Extended Longevity Photoactivated Surface Enhanced Raman Spectroscopy for the Detection of Biosignatures on Icy Worlds and Martian Polar Caps

Surface Enhanced Raman Spectroscopy (SERS) has traditionally not been considered for planetary sciences due to issues associated with SERS substrate degradation and spectra reproducibility. Here we present ongoing work on the Compact Integrated Raman Spectrometer (CIRS) instrument developed for the Europa Lander Mission concept [1], [2], which incorporates SERS capability into the green-wavelength Raman system in order to allow detection of biosignatures at extremely low concentrations. In this work we optimize a SERS method based on chemically stable AgCl precursor coating [3], which is reduced to SERS-active Ag nanoparticles (NPs) in-situ, thus eliminating any potential degradation of the SERS-active AgNPs during transit. We use the modified AgCl coating to detect biosignatures relevant for the search for extraterrestrial life, evaluate the detection limit and characterize the stability and reproducibility of the resulting spectra. To assess the impact of environmental conditions on Icy Worlds and Mars, we also investigate the effect of salts and varying pH. The results show L-Histidine can be detected 10nM and BPE as low as 10-24M, which is within the estimated biomolecule concentration range for Icy Worlds [2], [4], [5]. Furthermore, the presence of salts significantly enhances the SERS signal, which makes this method particularly favourable for detecting in salty brines, such as on Ocean Worlds or Mars. This method thus greatly enhances the scientific capabilities of the CIRS instrument for the exploration of Icy Worlds and Martian polar caps. Furthermore, the SERS coating is applied to the sample cup at little additional cost or complexity and requires no sample preparation.