Ammonia oxidation in a microreactor

Picture for: What is a microreactor? / Continuous or batch? / How do you make a microreactor?

(Note: source has © on the figure)

Here's a diagram of a microreactor that's been developed for DNA analysis studies. Photolithography was used to create built-in devices that include a nanoliter liquid injector, sample mixer, reaction chamber, electrophoretic separator, and a fluorescence detector. Detectors and heaters were built up on a silicon wafer while the fluid channels were photoetched in a glass wafer that was then bonded to the silicon wafer. The liquid channels are 500 microns wide by 50 microns deep. The bonded assembly measures 47 mm long by 5 mm wide by 1 mm high. Four reactors placed side by side would cover an area equal to that of two standard postage stamps. The silicon/glass assembly is ultimately bonded to a printed circuit board.

The size of the sample metered into the reactor is 120 nanoliters. The reaction temperature can be controlled to within ± 0.1 degree C and the temperature can be ramped at rates up to 10 degrees C per second. (Cyclic temperature ramping is needed for the polymerase chain reaction that's used to amplify, or increase, the concentration of DNA in a sample.) The variation of temperature in the microreactor chamber from the bottom, where the heaters are located, to the top was found to be less than 1 degree C. The authors note the fluorescence detector is sensitive and is able to detect DNA at concentrations as low as 10 nanograms per microliter.

The potential applications for a device like this include handheld analyzers for medical testing and forensics.

Source: Burke DT et al. 16 October 1998. Science. (282) 484-487.