Research Details

Employing a novel three-dimensional alternating-current electro-osmotic (3D ACEO) pump, a group of MIT researchers led by Prof. Martin Z. Bazant may have just taken a substantial leap forward in the development of microfluidics, a leap that could enable portable, or even implantable, biomedical lab-on-a-chip devices. Existing ACEO pumps move fluids over a planar microelectrode array applying an AC voltage. “However,” says Prof. Bazant, “this design is inefficient, since it involves opposing surface flows, where one direction slightly ‘wins’ over the other due unequal electrode widths.” Prof. Bazant theoretically predicted that dramatic increases in flow rate could be achieved – by more than order of magnitude – by using electrodes with raised steps. His 3D design actually turns what was previously considered a drawback of ACEO into a means of increasing flow speed. “The basic idea,” says Bazant, “is to recess the reverse flows to form ‘rollers’ for the raised pumping flow, thus forming a ‘fluid conveyor belt.’” Bazant’s collaborators in the lab of Prof. Todd Thorsen have demonstrated that the concept really works. Using the new 3D design, the team has fabricated, by far, the fastest low voltage (<10 Volt) AC electrokinetic pumps. They expect to achieve mm/second velocities after design optimization. To reach similar flow speeds, standard DC electro-osmotic pumps require a high voltage power supply (> 100 Volt) and produce undesirable electrochemical reactions. By working at battery voltages with low power consumption (< 10 milliWatt), the team foresees the possibility of portable lab-on-a-chip devices, where fluids are pumped and mixed at the micron scale by 3D ACEO and other phenomena of induced-charge electro-osmosis (ICEO), also springing from Bazant’s theoretical work. Research in ICEO flows is ongoing, with the goal of being able to manipulate common electrolytes, such as blood and other biological fluids, through microchannels. Current pressure-driven systems, many of which require substantial external plumbing, are not very sensitive to the fluid, but they offer little local flow control and require extraordinary – even unfeasible – pressures when channel sizes approach the micron scale. ICEO can generate fast, tunable flows in microchannels, but seems limited to relatively dilute electrolytes (< 10 mM), for reasons currently under investigation. Nevertheless, Jeremy Levitan (Bazant's postdoc) has successfully demonstrated rapid DNA hydridization microarrays and ELISA immunoassays using ICEO flows in 10x diluted buffer solutions. These are important milestones for Prof. Thorsen’s vision of a portable ICEO-based microfluidic device for early detection of exposure to toxic warfare agents. Similar devices could also be used for point-of-care diagnostics in civilian medical applications. The new pumping devices are being developed as part of a broader effort to increase the safety of Soldiers and first responders at MIT's Institute for Soldier Nanotechnologies.