Instruments
Lab-On-a-Chip Application Development Portable Test System (LOCAD-PTS)
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| The LOCAD-PTS reader, cartridge (below reader) and swabbing unit (to the right). |
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The Lab-on-a-Chip Application Development Portable Test System (LOCAD-PTS) is a macrofluidic capillary-based instrument that can detect and measure the concentration of microbes on surfaces. It is currently undergoing trials on the International Space Station (ISS).
As of this writing, the instrument is being used to test for Gram-negative bacteria. Upcoming experiments will test for yeast, mold, and Gram-positive bacteria.
The technology provides rapid assessment, taking only 5 to 15 minutes to produce results. This is much quicker than standard culturing methodologies, which can take two days to detect many bacteria and up to a week for some yeasts and molds. It is also extremely sensitive, capable of detecting as little as ten bacterial cells per milliliter (0.05 to 5.0 EU/ml).
Testing aboard the ISS has demonstrated that the principle behind the LOCAD-PTS works and has enabled the space program to gain on-orbit experience with this technology in preparation for potential use on flights to the Moon or Mars.
How it works
LOCAD-PTS consists of a swabbing device, a cartridge containing biological compounds that react with the analyte (whatever is being detected--in the current experiments, Gram-negative bacteria) by changing color, and a handheld spectrophotometer that measures the intensity of the color as an indicator of the concentration of the analyte.
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| An astronaut uses the swabbing tool to take samples from a surface... |
...and then injects the sample, which has been mixed with water, into the LOCAD-PTS cartridge. |
The swabbing tool includes a felt pad which an astronaut wipes on the surface under investigation. He or she then attaches a dispensing tip and uses the tool's syringe-like action to push sterile water through the pad, through the tip, and into the cartridge that has been inserted into the meter. Prior to dispensing the sample into the cartridge, water is flushed through the dispensing tip to eliminate any air bubbles it may hold.
As it travels through the pad, the water picks up any microbes that may be there and carries them to the cartridge. In the current experiments, the sample fluid reacts with a preparation of enzymes inside the cartridge. These enzymes, part of a substance known as LAL (limulus amebocyte lysate), are extracted from the blood of a horseshoe crab and modified so that the substance turns yellow in the presence of lippopolysaccharide (LPS), an endotoxin found in the cell walls of Gram-negative bacteria.
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| LAL is a chemical harvested from the horseshoe crab, a 300-million year old species closely related to scorpions and spiders. The animals are not harmed in the process. |
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The meter measures the intensity of the color and presents the results in an LCD (liquid crystal diode) display. The stronger the color, the higher the concentration of bacteria in the sample.
The instrument flying aboard the ISS is an adaptation of a commercial version called the "Endosafe PTS." While the commercial version ran on batteries, the ISS version is powered by the ISS electrical system. The ISS instrument also features a computer interface and circuit boards dipped in a plastic solution--in a process known as conformal coating--to prevent the growth of metallic whiskers that can cause short-circuiting.
As mentioned earlier, a cartridge that detects Gram-negative bacteria is currently being tested on the ISS. Cartridges that detect yeast, mold, and Gram-positive bacteria are scheduled for launching to the ISS in 2008. Future cartridges may be capable of detecting viruses, hazardous chemicals, and other substances. Sampling of air and water supplies may join the current sampling of solid surfaces.
The versions of LOCAD-PTS being tested now and in the near future are the first steps in a planned series of instruments that will give astronauts a picture of their microbiological environment.
"What we have now was never intended to be the final product," said Tony Lyons, the project manager for LOCAD-PTS. "This is one step towards a more comprehensive, portable, rapid-analysis machine that can tell you a whole lot more about what you're taking samples of than what we can do now, typically using microfluidic (in contrast to the current macrofluidic) technology. This is a step in the maturing of the technology to do that."
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