A magnetic bead trap-and-mixer includes a channel having openings at opposing ends, and a rotor adjacent to the channel and comprising a permanent magnet, wherein the rotor is adapted to apply a magnetic field to the channel of sufficient strength to direct the movement of magnetic beads therein. In aspects, the channel is straight and/or has narrowed end. In further aspects, the rotor generates in the channel areas of areas of strong magnetic fields alternating with areas of very weak magnetic fields and the strong magnetic fields extend entirely across the channel.