When injected into mice, the nanoworms accumulated in tumors, which was not surprising. "When [tumors] recruit blood vessels to feed themselves, the blood vessels tend to be very leaky," Sailor says, so any kind of nanoparticle would have a tendency to collect there. But the nanoworms also stuck around much longer than individual iron oxide nanoparticles, which the body can eliminate in minutes. "If you make [a nanoparticle] bigger, then the body should have a better chance of finding it and eliminating it," Sailor says. "So one of the surprises of the study was that these things would circulate for quite a long time. They had up to a 24-hour half-life."

The researchers also took the nanoworms and attached a peptide called F3, developed by Ruoslahti and his colleagues, that targets the surface of cancer cells. In vitro, the modified nanoworms attached to cancer cells more effectively than individual nanoparticles did. Linking several nanoparticles together creates a cooperative effect, Sailor says. Once one F3 molecule contacts a cell surface, there are others nearby to do the same.

Sailor and his group are now looking at methods to amplify the effect of the nanoworms, finding means for them to recruit other particles to a tumor site in a way that blood might clot.