The evaluation of time‐resolved Raman spectroscopy for the suppression of background fluorescence from space‐relevant samples

Abstract

One of the primary goals in space research is the search for signs of extant or extinct extraterrestrial life, and Raman spectroscopy can play a role in this field. Raman spectrometers are planned for future missions to Mars and possibly the Moon to identify the mineralogical surface composition and potentially existing organic compounds (especially on Mars). However, a major challenge in Raman spectroscopy, especially in the visible range, is the strong fluorescence background. Time-resolved Raman spectroscopy (TRRS) can provide selective detection of Raman signals over the generally longer living fluorescence. This study investigates the potential of a TRRS system, using 3-ps, 440-nm laser pulses and time-gated detection with an intensified chargecoupled device (CCD) camera. Test samples were the lichen Xanthoria elegans as an extraterrestrial life analogue, and a lunar regolith analogue material (LRS) as a planetary surface analogue. The TRRS technique is evaluated by comparing gated to nongated Raman spectroscopy using different detectors but with otherwise the same instrument and identical measurement conditions. The gated spectra of X. elegans showed significant signal-to-noise ratio (SNR) improvements compared to the nongated spectra. The visible Raman lines could be assigned to the photoprotective pigment parietin. For the LRS sample, measurement spots with a good SNR in the nongated spectrum were not significantly improved by measuring in gated mode. However, spots dominated by fluorescence showed significant improvement in gated mode because of fluorescence suppression. Minerals such as plagioclase, diopside, olivine, apatite, and a carbonate mineral were detected. In most cases, TRRS provided better results compared to nongated measurements, demonstrating the suitability for future space-exploration missions. ---This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Biosignature stability in space enables their use for life detection on Mars

“…Therefore, it would also be worth exploring the detection of biomolecules in other mineral matrices, such as silica ( 33 ), which have also been identified at the landing sites for both the Perseverance and Rosalind Franklin rovers ( 34 , 35 ). Alternatively, improvements to standard Raman spectroscopy, such as time-resolved Raman spectroscopy, show promising results to analyze highly fluorescent samples ( 36 ) but are still in need of miniaturization for space missions. Last, the use of internal and external standards coupled with data normalization models has also recently been shown to be able to provide quantitative information on organic mineral mixtures and is an interesting approach for current and future missions ( 37 ).…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIV

“…They expect that their platform will pave the way to systematic screening of water flood compositions in more complex systems. Hanke et al [ 192 ] evaluated time‐resolved Raman spectroscopy (TRRS) for the suppression of background fluorescence from space‐relevant samples. For most cases, TRRS provided better results compared to nongated measurements, demonstrating its suitability for future space‐exploration missions.…”

In situ organic biosignature detection techniques for space applications

“…Background fluorescence, however, remains an important issue, which is often several orders of magnitude stronger than the Raman scattering signal, and inhibits the detection-for example, of cells in Martian simulant samples (Stevens et al, 2019). Two main strategies are used to reduce the background fluorescence signal: UV-range excitation wavelengths and time-gated (TG) Raman spectroscopy (Frosch et al, 2007;Shkolyar et al, 2018;Hanke et al, 2019). Fluorescence signals from minerals have a decay lifetime of >1 ms compared to organic fluorophores that typically have decay lifetimes of ~<100 ns (Misra et al, 2016;Shkolyar et al, 2018).…”