  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.
