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Icy resolution
In the competitive realm of microarrays for screening DNA, the goal is always to make the process better, faster, and cheaper, and David R. Walt and colleagues at Tufts University think they have just the trick. They describe a new fiber-optic system that does not require labeling of the target DNA and, thus, eliminates a major bottleneck. The researchers begin with a bundle of optical fibers and use a wet-etching procedure to fabricate an array of tiny wells at the bundle’s end. Then they create a variety of molecular beacons—hairpin-shaped pieces of DNA with a fluorophore at one end and a quencher at the other. Each beacon is a DNA probe that unfolds when it finds its target. Because the fluorophore and quencher are separated as the beacon unfolds, the beacon lights up, making it obvious that a match has been found. Also attached to each molecular beacon is a microsphere that has been loaded with dyes. The combination of dyes serves as a kind of bar code for the microsphere. For example, one combination will be used for the microspheres attached to beacons with a certain mutated DNA sequence, and another combination will indicate a second mutated sequence. Once the beacon–microsphere units are ready, they are randomly distributed over the array at the end of the fiber-optic bundle. Each well in the array winds up with one microsphere. This arrangement makes detection easy: Each optical fiber carries only the signal from the corresponding microsphere, so the signals are spatially resolved. The researchers report that there is little crosshybridization (
