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“O-PTIR spectroscopy is suggested be 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.”
Reporting in the International Journal of Astrobiology, researchers have reported a significant advancement in planetary protection protocols through the application of optical-photothermal infrared (O-PTIR) spectroscopy to detect microbial life in Mars-analogue basalt samples.
Suzuki et al. address critical analytical challenges facing the Mars Sample Return (MSR) mission, where conventional techniques suffer from insufficient spatial resolution and require destructive sample preparation that compromises precious returned materials. The research team needed to validate non-destructive analytical methods capable of achieving the stringent detection requirements—a risk value of 1 in a million chance of failing to detect life if present.
The authors demonstrate that O-PTIR spectroscopy successfully identified diagnostic spectra for microbial cells at submicron resolution in 100 μm thick basalt sections. They report obtaining clear amide I and II peaks (indicators of peptides) at 1530 cm⁻¹, along with characteristic CH₂ bending vibrations at 1450 cm⁻¹ and COO stretching at 1390 cm⁻¹, providing unambiguous evidence of biological material. The researchers note that these spectroscopic signatures were consistent with reference microbial cultures, confirming the technique’s reliability for biosignature detection.
Simultaneously, the authors report successful identification of Fe(III)-bearing smectites, specifically nontronite, through characteristic Fe(III)₂-OH bending modes at 815-817 cm⁻¹ and H₂O bending at 1635 cm⁻¹. They emphasize that O-PTIR achieved this dual detection capability without sample damage, as confirmed through repeated measurements. Significantly, the authors note that conventional μ-Raman spectroscopy failed to provide useful data due to autofluorescence interference, while FT-IR microscopy in ATR mode produced spectra with inadequate signal-to-noise ratios.
The authors conclude that O-PTIR spectroscopy represents a transformative analytical capability for Mars Sample Return missions, offering 0.5 μm spatial resolution—20 times better than conventional FT-IR microscopy—while eliminating destructive sample preparation requirements.
They also report that this non-destructive approach enables simultaneous mapping of biological and geological signatures, which is essential for distinguishing authentic biosignatures from abiotic backgrounds in precious extraterrestrial samples.
Suzuki et al,
University of Tokyo.
DOI: https://doi.org/10.1017/S1473550425000011
