MIT is reporting that its Dr. Martin Bazant and colleagues from the Institute for Soldier Nanotechnologies have developed a way to push fluids at high speed through microchannels inside portable “lab on a chip” devices. This novel method, called alternating current electro-osmosis, will allow for the development of miniaturized devices for on and off the battlefield diagnostic uses.
Within the lab on a chip, biological fluids such as blood are pumped through channels about 10 microns, or millionths of a meter, wide. (A red blood cell is about 8 microns in diameter.) 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, but the MIT researchers have now developed a micropump which requires only battery power (a few volts) 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, Bazant said. 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 twenty, so that fast (mm/sec) flows, comparable to pressure-driven systems, can be attained with battery voltages. Experiments in the lab of Todd Thorsen, assistant professor of mechanical engineering, have recently demonstrated the effectiveness of the design.
Thorsen’s group is working toward integrating the pumps into a portable blood analysis device, which soldiers could carry onto the battlefield. If exposure to chemical or biological weapons were suspected, the device could automatically and rapidly test a miniscule blood sample, rather than sending a large sample to a lab and waiting for the results. The chips are so small and cheap to make that they could be designed to be disposable, Bazant said, or they could be made implantable.
Link at MIT…