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The scientists constructed their nanoworms from spherical iron oxide nanoparticles that join together, like segments of an earthworm, to produce tiny gummy worm-like structures about 30 nanometers longor about 3 million times smaller than an earthworm. Their iron-oxide composition allows the nanoworms to show up brightly in diagnostic devices, specifically the MRI, or magnetic resonance imaging, machines that are used to find tumors.

The iron oxide used in the nanoworms has a property of superparamagnetism, which makes them show up very brightly in MRI, said Sailor. The magnetism of the individual iron oxide segments, typically eight per nanoworm, combine to provide a much larger signal than can be observed if the segments are separated. This translates to a better ability to see smaller tumors, hopefully enabling physicians to make their diagnosis of cancer at earlier stages of development.

In addition to the polymer coating, which is derived from the biopolymer dextran, the scientists coated their nanoworms with a tumor-specific targeting molecule, a peptide called F3, developed in the laboratory of Erkki Ruoslahti, a cell biologist and professor at the Burnham Institute for Medical Research at UC Santa Barbara. This peptide allows the nanoworms to target and home in on tumors.

Because of its elongated shape, the nanoworm can carry many F3 molecules that can simultaneously bind to the tumor surface, said Sailor. And this cooperative effect significantly improves the ability of the nanoworm to attach to a tumor.

The scientists were able to verify in their experiments that their nanoworms homed in on tumor sites by injecting them into the bloodstream of mice with tumors and following the aggregation of the nanoworms on the tumors. They found that the nanoworms, unlike the spherical nanoparticles of similar size that were shuttled out of the blood by the immune system, remained in the bloodstream for hour
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