Functional colloidal micro-sieves assembled and guided above a   channel-free magnetic striped film
  Colloidal inclusions in lab-on-a-chip devices can be used to perform analytic operations in a non-invasive fashion. We demonstrate here a novel approach to realize fast and reversible micro-sieving operations by manipulating and transporting colloidal chains via mobile domain walls in a magnetic structured substrate. We show that this technique allows to precisely move and sieve non-magnetic particles, to tweeze microscopic cargos or to mechanically compress highly dense colloidal monolayers. 
Fernando Martinez-Pedrero, Arthur V. Straube, Tom H. Johansen, Pietro   Tierno
cond-mat.soft cond-mat.stat-mech