We report noise and detection limitations in cantilever-based immunomagnetic biosensors. A differential cantilever system with sensing and control arms was used whereby the control arm was passivated with bovine serum albumin (BSA) and the sensing arm was functionalized with biotin-BSA. Streptavidin-coated magnetic beads were exposed to cantilever arms. An oscillatory magnetic field induced a magnetic force on the beads which caused a relative deflection of the sensing arm. Increasing the excitation frequency suppressed the 1/f noise by 100-fold, resulting in a deflection resolution of 0.065 angstrom in air. (c) 2008 American Institute of Physics.