By modifying the surface of tiny, fluorescent crystals called quantum dots, Carnegie Mellon scientists believe they may have made a “promising step” toward non-invasive imaging in humans to detect, monitor and treat diseases such as cancer. The scientists, led by Byron Ballou in the Mellon College of Science's Molecular Biosensor and Imaging Center, altered quantum dots to fluoresce for an unprecedented eight months in a living animal, a technological feat that should improve long-term studies and help pave the way for clinical applications.

Ballou and his colleagues, in collaboration with the Quantum Dot Corporation, found that coating the company's quantum dots (Qdot® Particles) with one type of polymer prevented them from breaking down inside a living mouse. By adding a second polymer coat, colleague Lauren Ernst showed that they could prolong the time quantum dots circulate within the animal. Both these features enabled the quantum dots to deposit effectively within tissues.

"Because uncoated quantum dots are too fragile for most biological studies in living animals, the coating is the most critical step," explained Ballou. "The new coatings allowed us to observe quantum dots much longer than previously demonstrated."

First commercialized by the Quantum Dot Corporation in 2002, Qdot Particles are nanosized crystalline particles composed of a few hundred to a few thousand atoms of a semiconductor material. They emit light in a variety of colors, depending on size.

In principal, scientists could modify the surface of these long-lived quantum dots by attaching molecules on their surface that target tumors. Acting as molecular beacons, these quantum dots would enable physicians to image tumors more effectively and remove cancers with greater accuracy, Ballou said. Their quantum dots also could be modified with molecules to create implantable biosensors for a range of clinical applications, such as reporting how tumors respond to therapy.

"Before these applications can happen, quantum dots must first be modified so that they remain in circulation long enough, and we must ensure that quantum dots don't harm healthy cells," he said.