Researchers develop portable lab on a chip to identify WMD contamination

Published 18 October 2006

Soldiers and first responders are exposed to chemical and biological threats, so there is a need to develop a quick and accurate technology to identify dangerous exposure — a technology, moreover, which can be carried easily into the field or the urban disaster area to perform on-the-spot contamination checks; researchers affiliated with MIT have developed such a technology

What with the growing risk to soldiers and first responders from nonconventional weapons, there is a premium on quick and accurate testing of military and law enforcement personnel to see whether they have been exposed to biological or chemical weapons. Researchers affiliated with MIT’s Institute for Soldier Nanotechnologies show the way for making such testing much faster and easier. The researchers have tweaked the design of a tiny pump to create a veritable “lab on a chip” — a tiny device which can perform hundreds of chemical experiments in any setting. Martin Bazant, associate professor of applied mathematics and leader of the research team, says: “In the same way that miniaturization led to a revolution in computing, the idea is that miniature laboratories of fluid being pumped from one channel to another, with reactions going on here and there, can revolutionize biology and chemistry.”

It works like this: Within the lab on a chip, biological fluids such as blood are pumped through channels about ten microns, or millionths of a meter, wide (just compare: A red blood cell is about eight microns in diameter). Each channel has its own pumps, and these pumps direct the fluids to certain areas of the chip so the fluid may be tested for the presence of specific molecules.

The MIT design offers an intriguing break from the two more traditional approaches to designing labs on a chip (neither of which, by the way, offered portability). The first is mechanical to force fluid through microchannels. This approach requires bulky external plumbing and cannot be easily miniaturized. The second approach is capillary electro-osmosis, in which flow is driven by an electric field across the chip. Current electro-osmotic pumps, however, require more than 100 volts of electricity, something not always easy to achieve in field conditions. The MIT design relies on a micropump which requires only battery power of a few volts to achieve similar flow speeds and also provides a greater degree of flow control.

For the scientifically inclined: The key to boosting energy efficiency is altering the electric field in the channel. Instead of placing electrodes at each end of the channel, as in capillary electro-osmosis, the voltage can be lowered substantially with AC applied at closely spaced microelectrode arrays on the channel floor. There is a problem here, though, as existing AC electro-osmotic pumps are too slow for many applications, with velocities below 100 microns per second. In the new system, called a three-dimensional AC electro-osmotic pump, tiny electrodes with raised steps generate opposing slip velocities at different heights, which together combine to push the fluid in one direction as a conveyor belt would. Simulations predict an 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.

In addition to the military and first responders, potential applications may include using the device in a doctor’s office and getting test results immediately. The system may also be used in traditional chemistry or biology labs to speed up processes such as DNA testing or screening for the presence of certain antigens.

The MIT group’s research was funded by the U.S. Army through the Institute for Soldier Nanotechnologies.

-read more in Martin Bazant and Yuxing Ben, “Theoretical Prediction of Fast 3D AC Electro-osmotic Pumps,” Lab on a Chip (4 September 2006) (sub. req.); see also this TechNewsDaily report