Detecting amino acids on the red planet
by Robert Sanders
professor Richard Mathies and his colleagues
are working on an instrument that would use gene sequencing technologies
to probe Mars dust for evidence of life-based amino acids, the building
blocks of proteins. With two development grants from NASA totaling nearly
$2.4 million, he and his collaborators hope to build a Mars Organic Analyzer
(MOA) to fly aboard NASA's roving, robotic Mars Science Laboratory mission
and/or the European Space Agency's ExoMars mission, both scheduled for
launch in 2009.
MOA looks not only for the chemical signature of amino acids, but tests
for a critical characteristic of life-based amino acids: They’re all left-handed.
Amino acids can be made by physical processes in space—they’re often found
in meteorites—but they’re about equally left- and right-handed. If amino
acids on Mars have a preference for left- handed over right-handed amino
acids, or vice versa, they could only have come from some life form on
the planet, Mathies said.
feel that measuring homochirality—a prevalence of one type of handedness
over another—would be absolute proof of life,” said Mathies, a member
of the California Institute for Quantitative Biomedical Research (QB3)
. “That’s why we focused on this type of experiment. If we go to Mars
and find amino acids but don’t measure their chirality, we’re going to
feel very foolish. Our instrument can do it.”
acids, the building blocks of proteins, can exist in two mirror-image
forms, designated L (levo) for left-handed and D (dextro) for right-handed.
All proteins on Earth are composed of amino acids of the L type, allowing
a chain of them to fold up nicely into a compact protein. “After amino
acids are detected, the labeled amino acid solution is pumped down into
microfluidics and crudely separated by charge,” Mathies said. “The mobility
of the amino acids tells us something about charge and size and, when
cyclodextrins are present, whether we have a racemic mixture, that is,
an equal amount of left- and right-handed amino acids. If we do, the amino
acids could be non-biological. But if we see a chiral excess, we know
the amino acids have to be biological in origin.”
The state-of-the-art chip, designed and built by graduate student Allison Skelley, consists of channels etched by photolithographic techniques and a microfluidic pumping system sandwiched into a four-layer disk four inches in diameter.