Gold-silver nanocages can be multi-photon imaging probes
An experimental ultrasensitive medical imaging technique that uses a pulsed laser and tiny metallic "nanocages" might enable both the early detection and treatment of disease, according to research published online April 6 in the Angewandte Chemie International Edition.

The gold-silver nanocages exhibit a bright "three-photon luminescence" when excited by the ultrafast pulsed laser, with ten-times greater intensity than pure gold or silver nanoparticles.

The signal allows live cell imaging and the new technique does not cause heat damage to tissue being imaged and does not produce a background "auto fluorescent" glow of surrounding tissues, which interferes with the imaging and reduces contrast and brightness, according to Ji-Xin Cheng, PhD, associate professor of biomedical engineering and chemistry at Purdue University in West Lafayette, Ind., and colleagues.

"The three-photon imaging capability will potentially allow us to combine imaging and therapy for better diagnosis and monitoring," said Younan Xia, PhD, professor for advanced materials in the department of biomedical engineering at Washington University in St. Louis, Mo.

The tiny gold-silver cages also might be used to deliver time-released anticancer drugs to diseased tissue, added Xia. The researchers intravenously injected the nanocages into mice and then took images of the tiny structures in tissue samples from organs such as the liver and spleen.

"With the near-infrared laser being completely off the plasmon resonance, the three-photon luminescence is not accompanied by photothermal effect from the nanostructures or autofluorescence from the tissue, making the gold-silver alloyed nanostructures a class of ideal probes for multi-photon imaging," concluded Cheng and colleagues.