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Nanotech News
Single Molecule Enzymology By measuring the energy transferred between a gold nanoparticle and a fluorescent molecule, researchers have created an optical ruler capable of accurately measuring distances 50-250 Angstroms, or 5-25 nanometers. This new technique should prove useful in detecting the dynamic movements of molecules as they interact with one another, and may be particularly amenable to studying how DNA changes shape as it interacts with various proteins during gene expression. There are other techniques for measuring small distances, but the technique most applicable to studying dynamic changes in biological systems is limited to measurements of less than 10 nanometers. This technique is based on a principle known as Förster Resonance Energy Transfer (FRET), which can occur between molecular energy donors and acceptors. To make measurements over longer spans, Geoffrey Strouse, Ph.D., and his colleagues at Florida State University and the University of California in Santa Barbara decided to increase this energy transfer by using a 1-2 nanometer gold particle as the energy acceptor, analogous to using a bigger, more sensitive antenna to pull in weak radio signals. To construct their optical ruler, the researchers linked a gold nanoparticle to the end of one DNA strand and fluorescein to the end of another piece of DNA. In the experiments reported in the Journal of the American Chemical Society, the two pieces of DNA were complementary to one another, so when the two strands came together to form a double helix, the gold nanoparticle and fluorescein molecule were a known distance apart, defined by the number and identify of the base pairs lying between the nanoparticle and fluorescein. Using different lengths of DNA, the researchers were able to calibrate their ruler. In theory, this ruler could be used as follows: Instead of using two pieces of DNA that were complementary to one another, the gold nanoparticle and fluorescein could be linked to DNAs that were complementary to the DNA surrounding a gene being studied. As various regulatory proteins bound to and altered the shape of the gene, the gold nanoparticle and fluorescein would move relative to each other, providing insights into how the structure of DNA is altered by the molecules that interact with it. This could also be useful in studying how DNA-binding anticancer drugs function. This work, which was supported by the National Institutes of Health, is detailed in a paper titled, "Nanometal surface energy transfer in optical rulers, breaking the FRET barrier," published in the March 9, 2005 issue of the Journal of the American Chemical Society. An abstract of the paper is available through PubMed. |
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