The Great Potential of Quantum Dot Imaging

The development of nanocrystals known as quantum dots over the past 20 years has evolved into a new method that allows scientists to study cell processes at the level of an individual molecule, and may result in better ways to detect and treat cancers.

Semiconductor fluorescent quantum dots, called qdots, also have potential for high-resolution cellular imaging and the long-term study of single molecules and their movement within cells, according to researchers at the University of California, Los Angeles (UCLA; CA, USA) and Stanford University (Palo Alto, CA, USA). The investigators published their work in the January 28, 2005, issue of the journal Science.

Qdot imaging is a new way to see biologic processes functioning within cells and in small animals. Probes can be attached to a specific protein or receptor to track it and see what other molecules it interacts with, what areas of the cell it is in, and what signaling pathways the protein may use for performing typical cell functions and abnormal functions that may result in cancer. Because qdots are nanocrystals--minuscule bits of rock one-billionth of a meter in size--they provide excellent contrast for imaging with an electron microscope.

The UCLA investigators believe that qdots might be utilized one day to do two things--diagnose and treat cancer. The technology will enable investigators to find a tumor within the body, look at it very specifically at the cellular level to determine what kind of cancer it is, and then maybe arm it with therapies developed to kill the disease.

Qdots have so much potential because they can be color-coded, with different colors utilized to label different cell mechanisms, different cancers, or different stages of the same cancer. At present, a positron emission tomography (PET) scan can tell clinicians the sites of tumors throughout the body, based on targeting the PET probe to an individual tumor marker. However, with qdots, several different markers of the same tumor could be simultaneously "painted,” producing a color barcode for real-time optical biopsy and diagnosis.

In the study, qdots were labeled with a positron-emitting isotope and injected into mice. Utilizing a PET scanner, scientists were able to watch over time as the qdots traveled through the vascular system and to the liver. The same technique may be used with patients, who could be injected with a mixture of different colored qdots that would label the cancer cells. Once they accumulate at the tumor site, the positrons emitted from the qdots could be imaged with PET scanners.






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