title: Magnetic nanoparticle sensors.
abstract: Many types of biosensors employ magnetic nanoparticles (diameter = 5-300 nm) or magnetic particles (diameter = 300-5,000 nm) which have been surface functionalized to recognize specific molecular targets. Here we cover three types of biosensors that employ different biosensing principles, magnetic materials, and instrumentation. The first type consists of magnetic relaxation switch assay-sensors, which are based on the effects magnetic particles exert on water proton relaxation rates. The second type consists of magnetic particle relaxation sensors, which determine the relaxation of the magnetic moment within the magnetic particle. The third type is magnetoresistive sensors, which detect the presence of magnetic particles on the surface of electronic devices that are sensitive to changes in magnetic fields on their surface. Recent improvements in the design of magnetic nanoparticles (and magnetic particles), together with improvements in instrumentation, suggest that magnetic material-based biosensors may become widely used in the future.
authors.affiliation: T2 Biosystems, 286 Cardinal Medieros Ave, Cambridge, MA 02141, USA; E-Mail:  ikoh@T2biosystems.com.
authors.forename: Isaac
authors.initials: I
authors.lastname: Koh
authors.forename: Lee
authors.initials: L
authors.lastname: Josephson