In the future, the value of gold might be measured in nanometers instead of in carats — especially for people with breast cancer. Joseph Irudayaraj’s lab at Purdue University is taking advantage of the optical and physical properties of gold to develop nanorods that can be used as diagnostic tools. Once in blood, these rods circulate and attach to specific cells. Right now, Irudayaraj is working on getting the gold nanorods to adhere to different types of breast cancer cells.
“We can manipulate optical properties and be able to detect several interactions in one scan,” says Irudayaraj, an associate professor of bioengineering.
Irudayaraj and his lab began by adapting gold nanorods to make them safer for use in biological systems. The original protocol that makes nanorods through chemical synthesis leaves them with a coating of a toxic chemical, called CTAP, that normally prevents the rods from clumping. Irudayaraj devised a way to remove the surface CTAP molecules and replace them with thiol compounds. “We’ve taken the protocol and made these nanorods biocompatible,” he says. “In that way, the whole surface is ready to interact with living cells and tissues.”
Cancer cells, which can be told apart by their cell surface proteins, were a natural choice for Irudayaraj to start testing these nanorods’ physical properties — and many of his colleagues in the biology and oncology departments focus their research on breast cancer. To adapt nanorods to sense cancer cells, Irudayaraj added anti-biomarkers, or compounds that are complementary to the markers on the cancer cell surface. Then, the rods could attach to the cancer cells floating around in blood samples. Once they bind, they can be detected by shining white light on them. The rods scatter the light and Irudayaraj captures that with a CCD camera.
With this technology, multiple cell types can be detected simultaneously, since varying the lengths of the gold nanorods makes them scatter light at different peaks. “We can have different peaks in the visible spectra and each peak can then denote a specific length of the rod, and that particular length can correspond to a specific marker on the cell surface,” says Irudayaraj. “This is optical sensing.”
Currently, the Irudayaraj lab is working to make the rods functional in the body. “We don’t want these rods to be floating in blood. We want to sense it and then we want to be able to recover it,” he says.