Cancer monitoring devices the size of a grain of rice that can be deposited at the site of a tumor have been developed by MIT and Harvard researchers.

The devices use magnetic nanoparticles coated with a chemical that can bind with cancer biomarker molecules, creating minuscule clumps that can be detected by a non-invasive scan like an MRI (or by a hand-held magnetic resonance detector in the future).

The technologies could help doctors when patients ask whether a tumor will respond to a particular therapy, and could be linked to another device that might then release the appropriate drug for treatment.