Portland, Ore. -- Laboratories-on-a-chip pack the punch of an overnight testing facility, but get results in minutes by virtue of nanoliter-size chambers that speed up chemical reactions. Of the dozens of kinds of micropumps that can be used to fill those chambers, only a few avoid contaminating the nanoliter-size samples. Recently the University of Utah showed a design that avoids contamination via the use of vacuum-driven, plastic layered membranes.
"Our handheld device takes a different approach--it runs on batteries that drive a small off-the-shelf air pump, which we use as a valve to run the micropumps that are fabricated into our chip," said professor Bruce Gale, a bioengineer at the University of Utah (Salt Lake City). Gale fabricated the prototypes with bioengineering doctoral candidate Mark Edding.
The beauty of the University of Utah design is that a tester the size of a deck of cards could contain hundreds or thousands of independent chambers, each prefilled with the reagents for an array of tests. Then, all the chambers could be supplied with the sample to be tested simultaneously, using nothing more that a battery-powered air pump. A reader no bigger than a deck of cards would accept blank, credit-card-size test cards. Its chambers would be filled with a sample from the patient, and the results of the test would be read out in minutes. After testing, the disposable card would be thrown away. Currently, patients have to wait overnight for a traditional medical lab to do the evening's batch run.
The prototype demonstrates the concept with a chip that contains an array of 10 tiny pumps, permitting 10 simultaneous tests, say for sarin, mustard gas, anthrax, botulism, ricin, smallpox, polio, malaria, C4 and dynamite. But in the future as many as a thousand micropumps could be fabricated on a similarly sized chip.
The micropump works by virtue of a three-layer process. The two outside layers contain channels and reservoirs, but the middle layer is impermeable to liquids, passing only the air that activates the pumping action on a channel.
In operation, the reservoirs on the top layer are filled with the sample, say, of blood. The sample is routed by microchannels into premeasured wells that are poised to be pumped. The bottom layer then controls the sequence in which the samples are tested. Air inlets from the pump feed the microchannels through which specific pressure, or vacuum, can be applied to work the liquid squeeze-bottle-style pumps. The air never mixes with the samples, but only applies pressure to the prefabricated membranes in the disposable test chip.
In testing, Gale's micropumps produce a flow of 200 nanoliters per minute--about five times less than the amount that fits on the head of a pin, but plenty to perform hundreds of tests simultaneously.
The micropump was created at the university's Center for Biomedical Fluidics, a part of Utah's Centers of Excellence program, with funding from the National Science Foundation.