Automatic alien amino acid analysis: Detecting amino acids on a single microfluidic device

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  • Published: Nov 21, 2011
  • Author: Jon Evans
  • Channels: Electrophoresis
thumbnail image: Automatic alien amino acid analysis: Detecting amino acids on a single microfluidic device

Signs of alien life

When searching for signs of life on an alien world, it helps if the whole analysis takes place with as little human involvement as possible, as that human involvement tends to be millions of miles away. To this end, scientists at Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, California, have developed the first fully automated system able to conduct all the necessary steps for analyzing amino acids on a single microfluidic device.

Amino acids are thought to be good chemical markers for life, especially on Mars, as unlike DNA and proteins they probably wouldn't be broken down too easily by the highly oxidizing Martian soil. Furthermore, although amino acids can be produced by inorganic processes, life tends to favour the left-handed versions of these chiral compounds. As such, one of the rovers forming part of the European Space Agency-Nasa joint ExoMars mission, which is set to launch in 2018, will carry an instrument specifically designed to try to detect amino acids on Mars (see Separating life on Mars).

This instrument comprises two microfluidic devices known as the Mars Organic Detector (MOD) and the Mars Organic Analyzer (MOA). The MOD isolates and fluorescently labels any amino acids in the soil samples and then passes them on to the MOA, a microchip capillary electrophoresis (CE) system that separates and identifies the labelled amino acids. Now while this instrument has proven its worth in numerous tests on Earth, there would be even less chance of anything going wrong if the entire analysis took place on a single microfluidic device. This is what Peter Willis and his team at JPL have now achieved.

Valves and pumps

Their microfluidic device consists of three circular glass discs, each with a diameter of just 10cm, stacked on top of each other. Using an etching process, the scientists patterned the first and second of these discs with a complex system of reservoirs, chambers and channels, while the third disc was left blank. Between the first and second discs, they then placed a layer of flexible polymer.

This design allows the microfluidic device to house 52 individually-controllable valves, eight reservoirs and a separation channel for CE. The valves are formed by the interaction between the flexible polymer and the structures etched into the first and second glass discs. Ordinarily, the polymer lies tight against structures poking down from the underside of the first glass disc, creating a system of channels between the polymer and the rest of the first glass disc. Fluids can pass through these channels, but they're blocked at the point where the polymer lies tight against the structures.

When a vacuum is applied to these points, however, it pulls the polymer down into a chamber etched into the top of the second glass disc, opening up the channel and allowing the fluid to pass. By placing three of these valves in series and operating them in sequence, Willis and team were able to make them act like pumps for transporting fluid around the microfluidic device.

Fully automated

With this system of valves and pumps, together with a light-emitting diode-based fluorescent detector, Willis and his team are able to conduct all the steps involved in amino acid analysis, including fluorescent labelling, separation and detection, on the microfluidic device. Furthermore, because each of the valves and pumps can be operated by computer, the whole system is fully automated, simply requiring the amino acid-containing sample to be placed in the sample reservoir.

Willis and his team tested this device on a specially-prepared mixture of five amino acids, including four that have previously been detected in meteorites (alanine, glycine, serine and valine) and one that is a potential marker of terrestrial contamination (citrulline). The found that their microfluidic device could detect all of the amino acids at concentrations of around 1nM. Following this success, they are now testing the device on a variety of real-world samples.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Automatic alien amino acid analysis: Detecting amino acids on a single microfluidic device
ExoMars rover
Image: ESA

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