A novel thermocycling machine based on a microcapillary equipped with bidirectional pressure-driven flow and in situ optical position sensors is described. A 1-microL droplet of reaction mixture moves between three heat zones in a 1-mm-i.d., oil-filled capillary using a multielement scattered light detector and active feedback. Dwell times and accelerations can be adjusted independently. As a demonstration of the device, 30 cycles of a 500-base pair product were performed in 23 min with 78% amplification efficiency. This result compares well with previous high-speed thermocyclers. Theoretically, the arrangement can approach a time of 2.5 min for 30 cycle amplifications of a 500-base pair product.

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