photo: nanoparticle
A quantum dot encapsulated in a
gold shell; © University of Washington

The result is the first structure that creates a multipurpose nanotechnology tool for medical imaging and therapy.

"This is the first time that a semiconductor and metal nanoparticles have been combined in a way that preserves the function of each individual component," said Xiaohu Gao, a University of Washington (UW) assistant professor of bioengineering.

Quantum dots are fluorescent balls of semiconductor material just a few nanometers across, a small fraction of the wavelength of visible light. At this tiny scale, quantum dots' unique optical properties cause them to emit light of different colors depending on their size. The dots are being developed for medical imaging.

Glowing gold nanoparticles have been used since ancient times in stained glass; more recently they are being developed for delivering drugs and for a type of medical imaging that uses infrared light. Gold also reradiates infrared heat and so could be used in medical therapies to cook nearby cells.

But combine a quantum dot and a gold nanoparticle, and the effects disappear. The electrical fields of the particles interfere with one another and so neither behaves as it would on its own.

The new manufacturing technique uses proteins to surround a quantum dot core with a thin gold shell held at 3 nanometers distance, so the two components' optical and electrical fields do not interfere with one another. The quantum dot likely would be used for fluorescent imaging. The gold sphere could be used for scattering-based imaging, which works better than fluorescence in some situations, as well as for delivering heat therapy.

The manufacturing technique developed by Gao and Yongdong Jin, a UW postdoctoral researcher, is general and could apply to other nanoparticle combinations, they said.; Source: University of Washington