Micromachined Linear Brownian Motor: A Nanosystem Exploting Brownian Motion of Nanobeads for Uni-directional Transport
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Micromachined Linear Brownian Motor: A Nanosystem Exploting Brownian Motion of Nanobeads for Uni-directional Transport Ersin Altintas1, Edin Sarajlic1, Karl F. Bohringer2, and Hiroyuki Fujita1 1 CIRMM / IIS, The University of Tokyo, Tokyo, 153-8505, Japan 2 The University of Washington, Seattle, WA, 98195 ABSTRACT Nanosystems operating in liquid media may suffer from random thermal fluctuations. Some natural nanosystems, e.g. biomolecular motors, which survive in an environment where the energy required for bio-processes is comparable to thermal energy, exploit these random fluctuations to generate a controllable unidirectional movement. Inspired by the nature, a transportation system of nanobeads achieved by exploiting Brownian motion were proposed and realized. This decreases energy consumption and saves the energy compared to ordinal pure electric or magnetic drive. In this paper we present a linear Brownian motor with a 3-phase electrostatic rectification aimed for unidirectional transport of nanobeads in microfluidic channels. The transport of the beads is performed in 1 µm deep, 2 µm wide PDMS microchannels, which constrain three-dimensional random motion of nanobeads into 1D fluctuation, so-called tamed Brownian motion. We have experimentally traced the rectified motion of nanobeads and observed the shift in the beam distribution as a function of applied voltage. The detailed computational analysis on the importance of switching sequence on the speed performance of motor is performed and compared with the experimental results showing a good agreement.
INTRODUCTION A Linear Brownian Motor (LBM) exploits random thermal fluctuations (Brownian motion), which is one of the dominating phenomena at the nanoscale [1-5], to fuel transportation of nanoscopic particles thanks to 3-phase electrostatic rectification. Our linear Brownian motor, schematically shown in Fig.1, employs microchannels to tame Brownian motion, i.e. to limit the 3D random motion of nanobeads into 1D motion, and 3phase electrodes to rectify its motion (Fig. 1-Left). The purpose of microchannel, whose crosssection is comparable to the size of a nanobead, resembles microtubules and/or actin filaments that constrain the motion of bio-motors [3, 4]. We designed the system such that electrodes are repeated to realize a 3-phase system. We employed a relatively large number of electrodes compared to our first design [6] in order to provide a long range transportation of the particles. In the design, the electrodes are 2 µm in width and equally spaced having a 4 µm separation gap. To ensure a proper working of the motor, the electrostatic force working on the beads should be (i) high enough to keep the particle on the active electrode against the Brownian motion but (ii) weak and localized enough not to attract the particle directly from an adjacent inactive electrode. In that case, a bead travels from one electrode to the next only by Brownian motion so energy used for the movement can be saved. With the rectification in one direction, the
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