By addressing voltage issues, researchers take another step toward enabling true portability.
MIT researchers are helping to develop a tiny diagnostic device that could be carried into battle. By tweaking the design of a tiny pump, researchers affiliated with MIT’s Institute for Soldier Nanotechnologies have taken a step toward making an existing miniature Lab on a Chip fully portable so the tiny device can perform hundreds of chemical experiments in any setting.

Within the lab on a chip, biological fluids, such as blood, are pumped through channels about 10 microns wide. Each channel has its own pumps, which direct the fluids to certain areas of the chip so they can be tested for the presence of specific molecules.

Until now, scientists have been limited to two approaches to designing labs on a chip, neither of which offer portability. The first is to mechanically force fluid through microchannels, but this requires bulky external plumbing and scales poorly with miniaturization. The second approach is capillary electro-osmosis, where flow is driven by an electric field across the chip. Current electro-osmotic pumps require more than 100 volts of electricity.

The MIT researchers have now developed a micropump, which requires only battery power to achieve similar flow speeds and also provides a greater degree of flow control. The key to boosting energy efficiency is altering the electric field in the channel, says Martin Bazant, associate professor of applied mathematics and leader of the research team.

Instead of placing electrodes at each end of the channel, as in capillary electro-osmosis, the voltage can be lowered substantially with alternating current (AC) applied at closely spaced microelectrode arrays on the channel floor. Existing AC electro-osmotic pumps, however, are too slow for many applications, with velocities below 100 microns per second.

In the new system, known as a three-dimensional AC electro-osmotic pump, tiny electrodes with raised steps generate opposing slip velocities at different heights, which combine to push the fluid in one direction, like a conveyor belt. Simulations predict a dramatic improvement in flow rate, by almost a factor of 20, so that fast flows, comparable to pressure-driven systems, can be attained with battery voltages.

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