A compact Hall-effect sensor array for the detection and imaging of single magnetic beads in biomedical assays

A 64-unit Hall-effect sensor array capable of detecting magnetic beads is implemented in 0.18 μm CMOS process. Two Hall sensor implementations, one using n-wells and another using MOS transistors, are analyzed. The n-well implementation can detect a single 4.5 μm bead in .5 ms with a probability of error below 1% while the MOS implementation takes 2.5 ms to detect the same bead. Each array is compact so that individual beads can be detected and counted even if they do not land directly over a sensor. As a result, the array is capable of imaging magnetic beads, much like a digital camera, and thereby provides information about their individual locations and distribution.