Gold nanorods coated with multilayer polyelectrolyte as contrast agents for multimodal imaging

A growing body of research has demonstrated that gold nanorods can serve as extremely bright imaging agents.

Now, by linking gold nanorods to an antibody that binds to tumor cells, researchers at the Georgia Institute of Technology have found that gold nanorods will align themselves in an ordered fashion on the surface of cancer cells, further intensifying the optical signal the nanorods produce and providing a unique optical signature for tumor cells.

Reporting its work in the journal Nano Letters, a team of investigators led by Mostafa El-Sayed, Ph.D., prepared gold nanoparticles linked to an antibody that binds the cell-surface receptor EGFR. When incubated with both normal cells and those from a human oral tumor and imaged using several different spectroscopic techniques, the gold nanorods produce a strong, sharp image only for the tumor cells. Indeed, the optical signal from tumor cells was twice as bright as from normal cells.

The investigators suspect that this difference results from the gold nanoparticles becoming aligned with one another when bound to the tumor cell surface through their linked antibody; previous research has shown that EGFR molecules occur in clusters on the surfaces of many types of tumor cells. When aligned with one another, adjacent nanorods interact electronically in such as way as to boost their combined optical output. The investigators note that this output boost can serve as a molecular signature unique to tumor cells.

In another paper, published in the Journal of Physical Chemistry C, a team of investigators led by Paras Prasad, Ph.D., principal investigator of the National Cancer Institute's Cancer Nanotechnology Platform Partnership at the State University of New York at Buffalo, has shown that gold nanorods linked to a protein known as transferrin also target cancer cells and enable them to be detected using optimal imaging. In this case, the nanorods were taken into tumor cells bearing the transferrin receptor, where they accumulate in sufficient numbers to shine brightly when irradiated by light. Healthy cells, which have but a few transferrin receptors on their surfaces, did not accumulate the targeted nanorods.

The work by El-Sayed and colleagues, which was supported by the National Cancer Institute's Alliance for Nanotechnology in Cancer, is detailed in the paper, "Cancer cells assemble and align gold nanorods conjugated to antibodies to produce highly enhanced, sharp, and polarized surface Raman spectra: a potential cancer diagnostic marker." Investigators from the University of California, San Francisco, and the University of California, Berkeley, also participated in this study. An abstract of this paper is available through PubMed. View abstract.

The work by Prasad and colleagues, which was also supported by the National Cancer Institute's Alliance for Nanotechnology in Cancer, is detailed in the paper, "Gold nanorods coated with multilayer polyelectrolyte as contrast agents for multimodal imaging." An abstract of this paper is available at the journal's Web site. View abstract.