Portland, Ore. On Sept. 11, 2001, water resource managers across the United States got a wake-up call. In addition to desalinization projects and efforts to remove industrial waste, they now faced the possibility of intentional acts of poisoning public water.
Sandia National Laboratories thinks it can help. To head off terrorist attacks on U.S. drinking water, Sandia has adapted its lab-on-a-chip, called the MicroChemLab, to real-time monitoring of public waterworks. The device aims to give water resource managers a real-time readout not only of poisons, but also of the naturally occurring toxins for which waterworks can now sample only randomly.
The microfluidic-chip-based MicroChemLab prototype, fabricated with microelectromechanical systems, today resembles a 25-pound suitcase with two water collectors protruding from it. It is currently being tested in the Contra Costa Water District in California, collecting and analyzing water samples every 30 minutes and reporting the results in real-time over a wired link to researchers at Sandia. If testing is successful, future production versions of the MicroChemLab will be eligible for installation in any of the more than 300,000 U.S. public-supply water wells, 55,000 utilities and 120,000 rest stops and campgrounds.
"We are actually testing two MicroChemLab platforms, using different approaches," said Wayne Einfeld, who heads the sensor development focus area within Sandia's Water Initiative (www.sandia.gov/water). "One is testing for the proteins of harmful bacteria in Contra Costa, Calif., by using capillary electroporesis to perform mass spectrometry. The other one, in New Mexico, looks for gas phase toxins that result from overchlorination."
The California and the New Mexico MicroChemLabs are completely battery-powered and use programmable PIC microprocessors with electrically erasable on-chip memory for quick software updates in the field. They draw less than 10 watts, compared with hundreds of watts per test in a normal lab, and can perform up to 12 tests a minute, against 12 days per test using normal lab turnaround.
Under the hood
Microfluidic devices use micron-size channels on a chip to pipe samples and reagents into picoliter-size reaction chambers that not only reduce the size and cost of test equipment, but also speed up testing. By realizing the operations of a mass spectrometer (California) and a gas chromatograph (New Mexico), microfluidic channels enable chip-size devices to perform in minutes the same kind of complex laboratory tests that now must be done with milliliters of samples and reagents over a period of days.
To realize a chip-size mass spectrometer, the water molecules from a sample are first tagged with fluorescent markers, then entered into a long microfluidic channel. As with a normal mass spectrometer, the heaviest elements are attracted to the detector electrically, with the lightest elements arriving last. A laser beam in front of the detector induces fluorescence, so that the time of arrival can be precisely timed. By calculating the atomic weight from the time of arrival, the Sandia researchers have been able to distinguish one protein from another.
"Our next step after the Contra Costa testing will be to get [the system] to perform a pattern recognition to identify bacteria from the mix of proteins we detect with the MicroChemLab," said Einfeld. "Eventually, we should be able to identify different bacterial species."
The second MicroChemLab, which is testing water at Sandia's main location in Albuquerque, is a pint-size gas chromatograph that tests in less than five minutes. Gas chromatography detects the chemical composition of toxins in water by bubbling a gas through the system and collecting trihalomethanes from that gas. The collector is heated, sending the trihalomethanes through the gas chromatograph's separation column and then over a surface-acoustic-wave detector to determine composition. Commercial gas chromatograph columns are about 4 to 5 inches in diameter, but the MicroChemLab columns measure about half a square inch.
"Right now we are field-testing it at detecting trihalomethanes, an undesirable by-product of chlorination," said Curtis Mowry, principal investigator for the New Mexico-based MicroChemLab.
The MicroChemLab is being developed under Sandia's cooperative research and development agreement with partners in California, including CH2M Hill Inc. and Tenix Pty Ltd., an Australian engineering-services company.