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MEETING NEWS HPLC 2004 —Philadelphia, Pa.
Microfluidics for Mars Richard Mathies of the University of California, Berkeley, and colleagues at the University of California, San Diego (UCSD), the Jet Propulsion Lab (JPL) at the California Institute of Technology, and Leiden University (The Netherlands) are eager to demonstrate the Mars Astrobiology Probe (MAP). The MAP is an instrument that extracts amino acids from samples and characterizes their presence, composition, and chirality. The aim is to send the MAP to Mars on future missions to analyze the soil for amino acids. If amino acids are found in Martian soil with an excess of a certain chiral isomer, it could be evidence of extraterrestrial life. The MAP consists of two parts, the Mars Organic Detector (MOD), developed by Frank Grunthaner (JPL) and Jeff Bada (UCSD), and the Mars Organic Analyzer (MOA). The MOD is used for purification and preliminary detection purposes (Planetary Space Sci. 2000, 48, 1087–1091). “It is an instrument that involves the sublimation of amino acids or amines from a sample onto a cold finger,” says Mathies. Amino acids have to be sublimed away from the samples because high concentrations of salts in the samples can interfere with subsequent analyses. As the amino acids condense on the cold finger, they react with a dye, fluorescamine, and become labeled. A buffer solution carried in tiny capillary tubing is pumped onto the cold finger to dissolve the labeled amino acids. Once the amino acids dissolve, the buffer gets drawn back into the capillary tubing and taken to the MOA. The MOA is a microfluidic device that separates amino acids by high-voltage CE. The MOA’s significant advantage is its ability to process submicroliter volumes. Microfluidic devices are commonly hampered by the inability to handle nanoliter volumes at the front end. “You have an analysis device that can analyze nanoliters
to picoliters, [but] you can only pipette in microliters. You can’t exploit the technology,” says Mathies.
COURTESY OF RICHARD MATHIES, UNIVERSITY OF CALIFORNIA, BERKELEY
Rajendrani Mukhopadhyay reports from
Manifold
PDMS membrane
Fluidic layer
Separation channels
The Mars Organic Analyzer separates nanoliter volumes of amino acids by high-voltage CE. See http://astrobiology.berkeley.edu for more information.
Mathies says that the design of the MOA as a four-layer stacked wafer addresses the challenge. Two of the layers form miniscule pumps, valves, and actuators, which can carry nanoliter volumes through the MOA. Mathies describes it in more detail: “Two of the layers are the traditional glass capillary systems. But one of the layers is a poly(dimethyl siloxane) (PDMS) membrane valve, and the other layer is a pneumatic actuation fluidic routing circuitry, which allows you to move fluids around on a plane above the microchip system that’s used for electrophoresis.” Alison Skelley, a graduate student involved in the project, adds, “We can finally deal with small volumes and make everything automated and finely controlled in a microfabricated device.” The PDMS membrane has been instrumental in the development of the MOA, but it will probably only be suitable for terrestrial applications. Skelley says instruments designed for Mars have to survive rigorous tests. “One of the tests you have to be able to withstand is
literally dumping your entire device into liquid N2 and showing that it works. PDMS is probably not going to be able to withstand that test. We are developing membranes that can withstand extremes of temperature and still be able to operate,” she says. Once the amino acids are separated by the MOA, they are characterized for chirality (J. Chromatogr. A 2003, 1021, 191–199). The ratio of optical isomers in the amino acids is key for determining the presence of life. Biological processes favor one chiral isomer over the other, so the presence of a single isomer in an amino-acid chain suggests that the chain was synthesized by a living entity. Racemic mixtures point to nonbiological processes. Since the detection limits of amino acids by the MAP instrument are in the parts per trillion, the hope is that even trace amounts left by extinct life forms can be picked up on Mars. Mathies and his co-workers have already taken the MAP instrument on a test run in the Panoche Valley in California. The valley has deposits of jarosite, a mineral that tends to be deposited from acidic, sulfate-rich liquids. Jarosite has been detected by the rover Opportunity on Mars. Mathies says the MAP instrument successfully extracted and analyzed parts-per-billion to partsper-trillion amounts of amino acids from jarosite samples from the Panoche Valley, demonstrating the feasibility and validity of such analyses. Mathies and his colleagues are excited by the prospects of microfluidic devices making their way to Mars. Mathies says, “The joke is that this is a technology where the sky is not the limit.” But Mathies points out that extraterrestrial science isn’t the only application for devices like the MAP. “This type of technology opens the door to what I call microfluidic microprocessors with applications in diagnostics, genomics, forensics, as well as infectious disease detection. It really paves the way for the practical implementation of labon-chip technology.”
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