Lasers and nanocages could improve disease diagnosis and treatment

West Lafayette, IN--New findings from Purdue University researchers suggest that an experimental ultra-sensitive medical imaging technique that uses a pulsed laser and tiny metallic "nanocages" might enable both the early detection and treatment of disease. The system works by shining near-infrared laser pulses through the skin to detect hollow nanocages and solid nanoparticles--made of an alloy of gold and silver--that are injected into the bloodstream (see also "Disease diagnosis and treatment goes for gold"). But unlike previous approaches using tiny metallic nanorods and nanospheres, the new technique does not cause heat damage to tissue being imaged, nor does it produce background "auto fluorescent" glow of surrounding tissues that interferes with the imaging and reduces contrast and brightness, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

"This lack of background fluorescence makes the images much more clear and is very important for disease detection," he said. "It allows us to clearly identify the nanocages and the tissues." The improved performance could make possible early detection and treatment of cancer. The tiny gold-silver cages also might be used to deliver time-released anticancer drugs to diseased tissue, said Younan Xia, the James M. McKelvey Professor for Advanced Materials in the Department of Biomedical Engineering at Washington University in St. Louis. His team fabricated the nanocages and nanoparticles used in the research.

The gold-silver structures yielded images 10 times brighter than other experimental imaging research using gold nanospheres and nanorods. The imaging technology provides brightness and contrast potentially hundreds of times better than conventional fluorescent dyes used for a wide range of biological imaging to study the inner workings of cells and molecules.

Findings were detailed in a research paper published online April 6 in the journal Angewandte Chemie's international edition. The paper was written by Purdue chemistry doctoral student Ling Tong, Washington University graduate student Claire M. Cobley and research assistant professor Jingyi Chen, Xia and Cheng.

The new imaging approach uses a phenomenon called "three-photon luminescence," which provides higher contrast and brighter images than conventional fluorescence imaging methods. Normally, three-photon luminescence is too dim to be used for imaging. However, the presence of gold and silver nanoparticles enhances the brightness, overcoming this obstacle. The ultrafast laser also is thought to possibly play a role by causing "third harmonic generation," which increases the brightness.

For the full story, go to http://www.purdue.edu/newsroom/research/2010/story-print-deploy-layout_1_5041_5041.html.

--Posted by Gail Overton; [email protected]; www.laserfocusworld.com.