A CMOS microsystem for detecting microparticles in magnetic immunoassays uses the intrinsic dynamics of magnetization in super-paramagnetic materials to reduce measurement baseline by >;300× compared to conventional methods, and to achieve a signal to baseline ratio>; 1, with an improvement of over 50 × compared to systems that ignore bead dynamics. The microsystem integrates a 64 × 160 Hall-sensor array with column-parallel readout electronics that combine auto-zeroing and nested chopping to enable low-offset, power efficient signal acquisition and has an Allan deviation floor of 9 nT.