Molecular beacons would be ideal diagnostics for detecting point mutations in disease genes if they weren’t so hard to distinguish. These noose-shaped DNA segments are engineered to light up when they bind to target DNA, such as a mutated cancer gene. However, it has been difficult to detect the difference between complete complementarity and binding that is mismatched by one or two nucleotides, because an imperfect match still has a chance—though a smaller one—of binding and fluorescing.

Xudong Fan and Yuze Sun of the University of Michigan bypassed the problem by creating an amplification step based on physics rather than biochemistry. They inserted the molecular beacons and target sequences that differed by one nucleotide into the head of a liquid laser, thereby replacing the laser’s light-generating crystal or usual liquid dye with the sample medium. When mismatched, the probes lit up in the laser chamber, but the fluorescence was...

The device is useful for low detection limits, says Weihong Tan at the University of Florida, but setting the threshold for laser activation will take a bit of work, so the tool is not ready for mass consumption just yet. (Angew Chem Int Ed, 51:1236-39, 2012.) .

LASER DETECTIONOptofluidic laser cavityOn/off laser (digital scale)Detection of target sequences from a pool of single-base mismatched sequences240: 1

FLUORESCENCE DETECTION Regular vial or cuvette Intensity of fluorescence (analog scale) Detection of target and single-base-mismatched sequences separately ~ 1



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