QUANTUM DOTS: A NEW HOPE FOR CANCER

Fluorescent semiconductor nanocrystals, also known as quantum dots, are atom-sized clusters that emit rainbow-colored light. Researchers anticipated using quantum dots in computing, optics, and electronics when they were initially created in the early 1980s. However, the first practical applications of these tiny semiconductor bits may be in biology and medicine, where they show promise as a substitute for fluorescent chemical dyes and proteins for tagging and imaging biological molecules in vitro and in vivo. Quantum dots provide distinct benefits over ordinary fluorescent dyes, ranging in size from 2 to 10 nanometers (approximately equivalent to a medium-sized protein). Scientists can make dots that emit light in a wide range of wavelengths, or colors, that are less prone to overlap than organic dyes by simply changing the crystal size. Moreover, whereas each organic dye requires a specific wavelength of light to be activated, a single light source may excite quantum dots of many hues, allowing scientists to identify and detect multiple targets at the same time. Quantum dots are significantly brighter than organic dyes and sustain their light for much longer, in addition to their “multiplexing” potential. According to Min Song, Ph.D., a program director at the National Cancer Institute, there are numerous possible cancer-related uses. They include sensitive in vitro diagnostic tests, high-throughput multiplex gene and protein expression analysis in clinical specimens, and long-term biomolecule observation during malignant cell transformation in culture.

Quantum dots were not suited for biological applications until roughly 5 years ago. The dots feature a water-repellent outer layer that renders them insoluble in biological environments with a lot of water. In September 1998, two research groups revealed in Science that they had developed methods to conjugate, or chemically link, water-soluble quantum dots to biological molecules such as antibodies, allowing them to be used to mark specific biological targets. Researchers either replaced the dots’ hydrophobic outer layer with a hydrophilic outer layer or replaced the dots’ hydrophobic outer layer with a hydrophilic outer layer to make the dots water-soluble and allow conjugation to biomolecules. However, there were still several technical constraints. In biological contexts, the first generation of water-soluble quantum dots fluoresced weakly and tended to clump together and cling to things other than their intended targets. Some of them were lethal to living cells. However, new ways for changing the surface chemistry of quantum dots have been demonstrated in a series of subsequent articles, demonstrating that these issues have been overcome. “We’re witnessing an explosion of [biological] applications—fantastic!” it’s said Shimon Weiss, D.Sc. of the University of California, Los Angeles, who led one of the seminal 1998 research. According to ShumingNie, Ph.D., principal author of the second important 1998 work, “certain bioconjugated quantum dots are now commercially available.” “That opens up the whole field—no it’s longer constrained to just a few research organizations,” said Nie, who works at Georgia Tech and Emory University in Atlanta.

References:

1Jemal A, Bray F, Center MM, et al. Global cancer statistics. cancer J Clin 2011; 61: 69-90.

2Lauffenburger DA, Horwitz AF. Cell migration: a physically integrated molecular process. Cell 1996; 84: 359-369.

3. Ridley AJ, Schwartz MA, Burridge K, et al. Cell migration: integrating signals from front to back. Science 2003; 302: 1704-1709.

4 Sanz-Moreno V, Marshall CJ.The plasticity of cytoskeletal dynamics underlying neoplastic cell migration.Currin CellBiol 2010; 22: 690-696