Quantum dots underneath the
microscope; © Pixelquelle.de
The technique involves an unusual blend of organic and inorganic components. "We are the first to demonstrate the use of quantum dots as a DNA sensor," Jeff Tza-Huei Wang, senior author of the paper said.
Wang, an assistant professor in the Department of Mechanical Engineering and the Whitaker Biomedical Engineering Institute at Johns Hopkins, led his team in exploiting an important property of quantum dots: They can easily transfer energy. When a laser shines on a quantum dot, it can pass the energy on to a nearby molecule, which in turn emits a fluorescent glow that is visible under a microscope.
To create their nanosensor, the researchers mixed two DNA probes and quantum dots. The probes are complement to the DNA sequence the researchers are seeking. One probe is connected to a Cy5 molecule that glows when it receives energy. The other probe is connected to Biotin. Biotin sticks to yet another molecule called streptavidin, which coats the surface of the quantum dot. Then all was put into a lab dish containing the DNA the researchers were trying to detect.
Then nature took its course. First, the two DNA probes linked up to the target DNA strand, holding it in a sandwich-like embrace. Then the biotin on one of the probes caused the DNA "sandwich" to stick to the surface of the quantum dot. Finally, when the researchers shined a laser on the mix, the quantum dot passed the energy on to the Cy5 molecule that was attached to the second probe. The Cy5 released this energy as a fluorescent glow.
To test the new technique, Wang's team obtained DNA samples from patients with ovarian cancer and detected DNA sequences containing a critical mutation. "This method may help us identify people at risk of developing cancer, so that treatment can begin at a very early stage," Wang said.
COMPAMED.de; Source: Johns Hopkins University