Illustration of microfluidic pump. Credit: Alan Hunt
A team University of Michigan researchers say they have figured out a way to nondestructively use glass as an electrode in certain microfluidic devices. Alan Hunt, a biomedical engineering associate professor at the university, and his research team accidentally discovered a way to get an electric current to pass nondestructively through a thin section of glass that they thought would be nonconductive dielectric.
They had been working on developing microfluidic devices, such as labs-on-a-chip, microrectors, etc., and trying to improve the circuitry in the chips. They team has been experimenting (PDF) with circuits that use ionic fluids instead of wire connections. Their method involves etching channels with a femtosecond pulsed laser in a transparent glass substrate through which ionic fluid can transmit electricity. They were designing these channels to end at certain glass termination points that served as a dielectric barrier. The use of glass is desirable because it can withstand high temperatures and organic solvents, is relatively inert and has low adsorption properties.
In one experiment, two channels in a device didn’t line up properly, Hunt says, but the researchers found that electricity did pass through the thin glass dead-end without harming the device in the process. They learned they could couple the presence of a high electric field (to provide a dielectric breakdown) and a heat-dissapation method, they could repeatedly turn the conductivity of the glass off and on.
“We were surprised by this, as it runs counter to accepted thinking about the behavior of nonconductive materials,” Hunt explains. “This is a new, truly nanoscale physical phenomenon. At larger scales, it doesn’t work. You get extreme heating and damage.
“What matters is how steep the voltage drop is across the distance of the dielectric,” he continues. “When you get down to the nanoscale and you make your dielectric exceedingly thin, you can achieve the breakdown with modest voltages that batteries can provide. You don’t get the damage because you’re at such a small scale that heat dissipates extraordinarily quickly.”
Hunt thinks his “liquid glass electrodes” will open up new opportunities in integrated circuits. “If you could utilize reversible dielectric breakdown to work for you instead of against you, that might significantly change things,” Hunt says.
He says these glass electrodes are ideal for use in lab-on-a-chip devices. “The design of microfluidic devices is constrained because of the power problem,” Hunt explains. “But we can machine electrodes right into the device.
They report that they have already build a nano-injector incorporating liquid glass electrodes. The injector acts as an electrokinetic pump capable of producing well-controlled flow rates below 1 femtoliter per second. They say the electrode can be integrated easily into other nanodevices and fluidic systems, including actuators and sensors.
A paper on the research, “Liquid glass electrodes for nanofluidics” is now published online in Nature Nanotechnology.