We demonstrate the dispersion free digital transport of emulsion droplets and biological cells in an aqueous solution using paramagnetic colloidal particles above a uniaxial magnetic garnet film. Magnetic modulations above the stripe domain pattern induce a step-wise transport of paramagnetic particles dispersed in water and deposited on the surface of the film. Capillary or hydrodynamic interactions are then used to couple the cargo to the paramagnetic beads. We achieve full control of the cargo motion up to velocities in the 100 microm/s range.

Paramagnetic particles in a magnetic ratchet potential were transported in discrete steps in an aqueous solution on the surface of a magnetic garnet film. The proposed technique allows the simultaneously controlled, dispersion-free movement of an ensemble of paramagnetic particles across the surface. External magnetic modulations were used to transport the particles in a defined direction, and a current reversal upon changing the size of the particles was used to separate particles having different diameters. Doublets consisting of a larger and a smaller particle functionalized with complimentary oligonucleotides and bound via Watson-Crick base pairing were separated after melting the double stranded DNA.