Time resolved Raman spectroscopy (TRRS) can provide subsurface information from multi-layered samples of transparent and translucent evaporative and silicate minerals up to several centimetres thick. Depth information was obtained using 3-ps pulsed laser excitation at 720 nm and a gated intensified charge-coupled device detector with stepwise increasing delay times. Blocks of different minerals were used as first, second or third layers, and Raman spectra from deeper layers could be detected through 10 mm of translucent calcite and up to 40 mm of transparent halite crystals. Measurements by conventional confocal Raman, as well as spatially offset Raman spectroscopy were also successful in distinguishing different mineral layers. This study establishes the great potential for the use of Raman spectroscopy in future planetary exploration, where TRRS could be used as a non-invasive tool for profiling the (sub-)surface at millimetre-depth resolution.

Carotenoids are among the key biomarkers in the search for life on other planets, and non‐destructive Raman spectroscopy on future rover missions is a potential sensitive detection method, especially under resonant conditions. In this research, reflectance spectra of minerals and microorganisms were measured using ultraviolet/visible diffuse reflectance spectroscopy in order to evaluate potential resonance Raman conditions and the possible degree of sample damage during laser irradiation. We report a photodegradation and semi‐quantitative Raman study of β‐carotene and the carotenoid‐containing extremophile Deinococcus radiodurans mixed with calcite at excitation wavelengths of 440 nm, 532 nm and 785 nm. A different type of carotenoid was detected in a culture of Chroococcidiopsis. Carotenoids embedded in bacterial membranes were found to be less sensitive to photodegradation than in a mineral matrix. Corrections for self‐absorption effects were performed using the 1085 cm−1 peak of calcite as an internal standard. Carotenoid‐type signals from 1 mg g−1 D. radiodurans in calcite could be detected, corresponding to about 5 µg g−1 β‐carotene in calcite (≈0.5% cell weight). This research emphasizes the potential suitability of Raman spectroscopy in the detection of organic biomarkers in future planetary exploration. Copyright © 2015 John Wiley & Sons, Ltd.

Raman spectroscopy appears to be an ideal technique for the initial detection of biomarkers, molecules that are potentially indicative of life on planetary bodies elsewhere in our solar system. Carotenoids are particularly useful biomarkers as they are used widely across the species, relatively resistant to breakdown and no inorganic source is known. They are used by microorganisms in their cell membranes for protection against UV radiation. In this paper we focus on the detection of carotenoids in microorganisms within a mineral matrix. We compare the Raman signatures of pure compounds with those of laboratory-made mixtures of β-carotene and minerals. Carotenoids covered by 2.5 mm of translucent calcite or 40 mm of transparent halite were detected using a conventional confocal Raman microscope. To improve sensitivity and hence detection levels, Raman measurements were successfully performed under resonant conditions. Raman analysis can be compromised by fluorescence interference. Data are presented to show how the contribution from the fluorescent background in the Raman spectra can be reduced when making use of gated detection in time-resolved Raman spectroscopy. Overall, this study demonstrates some of the potential of Raman spectroscopy as a method for the detection of (past) life signatures during future planetary missions without taking current technical limitations such as instrumental size into account as recent rapid technical developments suggest these limitations will be resolved in time.

Raman spectroscopy can provide highly specific chemical fingerprints of inorganic and organic materials and is therefore expected to play a significant role in interplanetary missions, especially for the search for life elsewhere in our solar system. A major challenge will be the unambiguous detection of low levels of biomarkers on a mineral background. In addition, these biomarkers may not be present at the surface but rather inside or underneath minerals. Strong scattering may prevent focusing deeper into the sample. In this paper, we report the detection of carotenoid-containing microorganisms behind mineral layers using time-resolved Raman spectroscopy (TRRS). Two extremophiles, the bacterium Deinococcus radiodurans and the cyanobacterium Chroococcidiopsis, were detected through translucent and transparent minerals using 440 nm excitation under resonance conditions to selectively enhance the detection of carotenoids. Using 3 ps laser pulses and a 250 ps gated intensified CCD camera provided depth selectivity for the subsurface microorganisms over the mineral surface layer and in addition lowered the contribution of the fluorescent background. Raman spectra of both organisms could be detected through 5 mm of translucent calcite or 20 mm of transparent halite. Multilayered mineral samples were used to further test the applied method. A separate tunable laser setup for resonance Raman and a commercial confocal Raman microscope, both with continuous (non-gated) detection, were used for comparison. This study demonstrates the capabilities of TRRS for the depth-selective analysis through scattering samples, which could be used in future planetary exploration to detect microorganisms or biomarkers within or behind minerals.

Binding of the antihistamine drug brompheniramine (BPA) to human serum albumin (HSA) is studied by measuring quenching of the fluorescence and room temperature phosphorescence (RTP) of tryptophan. The modified Stern-Volmer equation was used to derive association constants and accessible fractions from the steady-state fluorescence data. Decay associated spectra (DAS) revealed three tryptophan fluorescence lifetimes, indicating the presence of three HSA conformations. BPA causes mainly static quenching of the long-living, solvent-exposed conformer. RTP spectra and lifetimes, recorded under deoxygenated conditions in the presence of 0.2 M KI, provided additional kinetic information about the HSA-BPA interactions. Fluorescence DAS that were also recorded in the presence of 0.2 M KI revealed that the solvent-exposed conformer is the major contributor to the RTP signal. The phosphorescence quenching is mostly dynamic at pH 7 and mostly static at pH 9, presumably related to the protonation state of the alkylamino chain of BPA. This provides direct insight into the binding mode of the antihistamine drug, as well as kinetic information at both the nanosecond and the millisecond time scales.