Gold nanorods, which fluoresce red, were photographed inside the blood vessels of a live mouse by researchers in Purdue's Weldon School of Biomedical Engineering and Department of Chemistry. The researchers have taken a step toward developing a new ultrasensitive medicalimaging technique that is nearly 60 times brighter than conventional fluorescent dyes.

Gold nanorods, which fluoresce red, were photographed inside the blood vessels of a live mouse by researchers in Purdue's Weldon School of Biomedical Engineering and Department of Chemistry. The researchers have taken a step toward developing a new ultrasensitive medicalimaging technique that is nearly 60 times brighter than conventional fluorescent dyes.


West Lafayette, Ind. ... Purdue University researchers are working on an ultrasensitive medical-imaging technique that may help detect cancer in its early stages, says Assistant Professor of Biomedical Engineering Ji-Xin Cheng. In tests, researchers injected tiny gold nanorods into the bloodstream of mice. Shining a laser through the animals' skin let researcher record images nearly 60 times brighter than is possible through conventional fluorescent-dye techniques.

The gold rods are 20-nm wide and 60-nm long. They may lead to advanced medical-imaging techniques that use light to analyze blood vessels and underlying tissues.

"One obstacle with conventional techniques is that visible light doesn't easily pass through tissue," says Associate Professor of Chemistry Alexander Wei. "But, there is a window of light in the near infrared (800 to 1,300 nm), which could be harnessed for new imaging technologies," Wei says.

At Purdue, gold rods with a specific aspect (length-to-width) ratio shine brightly when illuminated by infrared light. According to researchers, the nanorods are ideal for two-photon fluorescence, a type of imaging in which two photons hit the nanorod simultaneously. Cheng is developing "nonlinear optical techniques" to glean more contrast and brighter images from the two-photon effect.

In the tests, researchers injected nanorods into mice and then took images of the structures as the nanorods flowed through blood vessels in the animals' ears. A half hour after being injected, the nanorods could no longer be seen in the animals' blood, presumably because the kidneys had filtered them out.

"To detect cells at early stages of a disease such as cancer, it's important to have a reliable technique that has sensitivity at the single-particle level," Wei says. "The gold nanorods demonstrate that Cheng's nonlinear imaging methods have this level of detection."