Nie was recently recruited from Indiana University as a professor and researcher in the joint biomedical engineering department established by Georgia Tech and Emory University. While at Indiana, Nie and his colleagues constructed a nanoscale semiconducter crystal. Also called a quantum dot, this particle is made of semiconductors with a limited ability to conduct electricity.
Because quantum dots are so small, their electrons are compacted, causing them to emit light or to act as a fluorescent tag. Quantum dots can bond chemically to biological molecules, enabling them to trace specific proteins within cells. Nie calls them "bioconjugated nanoparticles" -- small particles that are chemically linked to biological materials.
Nanoparticle probes can be used as contrast markers in magnetic resonance imaging (MRI), in positron emission tomography (PET) for in-vivo molecular imaging, or they can be used as fluorescent tracers in optical microscopy. These tags can trace specific proteins in cells for cancer diagnosis or monitor the effectiveness of drug therapy. Because the dots glow with bright, fluorescent colors, scientists hope they will improve the sensitivity of diagnostic tests for molecules that are difficult to detect, such as those in cancer cells, or even the AIDS virus, Nie said.
"Basically, it is a barcoding technology that can encode genes and proteins," Nie said. He plans to use bioconjugated nanoparticles for early identification, quantification, and localization of gene sequences, proteins, infectious organisms, or genetic disorders.
Many of the practical applications of nanoparticles are based on the different colors they absorb or emit in the light spectrum as their sizes change. A piece of gold, for instance, appears yellow in color, but appears red at nanoscale size. Broken down even smaller, it could appear to be blue.