanism that is effective in nanoscale for ion transport and molecular motor, in which isotropic thermal diffusion of charged particles such as ions is rectified by some asymmetric ratcheting and net mass flux in a certain direction is generated. The principle is important for future design of novel devices for particles separation, molecular motors, and ion pumps. In the present article, it is demonstrated that the combination of a nonuniform temperature field and a spatially symmetric ratchet, either of which induces no net mass transport when being applied alone, works to rectify the thermal mass diffusion and generate net mass flux of charged particles. This finding is important in the following two points: It adds a new mode of the Brownian ratchet to rectify the diffusion of particles and suggests a new method to transport particles utilizing a preexisting temperature gradient.

KEY WORDS:

• Brownian ratchet
• temperature gradient
• ion transport
• microchip

This work has been carried out utilizing the SGI ORIGIN2000 system of the Advanced Fluid Information Research Center, Institute of Fluid Science, Tohoku University. Taku Ohara expresses his gratitude to Professor A. Majumdar, University of California, Berkeley, who first brought his attention to the Brownian ratchet.