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Posted: December 4, 2006

Quantum dots speed analysis of cellular cancer markers

(Nanowerk News) In attempt to identify biological markers, or biomarkers, that can signal the presence of cancer and help oncologists determine the best course of therapy when cancer is present, teams of investigators are scouring stored tissue samples obtained from thousands of cancer patients. Such studies are laborious and suffer from limited sensitivity, making it difficult to quantify rare biomarkers and develop data that might reveal a correlation among specific patterns of protein expression and specific types of cancer.
Researchers at the University of Toronto may have a solution to this problem, one that uses quantum dots to quantify protein expression in tumors in an accurate and sensitive manner and is amenable for use in high-throughput assays of clinical tissue samples. The investigators, led by Warren Chan, Ph.D., have published the specifics of this new system in the journal Nano Letters ("High Throughput Quantification of Protein Expression of Cancer Antigens in Tissue Microarray Using Quantum Dot Nanocrystals).
The breakthrough in sensitivity and accuracy comes from two parallel developments. First, Chan and his colleagues labeled biomarker detection molecules with quantum dots. In the reported study, the investigators used antibodies that bind to specific cancer biomarkers, but they could have used aptamers or peptides, such as those being developed as part of the National Cancer Instituteís Alliance for Nanotechnology in Cancer program. Quantum dots generate a much more powerful fluorescent signal than typical fluorescent dyes, which provides a large increase in sensitivity compared to other methods. Quantum dots are also available in multiple colors, allowing the investigators to tag each antibody with a uniquely colored quantum dot.
Next, the investigators built a novel optical spectroscopy and data analysis system that cancels out the significant background fluorescence that tissue samples themselves emit. The data analysis system also determines the amount of a given biomarker relative to each cellís contents, providing data that is then more easily compared across different tissue samples.
When used to image quantum dot labeled tissue samples, the new system can accurately detect a single quantum dot bound to a single biomarker in the imaged tissue. The high sensitivity and accuracy afforded by this new system should enable pathologists to detect even small changes in tumor progression and differentiate among multiple tumor types.
Source: National Cancer Institute
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