A CMOS 10kpixel baseline-free magnetic bead detector with column-parallel readout for miniaturized immunoassays

The specific detection of anti-bodies or proteins in a point-of-care setting remains an unsolved technological challenge. While laboratory instruments rely on enzymatic labels and require complex, difficult-to-miniaturize optics, devices using super-paramagnetic labels have emerged as an attractive alternative for point-of-care systems [1]. The key challenge for all magnetic-bead detection systems [2-5] is the presence of a large measurement “baseline.” Since beads are paramagnetic, a polarization field must be applied in order to excite a magnetic response. This response is ~1000× smaller than the polarization field, necessitating a combination of calibration, reference sensors [2], and temperature stabilization [5] to reject the polarization field. In addition to a low and stable baseline, a practical system should have low measurement time and large sensing area to reduce biological variations [6].