A method for controlling the movement of magnetic or magnetizable objects (10) in a biosensor cartridge. The method comprises the step of providing a biosensor cartridge with a laterally extending sensor surface (A) and at least a magnetic field generating means (20, 30, 30′) for generating a magnetic field with a field gradient substantially perpendicular to the sensor surface (A). The magnetic field generating means (20, 30, 30′) are alternatingly actuated such that the generated magnetic field directs alternatingly the magnetic or magnetizable objects (10) substantially perpendicular to the sensor surface (A) away and toward the sensor surface, wherein pulse lengths of the alternating actuation are adjusted such that a lateral movement of magnetizable objects along the laterally extending sensor surface is substantially avoided.