Molecular ID Codes
Existing ways of labeling and visualizing DNA and protein molecules rely on a limited palette of radioactive elements, chemical dyes, or natural fluorescent protein molecules, such as green fluorescent protein. Biological research urgently needs a wider array of reliable, robust, and safe labeling molecules to facilitate studies for determining the types of molecules present in a cell, their cellular location, activity, and concentration. Now, a team of scientists led by Shuming Nie of Indiana University has invented a way to bar code DNA using tiny light-emitting crystals known as quantum dots. By embedding these quantum dots in microbeads bearing short strands of DNA, the researchers have created labels that can recognize particular DNA molecules of interest and tag them with a unique identification code (Nature Biotechnology, Vol. 19, No. 7, 01 July 2001).
Alternative labeling techniques, which often rely on radioactivity or organic dyes, have several drawbacks: Radioactive markers can have short half-lives and are toxic, while organic dyes come in a limited number of colors and may lose their glow too quickly. Quantum-dot microbeads are superior to these approaches in several ways. For instance, compared with organic dyes, quantum dots are brighter, more stable, and give sharper signals. Moreover, the color of a quantum dot can easily be changed by changing its size, yet differently colored dots can all be excited by a single wavelength of light-an approach not possible with other labeling systems.
The researchers predict that several tens of thousands of uniquely coded beads could be built using different combinations of colors and intensity levels. These molecular ID codes could then be used to simultaneously analyze a large number of molecules. Ultimately, the codes should be easily be tagged onto both nucleic acids and proteins-facilitating research in many areas of biomedical research, including drug screening, gene expression studies, and clinical diagnostics.
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