A makeshift apparatus has been designed composed of a sealed, hydrophobic 2-propanol/SiO2 aerogel component to filter outside air particles. Following verification and assessment, the apparatus was crafted with a Buchner funnel. Aerogel matrices were tightly fitted into filter housings and secured in side-arm flasks, which were then equipped to a vacuum pump to pull air through the aerogel matrices. Aerogels, both with and without fiberglass reinforcement, were used to collect airborne particulates for one- and three-hour increments. An untreated negative control aerogel, employing air collection from a laminar hood, and a positive aerogel matrix were seeded with endospores that verified the extraction from the matrices.
The aerogel matrices were then cryogenically milled at liquid nitrogen temperatures in a SPEX SamplePrep 6870 solenoid powered cryogenic grinder. After cryo-grinding, the material was transferred to an automated DNA extraction cartridge where the DNA was purified. After extraction, downstream DNA-dependent qPCR (quantitative polymerase chain reaction) analyses indicated that the one-hour and three-hour sampling events yielded ≈1 × 104 and ≈1 × 108 16S rRNA gene copies per aerogel, respectively. When a positive control was seeded with ≈1 × 108 bacterial endospores and subsequently processed and analyzed, it gave rise to a recovery rate of ≈1.6%. Notably, the negative control that was processed in an ISO-5 laminar hood yielded undetectable results.
These findings support the notion that aerogel degradation via cryogenic grinding is feasible with downstream nucleic-acid-based molecular modes of analysis. This key finding demonstrates an effective end-to-end process flow for determining the source-specific density of encapsulated microorganisms in a nonmetallic matrix. This approach, and future iterations thereof, can be tailored to assess embedded bioburden for future mission sets, where comprehensive assessments will certainly be requisite, by simply using aerogel matrices as surrogates to render actual specification values for a reduction in endospores burden. Furthermore, such an aerogelbased system could be engineered to the exterior of an aircraft to collect particulates at varying time points and altitudes over the course of a flight. These successful outdoor airborne particulate sampling events confirm the expected increase in biological particles over the course of a one- to three-hour sampling event.
This work was done by Myron T. La Duc, Kasthuri J. Venkateswaran, Wayne W. Schubert, Steven M. Jones, and James N. Benardini of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48880
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Assessment of Microbial Bioburden Within Aerogel Matrices
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