Virus has the Midas touch.

Researchers have recruited a stringlike virus to carry nanoscale loads of gold that could serve as imaging agents in cancer diagnosis.

The team at the M.D. Anderson Cancer Center in Houston used a virus called an M13 phage, which normally infects bacteria. In the past, scientists had genetically engineered the 1-micrometer-long virus to attach to various receptors on mammalian cells. In this experiment, Renata Pasqualini and Glaueo R. Souza and their colleagues enlisted a virus that binds to a receptor found on tumor cells.

The group mixed multiple copies of the modified virus with gold particles roughly 45 nanometers in diameter. The components self-assembled into a network of overlapping strings and spheres held together by the attraction between the viruses' positively charged bodies and the negatively charged gold spheres, says Souza.

In the Jan. 31 Proceedings of the National Academy of Sciences, the researchers demonstrate in cancer cells growing in the lab that the gold-phage networks attach to the cells. The gold nanoparticles give the targeted cells a distinct signal in a detection system called surface-enhanced Raman scattering.

"You could envision using these bio-gold nanoparticles in order to seek out tumors and then conceivably send out a signal when they've arrived," says cancer biologist Bruce Zetter of Children's Hospital Boston.--A.C.