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Search for signs of life by means of ATR spectroscopy (experiment "MATROS")

Grigoriev A.V. Korolev Yu.N. Vorobyova E.A.

(IKI RAS) (MSU, Biology faculty) (MSU, Soil Science faculty)


MATROS
Microbiologic Attenuated Total Reflection Optical Spectrometer
Space Research Institute Biology faculty Soil Science faculty Institute for Spectroscopy RAS Lomonosov Moscow State University Lomonosov Moscow State University RAS


Objectives for Astrobiology
· Europa may have an sub-surface ocean and it may be inhabited by Earth-like microbes · Earth microorganisms in situ are proved to be very stable to radiation, low temperature, high pressure and other unfavorable factors present at Europa. Actually, the limits for cells surviving are not known yet. · Fast freezing doesn't destroy bacterial cells, they transit to anabiotic state. Therefore, in frozen outbursts on Europa microorganisms may be present (at about 0.5m depth)


Objectives for methodology

· Possibility of direct express in-situ analysis · Method's multifunctionality · Possibility of hardware operation at Europa surface environment · Duration of the experiment must fit to spacecraft life time


ATR spectroscopy
· Fits to all above-listed requirements · Does not request any complicated sample preparation · Detects directly proteins, DNA/RNA, carbohydrates, lipids and other metabolites · Does not destroy or damage cell, investigates object "as is" · Can detect cell presence independently of its physiological state (viable or anabiotic)


The principles of ATR spectroscopy
Total Reflection occurs, if > arcsin[nsubstance / nprism] E.g., for ZnSe (np=2.4) and =45°: ns <1.7 An ATR spectrum is:
- basically, spectrum of absorption - spectrum of a very thin sample - the bigger ­ the "thicker" sample

Spectral range: 2.5 - 25 m Spectral resolution: 5 - 10 cm-1


Sources of bio-bands
Protein


Sources of bio-bands
DNA

DNA characteristic band originates from vibrations in O=P­O- linking group


Sources of bio-bands
DNA


Spectral bands of bio-cells
Eucaryote (cell with nucleus)


Spectral bands of bio-cells


Spectral bands of bio-cells


Spectral bands of bio-cells


Bio-molecules or minerals?
Minerals have very different spectra and by a proper mixture one can construct any spectral features. So, some additional information (except spectral bands position) is needed for sure detection of bio-cells: Study at different penetration depths Bands deepening due to bacteria propagation Dichroic ratio measurements in bio-bands


Study at different penetration depths


Bands deepening due to propagation


Dichroic ratio in bio-bands

In 1978 Korolev with colleagues for the first time implemented ATR measurements of dichroic ratio in bio-bands for investigation of bacterial spores (e.g., Mikrobiologiya. 1978. V.47. P.750). Dichroic ratio in cell membranes varies a lot, distinguishing them from minerals. Now such measurements became a normal laboratory practice (e.g. D.Marsh. Biophysical J. ,1997 V.72 P.2710) MATROS will have a polarizer for measurements of dichroic ratio. It will give an additional criterion for proving the biological origin of the bands.


Technical realization


Main parameters
Specification / Parameter Spectroscopy technique Spectral range Spectral resolution Size Mass Power consumption External assistance Type / Value Attenuated Total Reflection 2.5 - 25 m 5 - 10 cm
-1

Notes By now not used in planetary missions Internal miniature Fourier-spectrometer Internal miniature Fourier-spectrometer Average, when operating By spacecraft robotic arm, preferably from ~20cm depth

11 x 17 x 13 cm 2 kg 6W Soil sample delivery


THANKS FOR ATTENTION!