An ultrasensitive medical imaging technique from Purdue University, which uses a pulsed laser and tiny metallic "nanocages," might enable 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. Unlike previous approaches using tiny metallic nanorods and nanospheres, the new technique does not cause heat damage to tissue being imaged. Another advantage is that it does not produce a background "auto fluorescent" glow of surrounding tissues, which interferes with the imaging and reduces contrast and brightness, said Ji-Xin Cheng, an associate professor of Biomedical Engineering and Chemistry.

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. The three-photon effect might enable scientists to develop advanced "non-linear optical techniques" that provide better contrast than conventional technologies.

Click here for the full story .