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Surface Enhanced Raman Spectroscopy (SERS) for astrobiological exploration
Rab Wilson2, Stephen A. Bowden1
1Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, UK 2Department of Electronics and Electrical Engineering, Oakfield Avenue, University of Glasgow, Glasgow, G12 8LT,UK


Snow Algae Cairngorm Plateau

·Snow Algal bloom ­Cairngorm Plateau ·Measurements performed on melted ice ·But this is best case scenario ­ Lots of analyte ­ knew what and where it was before we performed analysis

20 x 20 km of snow field


Analysing Organic compounds for Astrobiology/geology

100 m

Inclusions in Halite

Inclusions with sulphate salt in ice; Light et al 2003.

< ppm analysis ­ what it means Solvent extraction/analyte concentration -For physicists ·Separation stages ·Deconvolution not enough -Difficult and complex analysis -In engineer speak: ·Many mechanisms ·High power ·High Mass


Analysing organic compounds in geological materials
Residue Soluble

Soluble 1. 2. 3. 4. 5. Crush Wash with solvent Extract with solvent Concentrate Transfer to analytical equipment

18 I

Pr I Ph I 21 I 22 I 23 I 25 II I

m/z 183

12.00

14.00

16.00

18.00

20.00

22.00

24.00 26.00 time

28.00

30.00

32.00

34.00

36.00

38.00


Benefits of SERS over conventional Raman Spectroscopy
·SERS selectively enhances only specific molecules (factor 105 enhancement) Can analyse organic compounds in solvents Fluorescence quenching? ·Natural extracts complex mixtures -either fluoresce -not possible to interpret spectra Raman

SERS

Limits of detection ·For scytonemin ·Detection of 2nM > 3 background noise ·Detect lower concentrations of R6G


Surface Enhanced Raman Spectroscopy (SERS)
Excited Electronic State

V'

Chemisorption ­ charge transfer
V1 Vo

Surface Enhanced Raman Roughened Metal

Surface Plasmon Resonance
Raman Enhanced Raman

Electromagnetic

Chemical LUMO Energy (eV)
charge transfer

Raman signal

incident

Fermi level

HOMO


Equipment
·Light source - 514 nm, (typically about 10 mW laser) ·OTS Ocean Optics spectrometers ·Nitric acid, citric acid used to improve metal ­ analyte interaction

Silver Colloid in flow cell

Silver Beads and bead trap


Biomolecules from hydrothermal system I

Purple

Orange

Green

1. Samples ground and crushed 2. Extracted with Acetone 3. Acetone analysed by SERS


C-phycocyanin

OH O

OH O

1230

1380

1448

O

1517

711

885

964

1000

1540 1560 1323

1553

N H

N H

N

N H

O

H

scytonemin
N HO H

O N O

OH

1156

500

600

700

800

900

1000

1066

1100

1200 1300 1400 Raman Shift (cm-1)

1500

1520

, carotene

1176

1600

1608

1609

1700

1800

1900

2000


Biomolecules in hydrothermal system II
scy scy phyc b,b phyc scy b,b b,b

Green

Orange

Brown/purple D2 C­S, C=S C­O­C D1

Sinter

Blank

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

Raman Shift (cm-1)


Bio/Geomolecules in hydrothermal system II
Measurement from grey goo most significant over time

D2 C­S, C=S C­O­C D1

Sinter

Blank

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

Raman Shift (cm-1)


Monitoring Arctic micro oases

~384

~490

adsorption units

Pigm crust

Scy

,

Unpigm crust blank

â5

200

300

400

500

600

700

800

900

Wavelength cm-1


Monitoring Arctic micro oases

end survey line Crust
500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Raman Shift (cm-1)

Loss of carotene relative to scytonemin, consistent with trends seen in UV-VIS data
140 120 100 80 60 40 20 0

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

bb/scy


Meanest measurements possible - Towards a SERS TAS
DMSO

water + DMSO

DMSO

water

H-cell ·Extract , carotene from epsomite crystals ·By circulating less extracting solvent can concentrate sample ·Next stage to integrate components +LC-SERS
DMSO Extract

Extracted water Standard Blank
0 500 1000 1500 2000 2500

Raman Shift (cm -1)


Conclusions
SERS can provide organic geochemical information ­ e.g. detect specific molecular structures in sediments at 10's ppm. This is something Raman Spectroscopy can't do This requires further sample processing ­ but this can all be automated Such a system could be a LOC device

Sample inlet

Fibre optics couple to Raman microscope

water/acid

*
colloid introduction extracting solvent 2 cm


B-Presentation Survival of Organic Compounds in ice-HVI
Stephen Bowden & John Parnell
University of Aberdeen

Mark J Burchell
Canterbury ­ University of Kent


Method
HVI-ice impact studies performed Canterbury, University of Kent ·Ice doped with organic compound ·1.5 mm d projectile at ~5 kms-1 ·Ejecta collected and analysed

HO O

target

~ 4.9 Km s-1
ice ejecta

organic-ice layer

~ 10 mm

collection trays


UV-VIS spectroscopy and GC-MS (data not shown) used to analyse products

4
Fa An C

4

3

d =1.5 mm d =1 mm

3

2
â15

2

1 0 1 2 3 4 5 6
ice

1

300

400 nanometers

500

mass ejecta collected (g)

UV-VIS adsorption spectra


a)

b)
> 75º most recalcitrant + most volatile
HO O HO O

c)
greatest shock alteration e.g. dehydrated glass phases such as Tektites in Distal Ballistic Ejecta

50 - 65º high volatility + high recalcitrance

HO O

5 - 50º low volatility + some labile
OH

least shock alteration e.g. whole rock clasts and altered/partial melt phases Proximal Layered Ejecta

O

HO O

?

·Most altered fraction is very altered ·Suspect that radicalisation of water helps drive reactions d)


Acknowledgements

EPSRC for funding Haughton Mars project; Communities of Griese Fjord; Resolute Bay Icelandic Institute of Natural History; Krisjan Jonasson; Paula Lindgren; Eric Strukel


Analysing organic compounds in geological materials
Residue Soluble

Residue 1. 2. 3. 4. 5. 6. Crush/break Dissolve matrix Collect residue Screen through residue Involves microscope Human discretion