A commonly available epifluorescence microscope and a digital camera lie at the heart of the novel approach described by Jay Shendure of Harvard Medical School and his colleagues. Employing tiny beads just one micron wide, the researchers replicated thousands of DNA sections simultaneously. The team next used four different fluorescent dyes, which each bind selectively to one DNA base, to "read" the DNA sequence by color, passing over 14 million beads laid out in an area the size of a dime. The microscope and camera covered the same sequence multiple times and a computer program interpreted the pattern and converted it to the more familiar linear base-pair sequence. Tests on the E. coli genome indicate that this technique has an error rate of less than one mistake per million bases and that it was able to pick up small mutations between the strain used in the experiment and one deciphered using the conventional approach.
The researchers calculate that the price tag associated with their sequencing strategy is one ninth that of current sequencing setups. Improvements are still required before it can become commonplace, however. For one, its raw accuracy is still at least an order of magnitude lower than the widely used Sanger technique. But if such enhancements can be made, genome sequencing could one day be available in even the smallest laboratories, which currently can't afford it, and possibly lead to better health care. "The cost of $1,000 for a human genome should allow prioritization of detailed diagnostics and therapeutics," Church says, "as is already happening with cancer."