Paradoxical Brownian motion in a microfluidic device: Absolute negative mobility

Eichhorn R, Ros A, Regtmeier J, Duong TT, Reimann P, Anselmetti D. Paradoxical Brownian motion in a microfluidic device: Absolute negative mobility. European Physical Journal - Special Topics. 2007;143(1):159-164.We report on a paradoxical migration mechanism in a microstructured lab-on-a-chip environment. The phenomenon is based on a subtle interplay between Brownian motion (thermal noise), a periodic and symmetric microstructure, and a biased AC electric field. The resulting non-linear dynamics far from thermal equilibrium gives rise to absolute negative mobility, i.e. a migrational transport, which is - both for negative and positive bias - always opposite to the net acting force, in good agreement between experiment and theory