(a) Schematic of a microfluidic device using magnets placed under a main flow channel, along with magnetically-labeled CTCs, to accomplish CTC isolation from a blood sample. (b) Microfluidic device with magnets placed under perpendicularly-oriented side chambers used for collection of magnetically-labeled CTCs; the low fluid shear stresses in the dead-ended side chambers keep the collected CTCs viable. (c) Microfluidic device with a flow-focusing configuration to establish a single-file stream of cells through a microfluidic channel. Device is bonded to a micro-Hall detector array, such that each magnetically-labeled CTC passing over the array induces a Hall voltage and is thus counted. Reproduced from Refs. 8, 9, 10 with permission from RSC and AAAS.