A fluid magnetic material intended to be injected in close proximity to a tumour to facilitate its migration to sentinel lymph nodes; the lymph nodes can subsequently be localized with a magnetic field detector (magnetometer) and surgically removed for histological analysis. The device includes a suspension of dextran-coated iron oxide nanoparticles, available in a vial or syringe, that exhibit superparamagnetism in the presence of a magnetic field. It is typically used to support staging of a variety of cancers including breast, melanoma, prostate, and bowel. This is a single-use device.