Fei Chen

Publications (3)0 Total impact

• Conference Proceeding: An Evaluation of Novel Cleaning Techniques for Planetary Protection Applications

  Fei Chen, G. Kazarians, R. Beaudet, R. Kern
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  ABSTRACT: NASA has an aggressive plan for exploring Mars. Future in situ life detection and sample return missions will rely on clean and effectively sterile spacecraft to ensure reliable, valid science measurements. These spacecraft levy substantial requirements for planetary protection. Here, we report the results of a comparative analysis of the efficacy of three different cleaning approaches to remove bacterial spores from a series of surrogate spacecraft materials, parts, as well as cleaning challenging structures. The purpose of this study is to identify cleaning methods that achieve a minimum of a 4-log reduction of bioburden from inoculated surfaces. We believe that surfaces efficiently cleaned do not transfer biological particles, particularly spores, which when placed in close proximity with other materials become "effectively sterile." Our results indicate that a novel cleaning method, which utilize vacuum cycle nucleation (VCN) enabled technologies, can effectively remove bacterial spores from surrogate spacecraft material coupons, piece parts and structures. This cleaning technology may be a potential candidate for sterilizing Mars Lander systems, reducing the cost, risk, and material constraints encumbered by use of dry heat sterilization and common cleaning practices.
  Aerospace Conference, 2008 IEEE; 04/2008
• Conference Proceeding: Cleaning to achieve sterility

  R. Kern, L. Kirschner, M. La Due, Fei Chen, K. Venkateswaran
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  ABSTRACT: NASA planetary protection regulations state that a surface may be considered "sterile" if a microbial burden of less than 300 aerobic bacterial spores per square meter can be further treated to achieve a 10 ⁴ fold reduction in viable endospores (spores). The results of previous studies have suggested that surfaces might be cleaned to a level that is essentially sterile. Here, we report the results of a comparative analysis of the efficacy/ability of three different cleaning approaches to remove bacterial spores from a series of surrogate spacecraft surfaces. In order to accomplish the most realistic and reproducible spore deposition, an aerosol chamber capable of nebulizing innocuous Bacillus atrophaeus (ATCC, 9372 [formerly B. subtilis var niger]) spores was developed and used. This enabled the relatively uniform inoculation of spores as individual entities at a concentration in excess of 10⁵ spores per 2.2 cm² surrogate surface coupon. Coupons prepared in this fashion were subsequently delivered to three cleaning facilities: vendor A for cleaning via standard aerospace precision cleaning protocols, vendor B for cleaning via ultra-pure water, and vendor C for cleaning via liquid boundary layer disruption. Variations in the chemistry of the cleaning solutions were also explored. Preliminary results suggest that "sterility," as defined by NASA, may indeed be achieved by various cleaning procedures, despite the fact that none of these methods were originally designed, nor are they currently conducted, with such a goal in mind
  Aerospace Conference, 2006 IEEE;
• Conference Proceeding: Rapid micro-detection system for the enumeration of bacterial endospores

  Fei Chen, G.A. Kazarians, K. Venkateswaran, R. Kern
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  ABSTRACT: NASA continuously monitors spacecraft surfaces to assure a very low presence of bacterial endospores upon landing on the surface of Mars. In order to meet the rigid schedules of spacecraft assembly, a more rapid, sensitive spore detection assay is being considered as an alternate method to the current three-day NASA standard culture-based assay. The millipore microstar rapid system (RMDS) has been used successfully for rapid bioburden enumeration in a wide range of applications. It combines membrane filtration, adenosine triphosphate (ATP) bioluminescence chemistry, and image analysis based on photon detection with a charge coupled device (CCD) camera. The RMDS is rapid and simple, shows high sensitivity (1 colony forming unit [CFU]/sample), and correlates excellently with traditional culture-based methods. In addition, by utilizing the milliflex filtration system, the RMDS is ideal for sampling both large sample volumes and those samples containing inhibitory substances. In this study, we have evaluated the use of the RMDS as a rapid spore detection tool for NASA planetary protection applications. This is accomplished by preceding the RMDS incubation protocol with a heat shock step, 15 minutes at 80degC, as a direct selection of spores. Different luciferase enzymes were tested in order to reduce the typical 18-24 hour incubation time to ~5 hours. Of the reagents evaluated, a formulation of a highly sensitive bioluminescence reagent was found to be more sensitive than the present millipore microstar reagents. Assay times of ~5 hours were repeatedly demonstrated along with low image background noise. In order to evaluate the applicability of this method, seven species of Bacillus (nine strains) that have been repeatedly isolated from clean room environments were assayed. All strains were detected in ~5 hours. The improved RMDS-based spore detection is under validation and is expected to achieve the goal of "same shift" measurement of spore bioburden during spacecraft- - assembly
  Aerospace Conference, 2006 IEEE;