A method for lysing cells in a fluid sample includes positioning an electromagnet within a predetermined distance from a sample chamber of a microfluidic device which contains the fluid sample and lytic agents including non-magnetic beads and at least one magnetic element. A magnetic field generated by the electromagnet is targeted at the sample and the lytic agents contained in the sample chamber. The electromagnet is spatially separated from the sample chamber and held stationary while generating the magnetic field, and the polarity of the magnetic field is reversed, thereby causing the magnetic element to move in a random manner within the sample chamber to agitate the non-magnetic beads to lyse cells contained within the fluid sample and release nucleic acids from the lysed cells.