March 13, 2006
Labeling Nanotubes with Quantum Dots
Utilizing a well-used workhorse of immunology laboratories, investigators at the Methodist Neurological Institute in Houston, TX, have developed a straightforward, enzyme-driven technique to label nanotubes with quantum dots, giving scientists a better way to see single-walled carbon nanotubes in living cells. This technique could lead to new ways of detecting malignant cells and delivering anticancer agents to tumors while sparing surrounding healthy cells.
Writing in the journal BioTechniques, David Baskin, M.D., and Vladimir Didenko, Ph.D., describe how they used the enzyme horseradish peroxidase to develop a versatile method for linking quantum dots to the surfaces of carbon nanotubes. Because nanotubes are largely transparent to light, researchers have tried to find ways to make them visible inside living organisms. The light absorption properties of the nanotubes are overcome by linking them to the brightly fluorescent quantum dots.
“By attaching these Q-dots like beads on a string, we have the potential to link tens, hundreds, thousands of these strings together, giving researchers a new view into cancer cells, proteins, and DNA molecules,” said Baskin. Once fluorescent, nanotubes can be observed by microscopes, which could enable the construction of more efficient drug and imaging agent delivery devices.
The key to this method was the investigators’ finding that horseradish peroxidase will catalyze a chemical reaction between the molecule biotin and a carbon nanotube. Biotin, a member of the B vitamin family, is renowned among biochemists for its ability to bind to a small bacterial protein known as streptavidin, which itself can be easily linked to a wide variety of molecules and nanoparticles, including quantum dots.
Mixing two molecules or nanostructures, one attached to biotin, the other to streptavidin, will lead to a strong link between the two. In this case, biotin on the carbon nanotube binds tightly to streptavidin on the quantum dot, creating a stable nanotube-quantum dot hybrid. The investigators note that the generality of this biotin-streptavidin pairing should enable researchers to attach a wide variety of molecules to carbon nanotubes.
This work is detailed in a paper titled, “Horseradish peroxidase-driven fluorescent labeling of nanotubes with quantum dots.” An abstract of this paper is available through PubMed.