[B-CG07] Geo-Bio Interactions and its Applications

[BCG07-P06] Single-Cell Mapping of the Rock Interior by Infrared Microscopy: A Potential Tool of Sample Safety Assessment for Mars Sample Return

*Mariko Kouduka¹, Yohey Suzuki¹ (1.Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.)

Keywords:optical-photothermal infrared spectroscopy (O-PTIR), fourier-transform infrared (FT-IR) microscopy, in-situ single-cell detection, clay-bearing rock fractures, backward planetary protection

For near-future missions planed for Mars Sample Return (MSR), an international working group organized by the Committee on Space Research (COSPAR) developed the sample safety assessment framework (SSAF). For the SSAF, analytical instruments were selected by taking the practical limitations of hosting them within a biosafety level 4 facility and the precious nature of returned samples into account. To prepare for MSR, analytical instruments of high sensitivity need to be tested on effective Mars analogue materials. As an analogue material, we selected a rock core of basalt, a prominent rock type on the Martian surface. Our previous use of destructive but spatially sensitive techniques such as nanoscale secondary ion mass spectrometry (NanoSIMS) and transmission electron microscopy coupled to energy-dispersive spectroscopy (TEM-EDS) revealed the dense microbial colonization at clay-filled fractures. We now extend that work to conventional Fourier transform infrared (FT-IR) microscopy with a spatial resolution of 10 μm. Although Fe-rich smectite called nontronite was identified, the application of conventional FT-IR microscopy is limited to a sample thickness of <30 μm. A new IR-based non-destructive technique called optical-photothermal infrared (O-PTIR) spectroscopy with a spatial resolution of 0.5 μm was applied to a 100- μm thick section of the rock core. By O-PTIR spectroscopic analysis of the clay-filled fracture, we obtained in-situ spectra diagnostic to microbial cells and nontronite. The sensitivity and specificity for microbial detection and smectite identification by O-PTIR spectroscopic analysis is comparable to those of NanoSIMS and TEM-EDS. In addition, O-PTIR spectroscopy is superior to deep ultraviolet fluorescence microscopy/μ-Raman spectroscopy, particularly for smectite identification. A simultaneous acquisition of the spatial distribution of structural motifs associated with biomolecules and smectites is critical for distinguishing biological material in samples as well as characterizing an abiotic background.