Bidirectional microfluidic pumping using an array of magnetic Janus microspheres rotating around magnetic disks

We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnetic field. By placing the disks close to the edge of the microchannel, a pumping rate of at least 0.3 nL/min was measured using tracking microspheres. Geometric programming of the pumping direction is possible by positioning the magnetic disk close to the side wall. A second degree of freedom in pumping direction is offered by the rotation direction of the external magnetic field. The method is especially suited for flow-controlled recirculation of chemical and biological species in microchannel applications - for example medium recirculation in culture chambers - opening the way towards novel, portable, on-chip applications without the need for external fluidic or electrical connections.